TY - CHAP TI - Thermal stability studies of advanced gate stack structures on Si (100) AU - Sivasubramani, P AU - Zhao, P AU - Kim, MJ AU - Gnade, BE AU - Wallace, RM AU - Edge, LF AU - Schlom, DG AU - Parsons, GN AU - Misra, V AU - Seiler, DG AU - Diebold, AC AU - McDonald, R AU - Ayre, CR AU - Khosla, RP AU - Secula, EM T2 - Characterization and Metrology for ULSI Technology 2005 PY - 2005/// VL - 788 SP - 156-160 PB - SE - UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000233588000023&KeyUID=WOS:000233588000023 ER - TY - JOUR TI - Designing interface composition and structure in high dielectric constant gate stacks AU - Parsons, GN AU - Huff, HR AU - Gilmer, DC T2 - High Dielectric Constant Materials DA - 2005/// PY - 2005/// VL - 16 SP - 287-310 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=CCC&KeyUT=CCC:000227551500010&KeyUID=CCC:000227551500010 ER - TY - CONF TI - Chemical looping combustion of coal AU - Gupta, P. AU - Velazquez-Vargas, L.G. AU - Li, F. AU - Fan, L.-S. C2 - 2005/// C3 - AIChE Annual Meeting, Conference Proceedings DA - 2005/// VL - 2005 SP - 7620-7625 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-33645638139&partnerID=MN8TOARS ER - TY - CONF TI - Hydrogen production from syngas using metal oxide composite particles AU - Velazquez-Vargas, L.G. AU - Gupta, P. AU - Li, F. AU - Fan, L.-S. C2 - 2005/// C3 - AIChE Annual Meeting Conference Proceedings DA - 2005/// VL - 2005 SP - 10119-10122 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-33646750981&partnerID=MN8TOARS ER - TY - JOUR TI - New Directions in Plastic Debris AU - Thompson, R. AU - Moore, C. AU - Andrady, A. AU - Gregory, M. AU - Takada, H. AU - Weisberg, S. T2 - Science AB - The largest ever meeting focusing on plastic debris in the environment was recently held in Redondo Beach, California ([1][1]). It is evident that plastic waste presents major concerns in aquatic habitats worldwide. However, this meeting differed from previous efforts/gatherings because representatives from industry, government, academia, and nongovernment organizations were united in their desire to identify solutions to reducing waste. There has been a switch in the types of litter recorded, from shipping- and fishing-related debris to landbased sources. This was poignantly underscored by reports of islands of plastic debris swept into the sea by Hurricane Katrina. Polymer scientist A. Andrady explained that all the plastic introduced into the oceans remains unmineralized as either entire objects or fragments, some of which are less than 20 μm in diameter ([2][2]). Large items of debris cause entanglement, impaired feeding, and mortality to birds, turtles, and mammals. Microscopic fragments are also ingested, but the consequences are unknown. H. Takada and C. Moore presented evidence on the ability of plastic to accumulate PCBs, DDE, and nonylphenol ([3][3]), and the potential for toxic chemicals to transfer to the food chain was identified as a key research direction. It was also recognized that better understanding of effects at an organismal level is required before consequences at population and ecosystem levels can be examined. In terms of solutions, much could be achieved by reductions in packaging. Keynote speaker W. McDonough made the case for a “cradle to cradle” ([4][4]) strategy to ensure that plastics are retained in a product- specific recycling loop-turning debris from a waste disposal liability into feedstock for production. Although debris can be removed from drains and rivers by physical separators, there is also a key role for education to help reduce littering. The importance of social research to establish the public's willingness to engage with these solutions was also clearly recognized. ![Figure][5] Toy cars amid debris in New Orleans after Hurricane Katrina.CREDIT: DAVID QUINN/AP PHOTO 1. 1.[↵][6]Plastic Debris Rivers to Seas, organized by the California Coastal Commission, 7 to 9 Sept 2005. 2. 2.[↵][7]1. R. C. Thompson 2. et al. , Science 304, 838 (2004). [OpenUrl][8][FREE Full Text][9] 3. 3.[↵][10]1. Y. Mato 2. et al. , Environ. Sci. Technol. 35, 318 (2001). [OpenUrl][11][CrossRef][12][PubMed][13][Web of Science][14] 4. 4.[↵][15]1. W. McDonough, 2. M. Braungart , Cradle to Cradle (North Point Press, New York, 2002). [1]: #ref-1 [2]: #ref-2 [3]: #ref-3 [4]: #ref-4 [5]: pending:yes [6]: #xref-ref-1-1 View reference 1. in text [7]: #xref-ref-2-1 View reference 2. in text [8]: {openurl}?query=rft.jtitle%253DScience%26rft.stitle%253DScience%26rft.aulast%253DThompson%26rft.auinit1%253DR.%2BC.%26rft.volume%253D304%26rft.issue%253D5672%26rft.spage%253D838%26rft.epage%253D838%26rft.atitle%253DLost%2Bat%2BSea%253A%2BWhere%2BIs%2BAll%2Bthe%2BPlastic%253F%26rft_id%253Dinfo%253Adoi%252F10.1126%252Fscience.1094559%26rft_id%253Dinfo%253Apmid%252F15131299%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [9]: /lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiRlVMTCI7czoxMToiam91cm5hbENvZGUiO3M6Mzoic2NpIjtzOjU6InJlc2lkIjtzOjEyOiIzMDQvNTY3Mi84MzgiO3M6NDoiYXRvbSI7czoyNToiL3NjaS8zMTAvNTc1MS8xMTE3LjIuYXRvbSI7fXM6ODoiZnJhZ21lbnQiO3M6MDoiIjt9 [10]: #xref-ref-3-1 View reference 3. in text [11]: {openurl}?query=rft.jtitle%253DEnvironmental%2BScience%2B%2526%2BTechnology%252C%2BES%2B%2526%2BT%26rft.stitle%253DEnvironmental%2BScience%2B%2526%2BTechnology%252C%2BES%2B%2526%2BT%26rft.aulast%253DMato%26rft.auinit1%253DY.%26rft.volume%253D35%26rft.issue%253D2%26rft.spage%253D318%26rft.epage%253D324%26rft.atitle%253DPlastic%2Bresin%2Bpellets%2Bas%2Ba%2Btransport%2Bmedium%2Bfor%2Btoxic%2Bchemicals%2Bin%2Bthe%2Bmarine%2Benvironment.%26rft_id%253Dinfo%253Adoi%252F10.1021%252Fes0010498%26rft_id%253Dinfo%253Apmid%252F11347604%26rft.genre%253Darticle%26rft_val_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26ctx_ver%253DZ39.88-2004%26url_ver%253DZ39.88-2004%26url_ctx_fmt%253Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Actx [12]: /lookup/external-ref?access_num=10.1021/es0010498&link_type=DOI [13]: /lookup/external-ref?access_num=11347604&link_type=MED&atom=%2Fsci%2F310%2F5751%2F1117.2.atom [14]: /lookup/external-ref?access_num=000166390700011&link_type=ISI [15]: #xref-ref-4-1 View reference 4. in text DA - 2005/11/18/ PY - 2005/11/18/ DO - 10.1126/science.310.5751.1117b VL - 310 IS - 5751 SP - 1117b–1117b SN - 0036-8075 1095-9203 UR - http://dx.doi.org/10.1126/science.310.5751.1117b ER - TY - JOUR TI - Environmental effects of ozone depletion and its interactions with climate change: Progress report, 2004 AU - Andrady, A. T2 - Photochemical & Photobiological Sciences AB - The complexity of the linkages between ozone depletion, UV-B radiation and climate change has become more apparent. DA - 2005/// PY - 2005/// DO - 10.1039/b418650h VL - 4 IS - 2 SP - 177 SN - 1474-905X 1474-9092 UR - http://dx.doi.org/10.1039/b418650h ER - TY - JOUR TI - Transmission Electron Microtomography (TEMT) of Nanostructured Polymers and Polymer Nanocomposites AU - Spontak, R J AU - Gozen, A O AU - Braunfeld, M B AU - Agard, D A T2 - Microscopy and Microanalysis AB - Extract HTML view is not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button. Extended abstract of a paper presented at Microscopy and Microanalysis 2005 in Honolulu, Hawaii, USA, July 31--August 4, 2005 DA - 2005/8// PY - 2005/8// DO - 10.1017/S1431927605510341 VL - 11 IS - S02 J2 - MAM LA - en OP - SN - 1431-9276 1435-8115 UR - http://dx.doi.org/10.1017/S1431927605510341 DB - Crossref ER - TY - JOUR TI - Inside Front Cover: Tailoring Cell Adhesion Using Surface-Grafted Polymer Gradient Assemblies (Adv. Mater. 23/2005) AU - Bhat, R. R. AU - Chaney, B. N. AU - Rowley, J. AU - Liebmann-Vinson, A. AU - Genzer, J. T2 - Advanced Materials AB - Abstract A three‐step approach to tailor cell adhesion via surface‐grafted polymer gradients is shown in this image from the work of Genzer and co‐workers on p. 2802. Surface‐anchored polymer assemblies with gradients in polymer molecular weight and/or grafting density are first employed to tailor adsorption of the protein, which in turn governs the number density as well as the extent of spreading of osteoblastic cells. Increasing the surface coverage of the polymer results in a decrease in the amount of protein adsorbed, which causes a decrease in the number of cells adhered and a change in cell morphology. DA - 2005/12/5/ PY - 2005/12/5/ DO - 10.1002/adma.200590122 VL - 17 IS - 23 SP - NA-NA J2 - Adv. Mater. LA - en OP - SN - 0935-9648 1521-4095 UR - http://dx.doi.org/10.1002/adma.200590122 DB - Crossref ER - TY - JOUR TI - Tertiary amide chemistry at the Ge(100)-2×1 surface AU - Keung, Albert J. AU - Filler, Michael A. AU - Porter, David W. AU - Bent, Stacey F. T2 - Surface Science AB - We have investigated the adsorption of several tertiary amides, including N,N-dimethylformamide, N,N-dimethylformamide-d7, 1-methyl-2-pyrrolidinone, and N-methylcaprolactam, on Ge(1 0 0)-2 × 1 using multiple internal reflection Fourier transform infrared spectroscopy and density functional theory. At 310 K, all four tertiary amides were observed to selectively form a dative bond to the germanium surface through the oxygen atom. While previous work has shown that oxygen dative bonds are unstable near room temperature, tertiary amides exhibit delocalization of electron density from nitrogen to oxygen, which appears to increase the stability of the oxygen dative-bonded state. Partial desorption of these surface adducts on the timescale of minutes indicates weakly bound surface adducts with coverage dependent binding energies. DA - 2005/12// PY - 2005/12// DO - 10.1016/j.susc.2005.09.035 VL - 599 IS - 1-3 SP - 41-54 J2 - Surface Science LA - en OP - SN - 0039-6028 UR - http://dx.doi.org/10.1016/j.susc.2005.09.035 DB - Crossref KW - density functional calculations KW - vibrational spectroscopies KW - germanium KW - organic molecules KW - organo-functionalization of surfaces KW - desorption KW - amide KW - Ge(100) ER - TY - JOUR TI - Conformational analysis of gossypol and its derivatives by molecular mechanics AU - Beisel, Chase L. AU - Dowd, Michael K. AU - Reilly, Peter J. T2 - Journal of Molecular Structure: THEOCHEM AB - Conformations and inversion pathways leading to racemization of all the tautomers of gossypol, gossypolone, anhydrogossypol, and a diethylamine Schiff's base of gossypol were investigated with MM3(2000). All forms have hindered rotation because of clashes between the methyl carbon atom and oxygen-containing moieties ortho to the bond linking the two naphthalene rings. Inversion energies generally agree with available experimental data. Gossypol preferentially inverts in its dihemiacetal tautomeric form through the cis pathway (where similar groups clash). Gossypolone inverts more easily than gossypol, and preferentially through the trans pathway (where dissimilar groups clash) when one of its outer rings has an enol-keto group and the other has an aldehyde group. Anhydrogossypol racemizes through the cis pathway. The bridge bond and the ortho exo-cyclic bonds in all the structures bend from planarity, and the inner naphthalene rings pucker to accommodate the inversion. For gossypol, the transition is achieved through greater bending of the exo-cyclic bonds (up to 12°) and less distortion of the inner benzyl rings (q≤0.34 Å), (up to 12.7°) . For gossypolone the transition occurs with greater distortion of the inner benzyl rings (q≤0.63 Å) and less out-of-plane bending (up to 8.4°). By isolating individual clashes, their contribution to the overall barrier can be analyzed, as shown for the dialdehyde tautomer of gossypol. DA - 2005/10// PY - 2005/10// DO - 10.1016/j.theochem.2005.05.010 VL - 730 IS - 1-3 SP - 51-58 J2 - Journal of Molecular Structure: THEOCHEM LA - en OP - SN - 0166-1280 UR - http://dx.doi.org/10.1016/j.theochem.2005.05.010 DB - Crossref ER - TY - JOUR TI - Permeability and reactivity of Thermotoga maritima in latex bimodal blend coatings at 80°C: a model high temperature biocatalytic coating AU - Lyngberg, Olav K. AU - Solheid, Chris AU - Charaniya, Salim AU - Ma, Yue AU - Thiagarajan, Venkata AU - Scriven, L. E. AU - Flickinger, Michael C. T2 - Extremophiles DA - 2005/3/19/ PY - 2005/3/19/ DO - 10.1007/S00792-005-0434-7 VL - 9 IS - 3 SP - 197-207 J2 - Extremophiles LA - en OP - SN - 1431-0651 1433-4909 UR - http://dx.doi.org/10.1007/S00792-005-0434-7 DB - Crossref KW - entrapped Thermotoga maritima KW - latex coatings KW - bimodal polymer blends KW - latex permeability KW - thermostable biocatalytic coatings ER - TY - JOUR TI - High-Affinity CD25-Binding IL-2 Mutants Potently Stimulate Persistent T Cell Growth† AU - Rao, Balaji M. AU - Driver, Ian AU - Lauffenburger, Douglas A. AU - Wittrup, K. Dane T2 - Biochemistry AB - We have used directed evolution to construct IL-2 mutants that bind the IL-2 alpha receptor subunit (IL-2Ralpha, CD25) with affinities comparable to that of the IL-15-IL-15 alpha receptor subunit (IL-15Ralpha) interaction. T cells proliferate for up to 6 days following a 30 minute incubation with these IL-2 mutants, which may lead to potential applications for cancer and viral immunotherapy. Several alternative mechanisms have been proposed to explain the contrasting effects of IL-2 and IL-15 on T cell proliferation and death. These IL-2 mutants exhibit T cell growth response-receptor occupancy curves indistinguishable from that for IL-15, suggesting that much of the difference between wild-type IL-2 and IL-15 effects arises simply from their 1000-fold differing affinities for their private alpha receptor subunits. DA - 2005/8// PY - 2005/8// DO - 10.1021/bi050436x VL - 44 IS - 31 SP - 10696-10701 J2 - Biochemistry LA - en OP - SN - 0006-2960 1520-4995 UR - http://dx.doi.org/10.1021/bi050436x DB - Crossref ER - TY - JOUR TI - Phase equilibrium for the hydrogenation of polystyrene in CO2–swollen solvents AU - Xu, Dawei AU - Carbonell, Ruben G. AU - Roberts, George W. AU - Kiserow, Douglas J. T2 - The Journal of Supercritical Fluids AB - Polystyrene (PS) can be hydrogenated using a heterogeneous catalyst suspended in a solvent swollen by supercritical carbon dioxide (scCO2). Various phase equilibria are involved in this system. First, the application of scCO2 to a solution of PS can cause the polymer to precipitate. Therefore, the effect of CO2 pressure and temperature on the phase behavior of various solvents containing dissolved PS was investigated, leading to the selection of decahydronaphthalene (DHN) for in-depth study. It was found that the CO2 pressure required to precipitate PS from DHN increased with the temperature. The volume of solutions containing various concentrations of PS in DHN increased considerably as the CO2 pressure was increased. Volume expansions of 35–40% were obtained between 40 and 150 °C and between 3 and 9 wt.% PS. Moreover, calculations using the Peng–Robinson equation of state showed that the H2 concentration in the liquid phase was higher in CO2–swollen DHN than in the pure solvent, at a constant H2 partial pressure. The rate constant for PS hydrogenation was found to be higher in CO2–swollen DHN than in the pure solvent. DA - 2005/5// PY - 2005/5// DO - 10.1016/j.supflu.2004.09.004 VL - 34 IS - 1 SP - 1-9 J2 - The Journal of Supercritical Fluids LA - en OP - SN - 0896-8446 UR - http://dx.doi.org/10.1016/j.supflu.2004.09.004 DB - Crossref KW - hydrogenation KW - polystyrene KW - supercritical carbon dioxide KW - phase equilibrium KW - Peng-Robinson ER - TY - JOUR TI - Growth of Bacillus methanolicus in seawater-based media AU - Komives, Claire F. AU - Cheung, Louis Yip-Yan AU - Pluschkell, Stefanie B. AU - Flickinger, Michael C. T2 - Journal of Industrial Microbiology & Biotechnology AB - Bacillus methanolicus has been proposed as a biocatalyst for the low cost production of commodity chemicals. The organism can use methanol as sole carbon and energy source, and it grows aerobically at elevated temperatures. Methanol can be made available from off-shore conversion of natural gas to methanol, through gas-to-liquid technology. Growth of the organism in seawater-based medium would further reduce the costs of chemical production performed near an off-shore natural gas source. The growth of strain PB1 (ATCC 51375) in shake flask experiments with trypticase soy broth medium showed minimal salt-inhibition at the concentration of NaCl in seawater. The ability of B. methanolicus PB1 to grow in Pacific Ocean water using methanol as a carbon and energy source was also tested. Following a simple adaptation procedure, PB1 was able to grow on methanol in semi-defined medium with 100% seawater with good growth yields and similar growth rates compared with those achieved on media prepared in deionized water. DA - 2005/2// PY - 2005/2// DO - 10.1007/S10295-004-0195-9 VL - 32 IS - 2 SP - 61-66 J2 - J IND MICROBIOL BIOTECHNOL LA - en OP - SN - 1367-5435 1476-5535 UR - http://dx.doi.org/10.1007/S10295-004-0195-9 DB - Crossref KW - Bacillus methanolicus KW - salt-tolerant KW - seawater KW - adaptation ER - TY - JOUR TI - Oxidative and hydrolytic stability of a novel acrylic terpolymer for biomedical applications AU - Veleva, Anka N. AU - Khan, Saad A. AU - Cooper, Stuart L. T2 - Journal of Biomedical Materials Research Part A AB - Abstract Oxidative and hydrolytic biostability assessment was carried out on a novel acrylic material made of hexamethyl methacrylate (HMA), methyl methacrylate (MMA), and methacrylic acid (MAA). To simulate the in vivo microenvironment, solutions of H 2 O 2 /CoCl 2 and buffered solutions of cholesterol esterase (CE) and phospholipase A2 (PLA) were used. As controls, film specimens were incubated in deionized water. Samples were incubated in these solutions at 37°C for 10 weeks before physical and mechanical properties were evaluated by size exclusion chromatography (SEC), 1 H‐ nuclear magnetic resonance ( 1 H‐NMR), acid‐base titration, and Instron tensile testing. The results from this study indicate excellent biostability of HMA‐MMA‐MAA terpolymers and thus their potential for use in biomedical devices for long‐term implantation. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res, 2005 DA - 2005/// PY - 2005/// DO - 10.1002/jbm.a.30349 VL - 74A IS - 1 SP - 117-123 J2 - J. Biomed. Mater. Res. LA - en OP - SN - 1549-3296 1552-4965 UR - http://dx.doi.org/10.1002/jbm.a.30349 DB - Crossref KW - acrylic terpolymers KW - in vitro biostability KW - oxidative stress KW - hydrolytic stress KW - small-diameter vascular grafts ER - TY - JOUR TI - Evolution of periodicity in periodical cicadas. AU - Lehmann-Ziebarth, Nicolas AU - Heideman, Paul P. AU - Shapiro, Rebecca A. AU - Stoddart, Sonia L. AU - Hsiao, Chien Ching Lilian AU - Stephenson, Gordon R. AU - Milewski, Paul A. AU - Ives, Anthony R. T2 - Ecology AB - Periodical cicadas present numerous puzzles for biologists. First, their period is fixed, with individuals emerging as adults precisely after either 13 or 17 years (depending on species). Second, even when there are multiple species of either 13- or 17-year cicadas at the same location, only one or rarely two broods (cohorts) co-occur, so that periodical cicada adults appear episodically. Third, the 13- or 17-year periods of cicadas suggest there is something important about prime numbers. Finally, single broods can dominate large areas, with geographical boundaries of broods remaining generally stable through time. While previous mathematical models have been used to investigate some of these puzzles individually, here we investigate them all simultaneously. Unlike previous models, we take an explicitly evolutionary approach. Although not enough information is known about periodical cicadas to draw firm conclusions, the theoretical arguments favor a combination of predator satiation and nymph competition as being key to the evolution of strictly fixed periods and occurrence of only one brood at most geographical locations. Despite ecological mechanisms that can select for strictly fixed periods, there seem to be no plausible ecological mechanisms that select for periods being prime numbers. This suggests that the explanation for prime-numbered periods, rather than just fixed periods, may reside in physiological or genetic mechanisms or constraints. DA - 2005/12// PY - 2005/12// DO - 10.1890/04-1615 VL - 86 IS - 12 SP - 3200-3211 SN - 0012-9658 UR - http://dx.doi.org/10.1890/04-1615 KW - Allee effects KW - evolution of periodicity KW - Magicicada KW - rock-paper-scissors competition KW - spatial dynamics ER - TY - JOUR TI - Advances in fuel cells AU - Zhang, X. T2 - DA - 2005/// PY - 2005/// VL - ER - TY - JOUR TI - Interfacial Properties of Fluorocarbon and Hydrocarbon Phosphate Surfactants at the Water−CO2Interface AU - Dickson, Jasper L. AU - Smith, P. Griffin AU - Dhanuka, Varun V. AU - Srinivasan, Vibha AU - Stone, Matthew T. AU - Rossky, Peter J. AU - Behles, Jacqueline A. AU - Keiper, Jason S. AU - Xu, Bin AU - Johnson, Charles AU - DeSimone, Joseph M. AU - Johnston, Keith P. T2 - Industrial & Engineering Chemistry Research AB - With high-pressure pendant-drop tensiometry, the interfacial tension (γ) and surface excess (Γ∞) for a family of ionic surfactants with identical phosphate headgroups and varying fluorocarbon and hydrocarbon tail structures were examined at the water−CO2 interface. To compensate for the unusually weak CO2−surfactant tail interactions, we designed hydrocarbon tails with weak tail−tail interactions to achieve a more favorable hydrophilic−CO2-philic balance. Branching of hydrocarbon surfactant tails is shown to lead to more favorable adsorption at the interface, closer to that of fluorocarbon surfactants. γ for a double-tail hydrocarbon phosphate surfactant with a relatively high degree of tail branching was lowered from the water−CO2 binary interface value of about 20 mN/m at 25 °C and 340 bar to 3.7 mN/m. This reduction in γ is attributed to both a decrease in the free volume between tails at the interface and reduced tail−tail interactions. In addition to tail structure, the effects of surfactant counterion, salt concentration, temperature, and CO2 density on γ and Γ∞ were investigated. The hydrophilic−CO2-philic balances of these surfactants are mapped by investigating changes in interfacial tension with these formulation variables. Low-molecular-weight branched hydrocarbon ionic surfactants are shown to stabilize concentrated CO2-in-water emulsions for greater than 1 h. DA - 2005/3// PY - 2005/3// DO - 10.1021/ie048999c VL - 44 IS - 5 SP - 1370-1380 J2 - Ind. Eng. Chem. Res. LA - en OP - SN - 0888-5885 1520-5045 UR - http://dx.doi.org/10.1021/ie048999c DB - Crossref ER - TY - JOUR TI - Fabrication of Ultramicroelectrodes Using A “Teflon-like” Coating Material AU - Liu, Biao AU - Rolland, Jason P. AU - DeSimone, Joseph M. AU - Bard, Allen J. T2 - Analytical Chemistry AB - A new method was developed for the preparation of ultramicroelectrodes (UMEs). In this method, a photocurable fluorinated functionalized perfluoropolyether, a liquid v-like polymer at room temperature, is used as the material for the insulation of metal microwires or carbon fibers. The UMEs prepared by this method were usually conical shaped and could be used both in aqueous solutions and with aprotic solvents. The relatively small thicknesses of the insulating sheath of the “Teflon-like” UME tips make them particularly useful for scanning electrochemical microscopy measurements. DA - 2005/5// PY - 2005/5// DO - 10.1021/ac0482918 VL - 77 IS - 9 SP - 3013-3017 J2 - Anal. Chem. LA - en OP - SN - 0003-2700 1520-6882 UR - http://dx.doi.org/10.1021/ac0482918 DB - Crossref ER - TY - JOUR TI - Pacific Rim Conference on Nanoscience AU - Quirke, N. AU - Parkinson, G. AU - Evans, D. AU - Gubbins, K.E. T2 - Molecular Simulation DA - 2005/// PY - 2005/// VL - 31 SP - 385–388 ER - TY - JOUR TI - Sorption of some azo-dyes on wool fiber from aqueous solutions AU - Saleem, M. AU - Pirzada, T. AU - Qadeer, R. T2 - Colloids and Surfaces A: Physicochemical and Engineering Aspects AB - Sorption of some azo-dyes (acid violet 17, acid blue 90, acid red 1 and direct red 80) on locally available wool fiber from aqueous solution has been investigated as a function of shaking time, pH and dyes concentration as a function of temperature. Sorption isotherms for dyes on wool fiber were obtained. It was found that the increasing temperature induces positive effect on the sorption process. Isosteric heat of adsorption (qst) have also been calculated at different surface coverage indicating that wool fiber used possessed heterogeneous surface with site of different activity. The results also indicate that initial sorption whether chemical or physical means, occurs first on the most active sites and then, as the concentration of dyes is increased, on sites of lesser activity. DA - 2005/// PY - 2005/// DO - 10.1016/j.colsurfa.2005.03.007 VL - 260 IS - 1-3 SP - 183-188 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-20444498547&partnerID=MN8TOARS KW - wool fiber KW - azo-dyes (acid violet 17 KW - acid blue 90 KW - acid red 1 KW - direct red 80) KW - sorption KW - aqueous solutions ER - TY - JOUR TI - The dynamics of single chains within a model polymer melt AU - McCormick, Julie A. AU - Hall, Carol K. AU - Khan, Saad A. T2 - The Journal of Chemical Physics AB - Discontinuous molecular dynamics simulations are performed on a system containing 32 hard chains of length 192 at a volume fraction of phi = 0.45 to explore the idea that localized entanglements have a significant effect on the dynamics of the individual chains within an entangled polymer melt. Anomalous behavior can still be observed when studying the dynamics of the individual chains, although increased time averaging causes the anomalous relaxation-memory-release behavior that was observed previously in the system to smooth out. First, the individual chain mean squared displacements and apparent diffusion coefficients are calculated, and a wide distribution of diffusive behavior is found. Although the apparent diffusion coefficient curve averaged over all chains displays the predicted long-time diffusive behavior, the curves for the individual chains differ both qualitatively and quantitatively. They display superdiffusive, diffusive, and subdiffusive behavior, with the largest percentage of chains exhibiting superdiffusive behavior and the smallest percentage exhibiting the predicted diffusive behavior. Next, the individual chain end-to-end vector autocorrelation functions and relaxation times are determined, and a wide distribution of stress relaxation behavior is found. The times when the end-to-end vector autocorrelation functions relax completely span almost an order of magnitude in reduced time. For some chains, the end-to-end vector autocorrelation function relaxes smoothly toward zero similar to the system average; however, for other chains the relaxation is slowed greatly, indicating the presence of additional entanglements. Almost half of the chains exhibit the anomalous behavior in the end-to-end vector autocorrelation function. Finally, the dynamic properties are displayed for a single chain exhibiting anomalous relaxation-memory-release behavior, supporting the idea that the relaxation-memory-release behavior is a single-chain property. DA - 2005/3/15/ PY - 2005/3/15/ DO - 10.1063/1.1863852 VL - 122 IS - 11 SP - 114902 J2 - The Journal of Chemical Physics LA - en OP - SN - 0021-9606 1089-7690 UR - http://dx.doi.org/10.1063/1.1863852 DB - Crossref ER - TY - JOUR TI - Molecular-Based Equations of State at the Graduate Level AU - Colina, C.M. AU - Olivera-Fuentes, C. AU - Gubbins, K.E. T2 - Chemical Engineering Education DA - 2005/// PY - 2005/// VL - 39 SP - 250–257 ER - TY - JOUR TI - Curvature dependency of surface tension in multicomponent systems AU - Santiso, Erik AU - Firoozabadi, Abbas T2 - AIChE Journal AB - Abstract The effect of curvature on the surface tension of droplets and bubbles in both single and multicomponent systems is modeled using the basic equations from classical thermodynamics. The three expressions used in our work are the Gibbs adsorption equation for multicomponent systems, the relation between the surface tension at the surface of tension and the distance parameter δ, and the Macleod–Sugden equation for surface tension and its extension to multicomponent systems. The Peng–Robinson equation of state is used to describe the bulk phases. We also assume that the surface tension expression remains valid in terms of the properties of the bulk phases for both flat and curved interfaces. For a flat surface we have developed a rigorous thermodynamics approach for the calculation of the Tolman distance parameter. For curved surfaces, the results from our model reveal a decrease in surface tension with curvature in bubbles and a nonmonotonic behavior in droplets for single‐component systems. Our predictions are in good agreement with the literature results when the interface is described using the framework of the density functional theory by three different groups. For multicomponent systems, the results show that the surface tension in a bubble, although monotonic with curvature, can increase or decrease in a large bubble depending on the temperature and composition of the mixture. In a droplet, the surface tension can have a nonmonotonic behavior similar to that of single‐component systems. © 2005 American Institute of Chemical Engineers AIChE J, 2006 DA - 2005/// PY - 2005/// DO - 10.1002/aic.10588 VL - 52 IS - 1 SP - 311-322 J2 - AIChE J. LA - en OP - SN - 0001-1541 1547-5905 UR - http://dx.doi.org/10.1002/aic.10588 DB - Crossref KW - curvature effect on multicomponents KW - surface tension KW - multicomponent mixtures ER - TY - CONF TI - Self-propelling semiconductor devices demonstrate new electroosmotic motility principles AU - Chang, S.T. AU - Velev, O.D. AU - Paunov, V.N. C2 - 2005/// C3 - AIChE Annual Meeting, Conference Proceedings DA - 2005/// UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-33645575757&partnerID=MN8TOARS ER - TY - JOUR TI - Molecular effects of anionic surfactants on lysozyme precipitation and crystallization AU - Velev, O.D. AU - Pan, Y.H. AU - Kaler, E.W. AU - Lenhoff, A.M. T2 - Crystal Growth and Design AB - Surfactants are used as additives in some protein separations and crystallization procedures, but the mechanism of their action is still poorly understood. By measuring the osmotic second virial coefficients of lysozyme solutions by static light scattering, we show that small amounts of anionic surfactants of varying molecular weight always make the protein−protein interactions in solution more attractive and that both the charge of the headgroup and the length of the hydrophobic tail mediate the interactions. The same surfactants also modify lysozyme crystallization and promote formation of twinned phases with gross morphologies different from those seen in the absence of surfactant, some of which display remarkably structured patterns on a micrometer scale. The surfactant effects are, however, often only kinetic, as the phases obtained initially recrystallize slowly into large stable crystals. These crystals are of excellent X-ray diffraction quality and resolution (up to 1.4 Å). Their symmetry, unit cell dimensions, crystal contacts, and protein backbone conformation are the same as those commonly observed for lysozyme, but sometimes occur at atypical pH values. The data suggest new techniques for modification of protein crystallization. DA - 2005/// PY - 2005/// DO - 10.1021/cg049852r VL - 5 IS - 1 SP - 351-359 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-12844258990&partnerID=MN8TOARS ER - TY - CONF TI - Graduate and undergraduate teaching of colloid science and nanoscale engineering - Combining fundamentals with emerging technologies AU - Velev, O.D. C2 - 2005/// C3 - AIChE Annual Meeting, Conference Proceedings DA - 2005/// UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-33645646847&partnerID=MN8TOARS ER - TY - CONF TI - Fabrication of novel types of colloidosome microcapsules for drug delivery applications AU - Paunov, V.N. AU - Noble, P.F. AU - Cayre, O.J. AU - Alargova, R.G. AU - Velev, O.D. C2 - 2005/// C3 - Materials Research Society Symposium Proceedings DA - 2005/// VL - 845 SP - 279-283 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-20344390030&partnerID=MN8TOARS ER - TY - CONF TI - Designing silver-enhnaced nanoparticle based immunoassays for antigen/antibody detection AU - Gupta, S. AU - Huda, S. AU - Velev, O.D. AU - Kilpatrick, P.K. C2 - 2005/// C3 - AIChE Annual Meeting, Conference Proceedings DA - 2005/// UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-33645648355&partnerID=MN8TOARS ER - TY - CONF TI - Controlled dielectrophoretic assembly of bio-inorganic composite materials using live cells and functionalized particles AU - Gupta, S. AU - Alargova, R.A. AU - Kilpatrick, P.K. AU - Velev, O.D. C2 - 2005/// C3 - AIChE Annual Meeting, Conference Proceedings DA - 2005/// SP - 14245-14248 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-33645634751&partnerID=MN8TOARS ER - TY - CONF TI - Controlled deposition and modification of antireflective coatings from silica nanoparticles AU - Prevo, B.G. AU - Hwang, Y. AU - McClain, J.B. AU - Carbonell, R.G. AU - Velev, O.D. C2 - 2005/// C3 - AIChE Annual Meeting Conference Proceedings DA - 2005/// VL - 2005 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-33646755458&partnerID=MN8TOARS ER - TY - BOOK TI - Assembly and application of carbon nanotube fibrils with controlled and variable lengths by dielectrophoresis AU - Tang, J. AU - Yang, G. AU - Zhang, J. AU - Geng, H. AU - Gao, B. AU - Qin, L.-C. AU - Zhou, O. AU - Velev, O.D. DA - 2005/// PY - 2005/// DO - 10.1142/9789812701879_0023 SE - 193-198 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84967679651&partnerID=MN8TOARS ER - TY - JOUR TI - Solvent-free composite peo-ceramic fiber/mat electrolytes for lithium secondary cells AU - Wang, C. AU - Zhang, X. AU - Appleby, A. J. T2 - Journal of the Electrochemical Society AB - Solvent-free composite poly(ethylene oxide) (PEO)-ceramic fiber or mat electrolytes with high ionic conductivity and good interfacial stability have been developed using high-ionic-conductivity fibers and mats. The conducting ceramic fibers can penetrate the cross section of the electrolyte film to provide long-range lithium-ion transfer channels, thus producing composite electrolytes with high conductivity. In this work, a maximum room-temperature conductivity of S cm−1 was achieved for 20 wt % fiber in a PEO- mixture containing 12.5 wt % in PEO. The maximum transference number obtained was 0.7. The ceramic fibers in this composite electrolyte are coated by a very thin PEO layer, which is sufficient to provide good interfacial stability with lithium-ion and lithium-metal anodes. © 2004 The Electrochemical Society. All rights reserved. DA - 2005/// PY - 2005/// DO - https://doi.org/10.1149/1.1828952 VL - 152 ER - TY - JOUR TI - Ionic transport and interfacial stability of sulfonate-modified fumed silicas as nanocomposite electrolytes AU - Zhang, X. W. AU - Fedkiw, P. S. T2 - Journal of the Electrochemical Society AB - Degussa A200 and R711 fumed silica surfaces were modified by attaching lithium sulfonate groups through alkyl or oligomer chains, respectively, in an attempt to form single-ion conducting fumed silicas: A200-lithium propanesulfonate (A200-LiPS), R711-poly(lithium vinylsulfonate) (R711-pLiVS), and R711-poly(lithium 2-acrylamido-2-methyl-1-propanesulfonate) (R711-pLiAMPS). Conductivity, lithium transference number, and Li/electrolyte interfacial stability measurements were conducted on nanocomposite electrolytes prepared by dispersing the conducting fumed silicas into solvents consisting of oligomeric polyethylene glycol dimethyl ether (PEGdm), polyethylene oxide (PEO), or PEGdm/PEO blends. Among the three sulfonate-modified fumed silicas, the highest conductivity was always obtained using R711-pLiAMPS. A maximum room-temperature conductivity of was obtained at a surface concentration of and a Li:O mole ratio of 1:100 ( filler). The maximum lithium transference number achieved for the same R711-pLiAMPS-based system is 0.78 at a surface concentration of and a Li:O mole ration of 1:20 ( filler). Adding lithium salts to the solvent, such as lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(perfluoroethylenesulfonyl)imide (LiBETI), lithium bis(oxalato)borate (LiBOB), and lithium phosphate , increases room-temperature conductivity and interfacial stability while maintaining relatively high lithium transference numbers. DA - 2005/// PY - 2005/// DO - https://doi.org/10.1149/1.2109661 VL - 152 ER - TY - JOUR TI - Impedance spectra of carbon black filled high-density polyethylene composites AU - Wang, Y. J. AU - Pan, Y. AU - Zhang, X. AU - Tan, K. T2 - Journal of Applied Polymer Science AB - Abstract Carbon black (CB) filled high‐density polyethylene (HDPE) composites are prepared by ordinary blending for use as an electrical conductive polymer composite. The composite changes from an electrical insulator to a conductor as the CB content is increased from 10 to 20 wt %, which is called the percolation region. For explanatory purposes, three models, namely, “conduction via nonohmic contacting chain,” “conduction via ohmic contacting chain,” and a mixture of them corresponding to the conductions in the percolation region, high CB loading region, and limiting high CB loading are proposed by the reasonable configurations of aggregate resistance, contact resistance, gap capacitance, and joining aggregates induction. The characters of the impedance spectra based on the three models are theoretically analyzed. In order to find some link between the electrical conductivity and the CB dispersion manner in the composites, the impedance spectra of three samples, HDPE/15 wt % CB (the center of the percolation region), HDPE/25 wt % CB (a typical point in the high CB loading region), and HDPE/19 wt % CB (the limiting high CB loading region), are measured by plotting the impedance modulus and phase angle against the frequency and by drawing the Cole–Cole circle of the imaginary part and real part of the impedance modulus of each sample. The modeled approached spectra and the spectra measured on the three samples are compared and the following results are found: the measured impedance spectrum of HDPE/15 wt % CB (percolation region) is quite close to the model of conduction via nonohmic contacting chain. The character of the measured spectrum of HDPE/25 wt % CB consists of the form of the model of conduction via ohmic contacting chain. The impedance behavior of HDPE/19 wt % CB exhibits a mixture of the two models. From the comparisons, it is concluded that the electrical conducting network in the percolation region of the CB filled HDPE composite is composed of aggregate resistance, nonohmic contact resistance, and gap capacitance, and that of the high CB loading region consists of continuously joined CB aggregate chains, which are possibly wound and assume helix‐like (not straight lines) conductive chains, acting as electrical inductions as the current passes through. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1344–1350, 2005 DA - 2005/// PY - 2005/// DO - https://doi.org/10.1002/app.22297 VL - 98 ER - TY - CHAP TI - A Brief Overview of Fuel Cells AU - Zhang, Xiangwu T2 - Advances in Fuel Cells A2 - Zhang, Xiangwu PY - 2005/// SP - 1-11, ER - TY - JOUR TI - On the use of ammonia electrolysis for hydrogen production AU - Vitse, F AU - Cooper, M AU - Botte, GG T2 - JOURNAL OF POWER SOURCES AB - An ammonia alkaline electrolytic cell for the production of hydrogen is presented. Challenges involved in using ammonia electro-oxidation for sustainable, low-cost, high-purity hydrogen production are identified and solutions are proposed. Electrodeposition was selected as a technique of preparing low-loading ammonia electrocatalysts. The efficiency of the electrolytic cell was improved by using bimetallic electrodeposited catalysts (at both electrodes) containing Pt and a low concentration of secondary metals (Ru, Ir). Pt–Ir deposits showed the highest activity toward ammonia oxidation. An experimental procedure is shown which minimizes the reversible deactivation of the electrode. Significant current densities were obtained (above 100 mA cm−2) during electrolysis testing at relatively low metal loading, low cell voltages, and high cell efficiencies. These results point to ammonia electrolysis as a promising candidate for an alternative process for low-cost, low-temperature, high-purity hydrogen production. DA - 2005/3/24/ PY - 2005/3/24/ DO - 10.1016/j.jpowsour.2004.09.043 VL - 142 IS - 1-2 SP - 18-26 SN - 1873-2755 KW - ammonia electrolysis KW - alkaline fuel cell KW - hydrogen production KW - electrodeposition KW - bimetallic catalyst KW - water reduction ER - TY - JOUR TI - Synchrotron photoionization measurements of combustion intermediates: Photoionization efficiency and identification of C3H2 isomers AU - Taatjes, CA AU - Klippenstein, SJ AU - Hansen, N AU - Miller, JA AU - Cool, TA AU - Wang, J AU - Law, ME AU - Westmoreland, PR T2 - PHYSICAL CHEMISTRY CHEMICAL PHYSICS AB - Photoionization mass spectrometry using tunable vacuum-ultraviolet synchrotron radiation is applied to the study of C3H2 Sampled from a rich cyclopentene flame. The photoionization efficiency has been measured between 8.5 eV and 11.0 eV. Franck-Condon factors for photoionization are calculated from B3LYP/ 6-311++-G(d,p) characterizations of the neutral and cation of the two lowest-energy C3H2 isomers, triplet propargylene (HCCCH, prop-2-ynylidene) and singlet cyclopropenylidene (cyclo-HCCCH). Comparison of the calculated Franck-Condon envelopes with the experimental photoionization efficiency spectrum determines the adiabatic ionization energy of triplet propargylene to be (8.96 +/- 0.04) eV. Ionization energies for cyclopropenylidene, propargylene and propadienylidene (H2CCC) calculated using QCISD(T) with triple-zeta and quadruple-zeta basis sets extrapolated to the infinite basis set limit are in excellent agreement with the present determination of the ionization energy for propargylene and with literature values for cyclopropenylidene and propadienylidene. The results suggest the presence of both propargylene and cyclopropenylidene in the cyclopentene flame and allow reanalysis of electron ionization measurements of C3H2 in other flames. Possible chemical pathways for C3H2 formation in these flames are briefly discussed. DA - 2005/// PY - 2005/// DO - 10.1039/b417160h VL - 7 IS - 5 SP - 806-813 SN - 1463-9084 ER - TY - JOUR TI - Studies of a fuel-rich propane flame with photoionization mass spectrometry AU - Cool, TA AU - Nakajima, K AU - Taatjes, CA AU - McIlroy, A AU - Westmoreland, PR AU - Law, ME AU - Morel, A T2 - PROCEEDINGS OF THE COMBUSTION INSTITUTE AB - Flame-sampling photoionization mass spectrometry, using continuously tunable synchrotron radiation, offers important advantages for studies of flame chemistry. Mole fraction profile measurements for 24 flame species are presented for a fuel-rich low-pressure premixed laminar C3H8/O2/Ar flame. Near-threshold photoionization efficiency measurements provide selective detection of individual isomers and unambiguous identifications of other flame species of near-equal mass. The absolute molar composition of the allene and propyne isomers of C3H4 was determined. Absolute cross-sections for photoionization of C2H2, C2H4, CH3OH, C3H4 (propyne), CH3CHO, (CH3)2CO, and C6H6 were used to determine molecular beam mass discrimination factors valid for ion masses ranging from 26 to 78 amu. DA - 2005/// PY - 2005/// DO - 10.1016/j.proci.2004.08.103 VL - 30 IS - Pt.1 SP - 1681-1688 SN - 1873-2704 KW - mass spectrometry KW - photoionization KW - premixed laminar flame ER - TY - JOUR TI - Recent advances in flame-sampling molecular-beam mass spectrometry AU - Westmoreland, P. R. AU - Law, M. E. AU - Gon, S. AU - Cool, T. A. AU - Wang, J. AU - McIlroy, A. AU - Taatjes, C. A. AU - Hansen, N. AU - Qi, F. AU - Kasper, T. AU - Kohse-Hoeinghaus, K. AU - Ahmed, M. AU - Peterka, D. S. AU - Poisson, L. T2 - Chemical and Physical Processes in Combustion DA - 2005/// PY - 2005/// SP - 205-212 ER - TY - JOUR TI - Photoionization mass spectrometer for studies of flame chemistry with a synchrotron light source AU - Cool, TA AU - McIlroy, A AU - Qi, F AU - Westmoreland, PR AU - Poisson, L AU - Peterka, DS AU - Ahmed, M T2 - REVIEW OF SCIENTIFIC INSTRUMENTS AB - A flame-sampling molecular-beam photoionization mass spectrometer, recently designed and constructed for use with a synchrotron-radiation light source, provides significant improvements over previous molecular-beam mass spectrometers that have employed either electron-impact ionization or vacuum ultraviolet laser photoionization. These include superior signal-to-noise ratio, soft ionization, and photon energies easily and precisely tunable [E∕ΔE(FWHM)≈250–400] over the 7.8–17-eV range required for quantitative measurements of the concentrations and isomeric compositions of flame species. Mass resolution of the time-of-flight mass spectrometer is m∕Δm=400 and sensitivity reaches ppm levels. The design of the instrument and its advantages for studies of flame chemistry are discussed. DA - 2005/9// PY - 2005/9// DO - 10.1063/1.2010307 VL - 76 IS - 9 SP - SN - 0034-6748 ER - TY - JOUR TI - Nd-doped GdVO4 films prepared by pulsed-laser deposition on SiO2/Si substance AU - Dong, ZG AU - Wang, FY AU - Fan, YX AU - Lu, P AU - Zhu, SN AU - Lim, PK AU - Tang, TB T2 - APPLIED PHYSICS LETTERS AB - Nd-doped GdVO4(Nd:GdVO4) films with a-axis preferred orientation were fabricated on SiO2∕Si substrate by pulsed-laser deposition. Fluorescences at around 1065.0 and 1342.5 nm, corresponding to F3∕24→I11∕24 and F3∕24→I13∕24 transitions, respectively, were excited simultaneously with an 808 nm diode laser. Waveguide behaviors in the film were investigated by using the prism coupling technique at the wavelength of 632.8 nm. Both TE and TM mode spectra revealed that favorable light confinements were achieved within the Nd:GdVO4 waveguide layer. Additionally, the optically anisotropic properties of the film were studied in detail. DA - 2005/4/11/ PY - 2005/4/11/ DO - 10.1063/1.1898439 VL - 86 IS - 15 SP - SN - 1077-3118 ER - TY - JOUR TI - Insights into a premixed stoichiometric cyclohexane flame AU - Law, M. E. AU - Westmoreland, P. R. AU - Cool, T. A. AU - Wang, J. AU - Hansen, N. AU - Taatjes, C. A. AU - Kasper, T. T2 - Chemical and Physical Processes in Combustion DA - 2005/// PY - 2005/// SP - 69-99 ER - TY - JOUR TI - Identification of species and separation of isomers in a premixed fuel-rich cyclohexane flame AU - Gon, S. AU - Law, M. E. AU - Westmoreland, P. R. AU - Cool, T. A. AU - Wang, J. AU - Hansen, N. AU - Taatjes, C. A. AU - Kasper, T. AU - Obwald, P. T2 - Chemical and Physical Processes in Combustion DA - 2005/// PY - 2005/// SP - 221-224 ER - TY - JOUR TI - IUPAC critical evaluation of thermochemical properties of selected radicals. Part I AU - Ruscic, B AU - Boggs, JE AU - Burcat, A AU - Csaszar, AG AU - Demaison, J AU - Janoschek, R AU - Martin, JML AU - Morton, ML AU - Rossi, MJ AU - Stanton, JF AU - Szalay, PG AU - Westmoreland, PR AU - Zabel, F AU - Berces, T T2 - JOURNAL OF PHYSICAL AND CHEMICAL REFERENCE DATA AB - This is the first part of a series of articles reporting critically evaluated thermochemical properties of selected free radicals. The present article contains datasheets for 11 radicals: CH, CH2(triplet), CH2(singlet), CH3, CH2OH, CH3O, CH3CO, C2H5O, C6H5CH2, OH, and NH2. The thermochemical properties discussed are the enthalpy of formation, as well as the heat capacity, integrated heat capacity, and entropy of the radicals. One distinguishing feature of the present evaluation is the systematic utilization of available kinetic, spectroscopic and ion thermochemical data as well as high-level theoretical results. DA - 2005/6// PY - 2005/6// DO - 10.1063/1.1724828 VL - 34 IS - 2 SP - 573-656 SN - 1529-7845 KW - critical evaluation KW - enthalpy of formation KW - free radicals KW - thermochemical properties ER - TY - JOUR TI - Enols Are Common Intermediates in Hydrocarbon Oxidation AU - Taatjes, C.A. AU - Hansen, N. AU - McIlroy, A. AU - Miller, J.A. AU - Senosiain, J.P. AU - Klippenstein, S.J. AU - Qi, F. AU - Sheng, L. AU - Zhang, Y. AU - Cool, T.A. AU - Wang, J. AU - Westmoreland, P.R. AU - Law, M.E. AU - Kasper, T. AU - Kohse-Höinghaus, K. T2 - Science AB - Models for chemical mechanisms of hydrocarbon oxidation rely on spectrometric identification of molecular structures in flames. Carbonyl (keto) compounds are well-established combustion intermediates. However, their less-stable enol tautomers, bearing OH groups adjacent to carbon-carbon double bonds, are not included in standard models. We observed substantial quantities of two-, three-, and four-carbon enols by photoionization mass spectrometry of flames burning representative compounds from modern fuel blends. Concentration profiles demonstrate that enol flame chemistry cannot be accounted for purely by keto-enol tautomerization. Currently accepted hydrocarbon oxidation mechanisms will likely require revision to explain the formation and reactivity of these unexpected compounds. DA - 2005/6/24/ PY - 2005/6/24/ DO - 10.1126/science.1112532 VL - 308 IS - 5730 SP - 1887-1889 SN - 0036-8075 1095-9203 UR - http://dx.doi.org/10.1126/science.1112532 ER - TY - JOUR TI - Allene addition to a fuel-lean ethylene flat flame AU - Law, ME AU - Carriere, T AU - Westmoreland, PR T2 - PROCEEDINGS OF THE COMBUSTION INSTITUTE AB - Two fuel-lean C2H4/O2/Ar flames, one doped with allene, were analyzed using molecular-beam mass spectrometry (MBMS) and modeled. Flame conditions were ϕ = 0.70 and 56.4% Ar for the undoped flame and ϕ = 0.69, 56.5% Ar and [allene]/[C2H4] = 0.0242 for the doped flame, both at 4.000 kPa (30 Torr) with a 30.6 cm/s burner velocity at 300 K. Modeling and measurements agreed well for the major species, but H, O, and OH were overpredicted. Perturbation effects by allene addition included an increase in propargyl (C3H3) and C6H6 species in both experiments and the model. Modeling suggested that the major C6H6 species is benzene. Measurements done on the Chemical Dynamics Beamline of the Advance Light Source, within Lawrence Berkeley National Laboratory, using photoionization molecular-beam mass spectrometry supported the model predictions by determining that the major C6H6 species is benzene (45%), followed by 1,5-hexadiyne (35%), and fulvene (20%). Using the rate constants of Miller and Klippenstein [J. Phys. Chem. A 107 (39) (2003) 7783], the model predicted C3H3 self-combination reactions to be the major benzene formation route through direct formation as well as through formation of thermal fulvene and linear C6H6, which can then isomerize to benzene. Benzene is destroyed mainly through hydrogen abstraction to form phenyl and through O attack to form phenoxy. A major phenyl destruction path is to benzene. The ultimate destruction of benzene goes through phenyl and phenoxy. Both species undergo CO elimination by O addition to phenyl and decomposition of phenoxy to form cyclopentadienyl, which undergoes further oxidation to form CO, CO2, and H2O. DA - 2005/// PY - 2005/// DO - 10.1016/j.proci.2004.08.239 VL - 30 IS - Pt.1 SP - 1353-1361 SN - 1873-2704 KW - allene KW - benzene KW - oxidation KW - flames ER - TY - JOUR TI - 1,5-Hexadiyne and fulvene presence in premixed allene and propyne flames AU - Law, M. E. AU - Gon, S. AU - Westmoreland, P. R. AU - Cool, T. A. AU - Wang, J. AU - Hansen, N. AU - Taatjes, C. A. T2 - Chemical and Physical Processes in Combustion DA - 2005/// PY - 2005/// SP - 4-7 ER - TY - JOUR TI - Direct imprinting of dielectric materials for dual Damascene processing AU - Stewart, MD AU - Wetzel, JT AU - Schmid, GM AU - Palmieri, F AU - Thompson, E AU - Kim, EK AU - Wang, D AU - Sotodeh, K AU - Jen, K AU - Johnson, SC AU - Hao, JJ AU - Dickey, MD AU - Nishimura, Y AU - Laine, RM AU - Resnick, DJ AU - Willson, CG T2 - Emerging Lithographic Technologies IX, Pts 1 and 2 AB - Advanced microprocessors require several (eight or more) levels of wiring to carry signal and power from transistor to transistor and to the outside world. Each wiring level must make connection to the levels above and below it through via/contact layers. The dual damascene approach to fabricating these interconnected structures creates a wiring level and a via level simultaneously, thereby reducing the total number of processing steps. However, the dual damascene strategy (of which there are several variations) still requires around twenty process steps per wiring layer. In this work, an approach to damascene processing that is based on step-and-flash imprint lithography (SFIL) is discussed. This imprint damascene process requires fewer than half as many steps as the standard photolithographic dual damascene approach. By using an imprint template with two levels of patterning, a single imprint lithography step can replace two photolithography steps. Further efficiencies are possible if the imprint resist material is itself a functional dielectric material. This work is a demonstration of the compatibility of imprint lithography (specifically SFIL) with back-end-of-line processing using a dual damascene approach with functional materials. DA - 2005/// PY - 2005/// DO - 10.1117/12.599977 VL - 5751 SP - 210-218 SN - 0277-786X KW - SFIL KW - dual damascene KW - nanoimprint lithography KW - multi-tier template KW - interconnect ER - TY - JOUR TI - Vinyl ether formulations for step and flash imprint lithography AU - Kim, EK AU - Stewart, MD AU - Wu, K AU - Palmieri, FL AU - Dickey, MD AU - Ekerdt, JG AU - Willson, CG T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B AB - Acrylates have been used as patterning monomers in step and flash imprint lithography. Vinyl ether formulations have a lower viscosity, faster curing rate, and higher tensile strength than acrylate formulations. However, the lack of commercially available, silicon-containing vinyl ether monomers has required the synthesis of several new vinyl ethers. An ideal monomer has low viscosity and low vapor pressure. The vapor pressure of silicon-containing vinyl ethers was predicted using the Joback-Reid, Lyderson, and Lee-Kesler methods. BVMDSO (1,1,3,3-tetramethyl-1,3-bis(vinyloxymethyl)-disiloxane) has the lowest viscosity of the synthesized silicon-containing vinyl ethers that meet the volatility requirement for a 80 pl dispense volume. The formulation of BVMDSO, CHDVE (cyclohexanedimethanol divinyl ether), and TEGDVE (triethylene glycol divinyl ether) shows good tensile strength and modulus. The formulation of BVMDSO, CHDVE, TEGDVE, and fluorinated acetate can print a 30 nm line because it has a low separation force and high tensile modulus. DA - 2005/// PY - 2005/// DO - 10.1116/1.2131881 VL - 23 IS - 6 SP - 2967-2971 SN - 2166-2746 ER - TY - JOUR TI - Study of the kinetics of step and flash imprint lithography photopolymerization AU - Dickey, MD AU - Burns, RL AU - Kim, EK AU - Johnson, SC AU - Stacey, NA AU - Willson, CG T2 - AICHE JOURNAL AB - Abstract Step and Flash Imprint Lithography (SFIL) is a promising high‐resolution, yet low‐cost patterning technique that uses a UV induced photopolymerization to replicate features on a patterned template. The SFIL process utilizes an acrylate‐based free radical polymerization, which is inhibited by oxygen. A semiempirical kinetic model is presented that demonstrates the effects of oxygen on SFIL. On the basis of kinetic measurements, dissolved oxygen causes an inhibition period at the onset of exposure that extends the required exposure time. Oxygen inhibition also results in a thin perimeter of under‐cured material surrounding the template due to oxygen diffusion from the ambient during polymerization. The model allows us to study the impact of oxygen on SFIL as a function of various formulation and exposure variables. Methods of limiting the impact of oxygen are presented, such as alternative chemistries and inerting techniques. © 2005 American Institute of Chemical Engineers AIChE J, 2005 DA - 2005/9// PY - 2005/9// DO - 10.1002/aic.10477 VL - 51 IS - 9 SP - 2547-2555 SN - 1547-5905 KW - nanoimprint lithography KW - reaction kinetics KW - photopolymerization ER - TY - JOUR TI - Mitochondrial mutation detection using enhanced multiplex denaturing high-performance liquid chromatography AU - Bayat, A AU - Walter, J AU - Lamb, H AU - Marino, M AU - Ferguson, MWJ AU - Ollier, WER T2 - INTERNATIONAL JOURNAL OF IMMUNOGENETICS AB - Summary In this study, we investigated the presence of mutations within the mitochondrial genome in 40 Caucasian subjects using an enhanced multiplex denaturing high‐performance liquid chromatography (DHPLC) approach. The enhanced DHPLC approach has increased sensitivity and throughput, and reduced analysis time per individual sample compared to conventional methods. This technique involved amplifying the mitochondrial genome in 18 fragments ranging in size from 300 to 2000 bp using a novel proofreading polymerase (Optimase TM , Transgenomic Inc., Omaha, NE) with a low misincorporation rate. Fourteen of these fragments underwent subsequent restriction digestion using a combination of five restriction enzymes to enable multiplex DHPLC analysis; the remaining four underwent conventional DHPLC. Using this complete mitochondrial genome‐screening approach, we confirmed a number of previously reported mutations and additionally identified a large number of novel mutations using an enhanced DHPLC technique. DA - 2005/6// PY - 2005/6// DO - 10.1111/j.1744-313x.2005.00508.x VL - 32 IS - 3 SP - 199-205 SN - 1744-313X ER - TY - JOUR TI - Electric field and dewetting induced hierarchical structure formation in polymer/polymer/air trilayers AU - Leach, KA AU - Gupta, S AU - Dickey, MD AU - Willson, CG AU - Russell, TP T2 - CHAOS AB - Electrohydrodynamics were studied in a trilayer thin film system consisting of two different polymeric layers and air. A polymer with a higher dielectric constant, poly(methyl methacrylate), was sandwiched between air and a lower dielectric constant polymer, polystyrene. An electric field was applied normal to the interfaces. Along with electrostatic forces, dewetting forces were significant at two of the interfaces, namely, the polystyrene/silicon wafer and the polystyrene/poly(methyl methacrylate) interfaces. These two combined forces produce novel closed-cell structures that are difficult to produce by other existing techniques. DA - 2005/12// PY - 2005/12// DO - 10.1063/1.2132248 VL - 15 IS - 4 SP - SN - 1089-7682 ER - TY - JOUR TI - Effects of etch barrier densification on step and flash imprint lithography AU - Johnson, S AU - Burns, R AU - Kim, EK AU - Dickey, M AU - Schmid, G AU - Meiring, J AU - Burns, S AU - Willson, CG AU - Convey, D AU - Wei, Y AU - Fejes, P AU - Gehoski, K AU - Mancini, D AU - Nordquist, K AU - Dauksher, WJ AU - Resnick, DJ T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY B AB - Previous work with the mechanical properties of step and flash imprint lithography etch barrier materials has shown bulk volumetric shrinkage trends that could impact imprinted feature dimensions and profile. This article uses mesoscopic and finite element modeling techniques to model the behavior of the etch barrier during polymerization. Model results are then compared to cross section images of template and etch barrier. Volumetric shrinkage is seen to impact imprinted feature profiles largely as a change in feature height. DA - 2005/// PY - 2005/// DO - 10.1116/1.2102971 VL - 23 IS - 6 SP - 2553-2556 SN - 1071-1023 ER - TY - JOUR TI - Conformational analysis of gossypol and its derivatives by molecular mechanics AU - Beisel CL, Dowd MK AU - PJ, Reilly T2 - Journal of Molecular Structure DA - 2005/// PY - 2005/// VL - 730 SP - 51-58 ER - TY - JOUR TI - Raman investigation of the ionic liquid N-methyl-N-propylpyrrolidinium bis(trifluoromethane-sulfonyl)imide and its mixture with LiN(SO2CF3)2 AU - Castriota, M. AU - Caruso, T. AU - Agostino, R. G. AU - Cazzanelli, E. AU - Henderson, W. A. AU - Passerini, S. T2 - Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment & General Theory DA - 2005/// PY - 2005/// VL - 109 IS - 1 SP - 92-96 ER - TY - JOUR TI - PEO-based polymer electrolytes with ionic liquids and their use in lithium metal-polymer electrolyte batteries AU - Shin, J.-H. AU - Henderson, W. A. AU - Passerini, S. T2 - Journal of the Electrochemical Society DA - 2005/// PY - 2005/// VL - 152 IS - 5 SP - A978-A983 ER - TY - JOUR TI - NMR investigation of ionic liquid-LiX mixtures: Pyrrolidinium cations and TFSI- anions AU - Nicotera, I. AU - Oliviero, C. AU - Henderson, W. A. AU - Appetecchi, G. B. AU - Passerini, S. T2 - Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces & Biophysical DA - 2005/// PY - 2005/// VL - 109 IS - 48 SP - 22814-22819 ER - TY - JOUR TI - Integrating cell-level kinetic modeling into the design of engineered protein therapeutics AU - Rao, BM AU - Lauffenburger, DA AU - Wittrup, KD T2 - NATURE BIOTECHNOLOGY DA - 2005/2// PY - 2005/2// DO - 10.1038/nbt1064 VL - 23 IS - 2 SP - 191-194 SN - 1546-1696 ER - TY - JOUR TI - Glyme-lithium bis(trifluoromethanesulfonyl)imide and glyme-lithium bis(perfluoroethanesulfonyl)-imide phase behavior and solvate structures AU - Henderson, W. A. AU - McKenna, F. AU - Khan, M. A. AU - Brooks, N. R. AU - Young, V. G., Jr. AU - Frech, R. T2 - Chemistry of Materials DA - 2005/// PY - 2005/// VL - 17 IS - 9 SP - 2284-2289 ER - TY - JOUR TI - Engineering protein therapeutics within a systems-level computational context AU - Rao, B.M. AU - Lauffenburger, D. A. AU - Wittrup, K. D. T2 - Nature Biotechnology DA - 2005/// PY - 2005/// VL - 23 IS - 2 SP - 191-194 ER - TY - JOUR TI - Cycling stability of a hybrid activated carbon//poly(3-methylthiophene) supercapacitor with N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquid as electrolyte AU - Balducci, A. AU - Henderson, W. A. AU - Mastragostino, M. AU - Passerini, S. AU - Simon, P. AU - Soavi, F. T2 - Electrochimica Acta DA - 2005/// PY - 2005/// VL - 50 IS - 11 SP - 2233-2237 ER - TY - JOUR TI - Culture development for human embryonic stem cell propagation: molecular aspects and challenges AU - Rao, BM AU - Zandstra, PW T2 - CURRENT OPINION IN BIOTECHNOLOGY AB - Basic fibroblast growth factor and members of the transforming growth factor-β superfamily are important regulators of human embryonic stem cell (hESC) self-renewal. Extensive cross-talk between the intracellular signaling pathways activated by these factors contributes to maintenance of the undifferentiated hESC state. Understanding the molecular regulation of hESC self-renewal will facilitate the design of improved systems for hESC propagation and provide a foundation for strategies to direct the differentiation of hESCs to clinically relevant cell types. DA - 2005/10// PY - 2005/10// DO - 10.1016/j.copbio.2005.08.001 VL - 16 IS - 5 SP - 568-576 SN - 1879-0429 ER - TY - JOUR TI - Crystal structures of poly(ethylene oxide)3:LiBF4 and (diglyme)n:LiBF4 (n = 1,2) AU - Andreev, Y. G. AU - Seneviratne, V. AU - Khan, M. AU - Henderson, W. A. AU - Frech, R. E. AU - Bruce, P. G. T2 - Chemistry of Materials DA - 2005/// PY - 2005/// VL - 17 IS - 4 SP - 767-772 ER - TY - JOUR TI - Computational analysis of EGFR inhibition by Argos AU - Reeves, Gregory T. AU - Kalifa, Rachel AU - Klein, Daryl E. AU - Lemmon, Mark A. AU - Shvartsman, Stanislav Y. T2 - Developmental Biology AB - Argos, a secreted inhibitor of the Drosophila epidermal growth factor receptor, and the only known secreted receptor tyrosine kinase inhibitor, acts by sequestering the EGFR ligand Spitz. We use computational modeling to show that this biochemically-determined mechanism of Argos action can explain available genetic data for EGFR/Spitz/Argos interactions in vivo. We find that efficient Spitz sequestration by Argos is key for explaining the existing data and for providing a robust feedback loop that modulates the Spitz gradient in embryonic ventral ectoderm patterning. Computational analysis of the EGFR/Spitz/Argos module in the ventral ectoderm shows that Argos need not be long-ranged to account for genetic data, and can actually have very short range. In our models, Argos with long or short length scale functions to limit the range and action of secreted Spitz. Thus, the spatial range of Argos does not have to be tightly regulated or may act at different ranges in distinct developmental contexts. DA - 2005/8// PY - 2005/8// DO - 10.1016/j.ydbio.2005.05.013 VL - 284 IS - 2 SP - 523-535 J2 - Developmental Biology LA - en OP - SN - 0012-1606 UR - http://dx.doi.org/10.1016/j.ydbio.2005.05.013 DB - Crossref KW - EGFR inhibition KW - Argos KW - Spitz ER - TY - JOUR TI - Recent developments in the ENEA lithium metal battery project AU - Shin, J.-H. AU - Henderson, W. A. AU - Appetecchi, G. B. AU - Alessandrini, F. AU - Passerini, S. T2 - Electrochimica Acta DA - 2005/// PY - 2005/// VL - 50 IS - 19 SP - 3859-3865 ER - TY - JOUR TI - An elegant fix for polymer electrolytes AU - Shin, J.-H. AU - Henderson, W. A. AU - Passerini, S. T2 - Electrochemical and Solid State Letters DA - 2005/// PY - 2005/// VL - 8 IS - 2 SP - A125-A127 ER - TY - JOUR TI - Web-based delivery of ChE design projects AU - Bullard, L. G. AU - Niehues, P. K. AU - Peretti, S. W. AU - White, S. H T2 - Chemical Engineering Education DA - 2005/// PY - 2005/// VL - 39 IS - 3 SP - 194-199 ER - TY - BOOK TI - Elementary principles of chemical processes AU - Felder., Richard M. DA - 2005/// PY - 2005/// PB - Hoboken, NJ: John Wiley & Sons, Inc. ER - TY - CONF TI - On the origins of adhesion in papermaking systems AU - Rojas, O. J. AU - Dedinaite, A. AU - Byrd, M. V. AU - Hubbe, M. A. AU - Claesson, P. M. C2 - 2005/// C3 - Advances in Paper Science and Technology: Transactions of the 13th Fundamental research symposium, vols 1-3 DA - 2005/// SP - 1351-1378 ER - TY - CONF TI - Graduated compression stockings (GCS): Effects of materials mechanical properties and structures on the skin pressure profiles AU - Liu, R. AU - Kwok, Y. L. AU - Li, Y. AU - Lao, T. T. AU - Zhang, X. C2 - 2005/// C3 - Intelligent ambience and well-being : Ambience 05, International Scientific Conference 19-20 September, 2005, Tampere, Finland ; proceedings DA - 2005/// SP - 4 PB - Tampere: Tampere University of Technology SN - 9789521514296 ER - TY - BOOK TI - Advances in fuel cells AU - Zhang, X. DA - 2005/// PY - 2005/// PB - Kerala, India: Research Signpost, SN - 9788130800264 ER - TY - JOUR TI - Solvent-free composite PEO-ceramic fiber/mat electrolytes for lithium secondary cells AU - Wang, CS AU - Zhang, XW AU - Appleby, AJ T2 - JOURNAL OF THE ELECTROCHEMICAL SOCIETY AB - Solvent-free composite poly(ethylene oxide) (PEO)-ceramic fiber or mat electrolytes with high ionic conductivity and good interfacial stability have been developed using high-ionic-conductivity fibers and mats. The conducting ceramic fibers can penetrate the cross section of the electrolyte film to provide long-range lithium-ion transfer channels, thus producing composite electrolytes with high conductivity. In this work, a maximum room-temperature conductivity of S cm−1 was achieved for 20 wt % fiber in a PEO- mixture containing 12.5 wt % in PEO. The maximum transference number obtained was 0.7. The ceramic fibers in this composite electrolyte are coated by a very thin PEO layer, which is sufficient to provide good interfacial stability with lithium-ion and lithium-metal anodes. © 2004 The Electrochemical Society. All rights reserved. DA - 2005/// PY - 2005/// DO - 10.1149/1.1828952 VL - 152 IS - 1 SP - A205-A209 SN - 0013-4651 UR - https://publons.com/publon/7178371/ ER - TY - JOUR TI - Impedance spectra of carbon black filled high-density polyethylene composites AU - Wang, YJ AU - Pan, Y AU - Zhang, XW AU - Tan, K T2 - JOURNAL OF APPLIED POLYMER SCIENCE AB - Abstract Carbon black (CB) filled high‐density polyethylene (HDPE) composites are prepared by ordinary blending for use as an electrical conductive polymer composite. The composite changes from an electrical insulator to a conductor as the CB content is increased from 10 to 20 wt %, which is called the percolation region. For explanatory purposes, three models, namely, “conduction via nonohmic contacting chain,” “conduction via ohmic contacting chain,” and a mixture of them corresponding to the conductions in the percolation region, high CB loading region, and limiting high CB loading are proposed by the reasonable configurations of aggregate resistance, contact resistance, gap capacitance, and joining aggregates induction. The characters of the impedance spectra based on the three models are theoretically analyzed. In order to find some link between the electrical conductivity and the CB dispersion manner in the composites, the impedance spectra of three samples, HDPE/15 wt % CB (the center of the percolation region), HDPE/25 wt % CB (a typical point in the high CB loading region), and HDPE/19 wt % CB (the limiting high CB loading region), are measured by plotting the impedance modulus and phase angle against the frequency and by drawing the Cole–Cole circle of the imaginary part and real part of the impedance modulus of each sample. The modeled approached spectra and the spectra measured on the three samples are compared and the following results are found: the measured impedance spectrum of HDPE/15 wt % CB (percolation region) is quite close to the model of conduction via nonohmic contacting chain. The character of the measured spectrum of HDPE/25 wt % CB consists of the form of the model of conduction via ohmic contacting chain. The impedance behavior of HDPE/19 wt % CB exhibits a mixture of the two models. From the comparisons, it is concluded that the electrical conducting network in the percolation region of the CB filled HDPE composite is composed of aggregate resistance, nonohmic contact resistance, and gap capacitance, and that of the high CB loading region consists of continuously joined CB aggregate chains, which are possibly wound and assume helix‐like (not straight lines) conductive chains, acting as electrical inductions as the current passes through. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1344–1350, 2005 DA - 2005/11/5/ PY - 2005/11/5/ DO - 10.1002/app.22297 VL - 98 IS - 3 SP - 1344-1350 SN - 1097-4628 UR - https://publons.com/publon/7178385/ KW - composites KW - polyethylene KW - modulus KW - chain ER - TY - PAT TI - Versatile system for triple-gated transistors with engineered corners AU - Visokay, M. R. AU - Chambers, J. J. C2 - 2005/// DA - 2005/// PY - 2005/// ER - TY - PAT TI - Method for fabricating split gate transistor device having high-k dielectrics AU - Rotondaro, A. L. AU - Visokay, M. R. AU - Chambers, J. J. AU - Colombo, L. C2 - 2005/// DA - 2005/// PY - 2005/// ER - TY - PAT TI - Metal gate MOS transistors and methods for making the same AU - Visokay, M. R. AU - Colombo, L. AU - Chambers, J. J. C2 - 2005/// DA - 2005/// PY - 2005/// ER - TY - PAT TI - IR-coated halogen lamp using reflective end coats AU - Bigion, L. AU - Israel, R. AU - Chowdhury, A. I. AU - Lieszkovsky, L. C2 - 2005/// DA - 2005/// PY - 2005/// ER - TY - PAT TI - High temperature interface layer growth for high-k gate dielectric AU - Colombo, L. AU - Chambers, J. J. AU - Rotondaro, A. L. AU - Visokay, M. R. C2 - 2005/// DA - 2005/// PY - 2005/// ER - TY - JOUR TI - The paradox of papermaking AU - Hubbe, M. A. AU - Rojas, O. J. T2 - Chemical Engineering Education DA - 2005/// PY - 2005/// VL - 39 IS - 2 SP - 146-155 ER - TY - JOUR TI - Adapting a core service-learning model for wide-ranging implementation: An institutional case study AU - Clayton, P. H. AU - Ash, S. L. AU - Bullard, L. G. T2 - Creative College Teaching Journal DA - 2005/// PY - 2005/// VL - 2 IS - 1 SP - 10-26 ER - TY - JOUR TI - Small Peptide Ligands for Affinity Separations of Biological Molecules AU - Wang, Guangquan AU - Salm, Jeffrey R. AU - Gurgel, Patrick V. AU - Carbonell, Ruben G. T2 - CHEMICAL ENGINEERING TRENDS AND DEVELOPMENTS AB - This chapter contains sections titled: Downstream Processing in Biopharmaceutical Production Affinity Chromatography Advantages of Small Peptide Ligands Combinatorial Peptide Libraries Screening of One-Bead-One-Peptide Libraries Characterization of Peptide Ligands Future Challenges and Opportunities References DA - 2005/// PY - 2005/// DO - 10.1002/0470025018.ch3 SP - 63-83 ER - TY - PAT TI - Compositions for fracturing subterranean formations AU - Kelly, R. M. AU - Khan, S. A. AU - Leduc, P. AU - Tayal, A. AU - Prud'homme, R. K. C2 - 2005/// DA - 2005/// PY - 2005/// ER - TY - JOUR TI - A discretization based smoothing method for solving semi-infinite variational inequalities AU - Ozcam, B. AU - Cheng, H. T2 - Journal of Industrial and Management Optimization DA - 2005/// PY - 2005/// VL - 1 IS - 2 SP - 219-233 ER - TY - JOUR TI - Viscoelastic properties of isomeric alkylglucoside surfactants studied by surface light scattering AU - Rojas, OJ AU - Neuman, RD AU - Claesson, PM T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - Surface light scattering (SLS) by capillary waves was used to investigate the adsorption behavior of non-ionic sugar surfactants at the air/liquid interface. SLS by the subphase (water) followed predictions from hydrodynamic theory. The viscoelastic properties (surface elasticity and surface viscosity) of monolayers formed by octyl beta-glucoside, octyl alpha-glucoside, and 2-ethylhexyl alpha-glucoside surfactants were quantified at submicellar concentrations. It is further concluded that a diffusional relaxation model describes the observed trends in high-frequency, nonintrusive laser light scattering experiments. The interfacial diffusion coefficients that resulted from fitting this diffusional relaxation model to surface elasticity values obtained with SLS reflect the molecular dynamics of the subphase near the interface. However, differences from the theoretical predictions indicate the existence of effects not accounted for such as thermal convection, molecular rearrangements, and other relaxation mechanisms within the monolayer. Our results demonstrate important differences in molecular packing at the air-water interface for the studied isomeric surfactants. DA - 2005/12/1/ PY - 2005/12/1/ DO - 10.1021/jp054132w VL - 109 IS - 47 SP - 22440-22448 SN - 1520-6106 ER - TY - JOUR TI - Tunable CO2 transport through mixed polyether membranes AU - Patel, NP AU - Hunt, MA AU - Lin-Gibson, S AU - Bencherif, S AU - Spontak, RJ T2 - JOURNAL OF MEMBRANE SCIENCE AB - Gas-separation membranes composed of polyethers such as poly(ethylene glycol)diacrylate (PEGda) or poly(propylene glycol)diacrylate (PPGda) exhibit high CO2 solubility selectivity, which makes them attractive for use in H2 and air purification. In this work, we investigate the factors governing CO2 and H2 transport in mixed polyether matrices. Addition of semicrystalline poly(ethylene oxide)s to amorphous PEGda lowers the net CO2 permeability and CO2/H2 selectivity due to crystal formation. Gas permeation through the amorphous fraction, however, remains unaffected, confirming the existence of a molecular weight limit below which the entire membrane participates in gas transport. The permeabilities of CO2 and H2, as well as their activation energy of permeation, in miscible PEGda/PPGda blends follow the linear rule of mixtures over the temperature range explored. Incorporation of amine moieties employed in liquid membranes into either the PEGda matrix during crosslinking or the PEG backbone generally reduces CO2/H2 selectivity but occasionally improves CO2 permeability. DA - 2005/4/1/ PY - 2005/4/1/ DO - 10.1016/j.memsci.2004.11.003 VL - 251 IS - 1-2 SP - 51-57 SN - 1873-3123 KW - polyether KW - gas-separation membrane KW - reverse selectivity ER - TY - JOUR TI - The effect of pore connectivity on water adsorption isotherms in non-activated graphitic nanopores AU - Striolo, A AU - Gubbins, KE AU - Chialvo, AA AU - Cummings, PT T2 - ADSORPTION-JOURNAL OF THE INTERNATIONAL ADSORPTION SOCIETY DA - 2005/// PY - 2005/// DO - 10.1007/s10450-005-5947-y VL - 11 IS - Suppl.1 SP - 337-341 SN - 0929-5607 KW - SPC/E water KW - carbon-slit pores KW - grand canonical Monte Carlo simulations ER - TY - JOUR TI - Temperature effect on adsorption/desorption isotherms for a simple fluid confined within various nanopores AU - Coasne, B AU - Gubbins, KE AU - Pellenq, RJM T2 - ADSORPTION-JOURNAL OF THE INTERNATIONAL ADSORPTION SOCIETY AB - We report a Grand Canonical Monte Carlo study of the temperature dependence of adsorption/desorption hysteresis for porous matrices having different morphologies and topologies. We aim at gaining some insights on the concept of critical hysteresis temperature, T cc , defined as the temperature at which the hysteresis loop disappears. Simulated T cc for cylindrical, ellipsoidal, and constricted pores follow the experimental scaling law established for MCM-41 silica materials. In contrast, T cc for Vycor samples with a largest pore size ~2.5 nm and 5.0 nm obey a different relationship, in qualitative agreement with experiments. DA - 2005/// PY - 2005/// DO - 10.1007/s10450-005-5939-y VL - 11 IS - Suppl. 1 SP - 289-294 SN - 1572-8757 KW - capillary condensation KW - Monte-Carlo simulation KW - nanoporous material KW - hysteresis ER - TY - JOUR TI - Simulated water adsorption isotherms in hydrophilic and hydrophobic cylindrical nanopores AU - Striolo, A AU - Naicker, PK AU - Chialvo, AA AU - Cummings, PT AU - Gubbins, KE T2 - ADSORPTION-JOURNAL OF THE INTERNATIONAL ADSORPTION SOCIETY DA - 2005/// PY - 2005/// DO - 10.1007/s10450-005-5957-9 VL - 11 IS - Suppl. 1 SP - 397-401 SN - 0929-5607 KW - SPC/E water KW - grand canonical Monte Carlo simulations KW - Debye-functional analysis KW - XRD pattern ER - TY - JOUR TI - Role of the micro- and nanostructure in the performance of surface-enhanced Raman scattering substrates assembled from gold nanoparticles AU - Kuncicky, DM AU - Christesen, SD AU - Velev, OD T2 - APPLIED SPECTROSCOPY AB - Highly active and stable substrates for surface-enhanced Raman scattering (SERS) can be fabricated by using colloidal crystals to template gold nanoparticles into structured porous films. The structure-dependent performance of these SERS substrates was systematically characterized with cyanide in continuous flow microfluidic chambers. A matrix of experiments was designed to isolate the SERS contributions arising from nano- and microscale porosity, long-range ordering of the micropores, and the thickness of the nanoparticle layer. The SERS results were compared to the substrate structure observed by scanning electron microscopy (SEM) and optical microscopy to correlate substrate structure to SERS performance. The Raman peak intensity was consistently highest for nanoporous substrates with three-dimensionally ordered micropores, and decreases if the micropores are not ordered or not templated. Removing the nanoscale porosity by fusion of the nanoparticles (without removing the large micropores) leads to a drastic plunge in substrate performance. The peak intensity does not strongly correlate to the thickness of the nanoparticle films. The results make possible the efficient controlled fabrication of stable, reproducible, and highly active substrates for SERS based chemical sensors with continuous sampling. DA - 2005/4// PY - 2005/4// DO - 10.1366/0003702053641559 VL - 59 IS - 4 SP - 401-409 SN - 1943-3530 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-17444364500&partnerID=MN8TOARS KW - surface-enhanced Raman spectroscopy KW - colloidal crystal templating KW - structured gold films KW - cyanide detection KW - nanoparticles ER - TY - JOUR TI - Rapid formation of soft hydrophilic silicone elastomer surfaces AU - Efimenko, K AU - Crowe, JA AU - Manias, E AU - Schwark, DW AU - Fischer, DA AU - Genzer, J T2 - POLYMER AB - We report on the rapid formation of hydrophilic silicone elastomer surfaces by ultraviolet/ozone (UVO) irradiation of poly(vinylmethyl siloxane) (PVMS) network films. Our results reveal that the PVMS network surfaces render hydrophilic upon only a short UVO exposure time (seconds to a few minutes). We also provide evidence that the brief UVO irradiation treatment does not cause dramatic changes in the surface modulus of the PVMS network. We compare the rate of formation of hydrophilic silicone elastomer surfaces made of PVMS to those of model poly(dimethyl siloxane) (PDMS) and commercial-grade PDMS (Sylgard-184). We find that relative to PVMS, 20 times longer UVO treatment times are needed to oxidize the PDMS network surfaces in order to achieve a comparable density of surface-bound hydrophilic moieties. The longer UVO treatment times for PDMS are in turn responsible for the dramatic increase in surface modulus of UVO treated PDMS, relative to PVMS. We also study the formation of self-assembled monolayers (SAMs) made of semifluorinated organosilane precursors on the PVMS-UVO and PDMS-UVO network surfaces. By tuning the UVO treatment times and by utilizing mono- and tri-functional organosilanes we find that while mono-functionalized organosilanes attach directly to the substrate, SAMs of tri-functionalized organosilanes form in-plane networks on the underlying UVO-modified silicone elastomer surface, even with only short UVO exposure times. DA - 2005/10/24/ PY - 2005/10/24/ DO - 10.1016/j.polymer.2005.07.046 VL - 46 IS - 22 SP - 9329-9341 SN - 1873-2291 KW - functionalized silicone rubber KW - surface modification KW - self-assembly ER - TY - JOUR TI - Property and morphology development in nanocomposite thermoplastic elastomer gels AU - Maanen, GJ AU - Seeley, SL AU - Capracotta, MD AU - White, SA AU - Bukovnik, RR AU - Hartmann, J AU - Martin, JD AU - Spontak, RJ T2 - LANGMUIR AB - Thermoplastic elastomer gels (TPEGs), molecular networks composed of a microphase-separated multiblock copolymer swollen to a large extent by a low-volatility midblock-selective solvent, are ubiquitous in a wide range of contemporary technologies, including home and office products, athletic equipment, and telecommunications devices. In this work, we investigate the effect of several network-forming nanoscale modifiers-two different silica nanoparticles, three different nanoclays, and a multiwalled carbon nanotube-on the property and morphology development of a TPEG prepared from a microphase-ordered poly(styrene-b-(ethylene-co-butylene)-b-styrene) (SEBS) triblock copolymer imbibed with an EB-compatible aliphatic mineral oil. Dynamic rheological measurements of the resultant nanocomposite TPEGs confirm that addition of these modifiers affects the linear viscoelastic threshold and increases, to different extents, the dynamic elastic modulus, the dynamic yield stress, and the maximum operating temperature of the parent TPEG. X-ray diffraction analysis reveals that the nanoclays used to generate three series of modified TPEGs are generally swollen with copolymer and/or solvent. DA - 2005/3/29/ PY - 2005/3/29/ DO - 10.1021/la047837i VL - 21 IS - 7 SP - 3106-3115 SN - 0743-7463 ER - TY - JOUR TI - Nonequilibrium model for sorption and swelling of bulk glassy polymer films with Supercritical carbon dioxide AU - Carla, V AU - Wang, K AU - Hussain, Y AU - Efimenko, K AU - Genzer, J AU - Grant, C AU - Sarti, GC AU - Carbonell, RG AU - Doghieri, F T2 - MACROMOLECULES AB - A new procedure is introduced for the calculation of solubility isotherms of plasticizing agents in glassy polymer matrices with particular application to the case of absorption of supercritical gases in bulk glassy polymer films. The model presented is an extension of the nonequilibrium thermodynamics for glassy polymers (NET-GP) approach, modified to allow for the calculation of the effects of pressure, temperature, and gas concentration on the glass transition. Mass sorption and one-dimensional swelling behavior are analyzed for the carbon dioxide (CO2)−poly(methyl methacrylate) (PMMA) system at high pressure. A quantitative comparison is presented between the model performance and experimental data measured using quartz crystal microbalance (QCM) and high-pressure ellipsometry (HPE). DA - 2005/11/29/ PY - 2005/11/29/ DO - 10.1021/ma0506684 VL - 38 IS - 24 SP - 10299-10313 SN - 1520-5835 ER - TY - JOUR TI - Nested self-similar wrinkling patterns in skins AU - Efimenko, K AU - Rackaitis, M AU - Manias, E AU - Vaziri, A AU - Mahadevan, L AU - Genzer, J T2 - NATURE MATERIALS DA - 2005/4// PY - 2005/4// DO - 10.1038/nmat1342 VL - 4 IS - 4 SP - 293-297 SN - 1476-4660 ER - TY - JOUR TI - NO decomposition over a Pd/MgO catalyst prepared from [Pd(acac)(2)] AU - Wang, XQ AU - Spivey, JJ AU - Lamb, HH T2 - APPLIED CATALYSIS B-ENVIRONMENTAL AB - A Pd/MgO catalyst was prepared by adsorption of palladium bis-acetylacetonate [Pd(acac)2] onto highly dehydroxylated MgO from toluene solution and subsequent reduction in flowing H2 at 300 °C. The resultant catalyst was characterized by Pd K-edge X-ray absorption fine structure (XAFS) spectroscopy, temperature-programmed desorption (TPD), and Fourier transform infrared (FTIR) spectroscopy of adsorbed NO. The adsorbed [Pd(acac)2] species decomposes on heating in H2 to form 20–25 Å supported Pd particles; however, organic residues from the acetylacetonate ligands remain on the catalyst surface. The FTIR spectrum of NO adsorbed on the reduced Pd/MgO catalyst at 25 °C contains one principal band at 1722 cm−1 due to atop Pd nitrosyl species. In situ XAFS of the Pd/MgO catalyst indicates that neither Pd oxidation nor particle sintering occurs during heating in flowing 1% NO/He to 300 °C. NO decomposition over the Pd/MgO catalyst was investigated using temperature-programmed reaction spectroscopy (TPRS) and steady-state activity measurements. During the initial TPRS cycle in flowing 1% NO/He, nearly complete NO consumption occurs at ∼270 °C due to oxidation of organic residues. O2 evolution commences at approximately 350 °C, and steady-state catalytic decomposition of NO to N2 and O2 occurs at 600 °C. Transient NO consumption during rapid cooling in 1% NO/He (after steady-state catalysis) is attributed to NOx adsorption on the Pd/MgO catalyst. DA - 2005/4/8/ PY - 2005/4/8/ DO - 10.1016/j.apcatb.2004.09.014 VL - 56 IS - 4 SP - 261-268 SN - 1873-3883 KW - NO decomposition KW - temperature-programmed reaction KW - temperature-programmed desorption KW - X-ray absorption fine structure spectroscopy KW - Fourier transform infrared spectroscopy ER - TY - JOUR TI - NMR and SANS studies of aggregation and microemulsion formation by phosphorus fluorosurfactants in liquid and supercritical carbon dioxide AU - Xu, B AU - Lynn, GW AU - Guo, J AU - Melnichenko, YB AU - Wignall, GD AU - McClain, JB AU - DeSimone, JM AU - Johnson, CS T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - 1H NMR relaxation and diffusion studies were performed on water-in-CO2 (W/C) microemulsion systems formed with phosphorus fluorosurfactants of bis[2-(F-hexyl)ethyl] phosphate salts (DiF8), having different counterions (Na+, NH4+, N(CH3)4+) by means of high-pressure in situ NMR. Water has a low solubility in CO2 and is mainly solubilized by the microemulsion droplets formed with surfactants added to CO2 and water mixtures. There is rapid exchange of water between the bulk CO2 and the microemulsion droplets; however, NMR relaxation measurements show that the entrapped water has restricted motion, and there is little “free” water in the core. Counterions entrapped by the droplets are mostly associated with the surfactant headgroups: diffusion measurements show that counterions and the surfactant molecules move together with a diffusion coefficient that is associated with the droplet. The outer shell of the microemulsion droplets consists of the surfactant tails with some associated CO2. For W/C microemulsions formed with the phosphate-based surfactant having the ammonia counterion (A-DiF8), the 1H NMR signal for NH4+ shows a much larger diffusion coefficient than that of the surfactant tails. This apparent paradox is explained on the basis of proton exchange between water and the ammonium ion. The observed dependence of the relaxation time (T2) on W0 (mole ratio of water to surfactant in the droplets) for water and NH4+ can also be explained by this exchange model. The average hydrodynamic radius of A−DiF8 microemulsion droplets estimated from NMR diffusion measurements (25 °C, 206 bar, W0 = 5) was Rh = 2.0 nm. Assuming the theoretical ratio of Rg/Rh = 0.775 for a solid sphere, where Rg is the radius of gyration, the equivalent hydrodynamic radius from SANS is Rh = 1.87 nm. The radii measured by the two techniques are in reasonable agreement, as the two techniques are weighted to measure somewhat different parts of the micelle structure. DA - 2005/5/26/ PY - 2005/5/26/ DO - 10.1021/jp0580322 VL - 109 IS - 20 SP - 10261-10269 SN - 1520-6106 ER - TY - JOUR TI - Metal foam supported Pt catalysts for the selective oxidation of CO in hydrogen AU - Sirijaruphan, A. AU - Goodwin, J. G. AU - Rice, R. W. AU - Wei, D. G. AU - Butcher, K. R. AU - Roberts, G. W. AU - Spivey, J. J. T2 - Applied Catalysis. A, General DA - 2005/// PY - 2005/// VL - 281 IS - 02-Jan SP - 09- ER - TY - JOUR TI - Low-temperature reactive coupling at polymer-polymer interfaces facilitated by supercritical CO2 AU - Harton, SE AU - Stevie, FA AU - Spontak, RJ AU - Koga, T AU - Rafailovich, MH AU - Sokolov, JC AU - Ade, H T2 - POLYMER AB - Supercritical CO2 (scCO2) has been used to facilitate reactions in thin film bilayers between functionalized polystyrene and poly(methyl methacrylate) at temperatures far below the glass transition temperatures of the respective polymers. Secondary ion mass spectrometry (SIMS) is used to monitor the reaction progression directly by measuring the interfacial excess of deuterated PS. Complementary X-ray reflectometry (XR) yields the interfacial width and surface roughness of bilayer films for reactive systems with and without the addition of scCO2, and comparisons are made with unreactive reference systems. From XR and SIMS analyses, the interfacial width and roughness have been found to be effectively independent of the reaction conditions employed here, and the primary impact of incorporated scCO2 is enhanced mobility of the reactive polymer chains. The use of scCO2 can change polymer mobility significantly enough over a very small temperature range (DTw15 8C) so that both diffusion- and reaction-controlled type behavior can be observed for otherwise identical systems. q 2005 Elsevier Ltd. All rights reserved. DA - 2005/11/14/ PY - 2005/11/14/ DO - 10.1016/j.polymer.2005.07.085 VL - 46 IS - 23 SP - 10173-10179 SN - 1873-2291 KW - polymer bends KW - reactive compatibilization KW - supercritical fluids ER - TY - JOUR TI - Freezing/melting of Lennard-Jones fluids in carbon nanotubes AU - Hung, FR AU - Gubbins, KE AU - Radhakrishnan, R AU - Szostak, K AU - Beguin, F AU - Dudziak, G AU - Sliwinska-Bartkowiak, M T2 - APPLIED PHYSICS LETTERS AB - We report molecular simulation and experimental results for the freezing/melting behavior of Lennard-Jones fluids adsorbed in pores of cylindrical geometry, using simple models for multiwalled carbon nanotubes (MWNTs) of inner diameter 5nm. For cylindrical pores, our results for a D=9.7σff MWNT show no formation of regular three-dimensional crystalline structures. They also suggest that the outer layers experience an increase in the freezing temperature, while the inner layers provoke a depression in the freezing temperature with respect to the bulk freezing point. Dielectric relaxation spectroscopy shows a solid-fluid transition at 234K for CCl4 in these MWNTs that is in qualitative agreement with that determined in our simulations for the inner adsorbed layers. DA - 2005/3/7/ PY - 2005/3/7/ DO - 10.1063/1.1862786 VL - 86 IS - 10 SP - SN - 1077-3118 ER - TY - JOUR TI - Freezing of mixtures confined in a slit nanopore AU - Coasne, B AU - Czwartos, J AU - Gubbins, KE AU - Hung, FR AU - Sliwinska-Bartkowiak, M T2 - ADSORPTION-JOURNAL OF THE INTERNATIONAL ADSORPTION SOCIETY AB - We report a Grand Canonical Monte Carlo study of the freezing/melting of Lennard-Jones A/B mixtures confined in a slit pore (H = 1.44 nm). The fluid/fluid interactions are chosen to model A = Ar and B = Kr. Fluid/wall interaction parameters are chosen so that the ratio of the wall/fluid to the fluid/fluid interactions for Kr and Ar is larger and smaller than 1, respectively. We find that the phase diagram of the confined mixture is of the same type than that for the bulk. The freezing temperature of confined mixtures rich in Kr is larger than the bulk. In contrast, we observe a decrease of the freezing temperature for mixtures rich in Ar. The confined crystal has a hexagonal structure (triangular symmetry), except for pure Ar where a square structure is observed. DA - 2005/// PY - 2005/// DO - 10.1007/s10450-005-5941-4 VL - 11 IS - Suppl. 1 SP - 301-306 SN - 1572-8757 KW - freezing KW - mixture KW - molecular simulation KW - confinement KW - solid-liquid phase diagram ER - TY - JOUR TI - Effects of activation on the structure and adsorption properties of a nanoporous carbon using molecular simulation AU - Jain, SK AU - Pikunic, JP AU - Pellenq, RJM AU - Gubbins, KE T2 - ADSORPTION-JOURNAL OF THE INTERNATIONAL ADSORPTION SOCIETY DA - 2005/// PY - 2005/// DO - 10.1007/s10450-005-5950-3 VL - 11 IS - Suppl.1 SP - 355-360 SN - 0929-5607 KW - reverse Monte Carlo KW - molecular simulation KW - activation KW - adsorption ER - TY - JOUR TI - Effect of metal foam supports on the selective oxidation of CO on Fe-promoted Pt/gamma-Al2O3 AU - Sirijaruphan, A. AU - Goodwin, J. G. AU - Rice, R. W. AU - Wei, D. G. AU - Butcher, K. R. AU - Roberts, G. W. AU - Spivey, J. J. T2 - Applied Catalysis. A, General DA - 2005/// PY - 2005/// VL - 281 IS - 02-Jan SP - 18- ER - TY - JOUR TI - Effect of Confinement on Chemical Reactions AU - Santiso, Erik E. AU - George, Aaron M. AU - Sliwinska-bartkowiak, Malgorzata AU - Nardelli, Marco Buongiorno AU - Gubbins, Keith E. T2 - Adsorption AB - Molecular simulation studies of chemical equilibrium for several reactions in pores of slit-like and cylindrical geometry have shown a significant effect of the confinement on the equilibrium compositions, with differences of several orders of magnitude with respect to the bulk fluid phase in some cases. As a first step towards the calculation of rate constants in confinement, we have studied the reaction mechanisms for several reactions involving small organic molecules in slit-like pores. We show results for the rotational isomerization of 1,3-butadiene and the unimolecular decomposition of formaldehyde obtained using plane wave pseudopotential density functional theory (DFT). These examples show the influence that confinement can have through both geometrical constraints and fluid-wall interactions. DA - 2005/7// PY - 2005/7// DO - 10.1007/s10450-005-5949-9 VL - 11 IS - S1 SP - 349-354 J2 - Adsorption LA - en OP - SN - 0929-5607 1572-8757 UR - http://dx.doi.org/10.1007/s10450-005-5949-9 DB - Crossref KW - chemical reactions KW - confinement KW - porous carbon KW - density functional theory ER - TY - JOUR TI - Denaturation and aggregation of three alpha-lactalbumin preparations at neutral pH AU - McGuffey, MK AU - Epting, KL AU - Kelly, RM AU - Foegeding, EA T2 - JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY AB - The denaturation and aggregation of reagent-grade (Σα-La), ion-exchange chromatography purified (IEXα-La), and a commercial-grade (Cα-La) α-lactalbumin were studied with differential scanning calorimetry (DSC), polyacrylamide gel electrophoresis, and turbidity measurement. All three preparations had similar thermal denaturation temperatures with an average of 63.7 °C. Heating pure preparations of α-lactalbumin produced three non-native monomer species and three distinct dimer species. This phenomenon was not observed in Cα-La. Turbidity development at 95 °C (τ95°C) indicated that pure preparations rapidly aggregate at pH 7.0, and evidence suggests that hydrophobic interactions drove this phenomenon. The Cα-La required 4 times the phosphate or excess Ca2+ concentrations to develop a similar τ95°C to the pure preparations and displayed a complex pH-dependent τ95°C behavior. Turbidity development dramatically decreased when the heating temperature was below 95 °C. A mechanism is provided, and the interrelationship between specific electrostatic interactions and hydrophobic attraction, in relation to the formation of disulfide-bonded products, is discussed. Keywords: α-Lactalbumin; whey proteins; denaturation and aggregation DA - 2005/4/20/ PY - 2005/4/20/ DO - 10.1021/jf048863p VL - 53 IS - 8 SP - 3182-3190 SN - 1520-5118 KW - alpha-lactalbumin KW - whey proteins KW - denaturation and aggregation ER - TY - JOUR TI - Continuous precipitation polymerization of acrylic acid in swercritical carbon dioxide: The polymerization rate and the polymer molecular weight AU - Liu, T AU - Desimone, JM AU - Roberts, GW T2 - JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY AB - Abstract The precipitation polymerization of acrylic acid in supercritical carbon dioxide was studied in a continuous stirred tank reactor with 2,2′‐azobis(2,4‐dimethylvaleronitrile) as the free‐radical initiator. The reactor temperature was between 50 and 90 °C, the pressure was 207 bar, and the average residence time was between 12 and 40 min. The product polymer was a white, dry, fine powder that dissolved in water. A wide range of polymer molecular weights (5–200 kg/mol) was obtained. The effects of the operating variables on the polymerization rate and on the polymer molecular weight were evaluated. The observed kinetics suggested that polymerization took place in both the supercritical fluid and the precipitated polymer particles. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2546–2555, 2005 DA - 2005/6/15/ PY - 2005/6/15/ DO - 10.1002/pola.20728 VL - 43 IS - 12 SP - 2546-2555 SN - 1099-0518 KW - acrylic acid KW - continuous polymerization KW - kinetics (polym.) KW - radical polymerization KW - supercritical carbon dioxide KW - water-soluble polymers ER - TY - JOUR TI - An experimental study of melting of CCl4 in carbon nanotubes AU - Jazdzewska, M AU - Hung, FR AU - Gubbins, KE AU - Sliwinska-Bartkowiak, M T2 - PHYSICAL CHEMISTRY CHEMICAL PHYSICS AB - We report dielectric relaxation spectroscopy measurements of the melting point of carbon tetrachloride confined within open-tip multi-walled carbon nanotubes with two different pore diameters, 4.0 and 2.8 nm. In both cases, a single transition temperature well above the bulk melting point was obtained for confined CCl4. These results contrast with what was obtained in our previous measurements using carbon nanotubes with a pore diameter of 5.0 nm, where multiple transition temperatures both above and below the bulk melting point of CCl4 were observed. Our experimental measurements are consistent with our recent molecular simulation results (F. R. Hung, B. Coasne, E. E. Santiso, K. E. Gubbins, F. R. Siperstein and M. Sliwinska-Bartkowiak, J. Chem. Phys., 2005, 122, 144706). Although the simulations overestimate the temperatures in which melting upon confinement occurs, both simulations and experiments suggest that all regions of adsorbate freeze at the same temperature, and that freezing occurs at higher temperatures upon reduction of the pore diameter. DA - 2005/// PY - 2005/// DO - 10.1039/b510245f VL - 7 IS - 22 SP - 3884-3887 SN - 1463-9084 ER - TY - JOUR TI - Adsorption of poly(ethylene oxide)-b-poly(E-caprolactone) copolymers at the silica-water interface AU - Vangeyte, P AU - Leyh, B AU - Rojas, OJ AU - Claesson, PM AU - Heinrich, M AU - Auvray, L AU - Willet, N AU - Jerome, R T2 - LANGMUIR AB - The adsorption of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) and poly(ethylene oxide)-b-poly(gamma-methyl-epsilon-caprolactone) copolymers in aqueous solution on silica and glass surfaces has been investigated by flow microcalorimetry, small-angle neutron scattering (SANS), surface forces, and complementary techniques. The studied copolymers consist of a poly(ethylene oxide) (PEO) block of M(n) = 5000 and a hydrophobic polyester block of poly(epsilon-caprolactone) (PCL) or poly(gamma-methyl-epsilon-caprolactone) (PMCL) of M(n) in the 950-2200 range. Compared to homoPEO, the adsorption of the copolymers is significantly increased by the connection of PEO to an aliphatic polyester block. According to calorimetric experiments, the copolymers interact with the surface mainly through the hydrophilic block. At low surface coverage, the PEO block interacts with the surface such that both PEO and PCL chains are exposed to the aqueous solution. At high surface coverage, a dense copolymer layer is observed with the PEO blocks oriented toward the solution. The structure of the copolymer layer has been analyzed by neutron scattering using the contrast matching technique and by tapping mode atomic force microscopy. The experimental observations agree with the coadsorption of micelles and free copolymer chains at the interface. DA - 2005/3/29/ PY - 2005/3/29/ DO - 10.1021/la047425+ VL - 21 IS - 7 SP - 2930-2940 SN - 0743-7463 ER - TY - JOUR TI - Using spectroscopic ellipsometry for quick prediction of number density of nanoparticles bound to non-transparent solid surfaces AU - Bhat, RR AU - Genzer, J T2 - SURFACE SCIENCE AB - We report on the use of spectroscopic ellipsometry (SE) in predicting number density of nanoparticles bound to the surfaces decorated with either organic monolayers or surface-grafted polymers. Two systems are considered that comprise citrate-stabilized gold nanoparticles adsorbed on: (1) 3-aminopropyltriethoxysilane (APTES) self-assembled monolayer (SAM), and (2) surface-tethered polyacrylamide (PAAm). Number density of gold nanoparticles on the surface is varied systematically by gradually increasing either the concentration of APTES molecules in the SAM or molecular weight of grafted PAAm. The adsorption of gold nanoparticles on APTES gradient surfaces is monitored via atomic force microscopy (AFM), near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and SE. The partition of gold nanoparticles on PAAm gradient assemblies is characterized by AFM, ultraviolet–visible (UV–vis) spectroscopy, and SE. By correlating the results obtained from the various techniques on nanoparticle coatings, we derive an empirical linear relationship between the number density of nanoparticles on surfaces and cos (Δ) parameter measured in SE. Excellent agreement between nanoparticle number density determined experimentally from AFM scans and that predicted by SE proves the potential of SE as a quick, predictive technique to estimate number density of nanoparticles bound to solid, non-transparent substrates. DA - 2005/12/10/ PY - 2005/12/10/ DO - 10.1016/j.susc.2005.09.014 VL - 596 IS - 1-3 SP - 187-196 SN - 1879-2758 KW - ellipsometry KW - self-assembly KW - nanoparticles KW - polymer brush KW - gradient KW - atomic force microscopy KW - NEXAFS KW - APTES ER - TY - JOUR TI - Reactions on cell membranes: Comparison of continuum theory and Brownian dynamics simulations AU - Monine, MI AU - Haugh, JM T2 - JOURNAL OF CHEMICAL PHYSICS AB - Biochemical transduction of signals received by living cells typically involves molecular interactions and enzyme-mediated reactions at the cell membrane, a problem that is analogous to reacting species on a catalyst surface or interface. We have developed an efficient Brownian dynamics algorithm that is especially suited for such systems and have compared the simulation results with various continuum theories through prediction of effective enzymatic rate constant values. We specifically consider reaction versus diffusion limitation, the effect of increasing enzyme density, and the spontaneous membrane association/dissociation of enzyme molecules. In all cases, we find the theory and simulations to be in quantitative agreement. This algorithm may be readily adapted for the stochastic simulation of more complex cell signaling systems. DA - 2005/8/15/ PY - 2005/8/15/ DO - 10.1063/1.2000236 VL - 123 IS - 7 SP - SN - 1089-7690 ER - TY - JOUR TI - Parameterization of molecular-based equations of state AU - Bouza, A AU - Colina, CM AU - Olivera-Fuentes, CG T2 - FLUID PHASE EQUILIBRIA AB - Despite significant advances in the development and formulation of molecular-based (MB) equations of state (EOS), their practical use has been limited, at least in part, by unavailability of the fluid-specific constants. In this work, we explore the possibility and consequences of obtaining the MBEOS parameters of a fluid directly from its critical constants Tc, Pc and acentric factor ω, as is done with cubic EOS. Four different models are used as examples: perturbed hard chain theory in original (PHCT) and simplified (SPHCT) forms, Huang–Radosz version of the statistical associating fluid theory (SAFT), and the augmented van der Waals theory as implemented in the Boublík–Alder–Chen–Kreglewski (BACK) EOS. For each model, the scaled critical and saturation properties are computed and approximated by polynomial expansions. Using these, the molecular parameters can be related to the macroscopic properties Tc, Pc and ω. In this way it is not necessary to fit the EOS parameters to extensive experimental data, because the parameters obtained are fully equivalent to those generated from complex minimization techniques. In particular, the BACK EOS, parameterized in terms of Tc, Pc, ω and critical compressibility factor Zc, gives excellent representation of the entire phase envelope. An alternative approach is also suggested where the experimental critical volume Vc and ω are matched, and a simple one-dimensional search is used to minimize the average absolute deviation of saturation pressures. The techniques presented in this work provide a simple way to estimate MBEOS parameters for a wide variety of fluids, and can be readily extended to other MBEOS. DA - 2005/2// PY - 2005/2// DO - 10.1016/j.fluid.2004.08.043 VL - 228 SP - 561-575 SN - 1879-0224 KW - PHCT KW - SPHCT KW - BACK KW - SAFT KW - critical properties KW - vapor-liquid equilibria ER - TY - JOUR TI - Orthogonal surface-grafted polymer gradients: A versatile combinatorial platform AU - Bhat, RR AU - Tomlinson, MR AU - Genzer, J T2 - JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS AB - Abstract Orthogonal polymer brush gradients are assemblies of surface‐anchored macromolecules, in which two material properties of the grafted chains ( e.g. , grafting density, molecular weight) vary independently in orthogonal directions. Here, we describe the formation and applications of two such orthogonal assemblies, involving: (1) molecular weight and grafting density (MW/σ) gradients of a given polymer and (2) molecular weight gradients (MW1/MW2), of two different polymers. Each point on orthogonal gradient substrate represents a unique combination of the two surface properties being varied, thus facilitating systematic investigation of a phenomenon that depends on the two said properties. We illustrate this point by employing orthogonal structures to study systematically: (1) formation of polymer brush‐nanoparticle composite assemblies, (2) protein adsorption and cell adhesion, and (3) chain conformations in tethered diblock copolymers exposed to selective solvents. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3384–3394, 2005 DA - 2005/12/1/ PY - 2005/12/1/ DO - 10.1002/polb.20640 VL - 43 IS - 23 SP - 3384-3394 SN - 1099-0488 KW - combinatorial polymer science KW - polymer gradient KW - polymer/nanoparticle ER - TY - JOUR TI - Novel associative polymer networks based on cyclodextrin inclusion compounds AU - Guo, XH AU - Abdala, AA AU - May, BL AU - Lincoln, SF AU - Khan, SA AU - Prud'homme, RK T2 - MACROMOLECULES AB - ADVERTISEMENT RETURN TO ISSUEPREVNoteNovel Associative Polymer Networks Based on Cyclodextrin Inclusion CompoundsXuhong Guo, Ahmed A. Abdala, Bruce L. May, Stephen F. Lincoln, Saad A. Khan, and Robert K. Prud'hommeView Author Information Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544; Departmant of Chemistry, University of Adelaide, Adelaide, SA 5005, Australia; and Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905 Cite this: Macromolecules 2005, 38, 7, 3037–3040Publication Date (Web):March 8, 2005Publication History Received12 January 2005Published online8 March 2005Published inissue 1 April 2005https://doi.org/10.1021/ma050071oCopyright © 2005 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1678Altmetric-Citations81LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (154 KB) Get e-AlertsSUBJECTS:Hydrophobicity,Macrocyclic compounds,Oligosaccharides,Polymers,Viscosity Get e-Alerts DA - 2005/4/5/ PY - 2005/4/5/ DO - 10.1021/ma050071o VL - 38 IS - 7 SP - 3037-3040 SN - 1520-5835 ER - TY - JOUR TI - Molecular simulation of gas adsorption in realistic models of silica nanopores AU - Coasne, B AU - Hung, FR AU - Siperstein, FR AU - Gubbins, KE T2 - ANNALES DE CHIMIE-SCIENCE DES MATERIAUX AB - Cet article presente une etude par simulation moleculaire de l'adsorption de Xe a 195 K dans deux modeles atomiques des pores de silice MCM-41. Le modele A consiste en un pore cylindrique regulier a section constante. Le modele B presente un important desordre de surface qui reproduit les aspects morphologiques d'un modele obtenu par simulation sur reseau du processus de synthese des pores de MCM-41. L'isotherme d'adsorption pour le modele A comporte une large boucle d'hysteresis, typique de la condensation capillaire dans des nanopores reguliers. Au contraire, le processus d'adsorption/desorption pour le modele B a une allure quasi continue et quasi reversible. A cause de l'importante rugosite de surface du modele B, la chaleur d'adsorption isosterique pour cet echantillon est beaucoup plus grande que celle obtenue pour le pore cylindrique regulier. Dans la mesure du possible, les resultats sont compares a des donnees experimentales. DA - 2005/// PY - 2005/// DO - 10.3166/acsm.30.375-383 VL - 30 IS - 4 SP - 375-383 SN - 1958-5934 ER - TY - JOUR TI - Effect of beta-sheet crystals on the thermal and rheological behavior of protein-based hydrogels derived from gelatin and silk fibroin AU - Gil, ES AU - Spontak, RJ AU - Hudson, SM T2 - MACROMOLECULAR BIOSCIENCE AB - Novel protein-based hydrogels have been prepared by blending gelatin (G) with amorphous Bombyx mori silk fibroin (SF) and subsequently promoting the formation of beta-sheet crystals in SF upon exposure to methanol or methanol/water solutions. Differential scanning calorimetry of the resultant hydrogels confirms the presence and thermoreversibility of the G helix-coil transition between ambient and body temperature at high G concentrations. At low G concentrations, this transition is shifted to higher temperatures and becomes progressively less pronounced. Complementary dynamic rheological measurements reveal solid-liquid cross-over at the G helix-coil transition temperature typically between 30 and 36 degrees C in blends prior to the formation of beta-sheet crystals. Introducing the beta-sheet conformation in SF stabilizes the hydrogel network and extends the solid-like behavior of the hydrogels to elevated temperatures beyond body temperature with as little as 10 wt.-% SF. The temperature-dependent elastic modulus across the G helix-coil transition is reversible, indicating that the conformational change in G can be used in stabilized G/SF hydrogels to induce thermally triggered encapsulant release. DA - 2005/8/12/ PY - 2005/8/12/ DO - 10.1002/mabi.200500076 VL - 5 IS - 8 SP - 702-709 SN - 1616-5187 KW - gelatin KW - helix-coil transition KW - hydrogels KW - polymer network KW - silk fibroin ER - TY - JOUR TI - Density-induced phase separation in poly(ethylene-co-1-butene)-dimethyl ether solutions AU - Li, D AU - McHugh, MA AU - Zanten, JH T2 - MACROMOLECULES AB - Dynamic light scattering measurements are reported for poly(ethylene-co-20.2 mol % 1-butene) (PEB10) in dimethyl ether (DME) at 110−170 °C and pressures to 2500 bar. The cloud-point curve for the PEB10−DME system exhibits both low- and high-pressure upper consolute solution temperature (UCST) branches. The polymer infinite dilution translational diffusion coefficient, D0, increases with increasing temperature and decreasing pressure as expected. The observed variation of D0 is inversely proportional to the solvent viscosity, indicating that the polymer coil hydrodynamic size is independent of temperature and pressure. The dynamic second virial coefficient, kD, which represents a balance between thermodynamic interactions and hydrodynamic forces, displays values that lie within the bounds expected for ϑ and good solvent conditions. While the low-pressure UCST is classical in that the polymer−solvent interactions become unfavorable upon approach to this phase boundary, the high-pressure UCST branch exhibits anomalous behavior wherein polymer−solvent interactions improve as this phase boundary is approached. Such behavior suggests that the phase separation is entropic in origin and is driven by unfavorable mixing effects. DA - 2005/4/5/ PY - 2005/4/5/ DO - 10.1021/ma048166y VL - 38 IS - 7 SP - 2837-2843 SN - 1520-5835 ER - TY - JOUR TI - Computer simulation of block copolymer/nanoparticle composites AU - Schultz, AJ AU - Hall, CK AU - Genzer, J T2 - MACROMOLECULES AB - Discontinuous molecular dynamics simulation is used to study the phase behavior of diblock copolymer/nanoparticle composites. The copolymers are modeled as chains of tangent hard-spheres with square shoulder repulsions between unlike species, while the nanoparticles are modeled as hard-spheres with a square shoulder repulsion with one of the copolymer blocks. The resulting phase diagrams are presented for composites containing nanoparticles of various sizes and interaction strengths and include lamellae, perforated lamellae, cylinders, and disordered phases. Composites containing large nanoparticles also exhibit two-phase coexistence between different copolymer phases or between a copolymer phase and a nanoparticle phase, depending on the nanoparticle interaction strength. We also present concentration profiles perpendicular to the lamellar interface for nanoparticles of different sizes and interaction strengths. Neutral nanoparticles concentrate at the interface between copolymer domains, while interacting nanoparticles concentrate within the favorable domain. The larger nanoparticles are more easily localized but have less impact on the copolymer concentration profiles. The lamellar spacing increases with nanoparticle volume fraction for interacting nanoparticles but decreases with nanoparticle size. The locations of the phase transitions are in qualitative agreement with theoretical predictions, but the concentration profiles are inconsistent with theoretical predictions. The variation of the spacing with nanoparticle volume fraction is consistent with experimental data. DA - 2005/4/5/ PY - 2005/4/5/ DO - 10.1021/ma0496910 VL - 38 IS - 7 SP - 3007-3016 SN - 1520-5835 ER - TY - JOUR TI - Swelling behavior and morphological evolution of mixed gelatin/silk fibroin hydrogels AU - Gil, ES AU - Frankowski, DJ AU - Spontak, RJ AU - Hudson, SM T2 - BIOMACROMOLECULES AB - Mixed protein-based hydrogels have been prepared by blending gelatin (G) with amorphous Bombyx mori silk fibroin (SF) and promoting β-crystallization of SF via subsequent exposure to methanol or methanol/water solutions. The introduction of β crystals in SF serves to stabilize the hydrogel network and extend the solidlike behavior of these thermally responsive materials to elevated temperatures beyond the helix→coil (h→c) transition of G. In this work, we investigate the swelling and protein release kinetics of G/SF hydrogels varying in composition at temperatures below and above the G h→c transition. At 20 °C, G and G-rich mixed hydrogels display evidence of moderate swelling with negligible mass loss in aqueous solution, resulting in porous polymer matrixes upon solvent removal according to electron microscopy. When the solution temperature is increased beyond the G h→c transition to body temperature (37 °C), these gels exhibit much higher swelling with considerable mass loss due to dissolution and release of G. The extent to which these properties respond to temperature decreases systematically with increasing SF content. The unique temperature- and composition-dependent properties of G/SF hydrogels dictate the efficacy of these novel materials as stimuli-responsive delivery vehicles. DA - 2005/// PY - 2005/// DO - 10.1021/bm050396c VL - 6 IS - 6 SP - 3079-3087 SN - 1526-4602 ER - TY - JOUR TI - Spatial analysis of 3 ' phosphoinositide signaling in living fibroblasts, III: Influence of cell morphology and morphological polarity AU - Schneider, IC AU - Parrish, EM AU - Haugh, JM T2 - BIOPHYSICAL JOURNAL AB - Activation of phosphoinositide (PI) 3-kinase is a required signaling pathway in fibroblast migration directed by platelet-derived growth factor. The pattern of 3′ PI lipids in the plasma membrane, integrating local PI 3-kinase activity as well as 3′ PI diffusion and turnover, influences the spatiotemporal regulation of the cytoskeleton. In fibroblasts stimulated uniformly with platelet-derived growth factor, visualized using total internal reflection fluorescence microscopy, we consistently observed localized regions with significantly higher or lower 3′ PI levels than adjacent regions (hot and cold spots, respectively). A typical cell contained multiple hot spots, coinciding with apparent leading edge structures, and at most one cold spot at the rear. Using a framework for finite-element modeling with actual cell contact area geometries, we find that although the 3′ PI pattern is affected by irregular contact area shape, cell morphology alone cannot explain the presence of hot or cold spots. Our results and analysis instead suggest that these regions reflect different local 3′ PI dynamics, specifically through a combination of mechanisms: enhanced PI 3-kinase activity, reduced 3′ PI turnover, and possibly slow/constrained 3′ PI diffusion. The morphological polarity of the cell may thus bias 3′ PI signaling to promote persistent migration in fibroblasts. DA - 2005/8// PY - 2005/8// DO - 10.1529/biophysj.105.061218 VL - 89 IS - 2 SP - 1420-1430 SN - 1542-0086 ER - TY - JOUR TI - Modeling triblock surfactant-templated mesostructured cellular foams AU - Bhattacharya, S AU - Gubbins, KE T2 - JOURNAL OF CHEMICAL PHYSICS AB - Lattice Monte Carlo simulations are used to understand the role of surfactant self-assembly in the synthesis of templated mesoporous materials with ultralarge pores. Our system consists of model triblock surfactants in the presence of oil, water, and inorganic oxide. Depending on the temperature and component concentrations, these systems phase separate, and the surfactant-rich phase forms structures such as cylinders, lamellae, and spheres ordered in repetitive arrangements. In the absence of oil, the structures are cylindrical with diameters of 100Å, but increasing oil concentration produces ultralarge spheres with diameters above 500Å. Our results closely resemble the cylinder to sphere transition associated with the synthesis of the mesostructured cellular foams (MCFs). Pore size distributions of our model structures are qualitatively comparable with the pore size distributions of MCFs obtained from adsorption experiments. We also observe an increase in average pore size with oil concentration, which is consistent with the experimental reportings. DA - 2005/10/1/ PY - 2005/10/1/ DO - 10.1063/1.2013250 VL - 123 IS - 13 SP - SN - 1089-7690 ER - TY - JOUR TI - In-situ infrared spectroscopy and density functional theory modeling of hafnium alkylamine adsorption on Si-OH and Si-H surfaces AU - Kelly, MJ AU - Han, JH AU - Musgrave, CB AU - Parsons, GN T2 - CHEMISTRY OF MATERIALS AB - In-situ attenuated total internal reflection infrared spectroscopy has been used to examine initial adsorption and reaction steps in atomic layer deposition of HfO2 from tetrakis(diethylamino) hafnium (TDEAHf) on SiO2 and hydrogen-terminated Si(100) surfaces. At low deposition temperatures (25−250 °C), TDEAHf directly reacts with the Si−H surface, resulting in partial removal of Si−H bonds and formation of a four-membered Si−O−Hf−Si bonding structure that can rapidly oxidize. The hydrogen removal process is observed to continue through many cycles of TDEAHf/H2O exposure, signifying continued reactivity of the Hf precursor with the silicon surface. Density functional theory calculations have been performed for various reactions between tetrakis(dimethylamino) hafnium and Si−H surfaces, and several possible reaction pathways for hydrogen removal have been identified and analyzed. The calculations suggest that hydrogen removal proceeds by H abstraction by an amine ligand of the Hf precursor and that the abstraction reaction is made more facile by the presence of OH on the otherwise H-terminated Si surface. DA - 2005/10/18/ PY - 2005/10/18/ DO - 10.1021/cm051064h VL - 17 IS - 21 SP - 5305-5314 SN - 1520-5002 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000232743700015&KeyUID=WOS:000232743700015 ER - TY - CHAP TI - Effect of annealing temperature on texture and creep anisotropy in Ti3Al2.5V alloy AU - Murty, K. L. AU - Kishore, R. AU - Yan, J. AU - Scattergood, R. O. AU - Helsel, A. W. T2 - Textures of materials: ICOTOM 14: Proceedings of the 14th International Conference on Textures of Materials, held in Leuven, Belgium, July 11-15, 2005 / Paul van Houtte; Leo Kestens. Uetikon-Zuerich, Switzerland ; Enfield, NH: Trans Tech Publications, 2005. (Materials science forum ; 495-497) AB - Effect of annealing temperature is investigated on texture and creep anisotropy in a thinwalled tubing of titanium alloy. Creep anisotropy is studied under equibiaxial loading using internally pressurized tubing superimposed with axial load while monitoring in-situ the time variations of both hoop and axial strains. Relatively weak hoop direction in the cold-worked material became stronger following complete recrystallization. The analyses of the data reveal that the anisotropy parameter, P which is the contractile strain ratio for testing along hoop direction increases from around 0.6 for the cold-worked material to around 1.5 following complete recrystallization. Results indicate that planar isotropy should occur following annealing at around 800K. Work on the effects of annealing on the textures and deformation microstructures is in progress. We summarize here results from some of our earlier work on a different lot of Ti3Al2.5V tubing in the recrystallized states where the ODFs were used in conjunction with crystal slip models to predict creep anisotropy. CN - [Not currently held by TRLN member libraries.] PY - 2005/// DO - 10.4028/www.scientific.net/msf.495-497.1645 VL - 495-497 SP - 1645-1650 PB - Utikon-Zurich, Switzerland: Trans Tech Publications ER - TY - JOUR TI - Direct fabrication and harvesting of monodisperse, shape-specific nanobiomaterials AU - Rolland, JP AU - Maynor, BW AU - Euliss, LE AU - Exner, AE AU - Denison, GM AU - DeSimone, JM T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - A versatile "top-down" method for the fabrication of particles, Particle Replication In Nonwetting Templates (PRINT), is described which affords absolute control over particle size, shape, and composition. This technique is versatile and general enough to fabricate particles with a variety of chemical structures, yet delicate enough to be compatible with sophisticated biological agents. Using PRINT, we have fabricated monodisperse particles of poly(ethylene glycol diacrylate), triacrylate resin, poly(lactic acid), and poly(pyrrole). Monodisperse particle populations, ranging from sub-200 nm nanoparticles to complex micron-scale objects, have been fabricated and harvested. PRINT uses low-surface energy, chemically resistant fluoropolymers as molding materials, which eliminates the formation of a residual interconnecting film between molded objects. Until now, the presence of this film has largely prevented particle fabrication using soft lithography. Importantly, we have demonstrated that PRINT affords the simple, straightforward encapsulation of a variety of important bioactive agents, including proteins, DNA, and small-molecule therapeutics, which indicates that PRINT can be used to fabricate next-generation particulate drug-delivery agents. DA - 2005/7/20/ PY - 2005/7/20/ DO - 10.1021/ja051977c VL - 127 IS - 28 SP - 10096-10100 SN - 1520-5126 ER - TY - JOUR TI - Creating responsive surfaces with tailored wettability switching kinetics and reconstruction reversibility AU - Crowe, JA AU - Genzer, J T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - We report on the formation of responsive surfaces with tailorable surface reconstruction kinetics and switching hysteresis by thiolene radical addition of mercaptoalkanols with variable lengths to poly(vinylmethylsiloxane) networks. Exposing these elastomer surfaces to water results in rearrangement of the hydrophilic alkanes at the surface. The rearrangement kinetics decreases with increasing number of the methylene spacers (n) in the mercaptoalkanol. The response kinetics is found to be very fast for n = 2 and 6. For instance, upon exposing to water, the water contact angle on 3-mercaptopropanol-based surfaces decreases by ≈35° at the rate of 2°/s. The high flexibility of the siloxane backbone endows these materials with switching longevity; the materials were able to switch their wettability over 10 cycles with minimum hysteresis. Increasing the number of methylene spacers to n = 11 decreases the surface reorganization dramatically. Formation of semicrystalline regions in such materials (detected via IR) is responsible for initial “sluggish” kinetics and eventual surface “freezing”. DA - 2005/12/21/ PY - 2005/12/21/ DO - 10.1021/ja056926u VL - 127 IS - 50 SP - 17610-17611 SN - 0002-7863 ER - TY - JOUR TI - Association behavior of pyrene compounds as models for asphaltenes AU - Akbarzadeh, K AU - Bressler, DC AU - Wang, JN AU - Gawrys, KL AU - Gray, MR AU - Kilpatrick, PK AU - Yarranton, HW T2 - ENERGY & FUELS AB - Asphaltene association in solution has been studied extensively using methods such as vapor-pressure osmometry and neutron scattering. These methods give relative data on association as a function of solvent strength, temperature, and concentration, but interpretation of the results is hampered by the polyfunctional nature of asphaltenes and the distribution of molecular weight. In this work, we present data on association of representative model structures for asphaltenes, as measured using vapor-pressure osmometry in o-dichlorobenzene at 75−130 °C, and using small-angle neutron scattering in toluene. A series of compounds were synthesized based on the four-ring aromatic compound pyrene. The synthetic compounds were designed to give interactions between aromatic rings, alkyl chains, and selected functional groups through aromatic interactions, hydrogen bonding, and polar interactions. Even in this strong solvent, polar interactions between oxygen functional groups gave average molecular weights of up to twice the true value, indicating dimer formation. An alkyl pyrene compound, dipyrenyl decane, gave much less significant association. Pyrene itself exhibited little or no self-association. DA - 2005/// PY - 2005/// DO - 10.1021/ef0496698 VL - 19 IS - 4 SP - 1268-1271 SN - 1520-5029 ER - TY - JOUR TI - Asphaltenes and waxes do not interact synergistically and coprecipitate in solid organic deposits AU - Yang, XL AU - Kilpatrick, P T2 - ENERGY & FUELS AB - Waxes and asphaltenes are the major components in organic deposits from petroleum fluids. A key unresolved issue is whether there are significant intermolecular interactions between wax and asphaltene molecules during precipitation that would lead to synergy and coprecipitation, i.e., the phase change of one class inducing the precipitation of the other class. To address this, we studied six organic deposits in great chemical and physical detail: three that we categorized as predominantly wax deposits, two that were asphaltenic deposits, and one that seemed to be an organic acid deposit. Chemical analyses included elemental analysis, Fourier transform infrared (FTIR) spectroscopy, high-temperature simulated distillation, melting range measurement, and solubility experiments, performed on both parent crude oils and their corresponding deposits. The wax deposits contain in excess of 44 wt % waxes, and the complement of the deposits was occluded oil, water, and inorganic solids. Less than 6.2% (w/w) of these deposits were asphaltenes. Waxy-deposit waxes have higher melting points, longer straight-chain methylene, higher carbon number distributions, and higher molecular weights than their parent crude waxes. Asphaltenic-deposit waxes have properties that are almost identical to their parent crude oil waxes. Asphaltenic deposits contained >27 wt % asphaltenes. The properties of asphaltenes isolated from asphaltenic deposits were compared with the properties of asphaltenes isolated from their parent crude oils. The metal content and apparent VPO molecular weight of asphaltenic-deposit asphaltenes are significantly higher than those of corresponding crude-oil asphaltenes. The solubility of asphaltenic-deposit asphaltenes is much lower than the solubility of asphaltenes from their parent crude oils. The results indicate that the asphaltenes in the wax deposits are likely a component of the occluded oil in the deposit. A key conclusion of our work is that there is no evidence for any intermolecular interaction between waxes and asphaltenes to suggest synergy in precipitation. In fact, the evidence very much points to only one of these components undergoing a phase change and precipitating in an organic deposit and the other component simply being a portion of the crude oil occluded in the deposit. DA - 2005/// PY - 2005/// DO - 10.1021/ef050022c VL - 19 IS - 4 SP - 1360-1375 SN - 1520-5029 ER - TY - JOUR TI - Adsorption and catalysis: The effect of confinement on chemical reactions AU - Santiso, EE AU - George, AM AU - Turner, CH AU - Kostov, MK AU - Gubbins, KE AU - Buongiorno-Nardelli, M AU - Sliwinska-Bartkowiak, M T2 - APPLIED SURFACE SCIENCE AB - Confinement within porous materials can affect chemical reactions through a host of different effects, including changes in the thermodynamic state of the system due to interactions with the pore walls, selective adsorption, geometrical constraints that affect the reaction mechanism, electronic perturbation due to the substrate, etc. In this work, we present an overview of some of our recent research on some of these effects, on chemical equilibrium, kinetic rates and reaction mechanisms. We also discuss our current and future directions for research in this area. DA - 2005/10/31/ PY - 2005/10/31/ DO - 10.1016/j.apsusc.2005.02.101 VL - 252 IS - 3 SP - 766-777 SN - 1873-5584 KW - chemical reactions KW - confinement KW - porous carbons KW - molecular modeling ER - TY - JOUR TI - Tailoring cell adhesion using surface-grafted polymer gradient assemblies AU - Bhat, RR AU - Chaney, BN AU - Rowley, J AU - Liebmann-Vinson, A AU - Genzer, J T2 - ADVANCED MATERIALS AB - Surface-grafted polymer assemblies with a gradient in molecular weight (MW) and/or grafting density (σ) are used to tune protein adsorption, which consequently governs cell adhesion. Increasing the surface coverage of the polymer by increasing the MW and/or σ results in a decrease in the amount of protein adsorbed, which causes a decrease in the number of cells adhered and a change in cell morphology. DA - 2005/12/5/ PY - 2005/12/5/ DO - 10.1002/adma.200500858 VL - 17 IS - 23 SP - 2802-+ SN - 1521-4095 ER - TY - JOUR TI - Quartz crystal microbalance in elevated temperature viscous liquids: Temperature effect compensation and lubricant degradation monitoring AU - Wang, DX AU - Mousavi, P AU - Hauser, PJ AU - Oxenham, W AU - Grant, CS T2 - COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS AB - The quartz crystal microbalance (QCM) was extended to investigate viscous liquids at elevated temperatures in both isothermal and non-isothermal systems. An analysis of the frequency–temperature behavior of the QCM resulted in a new approach to compensate for the effect of the rate of temperature rise on the theoretical QCM temperature coefficients. The temperature-dependent viscosities of a series of liquids were evaluated by measuring the damping voltage of QCM. Thermal degradation experiments on pentaerythritol tetrapelargonate based lubricants demonstrated the potential application of QCM as an in situ sensor to evaluate the thermal stability of lubricants or other viscous fluids. The solid residue deposition rates and liquid phase property changes (i.e., product of density and viscosity) were extensively investigated by monitoring variations in the QCM frequency and damping voltage during the lubricant thermally stressing over a temperature range of 150–220 °C. DA - 2005/10/31/ PY - 2005/10/31/ DO - 10.1016/j.colsurfa.2005.05.075 VL - 268 IS - 1-3 SP - 30-39 SN - 1873-4359 KW - quartz crystal microbalance KW - viscosity KW - deposition KW - lubricant KW - thermal degradation ER - TY - JOUR TI - Quantitative elucidation of a distinct spatial gradient-sensing mechanism in fibroblasts AU - Schneider, IC AU - Haugh, JM T2 - JOURNAL OF CELL BIOLOGY AB - Migration of eukaryotic cells toward a chemoattractant often relies on their ability to distinguish receptor-mediated signaling at different subcellular locations, a phenomenon known as spatial sensing. A prominent example that is seen during wound healing is fibroblast migration in platelet-derived growth factor (PDGF) gradients. As in the well-characterized chemotactic cells Dictyostelium discoideum and neutrophils, signaling to the cytoskeleton via the phosphoinositide 3-kinase pathway in fibroblasts is spatially polarized by a PDGF gradient; however, the sensitivity of this process and how it is regulated are unknown. Through a quantitative analysis of mathematical models and live cell total internal reflection fluorescence microscopy experiments, we demonstrate that PDGF detection is governed by mechanisms that are fundamentally different from those in D. discoideum and neutrophils. Robust PDGF sensing requires steeper gradients and a much narrower range of absolute chemoattractant concentration, which is consistent with a simpler system lacking the feedback loops that yield signal amplification and adaptation in amoeboid cells. DA - 2005/12/5/ PY - 2005/12/5/ DO - 10.1083/jcb.200509028 VL - 171 IS - 5 SP - 883-892 SN - 1540-8140 ER - TY - JOUR TI - Proceedings of the Tenth International Conference on Properties and Phase Equilibria for Product and Process Design - Preface AU - Hall, CK T2 - FLUID PHASE EQUILIBRIA DA - 2005/2// PY - 2005/2// DO - 10.1016/j.fluid.2004.12.002 VL - 228 SP - 3-3 SN - 1879-0224 ER - TY - JOUR TI - Observation of polymer chain contraction near the overlap concentration AU - DiNoia, TP AU - Park, IH AU - McHugh, MA AU - Zanten, JH T2 - MACROMOLECULES AB - Department of Chemical Engineering, Johns HopkinsUniversity, Baltimore, Maryland 21218; Department ofPolymer Science & Engineering, Kumoh National Universityof Technology, Kyungbuk, Korea; Department of ChemicalEngineering, Virginia Commonwealth University,Richmond, Virginia 23284; and Department of Chemicaland Biomolecular Engineering, North Carolina StateUniversity, Raleigh, North Carolina 27695-7905Received June 9, 2005Revised Manuscript Received August 2, 2005 DA - 2005/11/1/ PY - 2005/11/1/ DO - 10.1021/ma051216u VL - 38 IS - 22 SP - 9393-9395 SN - 1520-5835 ER - TY - JOUR TI - Measuring thermal degradation of a polyol ester lubricant in liquid phase AU - Mousavi, P AU - Wang, DX AU - Grant, CS AU - Oxenham, W AU - Hauser, PJ T2 - INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH AB - Thermal degradation of two polyol ester lubricants with the same base chemical structures from two different manufacturers at high temperature (i.e., 220 °C) has been studied. Gel permeation chromatography was used to identify the high molecular weight products formed during thermal stressing of these lubricants. The amount of high molecular weight products generated at different stages of the degradation (e.g., dimers, oligomers) was quantified. Several other techniques were utilized as a combined analytical approach to provide comprehensive measurement of lubricant degradation in the liquid phase. The mechanism of degradation and the formation of oxidation products have been presented. A significant difference in the extent of degradation of the two lubricants was observed using different analytical techniques. DA - 2005/7/20/ PY - 2005/7/20/ DO - 10.1021/ie049135u VL - 44 IS - 15 SP - 5455-5464 SN - 0888-5885 ER - TY - JOUR TI - Interactions between nonpolar surfaces coated with the nonionic surfactant n-dodecyl-beta-D-maltoside AU - Rojas, OJ AU - Stubenrauch, C AU - Schulze-Schlarmann, J AU - Claesson, PM T2 - LANGMUIR AB - The forces acting between nonpolar surfaces coated with the nonionic surfactant n-dodecyl-β-d-maltoside (β-C12G2) were investigated at concentrations below and above the critical micelle concentration. The long-range and adhesive forces were measured with a bimorph surface force apparatus (MASIF). It was found that the effect of hydrodynamic interactions had to be taken into account for an accurate determination of the short-range static interactions. The results were compared with disjoining pressure versus thickness curves that were obtained earlier with a thin film pressure balance (TFPB). This comparison led to the conclusion that the charges observed at the air−water interface are not due to charged species present in the surfactant sample. In addition, it was observed that the stability of thin liquid films crucially depends on the surfactant's bulk concentration (c) and thus on the packing density in the adsorbed layer. The force barrier preventing removal of the surfactant layer from between two solid−liquid interfaces increases with increasing c, while for foam films it is the stability of the Newton black film that increases with c. Finally, the results obtained for β-C12G2 were compared with those obtained for the homologue n-decyl-β-d-maltoside (β-C10G2) as well as with those obtained for nonionic surfactants with polyoxyethylene moieties as polar groups. DA - 2005/12/6/ PY - 2005/12/6/ DO - 10.1021/la051938e VL - 21 IS - 25 SP - 11836-11843 SN - 0743-7463 ER - TY - JOUR TI - Evolution of surface morphologies in multivariant assemblies of surface-tethered diblock copolymers after selective solvent treatment AU - Tomlinson, MR AU - Genzer, J T2 - LANGMUIR AB - We study systematically the topography behavior of PHEMA-b-PMMA block as a function of the PHEMA and PMMA block lengths after selectively collapsing the top (PMMA) block by using surface-anchored assemblies of poly(2-hydroxyethyl methacrylate-b-methyl methacrylate), PHEMA-b-PMMA, block copolymer with orthogonally varying lengths of each block. Our experimental results are in excellent qualitative agreement with topology diagrams predicted by self-consistent field calculations of Zhulina and co-workers. DA - 2005/12/6/ PY - 2005/12/6/ DO - 10.1021/la051523t VL - 21 IS - 25 SP - 11552-11555 SN - 0743-7463 ER - TY - JOUR TI - Effect of temperature on the adsorption of water in porous carbons AU - Striolo, A AU - Gubbins, KE AU - Gruszkiewicz, MS AU - Cole, DR AU - Simonson, JM AU - Chialvo, AA T2 - LANGMUIR AB - We report experimental and simulation studies to investigate the effect of temperature on the adsorption isotherms for water in carbons. Adsorption isotherms are measured by a gravimetric technique in carbon-fiber monoliths at 378 and 423 K and studied by molecular simulation in ideal carbon pores in the temperature range 298−600 K. Experimental adsorption isotherms show a gradual water uptake, as the pressure increases, and narrow adsorption−desorption hysteresis loops. In contrast, simulated adsorption isotherms at room temperature are characterized by negligible uptake at low pressures, sudden and complete pore filling once a threshold pressure is reached, and wide adsorption−desorption hysteresis loops. As the temperature increases, the relative pressure at which pore filling occurs increases and the size of the hysteresis loop decreases. Experimental adsorption−desorption hysteresis loops are narrower than those from simulation. Discrepancies between simulation and experimental results are attributed to heterogeneities in chemical composition, pore connectivity, and nonuniform pore-size distribution, which are not accounted for in the simulation model. The hysteresis phase diagram for confined water is obtained by recording the pressure−density conditions that bound the simulated hysteresis loop at each temperature. We find that the hysteresis critical temperature, i.e., the lowest temperature at which no hysteresis is detected, can be hundreds of degrees lower than the vapor−liquid critical temperature for bulk model water. The properties of confined water are discussed with the aid of simulation snapshots and by analyzing the structure of the confined fluid. DA - 2005/10/11/ PY - 2005/10/11/ DO - 10.1021/la051120t VL - 21 IS - 21 SP - 9457-9467 SN - 0743-7463 ER - TY - JOUR TI - An expression-driven approach to the prediction of carbohydrate transport and utilization regulons in the hyperthermophilic bacterium Thermotoga maritima AU - Conners, SB AU - Montero, CI AU - Comfort, DA AU - Shockley, KR AU - Johnson, MR AU - Chhabra, , SR AU - Kelly, RM T2 - JOURNAL OF BACTERIOLOGY AB - ABSTRACT Comprehensive analysis of genome-wide expression patterns during growth of the hyperthermophilic bacterium Thermotoga maritima on 14 monosaccharide and polysaccharide substrates was undertaken with the goal of proposing carbohydrate specificities for transport systems and putative transcriptional regulators. Saccharide-induced regulons were predicted through the complementary use of comparative genomics, mixed-model analysis of genome-wide microarray expression data, and examination of upstream sequence patterns. The results indicate that T. maritima relies extensively on ABC transporters for carbohydrate uptake, many of which are likely controlled by local regulators responsive to either the transport substrate or a key metabolic degradation product. Roles in uptake of specific carbohydrates were suggested for members of the expanded Opp/Dpp family of ABC transporters. In this family, phylogenetic relationships among transport systems revealed patterns of possible duplication and divergence as a strategy for the evolution of new uptake capabilities. The presence of GC-rich hairpin sequences between substrate-binding proteins and other components of Opp/Dpp family transporters offers a possible explanation for differential regulation of transporter subunit genes. Numerous improvements to T. maritima genome annotations were proposed, including the identification of ABC transport systems originally annotated as oligopeptide transporters as candidate transporters for rhamnose, xylose, β-xylan, andβ -glucans and identification of genes likely to encode proteins missing from current annotations of the pentose phosphate pathway. Beyond the information obtained for T. maritima , the present study illustrates how expression-based strategies can be used for improving genome annotation in other microorganisms, especially those for which genetic systems are unavailable. DA - 2005/11// PY - 2005/11// DO - 10.1128/JB.187.21.7267-7282.2005 VL - 187 IS - 21 SP - 7267-7282 SN - 1098-5530 ER - TY - JOUR TI - Genorne-wide transcriptional variation within and between steady states for continuous growth of the hyperthermophile Thermotoga maritima AU - Shockley, KR AU - Scott, KL AU - Pysz, MA AU - Conners, SB AU - Johnson, MR AU - Montero, CI AU - Wolfinger, RD AU - Kelly, RM T2 - APPLIED AND ENVIRONMENTAL MICROBIOLOGY AB - Maltose-limited, continuous growth of the hyperthermophile Thermotoga maritima at different temperatures and dilution rates (80 degrees C/0.25 h(-1), 80 degrees C/0.17 h(-1), and 85 degrees C/0.25 h(-1)) showed that transcriptome-wide variation in gene expression within mechanical steady states was minimal compared to that between steady states, supporting the efficacy of chemostat-based approaches for functional genomics studies. DA - 2005/9// PY - 2005/9// DO - 10.1128/AEM.71.9.5572-5576.2005 VL - 71 IS - 9 SP - 5572-5576 SN - 1098-5336 ER - TY - JOUR TI - Ferroelectric response from lead zirconate titanate thin films prepared directly on low-resistivity copper substrates AU - Losego, MD AU - Jimison, LH AU - Ihlefeld, JF AU - Maria, JP T2 - APPLIED PHYSICS LETTERS AB - We demonstrate films of the well-known ferroelectric lead zirconate titanate (PZT) prepared directly on copper foils by chemical solution deposition (CSD). The films exhibit saturating polarization hysteresis, remanent polarization values of 26μC∕cm2, and permittivities of 800; these properties are comparable to those achieved using semiconductor-grade substrates. The preparation methodology is founded upon an understanding of solution chemistry as opposed to conventional gas-phase ∕ condensed-phase equilibrium approaches. By adopting this technique, base-metal compatibility can be achieved using much lower temperatures, and a broader set of devices can be prepared offering intimate contact with high conductivity, easily patternable, or ferromagnetic metals. DA - 2005/4/25/ PY - 2005/4/25/ DO - 10.1063/1.1919388 VL - 86 IS - 17 SP - SN - 0003-6951 ER - TY - JOUR TI - Electrical, structural, and chemical analysis of defects in epitaxial SiGe-based heterostructures AU - Bray, K. R. AU - Zhao, W. AU - Kordas, L. AU - Wise, R. AU - Robinson, M. AU - Rozgonyi, G. T2 - Journal of the Electrochemical Society DA - 2005/// PY - 2005/// VL - 152 IS - 5 SP - C310-315 ER - TY - JOUR TI - Dissociation of water on defective carbon substrates AU - Kostov, MK AU - Santiso, EE AU - George, AM AU - Gubbins, KE AU - Nardelli, MB T2 - PHYSICAL REVIEW LETTERS AB - Using calculations from first principles, we found that water can dissociate over defective sites in graphene or nanotubes following many possible reaction pathways, some of which have activation barriers lower than half the value for the dissociation of bulk water. This reduction is caused by spin selection rules that allow the system to remain on the same spin surface throughout the reaction. DA - 2005/9/23/ PY - 2005/9/23/ DO - 10.1103/physrevlett.95.136105 VL - 95 IS - 13 SP - SN - 1079-7114 ER - TY - JOUR TI - Computer simulation study of pattern transfer in AB diblock copolymer film adsorbed on a heterogeneous surface AU - Jayaraman, A AU - Hall, CK AU - Genzer, J T2 - JOURNAL OF CHEMICAL PHYSICS AB - In this work we investigate how a pattern imposed in a copolymer film at a certain distance from the surface propagates through the film onto an adsorbing heterogeneous surface. We bias the copolymer film to adopt a specified target pattern and then use simulation to design a surface pattern that helps the adsorbed film to maintain that target pattern. We examine the effect of varying the copolymer chain length, the size of the target pattern, and the distance from the surface where the target pattern is applied, z', on the extent of pattern transfer. For each chain length, target pattern, and z' we compare the energy of the system when a pattern is applied in the bulk to the energy when no pattern is applied in order to understand why a certain pattern size is transferred to the surface with higher fidelity than the others. At constant chain length, pattern transfer is best when the pattern size brings the energy of the system close to the energy when no pattern is applied. At constant pattern size, pattern transfer is best in the systems with longer chains. This is because longer chains are more likely to adsorb as brushes and loops which then helps transfer the pattern through the adsorbed film down to the surface. DA - 2005/9/22/ PY - 2005/9/22/ DO - 10.1063/1.2043048 VL - 123 IS - 12 SP - SN - 1089-7690 ER - TY - JOUR TI - Characterization of microcellular biodegradable polymeric foams produced from supercritical carbon dioxide solutions AU - Cotugno, S AU - Di Maio, E AU - Mensitieri, G AU - Iannace, S AU - Roberts, GW AU - Carbonell, RG AU - Hopfenberg, HB T2 - INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH AB - The formation of foams of biodegradable poly(ε-caprolactone) (PCL) from CO2 solutions in molten PCL was investigated. This study included characterization of the CO2 diffusion and equilibrium solubility in molten PCL in contact with supercritical CO2 (scCO2). Experiments were performed at 70, 80, and 90 °C at CO2 pressures up to 25 MPa. The effective mutual diffusivity of CO2 in molten PCL was measured as a function of the CO2 pressure. The data revealed a dramatic increase in apparent effective diffusivity at elevated pressure, likely related to the formation of fluid bubbles, phase-separated from the previously homogeneous, molten PCL solution of CO2. Microcellular PCL foams were produced by starting from an equilibrium CO2−PCL solution at 70 °C over a wide range of initial pressures (from 6.9 to 32 MPa) by quenching down to foaming temperatures (from 24 to 30 °C) followed by rapid depressurization to atmospheric pressure. Foam structures were characterized by scanning electron microscopy, and cell sizes and density were determined quantitatively. The various foam structures were analyzed and interpreted in connection with the independently measured kinetics and equilibrium of CO2 sorption in PCL by considering the effects of starting pressure and foaming temperature on bubble nucleation and growth. DA - 2005/3/16/ PY - 2005/3/16/ DO - 10.1021/ie049445c VL - 44 IS - 6 SP - 1795-1803 SN - 0888-5885 ER - TY - JOUR TI - Argon and nitrogen adsorption in disordered nanoporous carbons: Simulation and experiment AU - Pikunic, J AU - Llewellyn, P AU - Pellenq, R AU - Gubbins, KE T2 - LANGMUIR AB - We report experimental measurements of the isosteric heats of adsorption for argon and nitrogen in two microporous saccharose-based carbons, using a Tian-Calvet microcalorimeter. These data are used to test recently developed molecular models of these carbons, obtained by a constrained reverse Monte Carlo method. grand canonical Monte Carlo simulation is used to calculate the adsorption isotherms and isosteric heats for these systems, and the results for the latter are compared to the experimental data. For argon, excellent quantitative agreement is obtained over the entire range of pore filling. In the case of nitrogen, very good agreement is obtained over the range of coverage 0.25 ≤ Γ/Γ0 ≤ 0.85, but discrepancies are observed at lower and higher coverages. The discrepancy at low coverage may be due to the presence of oxygenated groups on the pore surfaces, which are not taken into account in the model. The differences at high coverage are believed to arise from the presence of a few mesopores, which again are not included in the model. Pair correlation functions (argon−carbon and argon−argon) are determined from the simulations and are discussed as a function of pore filling. Snapshots of the simulations are presented and provide a picture of the pore filling process. DA - 2005/5/10/ PY - 2005/5/10/ DO - 10.1021/la047165w VL - 21 IS - 10 SP - 4431-4440 SN - 0743-7463 ER - TY - JOUR TI - Understanding student differences AU - Felder, RM AU - Brent, R T2 - JOURNAL OF ENGINEERING EDUCATION AB - Students have different levels of motivation, different attitudes about teaching and learning, and different responses to specific classroom environments and instructional practices. The more thoroughly instructors understand the differences, the better chance they have of meeting the diverse learning needs of all of their students. Three categories of diversity that have been shown to have important implications for teaching and learning are differences in students' learning styles (characteristic ways of taking in and processing information), approaches to learning (surface, deep, and strategic), and intellectual development levels (attitudes about the nature of knowledge and how it should be acquired and evaluated). This article reviews models that have been developed for each of these categories, outlines their pedagogical implications, and suggests areas for further study. DA - 2005/1// PY - 2005/1// DO - 10.1002/j.2168-9830.2005.tb00829.x VL - 94 IS - 1 SP - 57-72 SN - 2168-9830 KW - learning styles KW - approaches to learning KW - intellectual development ER - TY - JOUR TI - Freezing and melting of azeotropic mixtures confined in nanopores: experiment and molecular simulation AU - Czwartos, J AU - Coasne, B AU - Gubbins, KE AU - Hung, FR AU - Sliwinska-Bartkowiak, M T2 - MOLECULAR PHYSICS AB - Abstract The paper reports on a qualitative comparison between experimental measurements and molecular simulations of the freezing and melting of azeotropic mixtures confined in nanoporous materials. Dielectric relaxation spectroscopy was used to determine the experimental solid/liquid phase diagram of CCl4/C6H12 mixtures confined in activated carbon fibres. Grand Canonical Monte Carlo simulations combined with the parallel tempering technique were used to model the freezing of the azeotropic Lennard–Jones mixture Ar/CH4 in a graphite slit pore. The structure of the crystal phase in the simulations is investigated by means of positional and bond-orientational pair correlation functions and appropriate bond-order parameters. Both simulations and experiments show that the phase diagram of the confined mixture is of the same type as that for the bulk, but the solid/liquid coexistence lines are located at higher temperatures. The effect of confinement and of the wall/fluid interaction on the location of the azeotrope is discussed. Acknowledgements We are grateful to Henry Bock and Erik Santiso (North Carolina State University) for helpful discussions and comments. This work was supported by the Petroleum Research Fund of the American Chemical Society and by the Polish Science Foundation (Komitet Badan Naukowych). Supercomputing time was provided by the National Partnership for Advanced Computational Infrastructure (NSF/NRAC – MCA93SO11) and the National Energy Research Scientific Computing Center (DOE – DE-FGO2–98ER14847). International cooperation was supported by a NATO Collaborative Linkage Grant (No. PST.CLG.978802). DA - 2005/// PY - 2005/// DO - 10.1080/00268970500200101 VL - 103 IS - 21-23 SP - 3103-3113 SN - 1362-3028 ER - TY - JOUR TI - Domain theory for capillary condensation hysteresis AU - Coasne, B AU - Gubbins, KE AU - Pellenq, RJM T2 - PHYSICAL REVIEW B AB - We discuss how the original domain theory for capillary condensation hysteresis [D. H. Everett, The Solid--Gas Interface, Vol. 2 (Marcel Dekker, New York, 1967), pp. 1055--1113] must be modified to account for the presence of the film adsorbed at the pore surface. We show that the original predictions (scanning behavior, congruence) are not valid unless the existence of the adsorbed film is neglected or the dependence of its thickness on the pressure is neglected. We also calculate the scanning curves and subloops that are expected for an assembly of pores having either a regular or irregular (nonconstant) section. These predictions over the scanning behavior within capillary condensation hysteresis can be used to check whether real materials are made up of independent pores or not. Our results are discussed in the light of experiments and density functional theory calculations for adsorption in porous media. DA - 2005/7// PY - 2005/7// DO - 10.1103/physrevb.72.024304 VL - 72 IS - 2 SP - SN - 1098-0121 ER - TY - JOUR TI - Controlled foaming of polymer films through restricted surface diffusion and the addition of nanosilica particles or CO2-philic surfactants AU - Siripurapu, S AU - DeSimone, JM AU - Khan, SA AU - Spontak, RJ T2 - MACROMOLECULES AB - Synergistic use of surface barriers and nanoscale additives is investigated as alternate means by which to promote bubble nucleation in, and thus improve the porosity of, poly(methyl methacrylate) (PMMA) thin films (i) constrained between impenetrable plates, (ii) modified with either nanosilica particles, commercial short-chain fluorosurfactants, or designer CO2-philic block/graft copolymers, and (iii) exposed to high-pressure CO2. Resultant foamed films exhibit a vast array of micro/mesocellular morphologies in the presence of supercritical, as well as liquid, CO2 and demonstrate that copolymer micelles afford better control over bubble nucleation (with pore cell densities, N, approaching 1012 cells/cm3) relative to hard nonporous nanoparticles, which alone increase N by more than 2 orders of magnitude at low CO2 pressures. Incorporation of these nanoscale additives in a surface-constrained polymer matrix serves to enhance foaming through concurrent restriction of CO2 diffusion, heterogeneous nucleation of CO2 bubbles, and/or reduced interfacial tension between PMMA and CO2. DA - 2005/3/22/ PY - 2005/3/22/ DO - 10.1021/ma047991b VL - 38 IS - 6 SP - 2271-2280 SN - 1520-5835 ER - TY - JOUR TI - Coarse-grained potentials from Widom's particle insertion method AU - Chennamsetty, N AU - Bock, H AU - Gubbins, KE T2 - MOLECULAR PHYSICS AB - Widom's particle insertion method is used to calculate effective pair potentials for binary A/B mixtures, where B molecules represent a solvent whose degrees of freedom are integrated out. Comparison of Widom's method with an alternative route via the potential of mean force shows good agreement; however, Widom's particle insertion method experiences sampling difficulties at high densities. An isotherm for a binary mixture of argon (‘solvent’, B) and krypton (‘solute’, A) is calculated. While the structure at the pair level is well represented by the effective system using only effective pair potentials and ignoring all higher multi-body contributions, increasing deviations in the pressure are observed as the density of the effective system is increased. These latter deviations are attributed to the neglect of three- and higher multi-body interactions. DA - 2005/// PY - 2005/// DO - 10.1080/00268970500208658 VL - 103 IS - 21-23 SP - 3185-3193 SN - 1362-3028 ER - TY - JOUR TI - Advantages of supercritical carbon dioxide for composite particle synthesis using water-soluble or water-reactive monomers AU - Young, JL AU - DeSimone, JM T2 - MACROMOLECULES AB - ADVERTISEMENT RETURN TO ISSUEPREVNoteAdvantages of Supercritical Carbon Dioxide for Composite Particle Synthesis Using Water-Soluble or Water-Reactive MonomersJennifer L. Young and Joseph M. DeSimoneView Author Information NSF Center for Environmentally Responsible Solvents and Processes, Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, and Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695 Cite this: Macromolecules 2005, 38, 10, 4542–4544Publication Date (Web):April 15, 2005Publication History Received20 October 2004Revised7 March 2005Published online15 April 2005Published inissue 1 May 2005https://doi.org/10.1021/ma0478310Copyright © 2005 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views364Altmetric-Citations9LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (121 KB) Get e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Composites,Nanoparticles,Polymer morphology,Polymer particles,Polymers Get e-Alerts DA - 2005/5/17/ PY - 2005/5/17/ DO - 10.1021/ma0478310 VL - 38 IS - 10 SP - 4542-4544 SN - 1520-5835 ER - TY - JOUR TI - Adsorption of comb copolymers on weakly attractive solid surfaces AU - Striolo, A AU - Jayaraman, A AU - Genzer, J AU - Hall, CK T2 - JOURNAL OF CHEMICAL PHYSICS AB - In this work continuum and lattice Monte Carlo simulation methods are used to study the adsorption of linear and comb polymers on flat surfaces. Selected polymer segments, located at the tips of the side chains in comb polymers or equally spaced along the linear polymers, are attracted to each other and to the surface via square-well potentials. The rest of the polymer segments are modeled as tangent hard spheres in the continuum model and as self-avoiding random walks in the lattice model. Results are presented in terms of segment-density profiles, distribution functions, and radii of gyration of the adsorbed polymers. At infinite dilution the presence of short side chains promotes the adsorption of polymers favoring both a decrease in the depletion-layer thickness and a spreading of the polymer molecule on the surface. The presence of long side chains favors the adsorption of polymers on the surface, but does not permit the spreading of the polymers. At finite concentration linear polymers and comb polymers with long side chains readily adsorb on the solid surface, while comb polymers with short side chains are unlikely to adsorb. The simple models of comb copolymers with short side chains used here show properties similar to those of associating polymers and of globular proteins in aqueous solutions, and can be used as a first approximation to investigate the mechanism of adsorption of proteins onto hydrophobic surfaces. DA - 2005/8/8/ PY - 2005/8/8/ DO - 10.1063/1.1993557 VL - 123 IS - 6 SP - SN - 1089-7690 ER - TY - JOUR TI - A new Journal for a field in transition AU - Felder, R. M. AU - Sheppard, S. D. AU - Smith, K. A. T2 - Journal of Engineering Education DA - 2005/// PY - 2005/// VL - 94 IS - 1 SP - 10- ER - TY - JOUR TI - Water in carbon nanotubes: Adsorption isotherms and thermodynamic properties from molecular simulation AU - Striolo, A AU - Chialvo, AA AU - Gubbins, KE AU - Cummings, PT T2 - JOURNAL OF CHEMICAL PHYSICS AB - Grand canonical Monte Carlo simulations are performed to study the adsorption of water in single-walled (6:6), (8:8), (10:10), (12:12), and (20:20) carbon nanotubes in the 248–548 K temperature range. At room temperature the resulting adsorption isotherms in (10:10) and wider single-walled carbon nanotubes (SWCNs) are characterized by negligible water uptake at low pressures, sudden and complete pore filling once a threshold pressure is reached, and wide adsorption/desorption hysteresis loops. The width of the hysteresis loops decreases as pore diameter narrows and it becomes negligible for water adsorption in (8:8) and (6:6) SWCNs. Results for the isosteric heat of adsorption, density profiles along the pore axis and across the pore radii, order parameter across the pore radii, and x-ray diffraction patterns are presented. Layered structures are observed when the internal diameter of the nanotubes is commensurate to the establishment of a hydrogen-bonded network. The structure of water in (8:8) and (10:10) SWCNs is ordered when the temperature is 298 and 248 K, respectively. By simulating adsorption isotherms at various temperatures, the hysteresis critical temperature, e.g., the lowest temperature at which no hysteresis can be detected, is determined for water adsorbed in (20:20), (12:12), and (10:10) SWCNs. The hysteresis critical temperature is lower than the vapor-liquid critical temperature for bulk Simple Point Charge-Extended (SPC∕E) water model. DA - 2005/6/15/ PY - 2005/6/15/ DO - 10.1063/1.1924697 VL - 122 IS - 23 SP - SN - 0021-9606 ER - TY - JOUR TI - Templating surfaces with gradient assemblies AU - Genzer, J T2 - JOURNAL OF ADHESION AB - ABSTRACT One of the most versatile and widely used methods of forming surfaces with position-dependent wettability is that conceived by Chaudhury and Whitesides more than a decade ago [Science 256, 1539 (1992)]. In this paper we review several projects that utilize this gradient-forming methodology for: controlled of deposition of self-assembled monolayers on surfaces, generating arrays of nanoparticles with number density gradients, probing the mushroom-to-brush transition in surface-anchored polymers, and controlling the speed of moving liquid droplets on surfaces. DA - 2005/// PY - 2005/// DO - 10.1080/00218460590944855 VL - 81 IS - 3-4 SP - 417-435 SN - 1545-5823 KW - molecular gradient KW - self-assembly KW - directed assembly ER - TY - JOUR TI - Parametric studies of interaction strengths in polymer/CO2 systems: Discontinuous molecular dynamics Simulations AU - Li, ZM AU - Hall, CK T2 - LANGMUIR AB - Discontinuous molecular dynamics simulations are performed on homopolymer/solvent and surfactant/solvent systems. The homopolymer and surfactant molecules are modeled as freely jointed square-well chains. Solvent molecules are modeled as both hard spheres and square-well spheres. We explore how the various interaction parameters affect the types of phase behavior and micellization observed in the homopolymer/solvent and surfactant/solvent systems. Increasing the packing fraction of homopolymers in both hard-sphere solvents and square-well solvents increases the solvent's ability to dissolve homopolymers only when the segment−solvent interaction strength exceeds a critical value. Although only upper critical solution temperature (UCST) behavior is observed for homopolymers in hard-sphere solvents, both UCST and lower critical solution temperature (LCST) behavior are observed for homopolymers in square-well solvents, depending upon the interaction strengths and chain length. This indicates that it is necessary to account for the solvent−solvent attraction to model LCST behavior in supercritical CO2. Our simulation results on surfactants in hard-sphere solvents show that it is necessary to account for the interactions experienced by both the head and tail blocks in order to capture the essential features of surfactant/supercritical CO2 systems. DA - 2005/8/2/ PY - 2005/8/2/ DO - 10.1021/la0500023 VL - 21 IS - 16 SP - 7579-7587 SN - 0743-7463 ER - TY - JOUR TI - Nanomechanics of opposing glycosaminoglycan macromolecules AU - Seog, J AU - Dean, D AU - Rolauffs, B AU - Wu, T AU - Genzer, J AU - Plaas, AHK AU - Grodzinsky, AJ AU - Ortiz, C T2 - JOURNAL OF BIOMECHANICS AB - In this study, the net intermolecular interaction force between a chondroitin sulfate glycosaminoglycan (GAG)-functionalized probe tip and an opposing GAG-functionalized planar substrate was measured as a function of probe tip-substrate separation distance in aqueous electrolyte solutions using the technique of high resolution force spectroscopy. A range of GAG grafting densities as near as possible to native cartilage was used. A long-range repulsive force between GAGs on the probe tip and substrate was observed, which increased nonlinearly with decreasing separation distance between probe tip and substrate. Data obtained in 0.1 M NaCl was well predicted by a recently developed Poisson-Boltzmann-based theoretical model that describes normal electrostatic double layer interaction forces between two opposing surfaces of end-grafted, cylindrical rods of constant volume charge density and finite length, which interdigitate upon compression. Based on these results, the nanomechanical data and interdigitated rod model were used together to estimate the electrostatic component of the equilibrium modulus of cartilage tissue, which was then compared to that of normal adult human ankle cartilage measured in uniaxial confined compression. DA - 2005/9// PY - 2005/9// DO - 10.1016/j.jbiomech.2004.09.010 VL - 38 IS - 9 SP - 1789-1797 SN - 1873-2380 KW - cartilage KW - glycosaminoglycan KW - atomic force microscopy KW - electrostatic KW - Poisson-Boltzmann ER - TY - JOUR TI - Local strain, defects, and crystallographic tilt in GaN(0001) layers grown by maskless pendeo-epitaxy from x-ray microdiffraction AU - Barabash, R. I. AU - Ice, G. E. AU - Liu, W. AU - Einfeldt, S. AU - Roskowski, A. M. AU - Davis, R. F. T2 - Journal of Applied Physics DA - 2005/// PY - 2005/// VL - 97 IS - 1 ER - TY - JOUR TI - Ionic transport and interfacial stability of sulfonate-modified fumed silicas as nanocomposite electrolytes AU - Zhang, XW AU - Fedkiw, PS T2 - JOURNAL OF THE ELECTROCHEMICAL SOCIETY AB - Degussa A200 and R711 fumed silica surfaces were modified by attaching lithium sulfonate groups through alkyl or oligomer chains, respectively, in an attempt to form single-ion conducting fumed silicas: A200-lithium propanesulfonate (A200-LiPS), R711-poly(lithium vinylsulfonate) (R711-pLiVS), and R711-poly(lithium 2-acrylamido-2-methyl-1-propanesulfonate) (R711-pLiAMPS). Conductivity, lithium transference number, and Li/electrolyte interfacial stability measurements were conducted on nanocomposite electrolytes prepared by dispersing the conducting fumed silicas into solvents consisting of oligomeric polyethylene glycol dimethyl ether (PEGdm), polyethylene oxide (PEO), or PEGdm/PEO blends. Among the three sulfonate-modified fumed silicas, the highest conductivity was always obtained using R711-pLiAMPS. A maximum room-temperature conductivity of was obtained at a surface concentration of and a Li:O mole ratio of 1:100 ( filler). The maximum lithium transference number achieved for the same R711-pLiAMPS-based system is 0.78 at a surface concentration of and a Li:O mole ration of 1:20 ( filler). Adding lithium salts to the solvent, such as lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(perfluoroethylenesulfonyl)imide (LiBETI), lithium bis(oxalato)borate (LiBOB), and lithium phosphate , increases room-temperature conductivity and interfacial stability while maintaining relatively high lithium transference numbers. DA - 2005/// PY - 2005/// DO - 10.1149/1.2109661 VL - 152 IS - 12 SP - A2413-A2420 SN - 1945-7111 UR - https://publons.com/publon/7178384/ ER - TY - JOUR TI - Hydrogenation of polystyrene in CO2-expanded solvents: Catalyst poisoning AU - Xu, DW AU - Carbonell, RG AU - Kiserow, DJ AU - Roberts, GW T2 - INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH AB - Organic solvents expanded with supercritical carbon dioxide can be excellent media for hydrogenation reactions. However, catalyst poisoning by CO formed via the reverse water-gas-shift reaction occurs during many hydrogenations in the presence of CO2. In this research, the hydrogenation of polystyrene in CO2-expanded decahydronaphthalene was studied in a batch reactor using two hydrogenation catalysts, 5%Pd/BaSO4 and 65%Ni/Al2O3/SiO2. The 5%Pd/BaSO4 catalyst deactivated at 150 °C and CO2 pressures of 250−2250 psig (1.8−15.6 MPa). Approximately 50 ppm CO was present in the CO2-rich light phase after about 10 h at 150 °C, 750 psig H2 pressure, and 2250 psig CO2 pressure. A model that incorporates CO poisoning was developed to describe deactivation of the Pd/BaSO4 catalyst. The 65%Ni/Al2O3/SiO2 catalyst was more active for ring hydrogenation than 5%Pd/BaSO4, and very little CO was formed in the presence of CO2. The Ni catalyst deactivated in the presence of CO2 at 180 °C, possibly due to H2O formed in a methanation reaction. DA - 2005/8/3/ PY - 2005/8/3/ DO - 10.1021/ie040243q VL - 44 IS - 16 SP - 6164-6170 SN - 0888-5885 ER - TY - JOUR TI - Electrochemical behavior of bis(beta-diketonate)copper complexes AU - Denison, GM AU - Evans, AO AU - Bessel, CA AU - Skaf, DW AU - Murray, RW AU - DeSimone, JM T2 - JOURNAL OF THE ELECTROCHEMICAL SOCIETY AB - The use of copper to produce interconnects for microchip manufacture has prompted a renewed interest in its corrosion, deposition, and passivation processes. The aqueous electrochemistry of four bis(β-diketonate)copper complexes (where , tfacH, hfacH, and tmhdH) in aqueous media has been investigated. Equilibrium constants were used to calculate potential-pH diagrams, varying the β-diketone ligand, ligand and∕or copper concentrations, and the ionic strength of the buffer solution. The theoretical potential-pH diagrams showed good correlation to the experimental data obtained in aqueous solutions. DA - 2005/// PY - 2005/// DO - 10.1149/1.2047387 VL - 152 IS - 11 SP - B435-B440 SN - 0013-4651 ER - TY - JOUR TI - Convective assembly of antireflective silica coatings with controlled thickness and refractive index AU - Prevo, BG AU - Hwang, Y AU - Velev, OD T2 - CHEMISTRY OF MATERIALS AB - Convective assembly at high volume fraction was used to deposit silica nanoparticle coatings onto glass and silicon substrates. By allowing control of the film structure and thickness, this technique provides a means for making large-scale coatings with antireflective properties. The reflectance was reduced by 50% for silicon (at 600 nm) and by 70% for single glass/air surface. Microstructural investigations using SEM, AFM, profilometry, and ellipsometry provided good correlation to the observed macroscopic optical properties. By virtue of the coatings' uniformity, the reflectance and transmission spectra from both substrates could be modeled well by classical reflection relations, using a volume-averaged refractive index. Data analysis showed that the relatively high packing fraction in nanocoatings made from monodisperse spheres is responsible for the limit on antireflective capabilities. To overcome this restriction, low-density silica coatings were made from binary colloidal mixtures of different diameter SiO2 particles. The packing fraction of these coatings was further optimized to yield 88% maximal reduction in the reflectance of glass surfaces. The technique is simple, inexpensive, and scalable. DA - 2005/7/12/ PY - 2005/7/12/ DO - 10.1021/cm050416h VL - 17 IS - 14 SP - 3642-3651 SN - 1520-5002 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-22944488858&partnerID=MN8TOARS ER - TY - JOUR TI - Asphaltenic aggregates are polydisperse oblate cylinders AU - Gawrys, KL AU - Kilpatrick, PK T2 - JOURNAL OF COLLOID AND INTERFACE SCIENCE AB - Small-angle neutron scattering (SANS) has proven to be very useful for deducing the sizes and morphologies of asphaltenic aggregates in solution. A wide variety of intra-particle structure factors have previously been applied to SANS scattering spectra, but the studies often provided limited information concerning the quality of the fits and the Q range over which the models were applied. Selection of an appropriate form factor that closely approximates the structure of asphaltenic aggregates is important for determining the properties of asphaltenic aggregates, such as the radius of gyration (RG), molar mass, and apparent fractal dimension. This study evaluates various mono- and polydisperse intra-particle structure factor models as applied to four asphaltene scattering spectra. Agreement of the model fit parameters (I0 and RG) with those obtained from Guinier analyses suggests that such a form factor model is physically reasonable. Reduced χ2 values for each non-linear least squares fit indicates how well a given model fits to the entire Q range studied for the scattering intensity distribution. In the polydispersity analyses, an analytical function is introduced to model the scattering behavior of oblate cylinders with a Schultz distribution of radii. Results indicate that the polydisperse radius oblate cylinder model best approximates the shape of asphaltenic aggregates. DA - 2005/8/15/ PY - 2005/8/15/ DO - 10.1016/j.jcis.2005.03.036 VL - 288 IS - 2 SP - 325-334 SN - 1095-7103 KW - asphaltenes KW - small-angle neutron scattering KW - polydispersity ER - TY - JOUR TI - A novel enzymatic technique for limiting drug mobility in a hydrogel matrix AU - Burke, MD AU - Park, JO AU - Srinivasarao, M AU - Khan, SA T2 - JOURNAL OF CONTROLLED RELEASE AB - An oral colon specific drug delivery platform has been developed to facilitate targetted release of therapeutic proteins as well as small molecule drugs. A simple enzymatic procedure is used to modify the molecular architecture of a lightly chemically crosslinked galactomannan hydrogel as well as a model drug-galactomannan oligomer conjugate, fluoroisocynate (FITC) tagged guar oligomer, to entrap the model drug. The enzyme-modified hydrogel retains the drug until it reaches the colonic environment where bacteria secrete enzymes (namely beta-mannanase) to degrade the gel and release the drug molecule. Laser scanning confocal microscopy combined with fluorescence recovery after photobleaching is used to quantify the diffusion of the drug conjugate. The diffusion coefficient of solutes in the lightly crosslinked galactomannan hydrogel is approximately equal to the diffusion coefficient in the guar solution for simple diffusional drug loading. After drug loading, alpha-galactosidase treatment generates additional physical crosslinks in the hydrogel matrix as well as between the drug-oligomer conjugate and the hydrogel, which reduces diffusion of the drug-oligomer conjugate significantly. Degradation of the hydrogel by beta-mannanase results in a slow and controlled rate of FITC-guar oligomer diffusion, which generates an extended release profile for the model drug. DA - 2005/5/5/ PY - 2005/5/5/ DO - 10.1016/j.jconrel.2005.01.017 VL - 104 IS - 1 SP - 141-153 SN - 1873-4995 KW - oral drug delivery KW - hydrogel KW - enzyme KW - diffusion KW - guar ER - TY - JOUR TI - White X-ray microbeam analysis of strain and crystallographic tilt in GaN layers grown by maskless pendeoepitaxy AU - Barabash, R. I. AU - Ice, G. E. AU - Liu, W. AU - Einfeldt, S. AU - Hommel, D. AU - Roskowski, A. M. AU - Davis, R. F. T2 - Physica Status Solidi. A, Applications and Materials Science DA - 2005/// PY - 2005/// VL - 202 IS - 5 SP - 732-738 ER - TY - JOUR TI - Solid-state polymerization of poly(bisphenol A carbonate) facilitated by supercritical carbon dioxide AU - Kiserow, DJ AU - Shi, CM AU - Roberts, GW AU - Gross, SM AU - DeSimone, JM T2 - ADVANCES IN POLYCARBONATES AB - During the solid state polymerization (SSP) of poly(bisphenol A carbonate), both the forward reaction rate constant and the phenol diffusion coefficient inside the polymer particle were significantly higher when SSP was carried out in supercritical carbon dioxide (scCO2) compared to in atmospheric N2. These enhancements depended on the reaction conditions, and can be understood in terms of the CO2 concentrations in the polymer. Polymer with a Mw as high as 78100 has been synthesized by SSP with scCO2 as the sweep fluid. DA - 2005/// PY - 2005/// DO - 10.1021/bk-2005-0898.ch007 VL - 898 SP - 86-94 SN - 0097-6156 ER - TY - JOUR TI - Molecular modeling of freezing of simple fluids confined within carbon nanotubes AU - Hung, FR AU - Coasne, B AU - Santiso, EE AU - Gubbins, KE AU - Siperstein, FR AU - Sliwinska-Bartkowiak, M T2 - JOURNAL OF CHEMICAL PHYSICS AB - Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation Francisco R. Hung, Benoit Coasne, Erik E. Santiso, Keith E. Gubbins, Flor R. Siperstein, Malgorzata Sliwinska-Bartkowiak; Molecular modeling of freezing of simple fluids confined within carbon nanotubes. J. Chem. Phys. 8 April 2005; 122 (14): 144706. https://doi.org/10.1063/1.1881072 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioThe Journal of Chemical Physics Search Advanced Search |Citation Search DA - 2005/4/8/ PY - 2005/4/8/ DO - 10.1063/1.1881072 VL - 122 IS - 14 SP - SN - 1089-7690 ER - TY - JOUR TI - Heterogeneous polymerization of fluoroolefins in supercritical carbon dioxide AU - Kennedy, KA AU - Roberts, GW AU - DeSimone, JM T2 - POLYMER PARTICLES AB - In recent years, carbon dioxide has been investigated for its potential to replace the aqueous and organic solvents used in polymerization processes. Carbon dioxide has several benefits, including being environmentally benign, a tunable solvent, resistant to chain transfer, and of low viscosity which facilitates high initiator efficiencies and fluid handling. Homo- and copolymerization of fluoroolefins such as tetrafluoroethylene (TFE), vinylidene fluoride (VF2), hexafluoropropylene (HFP), and perfluorinated vinyl ethers in carbon dioxide are particularly interesting because of the significant waste reduction and the elimination of potentially harmful processing agents. This review focuses on recent developments in polymerizing fluoroolefins via heterogeneous polymerization in carbon dioxide. At least one CO2-based polymerization process has recently been commercialized, and additional research is underway to understand the kinetics associated with polymerizing fluoroolefins in carbon dioxide. As researchers improve their understanding of CO2-based polymerizations, and as industry continues to look for more economically and environmentally-sound alternatives to existing processes, it will become more and more common to employ carbon dioxide as a polymerization medium. DA - 2005/// PY - 2005/// DO - 10.1007/b100114 VL - 175 SP - 329-346 SN - 1436-5030 KW - supercritical carbon dioxide KW - fluoropolymers KW - tetrafluoroethylene KW - vinylidene fluoride ER - TY - JOUR TI - Heat transfer performance of a cooling system using vibrating piezoelectric beams AU - Wu, T AU - Ro, PI T2 - JOURNAL OF MICROMECHANICS AND MICROENGINEERING AB - A prototype of a miniature cooling system for microelectronics using vibrating piezoelectric beam was proposed and constructed. The flow patterns and cooling effects of the system were investigated experimentally. The vibration characteristics of the piezoelectric beam were simulated by the finite element method. Cooling effects were measured in terms of the temperature drop of the heat source above the vibrating beam. The electric field applied on the piezoelectric beam and the gap between heat source and actuator were adjusted to find the best cooling result. A temperature drop of 25.9 °C from 92 °C can be observed for the heat source when operating at a certain condition, which indicates the feasibility of using the present miniature cooling system in small devices. The heat transfer performance of the cooling system was analyzed as well. The results show that the enhancement of heat transfer between the heat source and the beam can be up to 210% with the acoustic streaming generated by the beam vibration in the present experimental studies. The enhanced heat transfer can be attributed to the generation of vortical streaming by the vibrating beam which was also captured in the flow visualization experiments. DA - 2005/1// PY - 2005/1// DO - 10.1088/0960-1317/15/1/030 VL - 15 IS - 1 SP - 213-220 SN - 1361-6439 ER - TY - JOUR TI - Forced convective cooling via acoustic streaming in a narrow channel established by a vibrating piezoelectric bimorph AU - Wan, Q AU - Wu, T AU - Chastain, J AU - Roberts, WL AU - Kuznetsov, AV AU - Ro, PI T2 - FLOW TURBULENCE AND COMBUSTION AB - Forced convection in a narrow channel is investigated both numerically and experimentally. The flow field is established through the mechanism of acoustic streaming. This is accomplished by high frequency vibration of one of the channel walls, which is composed of a piezoelectric bimorph. In the numerical computations, the Navier-Stokes equations are decomposed into the acoustic equations and the streaming equations by the perturbation method. The acoustic field is first numerically obtained, which provides the driving force for the streaming field. The streaming field and the associated temperature field are then obtained numerically. Heat losses from a heat source are measured to determine the efficiency of this as a cooling method. The air-flow patterns in the channel between the heat source and the bimorph actuator are visualized using the particle tracking velocimetry. The visualization clearly shows that vortical streaming (acoustic streaming) can be induced by bimorph vibration, which enhances heat transfer between the heat source and the surrounding air. The temperature decreases obtained computationally and experimentally are in good agreement. DA - 2005/3// PY - 2005/3// DO - 10.1007/s10494-005-4132-4 VL - 74 IS - 2 SP - 195-206 SN - 1573-1987 KW - acoustic streaming KW - forced convection KW - cooling enhancement KW - vibrating surface ER - TY - JOUR TI - Applications, reliability and validity of the Index of Learning Styles AU - Felder, R. M. AU - Spurlin, J. T2 - International Journal of Engineering Education DA - 2005/// PY - 2005/// VL - 21 IS - 1 SP - 103-112 ER - TY - JOUR TI - An AC electrokinetic technique for collection and concentration of particles and cells on patterned electrodes AU - Bhatt, KH AU - Grego, S AU - Velev, OD T2 - LANGMUIR AB - We report an electrohydrodynamic effect arising from the application of alternating electric fields to patterned electrode surfaces. The AC fields were applied to dilute suspensions of latex microspheres enclosed between a patterned silicon wafer and an ITO-coated glass slide in a small chamber. The latex particles became collected in the center of the conductive "corrals" on the silicon wafer acting as bottom electrode. The particle collection efficiency and speed depended only on the frequency and strength of the field and were independent of the material properties of the particles or the electrodes. The leading effect in the particle collection process is AC electrohydrodynamics. We discuss how the electrohydrodynamic flows emerge from the spatially nonuniform field and interpret the experimental results by means of electrostatic and hydrodynamic simulations. The technique allows three-dimensional microfluidic pumping and transport by the use of two-dimensional patterns. We demonstrate on-chip collection of latex particles, yeast cells, and microbes. DA - 2005/7/5/ PY - 2005/7/5/ DO - 10.1021/la050658w VL - 21 IS - 14 SP - 6603-6612 SN - 0743-7463 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-22444436490&partnerID=MN8TOARS ER - TY - JOUR TI - Vapor-liquid and vapor-liquid-liquid equilibria of carbon dioxide/n-perfluoroalkane/n-alkane ternary mixtures AU - Colina, CM AU - Gubbins, KE T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - Perfluoroalkanes have numerous applications (e.g., in the medical field and the chemical industry), and their high affinity for carbon dioxide makes them attractive as surfactants and cosolvents. Although research in this area has grown in the past few years, very little phase-equilibrium data is available in the open literature for these systems. In this work, we present, for the first time, predictions of vapor-liquid and vapor-liquid-liquid equilibria of binary and ternary systems of carbon dioxide/n-perfluoroalkane/n-alkane. Our results are based on the SAFT-VR EOS (statistical associating fluid theory of variable range, equation of state), and we study the influence of temperature, pressure, composition, and chain length on the phase diagram. The predicted phase diagrams are based on temperature-independent binary interaction parameters, and no ternary parameters are introduced. Comparisons to the available experimental and molecular simulation data show that the predicted diagrams should provide a good representation of the phase equilibria. DA - 2005/2/24/ PY - 2005/2/24/ DO - 10.1021/jp046612d VL - 109 IS - 7 SP - 2899-2910 SN - 1520-6106 ER - TY - BOOK TI - Unit operations of chemical engineering (7th ed.) AU - McCabe, W. L. CN - TP155.7 .M3 2005 DA - 2005/// PY - 2005/// PB - Boston: McGraw-Hill SN - 0072848235 ER - TY - JOUR TI - Microcontact patterning of ruthenium gate electrodes by selective area atomic layer deposition AU - Park, KJ AU - Doub, JM AU - Gougousi, T AU - Parsons, GN T2 - APPLIED PHYSICS LETTERS AB - Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation K. J. Park, J. M. Doub, T. Gougousi, G. N. Parsons; Microcontact patterning of ruthenium gate electrodes by selective area atomic layer deposition. Appl. Phys. Lett. 31 January 2005; 86 (5): 051903. https://doi.org/10.1063/1.1852079 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioApplied Physics Letters Search Advanced Search |Citation Search DA - 2005/1/31/ PY - 2005/1/31/ DO - 10.1063/1.1852079 VL - 86 IS - 5 SP - SN - 0003-6951 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000227144700016&KeyUID=WOS:000227144700016 ER - TY - JOUR TI - Designing pattern-recognition surfaces for selective adsorption of copolymer sequences using lattice Monte Carlo simulation AU - Jayaraman, A AU - Hall, CK AU - Genzer, J T2 - PHYSICAL REVIEW LETTERS AB - We describe a simulation method to design surfaces for recognizing specific monomer sequences in copolymers. We fix the monomer sequence statistics of the AB copolymers on a surface containing two types of sites and allow the simulation to iterate towards an optimal surface pattern that can recognize and selectively adsorb the sequence in the copolymer. During the simulation the surface pattern is designed by switching identities of two randomly picked sites. For copolymers with less blocky sequences the designed surfaces recognize the correct sequence well when the segment-surface interactions dominate over the intersegment interactions. For copolymers with more blocky sequences recognition is good when the segment-surface interactions are only slightly stronger than the intersegment interactions. DA - 2005/2/25/ PY - 2005/2/25/ DO - 10.1103/physrevlett.94.078103 VL - 94 IS - 7 SP - SN - 1079-7114 ER - TY - JOUR TI - Solid/solid phase transitions in confined thin films: A zero temperature approach AU - Bock, H AU - Gubbins, KE AU - Ayappa, KG T2 - JOURNAL OF CHEMICAL PHYSICS AB - We report a density functional theory study of confinement induced solid/solid phase transitions in a thin film (modeled as methane) at T=0. The solid film is confined by two graphite surfaces represented by a mean-field potential. As the wall separation is varied the structure of the confined film changes, which influences its density and the solvation force. Using the directly accessible grand canonical potential density we determine the stable phases and calculate the exact location of the phase transitions. We observe a series of phases having square and triangular symmetry. At low wall separations we find zig-zag buckling and an asymmetric buckled phase, whose structure is consistent with the strongest buckling instability of a triangular monolayer predicted by Chou and Nelson [Phys. Rev. E 48, 4611 (1993)] but, to our knowledge, has not been observed as a stable phase before. We find that the two-dimensional order parameters Psi(4) (square symmetry) and Psi(6) (triangular symmetry) show unphysical behavior in the transition region between square and triangular symmetry. Thus, in the present model they fail to predict the right location of the phase transitions. DA - 2005/3/1/ PY - 2005/3/1/ DO - 10.1063/1.1856921 VL - 122 IS - 9 SP - SN - 1089-7690 ER - TY - JOUR TI - Ordered silicon nanocavity arrays in surface-assisted desorption/ionization mass spectrometry AU - Finkel, NH AU - Prevo, BG AU - Velev, OD AU - He, L T2 - ANALYTICAL CHEMISTRY AB - We report here a simple method to generate ordered nanocavity arrays on a Si wafer and use it in surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). A close-packed SiO2 nanosphere array was first deposited on a low-resistivity Si wafer using a convective self-assembly method. The nanoparticle array was then used as a mask in a reactive ion etching (RIE) process to selectively remove portions of the Si surface. Subsequent sonication removed those physically adsorbed SiO2 nanoparticles and exposed an ordered nanocavity array underneath. The importance of this approach is its capability of systematically varying surface geometries to achieve desired features, which makes detailed studies of the impacts of surface features on the desorption/ionization mechanism feasible. We demonstrated that the in-plane width and out-of-plane depth of the cavities were adjustable by varying etching times, and the intercavity spacing was controllable by varying the number of particle layers deposited. MS detection of small peptides on these substrates showed comparable sensitivity to conventional porous Si substrates (DIOS, desorption/ionization on porous silicon). The desorption and ionization efficiency of these roughened surfaces exhibited a nonmonotonic relationship to the increased total surface area. Several possible factors contributing to the observed phenomenon are speculated upon. The application of this arrayed surface in metabolite detection of Arabidopsis thaliana root extracts is also demonstrated. DA - 2005/2/15/ PY - 2005/2/15/ DO - 10.1021/ac048645v VL - 77 IS - 4 SP - 1088-1095 SN - 1520-6882 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-13844320727&partnerID=MN8TOARS ER - TY - JOUR TI - Kinetics of fibril formation by polyalanine peptides AU - Nguyen, HD AU - Hall, CK T2 - JOURNAL OF BIOLOGICAL CHEMISTRY AB - Ordered β-sheet complexes, termed amyloid fibrils, are the underlying structural components of the intra- and extracellular fibrillar protein deposits that are associated with a variety of human diseases, including Alzheimer's, Parkinson's, and the prion diseases. In this work, we investigated the kinetics of fibril formation using our newly developed off-lattice intermediate resolution model, PRIME. The model is simple enough to allow the treatment of large multichain systems while maintaining a fairly realistic description of protein dynamics without built-in bias toward any conformation when used in conjunction with constant temperature discontinuous molecular dynamics, a fast alternative to conventional molecular dynamics. Simulations were performed on systems containing 48–96 model Ac-KA14K-NH2 peptides. We found that fibril formation for polyalanines incorporate features that are characteristic of three models, the templated assembly, nucleated polymerization, and nucleated conformational conversion models, but that none of them gave a completely satisfactory description of the simulation kinetics. Fibril formation was nucleation-dependent, occurring after a lag time that decreased with increasing peptide concentration and increased with increasing temperature. Fibril formation appeared to be a conformational conversion process in which small amorphous aggregates → β-sheets → ordered nucleus → subsequent rapid growth of a small stable fibril or protofilament. Fibril growth in our simulations involved both β-sheet elongation, in which the fibril grew by adding individual peptides to the end of each β-sheet, and lateral addition, in which the fibril grew by adding already formed β-sheets to its side. The initial rate of fibril formation increased with increasing concentration and decreased with increasing temperature. Ordered β-sheet complexes, termed amyloid fibrils, are the underlying structural components of the intra- and extracellular fibrillar protein deposits that are associated with a variety of human diseases, including Alzheimer's, Parkinson's, and the prion diseases. In this work, we investigated the kinetics of fibril formation using our newly developed off-lattice intermediate resolution model, PRIME. The model is simple enough to allow the treatment of large multichain systems while maintaining a fairly realistic description of protein dynamics without built-in bias toward any conformation when used in conjunction with constant temperature discontinuous molecular dynamics, a fast alternative to conventional molecular dynamics. Simulations were performed on systems containing 48–96 model Ac-KA14K-NH2 peptides. We found that fibril formation for polyalanines incorporate features that are characteristic of three models, the templated assembly, nucleated polymerization, and nucleated conformational conversion models, but that none of them gave a completely satisfactory description of the simulation kinetics. Fibril formation was nucleation-dependent, occurring after a lag time that decreased with increasing peptide concentration and increased with increasing temperature. Fibril formation appeared to be a conformational conversion process in which small amorphous aggregates → β-sheets → ordered nucleus → subsequent rapid growth of a small stable fibril or protofilament. Fibril growth in our simulations involved both β-sheet elongation, in which the fibril grew by adding individual peptides to the end of each β-sheet, and lateral addition, in which the fibril grew by adding already formed β-sheets to its side. The initial rate of fibril formation increased with increasing concentration and decreased with increasing temperature. Ordered β-sheet complexes are the underlying structural components of the intra- and extracellular fibrillar protein deposits, termed amyloid fibrils, that are associated with a variety of human diseases, including Alzheimer's, Parkinson's, and the prion diseases (1Kirschner D.A. Abraham C. Selkoe D.J. Proc. Natl. Acad. Sci. U. S. A. 1986; 83: 503-507Crossref PubMed Scopus (477) Google Scholar, 2Kelly J.W. Curr. Opin. Struct. Biol. 1998; 8: 101-106Crossref PubMed Scopus (938) Google Scholar, 3Koo E.H. Lansbury Jr., P.T. Kelly J.W. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 9989-9990Crossref PubMed Scopus (584) Google Scholar, 4Selkoe D.J. Nature. 1999; 399: A23-A31Crossref PubMed Scopus (1515) Google Scholar, 5Lynn D.G. Meredith S.C. J. Struct. Biol. 2000; 130: 153-173Crossref PubMed Scopus (105) Google Scholar, 6Conway K.A. Lee S.J. Rochet J.C. Ding T.T. Williamson R.E. Lansbury Jr., P.T. Proc. Natl. Acad. Sci. U. S. A. 2000; 97: 571-576Crossref PubMed Scopus (1305) Google Scholar). Although extensively studied, the mechanisms that govern the formation of amyloid fibrils have not yet been fully determined. However, recent evidence that proteins other than those associated with amyloid diseases form fibrils in vitro under mildly denaturing conditions (7Guijarro J.I. Sunde M. Jones J.A. Campbell I.D. Dobson C.M. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 4224-4228Crossref PubMed Scopus (621) Google Scholar, 8Chiti F. Webster P. Toddei N. Clark A. Stefan M. Ramponi G. Dobson C.M. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 3590-3594Crossref PubMed Scopus (979) Google Scholar, 9Chiti F. Bucciantini M. Capanni C. Taddei N. Dobson C.M. Stefan M. Protein Sci. 2001; 10: 2541-2547Crossref PubMed Scopus (122) Google Scholar) has led leaders in the field to suggest that fibril formation is an intrinsic property of polypeptides, albeit under appropriate conditions. This implies that progress toward understanding the origins of various protein deposition diseases can be made by in vitro or in silico examination of the general features of protein fibrillization using model proteins that are less complex than the specific amyloidogenic protein. Here we performed computer simulations on systems containing polyalanine-based peptides of the sequence Ac-KA14K-NH2 in an attempt to help further understanding of the molecular level mechanisms that are responsible for fibril formation. Our molecular dynamics simulations were conducted on systems containing many peptides initially in the random-coil state. Four mechanisms have been proposed to describe the conformational transformation and assembly of normally soluble proteins into ordered aggregates (10Kelly J.W. Nat. Struct. Biol. 2000; 7: 824-826Crossref PubMed Scopus (154) Google Scholar). The first is the templated assembly mechanism (11Uratani Y. Asakura S. Imahori K. J. Mol. Biol. 1972; 67: 85-98Crossref PubMed Scopus (55) Google Scholar, 12Griffith J.S. Nature. 1967; 215: 1043-1044Crossref PubMed Scopus (888) Google Scholar), in which a soluble random-coil peptide binds to a preassembled β-sheet-rich nucleus and then undergoes a rate-determining structural change. The second is the monomer-directed conversion mechanism (13Prusiner S.B. Science. 1982; 216: 136-144Crossref PubMed Scopus (4014) Google Scholar), in which a monomeric peptide adopts a conformation that is identical to that found in the fibril, binds to another soluble monomer in a rate-determining step, converts that monomer to the conformation found in the fibril, and then dissociates, with both peptides rapidly added to the end of the growing fibril. The third is the nucleated polymerization mechanism (14Jarrett J.T. Lansbury P.T. Cell. 1993; 73: 1055-1058Abstract Full Text PDF PubMed Scopus (1886) Google Scholar, 15Hofrichter J. Ross P.D. Eaton W. Proc. Natl. Acad. Sci. U. S. A. 1974; 71: 4864-4868Crossref PubMed Scopus (424) Google Scholar, 16Beaven G.H. Gratzer W.B. Davies H.G. Eur. J. Biochem. 1969; 11: 37-42Crossref PubMed Scopus (109) Google Scholar), which is characterized by the rate-limiting formation of a nucleus followed by the rapid addition of monomers to the growing end of the nucleus. The fourth is the nucleated-conformational conversion mechanism (17Serio T.R. Cashikar A.G. Kowal A.S. Sawicki G.J. Moslehi J.J. Serpell L. Arnsdorf M.F. Lindquist S.L. Science. 2000; 289: 1317-1321Crossref PubMed Scopus (813) Google Scholar), in which the formation of small amorphous aggregates precedes the rate-limiting formation of a critical nucleus and subsequent rapid growth of large fibrils through the addition of globular multimers to fibril ends. All of the above mentioned mechanisms require that the system go through a nucleation event before fibrils can be formed. The nucleus in the monomer-directed conversion mechanism is a monomeric peptide, whereas the nuclei in the templated assembly, nucleated polymerization, and nucleated-conformational conversion mechanisms are oligomers. The general picture of the fibril formation process that accompanies three of the four mechanisms described above, the templated assembly, nucleated polymerization, and nucleated-conformational conversion mechanisms, is the following. Fibril formation is initiated when the native state of a protein is slightly destabilized, for example, by changing pH, exposing structural elements on the resulting partially folded intermediates, which then begin to associate intermolecularly rather than intramolecularly. If the protein monomer concentration is greater than some critical concentration, the partially folded intermediates slowly associate via a series of energetically unfavorable steps, resulting in the formation of an oligomer after a defined period, called the lag time. This oligomer serves as the nucleus for the rapid growth and elongation of protofilaments or small fibrils, either through monomer addition at the protofilament tip or through end-to-end association of short protofilaments. Eventually, several protofilaments associate to form fibrils, which then grow further by the addition of more protofilaments. If the protein monomer concentration is less than the critical concentration, fibrillization can still take place by homogeneous (or heterogeneous) seeding in which case nucleation occurs on protein (or non-protein) species. Most simulation studies to date of fibril-forming peptides by other investigators have been limited to the study of either isolated peptides (18Kortvelyesi T. Kiss G. Murphy R.F. Penke B. Lovas S. J. Mol. Structure. 2001; 545: 215-223Crossref Scopus (4) Google Scholar, 19Straub J.E. Guevara J. Huo S. Lee J.P. Acc. Chem. Res. 2002; 35: 473-481Crossref PubMed Scopus (59) Google Scholar, 20Massi F. Peng J.W. Lee J.P. Straub J.E. Biophys. J. 2001; 81: 31-44Abstract Full Text Full Text PDF Scopus (107) Google Scholar, 21Massi F. Klimov D. Thirumalai D. Straub J.E. Protein Sci. 2002; 11: 1639-1647Crossref PubMed Scopus (66) Google Scholar, 22Massi F. Straub J.E. J. Comput. Chem. 2001; 24: 143-153Crossref Scopus (47) Google Scholar, 23Massi F. Straub J.E. Biophys. J. 2001; 81: 697-709Abstract Full Text Full Text PDF PubMed Scopus (43) Google Scholar, 24Moraitakis G. Goodfellow J.M. Biophys. J. 2003; 84: 2149-2158Abstract Full Text Full Text PDF PubMed Scopus (35) Google Scholar, 25Ilangovan U. Ramamoorthy A. Biopolymers. 1998; 45: 9-20Crossref PubMed Scopus (19) Google Scholar, 26Yang M. Lei M. Huo S. Protein Sci. 2003; 12: 1222-1231Crossref PubMed Scopus (41) Google Scholar) or model amyloid fibrils that have already formed (27Li L. Darden T.A. Bartolotti L. Kominos D. Pedersen L.G. Biophys. J. 1999; 76: 2871-2878Abstract Full Text Full Text PDF PubMed Scopus (109) Google Scholar, 28George A.R. Howlett D.R. Biopolymers. 1999; 50: 733-741Crossref PubMed Scopus (47) Google Scholar, 29Ma B. Nussinov R. Protein Sci. 2002; 11: 2335-2350Crossref PubMed Scopus (143) Google Scholar, 30Ma B. Nussinov R. Proc. Natl. Acad. Sci. U. S. A. 2002; 99: 14126-14131Crossref PubMed Scopus (386) Google Scholar, 31Zanuy D. Ma B. Nussinov R. Biophys. J. 2003; 84: 1884-1894Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar, 32Zanuy D. Nussinov R. J. Mol. Biol. 2003; 329: 565-584Crossref PubMed Scopus (80) Google Scholar, 33Lakdawala A.S. Morgan D.M. Liotta D.C. Lynn D.G. Snyder J.P. J. Am. Chem. Soc. 2002; 124: 15150-15151Crossref PubMed Scopus (40) Google Scholar, 34Hwang W. Marini D.M. Kamm R.D. Zhang S. J. Chem. Phys. 2003; 118: 389-397Crossref Scopus (86) Google Scholar, 35Kuwata K. Matumoto T. Cheng H. Nagayama K. James T.L. Roder H. Proc. Natl. Acad. Sci. U. S. A. 2003; 100: 4790-4795Crossref PubMed Scopus (117) Google Scholar). These studies have employed high resolution protein models, which are based on a realistic representation of protein geometry and a fairly faithful accounting for the energetics of every atom on the protein and on the solvent. Although there have been several attempts (29Ma B. Nussinov R. Protein Sci. 2002; 11: 2335-2350Crossref PubMed Scopus (143) Google Scholar, 36Gsponer J. Haberthur U. Caflisch A. Proc. Natl. Acad. Sci. U. S. A. 2003; 100: 5154-5159Crossref PubMed Scopus (239) Google Scholar, 37Mager P.P. Molecular Simulation. 1998; 20: 201-222Crossref Scopus (13) Google Scholar, 38Mager P.P. Med. Res. Rev. 1998; 18: 403-430Crossref PubMed Scopus (30) Google Scholar, 39Mager P.P. Reinhardt R. Fischer K. Molecular Simulation. 2001; 26: 367-379Crossref Scopus (8) Google Scholar, 40Fernandez A. Boland Mde.L. FEBS Lett. 2002; 529: 298-302Crossref PubMed Scopus (17) Google Scholar, 41Klimov D.K. Thirumalai D. Structure (Camb.). 2003; 11: 295-307Abstract Full Text Full Text PDF PubMed Scopus (320) Google Scholar) using high resolution protein models to simulate the formation of fibrils from random coils, the systems considered did not contain enough peptides to mimic the nucleus that stabilizes the large fibrils that are observed in experiments. Given current computational capabilities, simpler models are required. This has been recognized by a few investigators who have combined intermediate resolution protein models with the Go potentials to look at fibril formation. Such an approach has been taken by Jang et al. (42Jang H. Hall C.K. Zhou Y. Biophys. J. 2004; 86: 31-49Abstract Full Text Full Text PDF PubMed Scopus (49) Google Scholar, 43Jang H. Hall C.K. Zhou Y. Protein Sci. 2004; 13: 40-53Crossref PubMed Scopus (29) Google Scholar), who studied the thermodynamics and kinetics of the assembly of four model β-sheet peptides into a tetrameric β-sheet complex, and by Ding et al. (44Ding F. Dokholyan N.V. Buldyrev S.V. Stanley H.E. Shakhnovich E.I. J. Mol. Biol. 2002; 324: 851-857Crossref PubMed Scopus (138) Google Scholar), who studied the formation of a fibrillar double β-sheet structure containing eight model Src SH3 domain proteins. However, since the Go potential contains a built-in bias toward the native conformation, this approach is not suitable for the study of spontaneous fibril formation from random configurations. We developed an alternative approach, inspired in part by the models of Sun (45Sun S. Protein Sci. 1993; 2: 762-785Crossref PubMed Scopus (188) Google Scholar), Sun et al. (46Sun S. Thomas P.D. Dill K.A. Protein. Eng. 1995; 8: 769-778Crossref PubMed Scopus (91) Google Scholar), and Takada et al. (47Takada S. Luthey-Schulten Z. Wolynes P.G. J. Chem. Phys. 1999; 110: 11616-11629Crossref Scopus (178) Google Scholar), that represents each amino acid residue with three backbone beads and one side chain bead. Our model, which we now call PRIME (Protein Intermediate Resolution Model), allows the treatment of large multichain systems while maintaining a fairly realistic description of protein dynamics without built-in bias toward any conformation (48Smith A.V. Hall C.K. Proteins Struct. Funct. Genet. 2001; 44: 344-360Crossref PubMed Scopus (157) Google Scholar, 49Nguyen H.D. Marchut A.J. Hall C.K. Protein Sci. 2004; 13: 2909-2924Crossref PubMed Scopus (79) Google Scholar). By combining PRIME (described below) with discontinuous molecular dynamics simulation, we have been able to simulate the formation of small fibrils or protofilaments by systems containing between 12 and 96 16-residue Ac-KA14K-NH2 peptides starting from the random-coil state. This model, which was developed by Smith and Hall (48Smith A.V. Hall C.K. Proteins Struct. Funct. Genet. 2001; 44: 344-360Crossref PubMed Scopus (157) Google Scholar, 50Smith A.V. Hall C.K. Proteins Struct. Funct. Genet. 2001; 44: 376-391Crossref PubMed Scopus (63) Google Scholar, 51Smith A.V. Hall C.K. J. Mol. Biol. 2001; 312: 187-202Crossref PubMed Scopus (102) Google Scholar) and later improved by us (49Nguyen H.D. Marchut A.J. Hall C.K. Protein Sci. 2004; 13: 2909-2924Crossref PubMed Scopus (79) Google Scholar), represents each amino acid with four beads, three for the backbone and one for the side chain. It is designed to be used with discontinuous molecular dynamics (DMD) 1The abbreviations used are: DMD, discontinuous molecular dynamics; HP, hydrophobic interactions; HB, hydrogen bonds.1The abbreviations used are: DMD, discontinuous molecular dynamics; HP, hydrophobic interactions; HB, hydrogen bonds. (52Alder B.J. Wainwright T.E. J. Chem. Phys. 1959; 31: 459-466Crossref Scopus (1717) Google Scholar, 53Rapaport D.C. J. Phys. A: Math. Gen. 1978; 11: L213-L217Crossref Scopus (105) Google Scholar, 54Rapaport D.C. J. Chem. Phys. 1979; 71: 3299-3303Crossref Scopus (173) Google Scholar, 55Bellemans A. Orban J. VanBelle D. Mol. Phys. 1980; 39: 781-782Crossref Scopus (92) Google Scholar), an extremely fast alternative to traditional molecular dynamics that is applicable to systems of molecules interacting via discontinuous potentials, e.g. hard sphere and square well potentials. Solvent is modeled implicitly by including hydrophobic interactions between non-polar side chains. Backbone hydrogen bonding is modeled in explicit detail. The applicability of our model to polyalanine was tested in a previous study of isolated polyalanine in which we examined the predicted folding transition and the conditions under which common structures such as the α-helix and β-hairpin appear (49Nguyen H.D. Marchut A.J. Hall C.K. Protein Sci. 2004; 13: 2909-2924Crossref PubMed Scopus (79) Google Scholar). Specifically, we examined the effect of temperature on the populations of the various structural states of the peptide, calculated the Zimm-Bragg equilibrium constants for propagation and nucleation of the helix, measured the hydrogen bond distances and angles for polyalanine in the α-helix and β-hairpin, and mapped out the Ramachandran plot. We found that our results agree with experimental and other simulation data very well. Although PRIME gives a fairly realistic description of polyalanine, it is essentially a work in progress; we are now in the process of extending the model to the rest of the amino acids. By combining PRIME with DMD, we were able to sample much wider regions of conformational space, longer time scales, and larger systems than in traditional molecular dynamics (56Nguyen H.D. Hall C.K. Proc. Natl. Acad. Sci. U. S. A. 2004; 101: 16180-16185Crossref PubMed Scopus (317) Google Scholar). Since the simulations take only days on a work station, we were able to conduct simulations at a wide variety of concentrations and temperatures and to learn how peptide concentration and temperature affect the formation of various Ac-KA14K-NH2 structures, including amorphous aggregates, α-helices, β-sheets, and fibrils. All simulations were performed in the canonical ensemble starting from a random coil configuration equilibrated at a high temperature and then slowly cooled to the temperature of interest so as to minimize kinetic trapping in local free energy minima. In this study, we investigated the kinetics of fibril formation of Ac-KA14K-NH2 peptides as a function of the peptide concentration and temperature. Simulations were conducted on systems containing 48 model 16-residue peptides at a wide variety of concentrations and temperatures using the same protein model as in our previous studies (56Nguyen H.D. Hall C.K. Proc. Natl. Acad. Sci. U. S. A. 2004; 101: 16180-16185Crossref PubMed Scopus (317) Google Scholar). All simulations were performed in the canonical ensemble; constant temperature was achieved by implementing the Andersen thermostat method (57Andersen H.C. J. Chem. Phys. 1980; 72: 2384-2393Crossref Scopus (4495) Google Scholar) in which united atoms were subjected to random collisions with ghost particles, the velocities of which were chosen randomly from a Maxwell-Boltzmann distribution centered at the system temperature. During each simulation, the formation of different structures such as α-helices, aggregates, β-sheets, or fibrils was monitored as a function of time. Key fibril-forming events associated with the four proposed fibril-forming mechanisms mentioned earlier were identified. Two types of simulations were conducted: unseeded and seeded. In the unseeded simulations, the peptides, which were initially in a random coil configuration, were equilibrated at a high temperature and then quickly cooled to the temperature of interest. The lag time and rate of fibril formation were monitored to study their dependence upon the peptide concentration and temperature. In the seeded simulations, a previously created single small fibril was immersed in a sea of denatured chains. The model peptide chosen for study is the polyalanine-based peptide Ac-KA14K-NH2. We focused on polyalanine-based peptides for three reasons. First, the small, uncharged, unbranched nature of alanine residues is amenable to simulation with the intermediate resolution protein model that we developed previously (48Smith A.V. Hall C.K. Proteins Struct. Funct. Genet. 2001; 44: 344-360Crossref PubMed Scopus (157) Google Scholar, 50Smith A.V. Hall C.K. Proteins Struct. Funct. Genet. 2001; 44: 376-391Crossref PubMed Scopus (63) Google Scholar). Second, polyalanine repeats have been implicated in human pathologies, notably in the formation of anomalous filamentous intranuclear inclusions in oculopharyngeal muscular dystrophy patients (58Brais B. Rouleau G.A. Bouchard J.P. Farde M. Tome F.M.S. Semin. Neurol. 1999; 19: 59-66Crossref PubMed Scopus (108) Google Scholar). Third, synthetic polyalanine-based peptides have been shown by Blondelle and co-workers (59Forood B. Perez-Paya E. Houghten R.A. Blondelle S.E. Biochem. Biophys. Res. Commun. 1995; 211: 7-13Crossref PubMed Scopus (64) Google Scholar, 60Blondelle S.E. Forood B. Houghten R.A. Perez-Paya E. Biochemistry. 1997; 36: 8393-8400Crossref PubMed Scopus (165) Google Scholar) to undergo a transition from α-helical structures to β-sheet complexes in vitro, mimicking the structural transition that is believed to be a prerequisite for fibril nucleation and growth (1Kirschner D.A. Abraham C. Selkoe D.J. Proc. Natl. Acad. Sci. U. S. A. 1986; 83: 503-507Crossref PubMed Scopus (477) Google Scholar, 61Simmons L. May P. Tomaselli K. Rydel R. Fuson K. Brigham E. Wright S. Lieberburg I. Becker G. Brems D. Li W. Mol. Pharmacol. 1994; 45: 373-379PubMed Google Scholar, 62Horwich A.L. Weissman J.S. Cell. 1997; 89: 499-510Abstract Full Text Full Text PDF PubMed Scopus (249) Google Scholar, 63Sunde M. Blake C. Adv. Protein Chem. 1997; 50: 123-159Crossref PubMed Google Scholar, 64Kusumoto Y. Lomakin A. Teplow D.B. Benedek G.B. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 12277-12282Crossref PubMed Scopus (228) Google Scholar, 65Harrison P.M. Chan H.S. Prusiner S.B. Cohen F.E. J. Mol. Biol. 1999; 286: 593-606Crossref PubMed Scopus (94) Google Scholar, 66Esler W.P. Felix A.M. Stimson E.R. Lachenmann M.J. Ghilardi J.R. Lu Y.A. Vinters H.V. Mantyh P.W. Lee J.P. Maggio J.E. J. Struct. Biol. 2000; 130: 174-183Crossref PubMed Scopus (54) Google Scholar). Blondelle and co-workers (59Forood B. Perez-Paya E. Houghten R.A. Blondelle S.E. Biochem. Biophys. Res. Commun. 1995; 211: 7-13Crossref PubMed Scopus (64) Google Scholar, 60Blondelle S.E. Forood B. Houghten R.A. Perez-Paya E. Biochemistry. 1997; 36: 8393-8400Crossref PubMed Scopus (165) Google Scholar) observed that the α-helical structures were stabilized in part by intramolecular α-helical bonds and that the macromolecular β-sheet complexes were stabilized by hydrophobic intersheet interactions. Using circular dichroism, Fourier transform infrared spectroscopy, and reversed phase high performance liquid chromatography, they found that: 1) β-sheet complex formation increased with increasing temperature, exhibiting an S-shaped dependence on temperature with a critical temperature of 45 °C at a peptide concentration of 1.8 mm and an incubation time of 3 h and 2) β-sheet complex formation increased with increasing peptide concentration above a critical concentration of 1 mm at 65 °C. Blondelle and co-workers (59Forood B. Perez-Paya E. Houghten R.A. Blondelle S.E. Biochem. Biophys. Res. Commun. 1995; 211: 7-13Crossref PubMed Scopus (64) Google Scholar, 60Blondelle S.E. Forood B. Houghten R.A. Perez-Paya E. Biochemistry. 1997; 36: 8393-8400Crossref PubMed Scopus (165) Google Scholar) did not investigate the in vitro kinetics of the assembly of amyloid fibril by polyalanines. This means that we could not compare our simulation data with experimental results directly. Instead we compared our results with the general features of the available kinetic models since these were formulated on the basis of experimental observations of fibril formation by other peptides. Highlights of our results are as follows. We observed that fibril formation of polyalanines in our simulations was not perfectly described by any of the proposed fibril formation mechanisms available in the literature. It did, however, share certain features in common with three of the proposed mechanisms: templated assembly, nucleated polymerization, and nucleated conformational conversion. These common features were that: 1) fibril formation was nucleation-dependent and 2) the lag time, which is the delay time before fibril formation commences, increased with increasing temperature. As suggested by the nucleated polymerization model, the lag time at high temperatures decreased more or less exponentially as a function of the peptide concentration. As suggested by the templated assembly model, the lag time at low temperatures decreased more or less linearly with increasing peptide concentration. As predicted by the nucleated conformational conversion model, small amorphous aggregate formation preceded critical nucleus formation. Fibril growth in our simulations involved both β-sheet elongation, in which the fibril grew by adding individual peptides to the end of each β-sheet, and lateral addition, in which the fibril grew by adding already formed β-sheets to its side. The initial rate of fibril growth increased with increasing concentration and decreased with increasing temperature. Model Peptide and Forces—The model peptide had the sequence PH14P, where H is a hydrophobic amino acid residue and P is a polar amino acid residue. This sequence was chosen to mimic Ac-KA14K-NH2 peptides, which have been shown to form stable, soluble β-sheet complexes in vitro (59Forood B. Perez-Paya E. Houghten R.A. Blondelle S.E. Biochem. Biophys. Res. Commun. 1995; 211: 7-13Crossref PubMed Scopus (64) Google Scholar, 60Blondelle S.E. Forood B. Houghten R.A. Perez-Paya E. Biochemistry. 1997; 36: 8393-8400Crossref PubMed Scopus (165) Google Scholar). The peptide was modeled using PRIME, an intermediate resolution model (48Smith A.V. Hall C.K. Proteins Struct. Funct. Genet. 2001; 44: 344-360Crossref PubMed Scopus (157) Google Scholar, 49Nguyen H.D. Marchut A.J. Hall C.K. Protein Sci. 2004; 13: 2909-2924Crossref PubMed Scopus (79) Google Scholar, 50Smith A.V. Hall C.K. Proteins Struct. Funct. Genet. 2001; 44: 376-391Crossref PubMed Scopus (63) Google Scholar, 51Smith A.V. Hall C.K. J. Mol. Biol. 2001; 312: 187-202Crossref PubMed Scopus (102) Google Scholar) based on a four-bead amino acid representation with realistic bond lengths and bond-angle constraints that has the ability to interact both intra- and intermolecularly via hydrogen bonding and hydrophobic interaction potentials. The geometry of the PRIME protein model is illustrated in Fig. 1. Each amino acid residue was composed of four spheres, a three-sphere backbone comprised of united atom NH, C–H, and C=O, and a single bead side chain R (labeled N, Cα, C, and R, respectively, in the figure). All backbone bond lengths and bond angles were fixed at their ideal values; the distance between consecutive Cα atoms was fixed so as to maintain the interpeptide bond in the trans configuration. The side chains were held in positions relative to the backbone so that all residues are l-isomers. Details of the model including values for all parameters are given in our earlier studies (48Smith A.V. Hall C.K. Proteins Struct. Funct. Genet. 2001; 44: 344-360Crossref PubMed Scopus (157) Google Scholar, 49Nguyen H.D. Marchut A.J. Hall C.K. Protein Sci. 2004; 13: 2909-2924Crossref PubMed Scopus (79) Google Scholar). The solvent was modeled implicitly in the sense that its effect was factored into the energy function as a potential of mean force. All forces were modeled by either hard sphere or square well potentials. The excluded volumes of the four beads were modeled using hard sphere potentials with realistic diameters. Covalent bonds were maintained between adjacent spheres along the backbone by imposing hard sphere repulsions whenever the bond lengths attempted to move outside of the range between l(1 – δ) and l(1 + δ), where l is the bond length and δ is a tolerance which we set equal to 2.375%. Ideal backbone bond angles, Cα-Cα distances, and residue l-isomerization were achieved by imposing pseudobonds, as shown in Fig. 1, which also fluctuated within a tolerance of 2.375%. Hydrogen bonding between amide hydrogen atoms and carbonyl oxygen atoms on the same or neighboring chains was represented by a square well attraction of strength ϵHB (where HB is hydrogen bonds) between NH and C=O united atoms whenever: 1) the virtual hydrogen and oxygen atoms (the location of which can be calculated at any time) we DA - 2005/3/11/ PY - 2005/3/11/ DO - 10.1074/jbc.M407338200 VL - 280 IS - 10 SP - 9074-9082 SN - 1083-351X ER - TY - JOUR TI - Influence of divalent cations on the structural thermostability and thermal inactivation kinetics of class II xylose isomerases AU - Epting, KL AU - Vieille, C AU - Zeikus, JG AU - Kelly, RM AU - Kelly, RM AU - Zeikus, JG AU - Vieille, C T2 - FEBS JOURNAL AB - The effects of divalent metal cations on structural thermostability and the inactivation kinetics of homologous class II d-xylose isomerases (XI; EC 5.3.1.5) from mesophilic (Escherichia coli and Bacillus licheniformis), thermophilic (Thermoanaerobacterium thermosulfurigenes), and hyperthermophilic (Thermotoga neapolitana) bacteria were examined. Unlike the three less thermophilic XIs that were substantially structurally stabilized in the presence of Co2+ or Mn2+ (and Mg2+ to a lesser extent), the melting temperature [(Tm) approximately 100 degrees C] of T. neapolitana XI (TNXI) varied little in the presence or absence of a single type of metal. In the presence of any two of these metals, TNXI exhibited a second melting transition between 110 degrees C and 114 degrees C. TNXI kinetic inactivation, which was non-first order, could be modeled as a two-step sequential process. TNXI inactivation in the presence of 5 mm metal at 99-100 degrees C was slowest in the presence of Mn2+[half-life (t(1/2)) of 84 min], compared to Co2+ (t(1/2) of 14 min) and Mg2+ (t(1/2) of 2 min). While adding Co2+ to Mg2+ increased TNXI's t(1/2) at 99-100 degrees C from 2 to 7.5 min, TNXI showed no significant activity at temperatures above the first melting transition. The results reported here suggest that, unlike the other class II XIs examined, single metals are required for TNXI activity, but are not essential for its structural thermostability. The structural form corresponding to the second melting transition of TNXI in the presence of two metals is not known, but likely results from cooperative interactions between dissimilar metals in the two metal binding sites. DA - 2005/3// PY - 2005/3// DO - 10.1111/j.1742-4658.2005.04577.x VL - 272 IS - 6 SP - 1454-1464 SN - 1742-4658 KW - inactivation kinetics KW - metal cofactors KW - thermostability KW - xylose isomerases ER - TY - JOUR TI - Dynamic model for mass transfer of solutes in cucumber fermentation AU - Passos, FV AU - Felder, RM AU - Fleming, HP AU - McFeeters, RF AU - Ollis, DF T2 - JOURNAL OF FOOD ENGINEERING AB - A mathematical model for the mass transfer of solutes between whole cucumbers and brine in cucumber fermentation has been developed that takes into account permeation of solutes through stomata in the cucumber skin and through the epidermal cells in the skin, as well as film diffusion through the surrounding brine boundary layer. The model was used to fit experimental data for the time-dependent concentrations of solutes that permeate into the cucumbers (glucose and malate) and out of them (lactic acid, acetic acid, ethanol, and sodium chloride). The rate of lactic acid transport through the stomata was found to be three orders of magnitude greater than that through the epidermis, and the permeabilities of lactic and acetic acids were effectively independent of the brine circulation rate. These results indicate that the rate of permeation of solutes into and out of cucumbers was controlled by mass transfer through the stomata, with neither film diffusion nor epidermal diffusion having a significant effect. The model differential equation for solute transfer combined with a set of rate equations for microbial growth will provide a good basis to establish a complete mechanistic model for the cucumber fermentation process. DA - 2005/6// PY - 2005/6// DO - 10.1016/j.jfoodeng.2004.06.002 VL - 68 IS - 3 SP - 297-302 SN - 0260-8774 KW - diffusion KW - cucumber KW - modeling KW - acids KW - sugar ER - TY - JOUR TI - Cosurfactant and cosolvent effects on surfactant self-assembly in supercritical carbon dioxide AU - Chennamsetty, N AU - Bock, H AU - Scanu, LF AU - Siperstein, FR AU - Gubbins, KE T2 - JOURNAL OF CHEMICAL PHYSICS AB - The impact of alcohol additives on the self-assembly of surfactants in supercritical carbon dioxide is investigated using lattice Monte Carlo simulations. We observe that all studied (model) alcohols reduce the critical micelle concentration. The reduction is stronger the longer the hydrocarbon chain of the alcohol, and the higher the alcohol concentration. Short-chain alcohols are found to concentrate in the surfactant layer of the aggregates, replacing surfactant molecules and leading to a strong decrease of the aggregation number and a large increase of the number of aggregates. On the other hand, only a small number of alcohol molecules with longer chain length are found in the aggregates, leading to a slight increase in the aggregation number. However, structural properties such as size and density profiles of aggregates at the same aggregation number are not influenced markedly. Consequently, short-chain alcohols act as cosurfactants, directly influencing the properties of the aggregates, while alcohols with longer hydrocarbon chains work as cosolvents, altering the properties of the solvent. However, the transition between both extremes is gradual. DA - 2005/3/1/ PY - 2005/3/1/ DO - 10.1063/1.1855291 VL - 122 IS - 9 SP - SN - 1089-7690 ER - TY - JOUR TI - Beneficial reuse and sustainability: The fate of organic compounds in land-applied waste AU - Overcash, M AU - Sims, RC AU - Sims, JL AU - Nieman, JKC T2 - JOURNAL OF ENVIRONMENTAL QUALITY AB - Land application systems, also referred to as beneficial reuse systems, are engineered systems that have defined and permitted application areas based on site and waste characteristics to determine the land area size requirement. These terrestrial systems have orders of magnitude greater microbial capability and residence time to achieve decomposition and assimilation compared with aquatic systems. In this paper we focus on current information and information needs related to terrestrial fate pathways in land treatment systems. Attention is given to conventional organic chemicals as well as new estrogenic and pharmaceutical chemicals of commerce. Specific terrestrial fate pathways addressed include: decomposition, bound residue formation, leaching, runoff, and crop uptake. Molecular decomposition and formation of bound residues provide the basis for the design and regulation of land treatment systems. These mechanisms allow for assimilation of wastes and nondegradation of the environment and accomplish the goal of sustainable land use. Bound residues that are biologically produced are relatively immobile, degrade at rates similar to natural soil materials, and should present a significantly reduced risk to the environment as opposed to parent contaminants. With regard to leaching and runoff pathways, no comprehensive summary or mathematical model of organic chemical migration from land treatment systems has been developed. For the crop uptake pathway, a critical need exists to develop information for nonagricultural chemicals and to address full-scale performance and monitoring at more land application sites. The limited technology choices for treatment of biosolids, liquids, and other wastes implies that acceptance of some risks and occurrence of some benefits will continue to characterize land application practices that contribute directly to the goal of beneficial reuse and sustainability. DA - 2005/// PY - 2005/// DO - 10.2134/jeq2005.0029 VL - 34 IS - 1 SP - 29-41 SN - 1537-2537 ER - TY - JOUR TI - Rapid deposition of gold nanoparticle films with controlled thickness and structure by convective assembly AU - Prevo, BG AU - Fuller, JC AU - Velev, OD T2 - CHEMISTRY OF MATERIALS AB - We report how convective assembly at high volume fraction combined with thermal treatment allows robust fabrication of gold nanocoatings whose structure can be varied and correlated to their optical properties and conductance. Uniform films of gold nanoparticles were deposited directly from aqueous suspensions, where neither the nanoparticles, nor the substrates, were covered with ligands or pretreated in any way. The number of layers, optical absorbance, and electrical conductance of these nanocoatings could be controlled by the speed of deposition. The electronic, optical, and structural properties of the nanoparticle multilayers could be further tuned by post-deposition heat treatment. Scanning electron microscopy observations and electrical conductance measurements showed that heating leads to a transition from a near-percolated nanoparticle structure (conductivity approaching 2000 Ω-1cm-1) to a discontinuous insular structure (conductivity <10-5 Ω-1cm-1). These structural transitions change the coating transmission spectra, where the surface plasmon resonance peak could be tuned by heating to any value from 800 to 565 nm. The ability to tune the nanocoating structure and spectral and electronic properties may allow for applications such as nonohmic switching, quantum electronics and sensors. DA - 2005/1/11/ PY - 2005/1/11/ DO - 10.1021/cm0486621 VL - 17 IS - 1 SP - 28-35 SN - 1520-5002 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-11844299566&partnerID=MN8TOARS ER - TY - JOUR TI - Population density-dependent regulation of exopolysaccharide formation in the hyperthermophilic bacterium Thermotoga maritima AU - Johnson, MR AU - Montero, CI AU - Conners, SB AU - Shockley, KR AU - Bridger, SL AU - Kelly, RM T2 - MOLECULAR MICROBIOLOGY AB - Co-cultivation of the hyperthermophiles Thermotoga maritima and Methanococcus jannaschii resulted in fivefold higher T. maritima cell densities when compared with monoculture as well as concomitant formation of exopolysaccharide and flocculation of heterotroph-methanogen cellular aggregates. Transcriptional analysis of T. maritima cells from these aggregates using a whole genome cDNA microarray revealed the induction of a putative exopolysaccharide synthesis pathway, regulated by intracellular levels of cyclic diguanosine 3',5'-(cyclic)phosphate (cyclic di-GMP) and mediated by the action of several GGDEF proteins, including a putative diguanylate cyclase (TM1163) and a putative phosphodiesterase (TM1184). Transcriptional analysis also showed that TM0504, which encodes a polypeptide containing a motif common to known peptide-signalling molecules in mesophilic bacteria, was strongly upregulated in the co-culture. Indeed, when a synthetically produced peptide based on TM0504 was dosed into the culture at ecologically relevant levels, the production of exopolysaccharide was induced at significantly lower cell densities than was observed in cultures lacking added peptide. In addition to identifying a pathway for polysaccharide formation in T. maritima, these results point to the existence of peptide-based quorum sensing in hyperthermophilic bacteria and indicate that cellular communication should be considered as a component of the microbial ecology within hydrothermal habitats. DA - 2005/2// PY - 2005/2// DO - 10.1111/j.1365-2958.2004.04419.x VL - 55 IS - 3 SP - 664-674 SN - 1365-2958 ER - TY - JOUR TI - Oxidative dissolution of copper and zinc metal in carbon dioxide with tert-butyl peracetate and a beta-diketone chelating agent AU - Visintin, PM AU - Bessel, CA AU - White, PS AU - Schauer, CK AU - DeSimone, JM T2 - INORGANIC CHEMISTRY AB - A series of β-diketone ligands, R1COCH2COR2 [tmhdH (R1 = R2 = C(CH3)3); tfacH (R1 = CF3; R2 = CH3); hfacH (R1 = R2 = CF3)], in combination with tert-butyl peracetate (t-BuPA), have been investigated as etchant solutions for dissolution of copper metal into carbon dioxide solvent. Copper removal in CO2 increases in the order tfacH < tmhdH < hfacH. A study of the reactions of the hfacH/t-BuPA etchant solution with metallic copper and zinc was conducted in three solvents: scCO2 (supercrical CO2); hexanes; CD2Cl2. The etchant solution/metallic zinc reaction produced a diamagnetic Zn(II) complex, which allowed NMR identification of the t-BuPA decomposition products as tert-butyl alcohol and acetic acid. Gravimetric analysis of the amount of zinc consumed, together with NMR studies, confirmed the 1:1:2 Zn:t-BuPA:hfacH reaction stoichiometry, showing t-BuPA to be an overall two-electron oxidant for Zn(0). The metal-containing products of the copper and zinc reactions were characterized by elemental analysis, IR spectroscopy, and, as appropriate, NMR spectroscopy and single-crystal X-ray diffraction [trans-M(hfac)2(H2O)(CH3CO2H) (1, M = Cu; 2, M = Zn)]. On the basis of the experimental results, a working model of the oxidative dissolution reaction is proposed, which delineates the key chemical variables in the etching reaction. These t-BuPA/hfacH etchant solutions may find application in a CO2-based chemical mechanical planarization (CMP) process. DA - 2005/1/24/ PY - 2005/1/24/ DO - 10.1021/ic049765o VL - 44 IS - 2 SP - 316-324 SN - 1520-510X ER - TY - JOUR TI - Anisotropic particle synthesis in dielectrophoretically controlled microdroplet reactors AU - Millman, , JR AU - Bhatt, KH AU - Prevo, BG AU - Velev, OD T2 - NATURE MATERIALS DA - 2005/1// PY - 2005/1// DO - 10.1038/nmat1270 VL - 4 IS - 1 SP - 98-102 SN - 1476-4660 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-11144319950&partnerID=MN8TOARS ER - TY - JOUR TI - Hexamer peptide affinity resins that bind the Fc region of human immunoglobulin G AU - Yang, H AU - Gurgel, PV AU - Carbonell, RG T2 - JOURNAL OF PEPTIDE RESEARCH AB - Abstract: A family of linear hexapeptides composed of histidine on the N‐terminus followed by aromatic amino acid(s) and positively charged amino acid(s) has been identified through a three‐step screening of a synthetic solid phase library. These peptides were able to recognize human immunoglobulin G (HIgG) through its Fc region, and their selectivity to Fc is comparable to Protein A. This is the first known report of short peptides that are able to bind HIgG by recognizing its Fc portion. One of the ligands from the identified family, HWRGWV, was examined for its ability to isolate HIgG from complex mixtures. It was found that HWRGWV possessed the potential to purify HIgG from complete mammalian cell culture medium containing 10% fetal calf serum with purity comparable to commercially available resins, but using milder elution conditions. HWRGWV bound all HIgG subclasses and IgGs from bovine, mouse, goat, and rabbit. The broad affinity spectrum as well as its Fc recognition ability may be useful in capturing and detecting both polyclonal and monoclonal antibodies. DA - 2005/12// PY - 2005/12// DO - 10.1111/j.1747-0285.2006.00342.x VL - 66 SP - 120-137 SN - 1397-002X KW - affinity chromatography KW - Fc fragment KW - hexapeptide KW - immunoglobulin ER - TY - JOUR TI - Phase behavior of triblock copolymers varying in molecular asymmetry AU - Hamersky, MW AU - Smith, SD AU - Gozen, AO AU - Spontak, RJ T2 - PHYSICAL REVIEW LETTERS AB - The transformation from ${A}_{1}B$ diblock copolymer to ${A}_{1}B{A}_{2}$ triblock copolymers varying in molecular asymmetry is investigated as the ${A}_{2}$ end block is progressively grown via chemical synthesis. Dynamic rheological measurements show that the order-disorder transition (ODT) temperatures of two copolymer series differing in composition and molecular weight decrease when the ${A}_{2}$ block is short relative to the ${A}_{1}$ block, and then increase as the length of the ${A}_{2}$ block is increased further. The resultant ODT minimum, predicted by mean-field theory, is attributed to mixing between long $B$ and short ${A}_{2}$ blocks. DA - 2005/10/14/ PY - 2005/10/14/ DO - 10.1103/physrevlett.95.168306 VL - 95 IS - 16 SP - SN - 0031-9007 ER - TY - JOUR TI - OTS adsorption: A dynamic QCM study AU - Hussain, Y AU - Krim, J AU - Grant, C T2 - COLLOIDS AND SURFACES A-PHYSICOCHEMICAL AND ENGINEERING ASPECTS AB - The uptake of octadecyltrichlorosilane (OTS) from an organic solution has been studied in situ and in real time by means of a quartz crystal microbalance (QCM) technique. Changes in both QCM frequency and resistance are reported for a range of OTS concentrations. In addition, the time dependence of OTS uptake has been used to calculate reaction constants. Silicon surfaces overall are characterized by higher levels of material uptake than gold. DA - 2005/7/15/ PY - 2005/7/15/ DO - 10.1016/j.colsurfa.2005.03.016 VL - 262 IS - 1-3 SP - 81-86 SN - 1873-4359 KW - quartz crystal rnicrobalance (QCM) KW - octaclecyltrichlorosilane (OTS) KW - adsorption ER - TY - JOUR TI - Metal oxide thin films deposited from metal organic precursors in supercritical CO2 solutions AU - Gougousi, T AU - Barua, D AU - Young, ED AU - Parsons, GN T2 - CHEMISTRY OF MATERIALS AB - This work demonstrates a novel method for deposition of metal oxide thin films, including Al2O3, ZrO2, MnOx, and RuOx where the metal−organic precursors and oxidizing agents are delivered in liquid and supercritical CO2. A cyclic deposition process is presented where reactants are introduced sequentially to control surface adsorption and byproduct removal steps. Reactions are studied in a hot wall reactor at pressures ranging from 1600 to 3600 psi at 80−200 °C, and X-ray photoelectron spectroscopy and infrared transmission confirmed metal oxide formation. We show that hydrogen peroxide is a viable O source for oxide deposition, whereas tert-butyl peracetate, which is a good electron acceptor, is less suited for oxygen donation. Capacitance versus voltage analysis of resulting Al2O3 films show good dielectric properties after post-deposition anneal. We believe that the good solvation properties of supercritical CO2 can aid in the delivery of precursors and in the removal of byproducts for advanced low-temperature processing of oxides and other materials of interest in electronic applications. DA - 2005/10/4/ PY - 2005/10/4/ DO - 10.1021/cm0510965 VL - 17 IS - 20 SP - 5093-5100 SN - 0897-4756 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000232326700027&KeyUID=WOS:000232326700027 ER - TY - JOUR TI - Kinetic disguises in heterogeneous photocatalysis AU - Ollis, DF T2 - TOPICS IN CATALYSIS DA - 2005/7// PY - 2005/7// DO - 10.1007/s11244-005-3827-z VL - 35 IS - 3-4 SP - 217-223 SN - 1572-9028 KW - photocatalysis KW - kinetics KW - disguise KW - mass transfer KW - diffusion KW - illumination ER - TY - JOUR TI - Effect of Confinement on Freezing of CCl4 in Cylindrical Pores AU - Sliwinska-Bartkowiak, Malgorzata AU - Hung, Francisco R. AU - Santiso, Erik E. AU - Coasne, Benoit AU - Dudziak, Grazyna AU - Siperstein, Flor R. AU - Gubbins, Keith E. T2 - Adsorption DA - 2005/7// PY - 2005/7// DO - 10.1007/s10450-005-5956-x VL - 11 IS - S1 SP - 391-396 J2 - Adsorption LA - en OP - SN - 0929-5607 1572-8757 UR - http://dx.doi.org/10.1007/s10450-005-5956-x DB - Crossref KW - confinement KW - solid-fluid transitions KW - molecular simulation KW - dielectric relaxation KW - carbon nanotubes ER - TY - JOUR TI - Chemical functionalization of silica and alumina particles for dispersion in carbon dioxide AU - Visintin, PM AU - Carbonell, RG AU - Schauer, CK AU - DeSimone, JM T2 - LANGMUIR AB - The steric stabilization and flocculation of modified silica and alumina particle suspensions in condensed CO2 were studied. Silica particles (average diameters of 7 and 12 nm) were functionalized using chlorosilanes of the form CnF2n+1CH2CH2Si(CH3)2Cl (n = 8, 4, or 1) to give CnF2n+1-silica. Alumina particles (diameter of 8−14 nm) were grafted with C8F17CH2CH2Si(OEt)3 and chemically modified with perfluorononanoic acid to yield C8F17-alumina and C8F17COOH-alumina, respectively. Elemental analysis and thermogravimetric analysis on the derivatized particles were carried out, and surface coverage was calculated. The stabilization of these modified particles in condensed CO2 was quantified using turbidimetry. Particle stability was found to increase with increasing fluorinated tail length, temperature, and CO2 density. Unmodified particles and those modified with only −CF3 tails were unstable in condensed CO2. Stabilization in supercritical CO2 is continuous up to 24 h for the CnF2n+1-silica (n ≥ 4) particles and 96 h for the C8F17-alumina particles. The C8F17COOH-alumina particles gave a significantly higher graft density than the C8F17-alumina particles but are not as stable in CO2. The C8F17-alumina particles were stable at lower CO2 densities than the modified silica particles. This stability difference may be attributed to the precursor organosilanes being monofunctional (modified silica) versus trifunctional (modified alumina), producing different structures on the surface. DA - 2005/5/24/ PY - 2005/5/24/ DO - 10.1021/la047823c VL - 21 IS - 11 SP - 4816-4823 SN - 0743-7463 ER - TY - JOUR TI - Characterization of a peptide affinity support that binds selectively to staphylococcal enterotoxin B AU - Wang, GQ AU - Carbonell, RG T2 - JOURNAL OF CHROMATOGRAPHY A AB - The influences of mass transfer and adsorption-desorption kinetics on the binding of staphylococcal enterotoxin B (SEB) to an affinity resin with the peptide ligand, Tyr-Tyr-Trp-Leu-His-His (YYWLHH) have been studied. The bed and particle porosities, the axial dispersion coefficient and the pore diffusivity were measured using pulse experiments under unretained conditions. Adsorption isotherms for SEB on YYWLHH resins with peptide densities in the range from 6 to 220 micromol/g were measured and fitted to a bi-Langmuir equation. At peptide densities below 9 micromol/g and above 50 micromol/g, dissociation constants were lower (2 x 10(-3) to 7 x 10(-3) mol/m3), and binding capacities were larger (43-47 mg SEB/g). In the range from 9 to 50 micromol/g dissociation constants were larger (13 x 10(-3) to 24 x 10(-3) mol/m3) and capacities were lower (33-37 mg SEB/g). These observations are consistent with a transition from single point attachment of the protein to the ligand at low peptide densities to multipoint attachment at high peptide densities. The general rate (GR) model of chromatography was used to fit experimental breakthrough curves under retained conditions to determine the intrinsic rate constants for adsorption, which varied from 0.13 to 0.50 m3 mol(-1) s(-1), and exhibited no clear trend with increasing peptide density. An analysis of the number of transfer units for the various mass transfer steps in the column indicated that film mass transfer, pore diffusion (POR) and the kinetics of adsorption can all play an important role in the overall rate of adsorption, with the intrinsic adsorption step apparently being the rate determining step at peptide densities below 50 micromol/g. DA - 2005/6/17/ PY - 2005/6/17/ DO - 10.1016/j.chroma.2005.05.010 VL - 1078 IS - 1-2 SP - 98-112 SN - 1873-3778 KW - mathematical modeling KW - peptide affinity chromatography KW - peptide density KW - staphylococcal enterotoxin B ER - TY - JOUR TI - Kinetics of liquid phase photocatalyzed reactions: An illuminating approach AU - Ollis, DF T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - Analysis of photocatalyst kinetics to date have relied largely on Langmuir−Hinshelwood rate forms, which assume equilibrated adsorption of reactants and, correspondingly, a slow, rate-controlling surface step. Alternatively, and more generally, a pseudo-steady state analysis based upon the stationary state hypothesis for reaction intermediates may be applied. We show here that only this second approach is consistent with the reported intensity dependence of apparent adsorption (and desorption) binding constants, as well as the catalytic rate constant. In consequence, we show that for at least some photocatalyzed reactions, adsorption/desorption reaction equilibria are not established during reaction, because the substantial reactivity of an adsorbed active species (e.g., hole (h+), radical (*OH), etc.) causes a continued displacement from equilibrium of the adsorbed reactant concentration. DA - 2005/2/17/ PY - 2005/2/17/ DO - 10.1021/jp040236f VL - 109 IS - 6 SP - 2439-2444 SN - 1520-6106 ER - TY - JOUR TI - Emulsion polymerization of N-ethylacrylamide in supercritical carbon dioxide AU - Ye, WJ AU - DeSimone, JM T2 - MACROMOLECULES AB - Herein, we report the emulsion polymerization of a water-soluble vinylic monomer in supercritical carbon dioxide. The water-soluble/CO2-insoluble monomer, N-ethylacrylamide, was effectively emulsified in CO2 continuous phase using an amphiphilic diblock copolymer consisting of a d-glucose-containing glycopolymer and a fluorinated block. The resulting high yield (>90%) of water-soluble poly(N-ethylacrylamide) was obtained in the form of a stable polymer colloid comprised of submicrometer-sized particles. The particle diameter and the distribution of sizes were shown to be influenced by various reaction parameters. Higher temperature and higher surfactant and initiator concentrations resulted in particles with smaller sizes. Two initiators, 2,2‘-azobisisobutyronitrile (AIBN) and a fluorinated azo-derivative, bis-[2-(F-octyl)ethyl]-4,4‘-azobis-4-cyanopentanoate, were used, and their thermal decomposition behaviors in supercritical CO2 were investigated. Compared with the AIBN-initiated system, the emulsion polymerizations initiated by the fluorinated azo-initiator showed no polymerized monomer droplets, and the resultant particles were more uniform. DA - 2005/3/22/ PY - 2005/3/22/ DO - 10.1021/ma048863q VL - 38 IS - 6 SP - 2180-2190 SN - 1520-5835 ER - TY - JOUR TI - Aflatoxin conducive and non-conducive growth conditions reveal new gene associations with aflatoxin production AU - Price, MS AU - Shannon, BCB AU - Sabrina, TB AU - Robert, AKB AU - Payne, GA T2 - FUNGAL GENETICS AND BIOLOGY AB - Research on aflatoxin (AF) production has traditionally focused on defining the AF biosynthetic pathway with the goal of identifying potential targets for intervention. To understand the effect of nitrogen source, carbon source, temperature, and pH on the regulation of AF biosynthesis, a targeted cDNA microarray consisting of genes associated with AF production over time was employed. Expression profiles for genes involved in AF biosynthesis grouped into five clades. A putative regulon was identified consisting of 20 genes that were induced in the conducive nitrogen and pH treatments and the non-conducive carbon and temperature treatments, as well as four other putative regulons corresponding to each of the four variables studied. Seventeen genes exhibited consistent induction/repression profiles across all the experiments. One of these genes was consistently downregulated with AF production. Overexpression of this gene resulted in repression of AF biosynthesis. The cellular function of this gene is currently unresolved. DA - 2005/6// PY - 2005/6// DO - 10.1016/j.fgb.2005.03.009 VL - 42 IS - 6 SP - 506-518 SN - 1096-0937 KW - aflatoxin KW - gene expression KW - regulation KW - Aspergillus flavus KW - Aspergillus parasiticus ER - TY - JOUR TI - Acid-induced gelation of enzymatically modified, preheated whey proteins AU - Eissa, AS AU - Khan, SA T2 - JOURNAL OF AGRICULTURAL AND FOOD CHEMISTRY AB - Low-pH whey protein gels are formulated using a sequential protocol of heat treatment, enzyme incubation, and cold-set acidification. The heat-induced disulfide and enzyme-catalyzed epsilon-(gamma-glutamyl)lysine linkages, both at neutral pH, produce a polymerized protein solution. The molecular weights of these samples show an exponential increase with protein concentration. The additional enzyme-catalyzed cross-links cause little change in molecular weight from that of heat-treated samples at low protein concentrations, indicating predominant intramolecular cross-linking. Enzyme treatment at higher protein concentration however causes increase in molecular weight, possibly due to formation of intermolecular cross-links. Acidification of the polymerized protein solutions through glucono-delta-lactone acid leads to gel formation at pH 4. The elastic (G') and viscous (G' ') moduli of gels with and without enzyme treatment show similar frequency dependence, indicating comparable microstructures, consistent with all samples exhibiting similar fractal dimensions of approximately 2 obtained independently using rheology and confocal microscopy. A substantial increase in fracture strain and stress of the gel is achieved by enzyme treatment. However, the elastic modulus (G') is only slightly larger after enzyme treatment compared with heat-treated samples. These results indicate that factors responsible for fracture properties may not be apparent in the gel microstructure and linear viscoelastic properties. DA - 2005/6/15/ PY - 2005/6/15/ DO - 10.1021/jf047957w VL - 53 IS - 12 SP - 5010-5017 SN - 1520-5118 ER -