TY - CONF TI - Biomass Pyrolysis under Reactive Gas Environments AU - Cooper, M. AU - Dayton, D. AU - Gupta, R. T2 - AIChE Annual Meeting C2 - 2009/// C3 - AIChE Annual Meeting CY - Nashville, TN DA - 2009/// PY - 2009/// ER - TY - CONF TI - Determination of the Effect of Coal/Biomass-Derived Syngas Contaminants on the Performance of Fischer-Tropsch and Water-Gas Shift Catalysts AU - Trembly, J. AU - Cooper, M. AU - Turk, B. AU - Gupta, R. T2 - 26th Annual International Pittsburgh Coal Conference C2 - 2009/// C3 - 26th Annual International Pittsburgh Coal Conference CY - Pittsburgh, PA DA - 2009/// PY - 2009/// ER - TY - RPRT TI - Electro-catalysts for the oxidation of ammonia in alkaline media AU - Botte, G. AU - Vitse, F. AU - Cooper, M. DA - 2009/2/3/ PY - 2009/2/3/ M1 - 7,485,211 M3 - U.S. Patent SN - 7,485,211 ER - TY - RPRT TI - Conversion of Carbonaceous Fuels into Carbon Free Energy Carriers AU - Fan, L.-S. AU - Li, Fanxing DA - 2009/// PY - 2009/// M1 - US8877147B2 M3 - Patent SN - US8877147B2 ER - TY - RPRT TI - Synthetic Fuels and Chemicals Production with in-situ CO2 Capture AU - Fan, L.-S. AU - Li, Fanxing AU - Zeng, Liang DA - 2009/// PY - 2009/// M1 - US9518236B2 M3 - Patent SN - US9518236B2 ER - TY - RPRT TI - Integration of Reforming/Water Splitting and Electrochemical Systems for Power Generation with Integrated Carbon Capture AU - Fan, L.-S. AU - Li, Fanxing AU - Zeng, Liang AU - Sridhar, Deepak DA - 2009/// PY - 2009/// M1 - US13394572B2 AU2010292313 EPO2010760504 M3 - Patent SN - US13394572B2 AU2010292313 EPO2010760504 ER - TY - CONF TI - Syngas chemical looping gasification process for hydrogen production AU - Li, F. AU - Sridhar, D. AU - Kim, H. AU - Zeng, L. AU - Tong, A. AU - Wang, F. AU - Fan, L.-S. C2 - 2009/// C3 - 8th World Congress of Chemical Engineering: Incorporating the 59th Canadian Chemical Engineering Conference and the 24th Interamerican Congress of Chemical Engineering DA - 2009/// UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-77951584147&partnerID=MN8TOARS ER - TY - CONF TI - Coal-derived products: Hydrogen production syngas chemical looping: Road to sub-pilot scale demonstrations AU - Sridhar, D. AU - Li, F. AU - Tong, A. AU - Kim, R. AU - Zeng, L. AU - Wang, F. AU - Fan, L.-S. C2 - 2009/// C3 - 26th Annual International Pittsburgh Coal Conference 2009, PCC 2009 DA - 2009/// VL - 2 SP - 1039-1049 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84877659226&partnerID=MN8TOARS ER - TY - CONF TI - Design of the syngas chemical looping sub-pilot scale unit AU - Tong, A. AU - Li, F. AU - Sridhar, D. AU - Zeng, L. AU - Wang, F. AU - Kim, H.R. AU - Fan, L.-S. C2 - 2009/// C3 - 26th Annual International Pittsburgh Coal Conference 2009, PCC 2009 DA - 2009/// VL - 1 SP - 474-478 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84877646835&partnerID=MN8TOARS ER - TY - CONF TI - Biomass conversion via direct chemical looping technology - Process simulations AU - Zeng, L. AU - Li, F. AU - Kim, R.H. AU - Sridhar, D. AU - Wang, F. AU - Tong, A. AU - Sun, Z. AU - Nobusuke, K. AU - Fan, L.S. C2 - 2009/// C3 - AIChE Annual Meeting, Conference Proceedings DA - 2009/// UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-77951695380&partnerID=MN8TOARS ER - TY - CONF TI - Exact title of paper: Chemical looping combustion of coal and woody biomass AU - Kim, H.R. AU - Li, F. AU - Sridhar, D. AU - Zeng, L. AU - Tong, A. AU - Kobayashi, N. AU - Fan, L.-S. C2 - 2009/// C3 - 26th Annual International Pittsburgh Coal Conference 2009, PCC 2009 DA - 2009/// VL - 1 SP - 466-473 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84877683156&partnerID=MN8TOARS ER - TY - JOUR TI - Antifungal Textiles Formed Using Silver Deposition in Supercritical Carbon Dioxide AU - Gittard, Shaun D. AU - Hojo, Daisuke AU - Hyde, G. Kevin AU - Scarel, Giovanna AU - Narayan, Roger J. AU - Parsons, Gregory N. T2 - Journal of Materials Engineering and Performance DA - 2009/7/10/ PY - 2009/7/10/ DO - 10.1007/s11665-009-9514-7 VL - 19 IS - 3 SP - 368-373 J2 - J. of Materi Eng and Perform LA - en OP - SN - 1059-9495 1544-1024 UR - http://dx.doi.org/10.1007/s11665-009-9514-7 DB - Crossref KW - antifungal materials KW - disk diffusion test KW - silver KW - supercritical carbon dioxide ER - TY - JOUR TI - Syngas Chemical Looping Gasification Process: Oxygen Carrier Particle Selection and Performance AU - Li, Fanxing AU - Kim, Hyung Ray AU - Sridhar, Deepak AU - Wang, Fei AU - Zeng, Liang AU - Chen, Joseph AU - Fan, L.-S. T2 - Energy & Fuels AB - The syngas chemical looping (SCL) process coproduces hydrogen and electricity. The process involves reducing metal oxides with syngas followed by regeneration of reduced metal oxides with steam and air in a cyclic manner. Iron oxide is determined to be a desired oxygen carrier for hydrogen production considering overall properties including oxygen carrying capacity, thermodynamic properties, reaction kinetics, physical strength, melting points, and environmental effects. An iron oxide based particle can maintain good reactivity for more than 100 reduction−oxidation (redox) cycles in a thermogravimetric analyzer (TGA). The particle exhibits a good crushing strength (>20 MPa) and low attrition rate. Fixed bed experiments are carried out which reaffirm its reactivity. More than 99.75% of syngas is converted during the reduction stage. During the regeneration stage, hydrogen with an average purity of 99.8% is produced. DA - 2009/8/20/ PY - 2009/8/20/ DO - 10.1021/ef900236x VL - 23 IS - 8 SP - 4182-4189 J2 - Energy Fuels LA - en OP - SN - 0887-0624 1520-5029 UR - http://dx.doi.org/10.1021/ef900236x DB - Crossref ER - TY - JOUR TI - Environmental effects of ozone depletion and its interactions with climate change: progress report, 2008 AU - Andrady, Anthony L. AU - Aucamp, Pieter J. AU - Bais, Alkiviadis F. AU - Ballaré, Carlos L. AU - Björn, Lars Olof AU - Bornman, Janet F. AU - Caldwell, Martyn AU - Cullen, Anthony P. AU - Erickson, David J. AU - de Gruijl, Frank R. AU - Häder, Donat P. AU - Ilyas, Mohammad AU - Kulandaivelu, G. AU - Kumar, H.D. AU - Longstreth, Janice AU - McKenzie, Richard L. AU - Norval, Mary AU - Paul, Nigel D. AU - Redhwi, Halim Hamid AU - Smith, Raymond C. AU - Solomon, Keith R. AU - Sulzberger, Barbara AU - Takizawa, Yukio AU - Tang, Xiaoyan AU - Teramura, Alan H. AU - Torikai, Ayako AU - van der Leun, Jan C. AU - Wilson, Stephen R. AU - Worrest, Robert C. AU - Zepp, Richard G. T2 - Photochemical & Photobiological Sciences AB - After the enthusiastic celebration of the 20th Anniversary of the Montreal Protocol on Substances that Deplete the Ozone Layer in 2007, the work for the protection of the ozone layer continues. The Environmental Effects Assessment Panel is one of the three expert panels within the Montreal Protocol. This EEAP deals with the increase of the UV irradiance on the Earth's surface and its effects on human health, animals, plants, biogeochemistry, air quality and materials. For the past few years, interactions of ozone depletion with climate change have also been considered. It has become clear that the environmental problems will be long-lasting. In spite of the fact that the worldwide production of ozone depleting chemicals has already been reduced by 95%, the environmental disturbances are expected to persist for about the next half a century, even if the protective work is actively continued, and completed. The latest full report was published in Photochem. Photobiol. Sci., 2007, 6, 201-332, and the last progress report in Photochem. Photobiol. Sci., 2008, 7, 15-27. The next full report on environmental effects is scheduled for the year 2010. The present progress report 2008 is one of the short interim reports, appearing annually. DA - 2009/// PY - 2009/// DO - 10.1039/B820432M VL - 8 IS - 1 SP - 13-22 ER - TY - JOUR TI - Integrating modern biology into the ChE DNA through a campus-wide core laboratory education program AU - Carson, S.E. AU - Chisnell, J.R. AU - Kelly, R.M. T2 - Chemical Engineering Education DA - 2009/// PY - 2009/// VL - 43 IS - 4 SP - 257–264 ER - TY - CHAP TI - Poly(vinylchloride) AU - Andrady, A.L. AU - Sen, T.Z. AU - Ahunbay, M.G. T2 - Polymer data handbook A2 - Mark, James E. PY - 2009/// ET - 2nd SP - 1145-1152 PB - Oxford University Press ER - TY - JOUR TI - Applications and societal benefits of plastics AU - Andrady, Anthony L. AU - Neal, Mike A. T2 - Philosophical Transactions of the Royal Society B: Biological Sciences AB - This article explains the history, from 1600 BC to 2008, of materials that are today termed ‘plastics’. It includes production volumes and current consumption patterns of five main commodity plastics: polypropylene, polyethylene, polyvinyl chloride, polystyrene and polyethylene terephthalate. The use of additives to modify the properties of these plastics and any associated safety, in use, issues for the resulting polymeric materials are described. A comparison is made with the thermal and barrier properties of other materials to demonstrate the versatility of plastics. Societal benefits for health, safety, energy saving and material conservation are described, and the particular advantages of plastics in society are outlined. Concerns relating to littering and trends in recycling of plastics are also described. Finally, we give predictions for some of the potential applications of plastic over the next 20 years. DA - 2009/7/27/ PY - 2009/7/27/ DO - 10.1098/rstb.2008.0304 VL - 364 IS - 1526 SP - 1977-1984 J2 - Phil. Trans. R. Soc. B LA - en OP - SN - 0962-8436 1471-2970 UR - http://dx.doi.org/10.1098/rstb.2008.0304 DB - Crossref KW - plastic KW - society KW - history KW - polymers KW - development ER - TY - JOUR TI - Composite Tissue Engineering on Polycaprolactone Nanofiber Scaffolds AU - Reed, Courtney R. AU - Han, Li AU - Andrady, Anthony AU - Caballero, Montserrat AU - Jack, Megan C. AU - Collins, James B. AU - Saba, Salim C. AU - Loboa, Elizabeth G. AU - Cairns, Bruce A. AU - van Aalst, John A. T2 - Annals of Plastic Surgery AB - Tissue engineering has largely focused on single tissue-type reconstruction (such as bone); however, the basic unit of healing in any clinically relevant scenario is a compound tissue type (such as bone, periosteum, and skin). Nanofibers are submicron fibrils that mimic the extracellular matrix, promoting cellular adhesion, proliferation, and migration. Stem cell manipulation on nanofiber scaffolds holds significant promise for future tissue engineering. This work represents our initial efforts to create the building blocks for composite tissue reflecting the basic unit of healing. Polycaprolactone (PCL) nanofibers were electrospun using standard techniques. Human foreskin fibroblasts, murine keratinocytes, and periosteal cells (4-mm punch biopsy) harvested from children undergoing palate repair were grown in appropriate media on PCL nanofibers. Human fat-derived mesenchymal stem cells were osteoinduced on PCL nanofibers. Cell growth was assessed with fluorescent viability staining; cocultured cells were differentiated using antibodies to fibroblast- and keratinocyte-specific surface markers. Osteoinduction was assessed with Alizarin red S. PCL nanofiber scaffolds supported robust growth of fibroblasts, keratinocytes, and periosteal cells. Cocultured periosteal cells (with fibroblasts) and keratinocytes showed improved longevity of the keratinocytes, though growth of these cell types was randomly distributed throughout the scaffold. Robust osteoinduction was noted on PCL nanofibers. Composite tissue engineering using PCL nanofiber scaffolds is possible, though the major obstacles to the trilaminar construct are maintaining an appropriate interface between the tissue types and neovascularization of the composite structure. DA - 2009/5// PY - 2009/5// DO - 10.1097/sap.0b013e31818e48bf VL - 62 IS - 5 SP - 505-512 LA - en OP - SN - 0148-7043 UR - http://dx.doi.org/10.1097/sap.0b013e31818e48bf DB - Crossref KW - nanofiber scaffolds KW - nanotechnology KW - composite tissue engineering KW - keratinocytes KW - fibroblasts KW - osteoinduction KW - fat-derived stem cells KW - periosteum KW - periosteal cells ER - TY - JOUR TI - Electrospun Nanoparticle-Nanofiber Composites via a One-Step Synthesis AU - Saquing, Carl D. AU - Manasco, Joshua L. AU - Khan, Saad A. T2 - Small AB - A facile approach to synthesize and incorporate metal nanoparticles (NPs) into electrospun polymer nanofibers (NFs) wherein the electrospinning polymer acts as both a reducing agent for the metal salt precursor, as well as a protecting and templating agent for the ensuing NPs, is reported. Such a true one-step process at ambient conditions and free of organic solvents is demonstrated using a system comprising AgNO(3) and poly(ethylene oxide) (PEO) at electrospinnable molecular weights of 600, 1000, or 2000 kDa. The PEO transforms Ag(+) into AgNPs, a phenomenon that has not been previously possible at PEO molecular weights less than 20 kDa without the addition of a separate reducing agent and stabilizer or the application of heat. Results from X-ray photoelectron spectroscopy and UV-Vis absorption spectrophotometry analyses support the formation of pseudo-crown ethers in high molecular weight PEO as the mechanism in the development of NPs. The AgNPs reduce fiber diameter and enhance fiber quality (reduced beading) due to increased electrical conductivity. Interestingly, several of the NFs exhibit AgNP-localized nanochain formation and protrusion from the NF surface that can be attributed to the combined effect of applied electrical field on the polymer and the differences between the electrical conductivity and polarizability of the polymer and metal NPs. DA - 2009/4/20/ PY - 2009/4/20/ DO - 10.1002/smll.200801273 VL - 5 IS - 8 SP - 944-951 J2 - Small LA - en OP - SN - 1613-6810 1613-6829 UR - http://dx.doi.org/10.1002/smll.200801273 DB - Crossref KW - electrospinning KW - nanofibers KW - nanoparticles KW - one-step synthesis KW - silver ER - TY - CONF TI - Crossover from Single-File to Fickian Diffusion in Carbon Nanotubes and Nanotube Bundles: Pure Components and Mixtures AU - Liu, Ying-Chun AU - Moore, Joshua D. AU - Chen, Qu AU - Roussel, Thomas J. AU - Wang, Qi AU - Gubbins, Keith E. T2 - Diffusion Fundamentals A2 - Chmelik, C. A2 - Kanellopoulos, N. A2 - Kärger, J. A2 - Theodorou, D. C2 - 2009/8// C3 - Diffusion Fundamentals III: Athens 2009 CY - Athens, Greece DA - 2009/8// PY - 2009/8/23/ SP - 164–182 PB - Leipziger Universitätsverlag SN - 9783865833877 ER - TY - CHAP TI - H2 Adsorption in Pristine and Li-Doped Carbon Replicas of FAU and EMT Zeolites AU - Roussel, T. AU - Bichara, C. AU - Pellenq, R.J.-M. AU - Gubbins, K.E. T2 - Characterization of Porous Solids VIII: Proceedings of the 8th International Conference on Characterization of Porous Solids A2 - Kaskel, S. A2 - Llewellyn, P. A2 - Rodriguez-Reinsos, F. A2 - Seaton, N.A. PY - 2009/3/10/ DO - 10.1039/9781847559418-00032 VL - 318 SP - 32–39 PB - Royal Society of Chemistry SN - 9781847559043 ER - TY - JOUR TI - Thermodynamic Feasibility of Enzymatic Reduction of Carbon Dioxide to Methanol AU - Baskaya, F. Suhan AU - Zhao, Xueyan AU - Flickinger, Michael C. AU - Wang, Ping T2 - Applied Biochemistry and Biotechnology DA - 2009/9/8/ PY - 2009/9/8/ DO - 10.1007/S12010-009-8758-X VL - 162 IS - 2 SP - 391-398 J2 - Appl Biochem Biotechnol LA - en OP - SN - 0273-2289 1559-0291 UR - http://dx.doi.org/10.1007/S12010-009-8758-X DB - Crossref KW - Carbon dioxide KW - Enzymatic biocatalysis KW - Reduction KW - Sequestration KW - Methanol KW - Thermodynamics ER - TY - JOUR TI - Microfluidic Endoskeletons: Materials of Controlled Shape and Stiffness with Photocurable Microfluidic Endoskeleton (Adv. Mater. 27/2009) AU - Chang, Suk Tai AU - Uçar, Ahmet Burak AU - Swindlehurst, Garrett R. AU - Bradley, Robert O., IV AU - Renk, Frederick J. AU - Velev, Orlin D. T2 - Advanced Materials AB - Photocurable microfluidic channel networks in thin layers of polydimethylsiloxane can act as on-demand endoskeletons to lock-in specific shapes, report Orlin Velev and co-workers on p. 2803. The light-induced solidification of photopolymer inside the microchannel networks leads to drastic increases in the elastic and bending moduli of the elastomeric material. The fabrication process is simple and scalable, and could make use of other shape-memory materials, creating the potential to fabricate custom shapes (e.g., containers, protective exoskeletons, or supports) using simple heat, light, or magnetic/electric field triggers. DA - 2009/7/10/ PY - 2009/7/10/ DO - 10.1002/adma.200990101 VL - 21 IS - 27 SP - n/a-n/a J2 - Adv. Mater. LA - en OP - SN - 0935-9648 UR - http://dx.doi.org/10.1002/adma.200990101 DB - Crossref ER - TY - JOUR TI - Macromol. Rapid Commun. 18/2009 AU - Han, Junwon AU - Jeon, Byung Ho AU - Ryu, Chang Y. AU - Semler, James J. AU - Jhon, Young K. AU - Genzer, Jan T2 - Macromolecular Rapid Communications AB - Front Cover: The image shows a schematic illustrating the adsorption- and solvency-mediated detection of chemical composition and co-monomer sequence distribution in random copolymers by means of interaction chromatography (THF: tetrahydrofuran; IO: isooctane; MC: methylene chloride; ACN: acetonitrile). Further details can be found in the article by J. Han, B. H. Jeon, C. Y. Ryu,* J. J. Semler, Y. K. Jhon, and J. Genzer* on page 1543. DA - 2009/9/17/ PY - 2009/9/17/ DO - 10.1002/marc.200990044 VL - 30 IS - 18 SP - NA-NA J2 - Macromol. Rapid Commun. LA - en OP - SN - 1022-1336 1521-3927 UR - http://dx.doi.org/10.1002/marc.200990044 DB - Crossref ER - TY - JOUR TI - Effects of nanoparticle and porous metal oxide supports on the activity of palladium catalysts in the oxidative coupling of 4-methylpyridine AU - Neal, Luke M. AU - Hernandez, Daniel AU - Hagelin-Weaver, Helena E. T2 - Journal of Molecular Catalysis A: Chemical AB - The oxidative coupling of 4-methylpyridine to 4,4′-dimethyl-2,2′-bipyridine over palladium oxide is a simple, environmentally friendly, one-step process to produce bipyridines, which are commonly used with transition metal ions to form complexes with interesting properties. However, the reaction is slow and the palladium catalyst deactivates during reaction, which means that catalyst improvements are needed for large-scale production of more economically viable bipyridine products. In this study, a number of metal oxides were investigated as catalyst supports and compared to the best performing catalysts to date, i.e. Pd/C and Pd/n-Al2O3(+). Catalysts supported on several nanoparticle oxides with varying properties as well as some conventional supports were prepared and characterized in an attempt to determine properties that lead to high catalytic activities in the oxidative coupling of 4-methylpyridine. It was found that two general categories of active catalysts can be prepared; (1) palladium supported on very high surface area materials, such as Pd/n-Al2O3(+) and Pd/MgO, and (2) palladium supported on metal oxides known to induce strong palladium-support interactions, e.g. Pd/ZrO2, Pd/(n-ZrO2 + n-CeO2) and Pd/n-ZnO. While there is no simple correlation between the palladium surface area and the catalytic activity, higher palladium dispersions generally gave higher yields compared to lower dispersion catalysts. The results indicate that the reaction is structure sensitive, i.e. not all the palladium on the surface is equivalent and some palladium species are more active than others. The acidic and basic properties of the supports were determined via chemisorption of ammonia and carbon dioxide, respectively. The data indicate that there is no correlation between the acidic or basic sites of the supports and the palladium dispersion or the catalytic activity, although highly acidic or highly basic supports should be avoided as they resulted in lower dispersions than expected from their corresponding surface areas. In terms of economic viability the porous TiO2 support was determined to be the most competitive with the nanoparticle alumina support as it results in a catalyst with comparable yields and is less expensive compared with nanoparticle alumina. The palladium supported on nanoparticle ZrO2 and MgO are also promising catalysts. DA - 2009/7// PY - 2009/7// DO - 10.1016/j.molcata.2009.03.006 VL - 307 IS - 1-2 SP - 29-36 J2 - Journal of Molecular Catalysis A: Chemical LA - en OP - SN - 1381-1169 UR - http://dx.doi.org/10.1016/j.molcata.2009.03.006 DB - Crossref KW - Palladium catalyst KW - 4-Methylpyridine KW - C-H activation KW - Oxidative coupling KW - Nanoparticle oxide ER - TY - JOUR TI - PI3K‐dependent cross‐talk interactions converge with Ras as quantifiable inputs integrated by Erk AU - Wang, Chun‐Chao AU - Cirit, Murat AU - Haugh, Jason M T2 - Molecular Systems Biology AB - Article17 February 2009Open Access PI3K-dependent cross-talk interactions converge with Ras as quantifiable inputs integrated by Erk Chun-Chao Wang Chun-Chao Wang Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA Search for more papers by this author Murat Cirit Murat Cirit Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA Search for more papers by this author Jason M Haugh Corresponding Author Jason M Haugh Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA Search for more papers by this author Chun-Chao Wang Chun-Chao Wang Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA Search for more papers by this author Murat Cirit Murat Cirit Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA Search for more papers by this author Jason M Haugh Corresponding Author Jason M Haugh Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA Search for more papers by this author Author Information Chun-Chao Wang1, Murat Cirit1 and Jason M Haugh 1 1Department of Chemical and Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA *Corresponding author. Department of Chemical and Biomolecular Engineering, North Carolina State University, Box 7905, Engineering Building I, 911 Partners Way, Raleigh, NC 27695-7905, USA. Tel.: +1 919 513 3851; Fax: +1 919 515 3465; E-mail: [email protected] Molecular Systems Biology (2009)5:246https://doi.org/10.1038/msb.2009.4 Correction(s) for this article PI3K-dependent cross-talk interactions converge with Ras as quantifiable inputs integrated by Erk16 August 2011 PDFDownload PDF of article text and main figures. ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InMendeleyWechatReddit Figures & Info Although it is appreciated that canonical signal-transduction pathways represent dominant modes of regulation embedded in larger interaction networks, relatively little has been done to quantify pathway cross-talk in such networks. Through quantitative measurements that systematically canvas an array of stimulation and molecular perturbation conditions, together with computational modeling and analysis, we have elucidated cross-talk mechanisms in the platelet-derived growth factor (PDGF) receptor signaling network, in which phosphoinositide 3-kinase (PI3K) and Ras/extracellular signal-regulated kinase (Erk) pathways are prominently activated. We show that, while PI3K signaling is insulated from cross-talk, PI3K enhances Erk activation at points both upstream and downstream of Ras. The magnitudes of these effects depend strongly on the stimulation conditions, subject to saturation effects in the respective pathways and negative feedback loops. Motivated by those dynamics, a kinetic model of the network was formulated and used to precisely quantify the relative contributions of PI3K-dependent and -independent modes of Ras/Erk activation. Synopsis Historically, intracellular signal transduction has been characterized in terms of distinct pathways, comprised of linear, sequential activation processes. This concept is exemplified by the canonical mitogen-activated protein kinase (MAPK) cascades, such as the Ras→Raf→MEK→extracellular signal-regulated kinase (Erk) pathway in mammals. Our current understanding of signal-transduction networks includes more complex interactions, including those between the classically defined pathways (cross-talk) and those responsible for feedback regulation/reinforcement. Although there is a great deal of qualitative information available as to how signaling networks are wired, an as yet unmet challenge is their systematic quantification; to understand cell regulation at the molecular level, we need to know the relative magnitudes of classical and cross-talk interactions that converge and collaborate to activate key nodes in the network. In most signaling networks, Erk isoforms are both master integrators of upstream inputs and master controllers of transcription factors and other effectors (Kolch, 2000). In this study, we systematically combine quantitative biochemical measurements and computational modeling to quantify the magnitudes of cross-talk and negative feedback interactions in a signaling network. We investigated signaling mediated by platelet-derived growth factor (PDGF) receptors in fibroblasts, leading to activation of the Ras/Erk pathway and exceptionally robust activation of phosphoinositide 3-kinases (PI3Ks), which control responses such as directed cell migration, survival, and proliferation through the production of specific lipid second messengers (Vanhaesebroeck et al, 2001; Engelman et al, 2006; Hawkins et al, 2006). Although cross-talk between the PI3K and Ras/Erk pathways has been studied extensively, a definitive pattern of regulation has not yet emerged, because the two pathways apparently affect each other in various ways and in a context-dependent manner. We measured Erk phosphorylation and PI3K-dependent Akt phosphorylation in PDGF-stimulated NIH 3T3 fibroblasts by quantitative immunoblotting for an array of 126 experimental conditions, sampling different combinations of ligand dose, stimulation time, and molecular manipulation; the Erk data set is shown in Figure 1. Considering biological replicates and parallel determination of total Erk and Akt levels, this data set comprises 2772 total measurements. As shown in Figure 1B and C, blocking the activity of either Ras or PI3K, by the expression of dominant-negative (S17N) H-Ras or incubation with a pharmacological inhibitor, respectively, only partially reduces PDGF-stimulated Erk phosphorylation; the degree of inhibition depends, in a complex manner, on both stimulation dose and time. By comparison, the Akt phosphorylation results showed that the PI3K pathway is not significantly affected by perturbations affecting Ras and Erk; cross-talk is apparently unidirectional, from PI3K to Ras/Erk, in this network. We went on to show that simultaneous inhibition of Ras and PI3K almost completely abolished PDGF-stimulated Erk phosphorylation, indicating that Ras and PI3K are responsible for all of the major pathways from PDGF receptors to Erk, and at least one mode of PI3K-dependent cross-talk to Erk is independent of Ras. We further refined this conceptual model by measuring Ras-GTP, the active form of Ras, for selected experimental conditions using a quantitative enzymatic assay (Scheele et al, 1995; Kaur et al, 2006). These experiments showed that PI3K-dependent cross-talk affects the Erk pathway both downstream and upstream of Ras, and they also served to characterize a known negative feedback mechanism affecting Ras as a consequence of signaling through the Erk cascade. A second regulatory loop that we characterized for this pathway is the increased expression of MAPK phosphatase-1 (MKP-1), which responds to and antagonizes Erk activation. Motivated by the dynamics revealed in our unique data set, a kinetic model of the network was formulated and used to precisely quantify the relative contributions of PI3K-dependent and -independent modes of Ras/Erk activation. In the context of the model, the magnitudes of the Ras- and PI3K-dependent inputs converging on MEK/Erk determines the saturability of Erk phosphorylation with respect to PDGF dose and also the degree to which the response adapts, and conversely, the observed dynamics can be used to quantify the magnitudes of the inputs. Unspecified parameter values were estimated using a Monte Carlo-based algorithm that directly and globally compares the model output to the experimental data; thus, an ensemble of 10 000 parameter sets that fit the data almost equally well was assembled (Brown and Sethna, 2003; Gutenkunst et al, 2007) and compared with the corresponding data as shown in Figure 7. Taken together, the data force the model to reconcile time- and PDGF dose-dependent features of the network observed under the various experimental conditions tested. Analysis of the parameter sets chosen by the algorithm revealed a consistent ratio of PI3K- and Ras-dependent contributions to the dual phosphorylation of MEK, the kinase activity directly upstream of Erk. We formulated a single number, the MEK activation comparator (MAC), which compares the capacities of the two pathways to generate dually phosphorylated MEK. Importantly, the MAC quantifies these inputs in a way that uncouples them from negative feedback effects. This analysis revealed that, although the PI3K-dependent MEK activation pathway is predicted to be intrinsically much less potent than the Ras-dependent pathway under maximal PDGF stimulation conditions, feedback regulation of Ras renders the PI3K-dependent pathway somewhat more important. We also used our computational approach to generate hypothetical predictions with an eye toward future experiments. Although inhibition of PI3K affects cross-talk interactions both upstream and downstream of Ras, the model ensemble predicts unique kinetic signatures that might be expected if either mechanism were silenced selectively, which could help validate the point of action of a particular pathway from PI3K to Erk. In turn, characterization of cross-talk mechanisms along these lines would allow both conceptual and quantitative models to be refined. The integration of high-quality, high-resolution measurements, directly compared with data-driven kinetic models, is demonstrated as a means to quantify cross-talk interactions in signaling networks. For the field to move forward, an issue that will need to be confronted is the generality of signaling networks across receptor and cell types. Certainly, major disparities in the regulation of signaling in different contexts, even among receptors of the same class, should be expected, and more quantitative approaches will be needed to unravel the mechanisms that distinguish particular signaling systems. Introduction Signal transduction is traditionally characterized in terms of intracellular pathways, which govern outcomes such as cell proliferation, survival, migration, and differentiation. Cross-talk interactions, which couple distinct pathways, are recognized for their importance in cell regulation yet remain poorly defined because of their complex nature (Hunter, 2000). They allow information flow and regulation to be distributed across multiple pathways, and perturbations targeting specific signaling molecules might therefore have unexpected effects (Bray, 1990). Here, we describe the systematic and quantitative characterization of cross-talk between two major signaling pathways, phosphoinositide 3-kinase (PI3K) and Ras/extracellular signal-regulated kinase (Erk), which play prominent roles in signaling networks accessed by many cell surface receptors. Signaling mediated by platelet-derived growth factor (PDGF) receptors, members of the receptor tyrosine kinase class of signal transducers (Claesson-Welsh, 1994; Schlessinger, 2000), is relevant to wound healing, development, and cancer (Heldin and Westermark, 1999) and is distinguished by potent activation of type IA PI3Ks, which control a host of cellular responses through the production of specific lipid second messengers (Vanhaesebroeck et al, 2001; Engelman et al, 2006; Hawkins et al, 2006). PDGF receptors also enhance signaling through Ras proteins by promoting Ras guanine nucleotide exchange factor (Ras-GEF) activity and hence an increase in GTP-bound Ras; in this state, Ras activates the canonical Raf/mitogen-activated protein kinase (MAPK) or Erk kinase (MEK)/Erk cascade. Erk isoforms are both master integrators of upstream signals and master controllers of transcription factors and other effectors (Kolch, 2000). Although cross-talk between the PI3K and Ras/Erk pathways has been studied extensively, a definitive pattern of regulation has not yet emerged, because the two pathways apparently affect each other in various ways and in a context-dependent manner. Despite striking evidence that PI3Ks bind to and are activated by Ras-GTP (Rodriguez-Viciana et al, 1994), the effects of blocking Ras signaling on growth factor-stimulated PI3K activation range from partial inhibition (Rodriguez-Viciana et al, 1994; Klinghoffer et al, 1996) to very little or no inhibition (Klippel et al, 1996; Kaur et al, 2006). Numerous reports have also implicated PI3K in the activation or regulation of Ras/Erk signaling, but again with disparate conclusions being drawn (discussed in Duckworth and Cantley, 1997). Although PI3K inhibitors apparently abrogate Erk activation but not Ras-GTP loading in certain contexts (Cross et al, 1994; Karnitz et al, 1995; Duckworth and Cantley, 1997; King et al, 1997), other reports indicate a role for PI3K upstream of Ras (Hu et al, 1995; DePaolo et al, 1996; Hawes et al, 1996; Wennström and Downward, 1999). Through a kinetic analysis of PI3K and Ras/Erk signaling in the PDGF receptor system, complemented by quantitative modeling (Tyson et al, 2003; Ma'ayan et al, 2005; Kholodenko, 2006), we find that PI3K signaling affects Erk activation both upstream and downstream of Ras, and that Ras and PI3K account for most, if not all, of the pathways from PDGF receptors to Erk. The magnitudes of the Ras- and PI3K-dependent effects are shown to depend strongly on the stimulation conditions, in ways that are readily explained based on the saturability of the respective pathways and negative feedback mechanisms. Interestingly, cross-talk from the Ras/Erk pathway to PI3K is shown to be far less significant, an observation that we speculate is tied to the ability of PDGF receptors to directly and potently activate PI3K signaling. Through modeling and computation, the magnitudes of PI3K-dependent cross-talk mechanisms are quantified, and predictions are generated to inform further refinement of those mechanisms. Results Ras and PI3K make independent contributions to Erk signaling, whereas PI3K is effectively insulated from cross-talk To systematically evaluate cross-talk between the PI3K and Ras/Erk pathways, Erk phosphorylation and PI3K-dependent Akt phosphorylation in PDGF-stimulated NIH 3T3 fibroblasts were measured by quantitative immunoblotting for an array of 126 experimental conditions, sampling different combinations of ligand dose, stimulation time, and molecular manipulation (Figures 1 and 2). Considering biological replicates and parallel determination of total Erk and Akt levels, this data set comprises 2772 total measurements. We have confirmed on multiple occasions that the immunoblot imaging system used produces a linear response as a function of epitope loaded, over a sufficiently broad dynamic range (unpublished results). Figure 1.Systematic analysis of PDGF-stimulated Erk phosphorylation kinetics. (A) Immunoblots, representative of five or six independent experiments, used to quantify relative amounts of phosphorylated Erk (p-Erk1/2) and total Erk (t-Erk1). NIH 3T3 fibroblasts were modulated by retroviral induction of dominant-negative (S17N) or constitutively active (G12V) H-Ras expression or incubation with inhibitors of PI3K (100 μM LY294002) or MEK (50 μM PD098059). The respective controls are empty pBM-puro vector or 0.2% DMSO. Lysates were prepared from cells that were unstimulated or stimulated with PDGF-BB for 5, 15, 30, 60, or 120 min. (B–E) Quantification of Erk phosphorylation, normalized as described under Materials and methods, comparing either S17N Ras expression (B; n=6), PI3K inhibition (C; n=5), G12V Ras expression (D; n=6), or MEK inhibition (E; n=5) with their respective controls. Values are reported as mean±s.e.m., and comparisons to control in (B, C) are by Student's t-test: *P<0.05; **P<0.01. Source data isavailable for this figure at www.nature.com/msb. Download figure Download PowerPoint Figure 2.Systematic analysis of PDGF-stimulated Akt phosphorylation kinetics. (A) Representative immunoblots used to quantify relative amounts of phosphorylated Akt (p-Akt) and total Akt (t-Akt) for the same set of experimental conditions as in Figure 1. (B–E) Quantification of Erk phosphorylation, normalized as described under Materials and methods, comparing either S17N Ras expression (B; n=6), MEK inhibition (C; n=5), G12V Ras expression (D; n=6), or PI3K inhibition (E; n=5) with their respective controls. Values are reported as mean±s.e.m. Source data is available for this figure at www.nature.com/msb. Download figure Download PowerPoint The results reveal that when either Ras or PI3K is inhibited, by the expression of dominant-negative (S17N) H-Ras or incubation with LY294002 compound, respectively, PDGF-stimulated Erk phosphorylation is partially inhibited (Figure 1A–C). Expression of S17N H-Ras sequesters Ras-GEFs and thus affects activation of all Ras isoforms, and we confirmed previously that it prevents PDGF-stimulated Ras-GTP loading in our cells (Kaur et al, 2006); we also confirmed that the control compound LY303511, which is pharmacologically similar to LY294002 except that it does not inhibit PI3K (Knight et al, 2006; Gharbi et al, 2007), does not affect Erk phosphorylation significantly (Supplementary Figure S1). The degree of Erk inhibition depends strongly on both stimulation dose and time; no single combination of these conditions is indicative of the relative roles of Ras and PI3K in activating Erk. At short stimulation times, PI3K inhibition significantly affects Erk activation at low but not high PDGF concentrations, in accord with a previous study (Duckworth and Cantley, 1997); however, even at saturating PDGF concentrations, Erk phosphorylation in PI3K-inhibited cells is less sustained, with significantly lower values than the control at later stimulation times. The effects of Ras inhibition are similar, except that Erk phosphorylation is less sensitive to PDGF concentration and shows a lower initial rate at higher PDGF doses (compare Figure 1B and C). As we will show, these subtle differences in the kinetics between PI3K- and Ras-inhibited cells are indicative of distinct pathways integrated by Erk. Expression of constitutively active (G12V) H-Ras yields not only an elevated level of Erk phosphorylation prior to stimulation but also a somewhat reduced responsiveness to PDGF (Figure 1D), consistent with high constitutive expression of MAPK phosphatase (MKP) as reported previously (Kaur et al, 2006); indeed, the basal expression of MKP-1 is roughly 17-fold higher in G12V Ras-expressing cells (results not shown). Thus, Erk signaling in these cells is the net result of both higher phosphorylation and higher dephosphorylation rates. Erk phosphorylation is mediated by both G12V H-Ras and PDGF-responsive signaling, which presumably includes activation of endogenous Ras isoforms and pathways that depend on PI3K. By comparison, the PI3K pathway is not significantly activated through cross-talk from Ras. Neither expression of dominant-negative Ras nor application of the MEK inhibitor PD098059 has a significant effect on Akt phosphorylation (Figure 2A–C); the latter treatment is expected to enhance Ras-GTP loading by relieving feedback desensitization of the Ras-GEF mSos (Klarlund et al, 1995; Langlois et al, 1995; Waters et al, 1995), but the only effect of the drug is a slight reduction of the peak Akt phosphorylation. Expression of constitutively active Ras results in a higher basal Akt phosphorylation level in unstimulated cells but does not grossly affect PDGF-stimulated Akt phosphorylation. When Akt phosphorylation is far from saturation, the PDGF-stimulated response is incremented by the basal level, suggesting an approximately additive relationship; there is also evidence that the saturated Akt phosphorylation response is more sustained in G12V Ras-expressing cells (Figure 2D). Therefore, whereas inhibiting activation of endogenous Ras did not significantly affect PDGF-stimulated PI3K/Akt signaling in this study, high levels of Ras-GTP cooperate with PDGF receptors in a subtle way to activate this pathway (Jiménez et al, 2002; Kaur et al, 2006). These results suggest two possible Erk activation mechanisms, or combinations thereof: Ras and PI3K promote Erk signaling independently, or PI3K lies upstream of Ras in the same pathway, in which case at least one additional pathway would be responsible for the residual Erk phosphorylation seen when either Ras or PI3K is inhibited. In each of three independent experiments, simultaneous inhibition of Ras and PI3K almost completely abolished PDGF-stimulated Erk phosphorylation, indicating that Ras and PI3K are responsible for all of the major pathways from PDGF receptors to Erk, and at least one mode of PI3K-dependent cross-talk to Erk operates in parallel with Ras (Figure 3). Incidentally, this result also provides further confirmation that Ras function is effectively blocked in our S17N Ras-expressing cells. Figure 3.Ras and PI3K account for all of the major PDGF-stimulated pathways that converge on Erk. NIH 3T3 fibroblasts were infected with retrovirus produced from empty vector or vector with S17N H-Ras, pretreated with either DMSO control or LY294002, then stimulated with PDGF-BB (dose and time indicated). Although inhibition of Ras or PI3K partially blocks Erk phosphorylation, consistent with Figure 1B and C, blocking both Ras and PI3K abolishes Erk phosphorylation. The results are representative of three independent experiments. Download figure Download PowerPoint PI3K enhances Erk activation at points both upstream and downstream of Ras Having established a role for PI3K-dependent signaling to Erk in parallel with Ras, we sought to determine whether or not PI3K also partially contributes to the PDGF receptor-mediated activation of Ras. Using a coupled enzymatic assay (Scheele et al, 1995; Kaur et al, 2006), we measured the kinetics of PDGF-stimulated Ras-GTP loading for selected conditions (Figure 4). In each of three independent experiments, incubation with LY294002 reduced the initial rate of Ras-GTP loading at a low PDGF concentration (50 pM), whereas Ras-GTP loading kinetics were minimally affected at 1 nM PDGF. Interestingly, the plateau level of Ras-GTP in PI3K-inhibited cells was similar to that of control cells, even at the lower dose of PDGF. Figure 4.Quantitative Ras-GTP loading measurements: characterization of PI3K-dependent cross-talk and Erk-dependent feedback regulation. NIH 3T3 fibroblasts were stimulated with PDGF-BB as indicated; pretreatments were control (0.2% DMSO), LY294002 (100 μM), or PD098059 (50 μM). Ras-GTP levels were measured using a quantitative enzymatic assay and normalized as described under Materials and methods; values are reported as mean±s.e.m. (n=3). Source data is available for this figure at www.nature.com/msb. Download figure Download PowerPoint As alluded to in the previous section, Ras-GTP loading is affected by a known negative feedback loop that destabilizes Ras-GEF recruitment, and accordingly, incubation with PD098059 yields a higher Ras-GTP level (Figure 4). The feedback loop might also explain the effect of PI3K inhibition seen at lower PDGF concentrations. Erk phosphorylation is dramatically reduced under those conditions (Figure 1C), and thus the feedback regulation might be relieved. The net effect of reduced but stable Ras-GEF recruitment would be a lower initial rate and more sustained level of Ras-GTP loading. Multiple negative feedback loops shape the integrated Erk phosphorylation response In addition to feedback regulation of Ras-GEF, we also characterized the upregulation of MKP expression induced by Erk and other MAPKs (Brondello et al, 1997; Bhalla et al, 2002; Plows et al, 2002) (Figure 5A and B). MKP-1 expression is upregulated ∼3-fold in response to 1 nM PDGF, after a lag time of approximately 15 min. At 30 pM PDGF, which elicits roughly half-maximal Erk phosphorylation (Figure 1B and C), MKP-1 expression increases only slightly, suggestive of a signaling threshold for triggering the feedback loop. A similar MKP-1 response is observed when either Ras or PI3K is inhibited, with a partial reduction in the fold induction (Figure 5B); this outcome can be attributed at least in part to the diminished Erk phosphorylation response, integrated over time, when either of the two major pathways is disrupted. As expected, inhibition of MEK/Erk or c-Jun N-terminal kinase (JNK) (but not of p38; results not shown) significantly reduces the induction of MKP-1 expression, and simultaneous inhibition of MEK and JNK blocks MKP-1 upregulation completely (Figure 5C). Figure 5.Delayed onset and threshold for MKP-1 upregulation, a known negative feedback loop in the Erk pathway. (A) Immunoblots of MKP-1 levels in control, PI3K-inhibited, or S17N H-Ras-expressing cells that were unstimulated or stimulated with PDGF-BB for 5, 15, 30, 60, or 120 min; each blot is representative of two or three independent experiments. (B) Quantification of MKP-1 expression, with either total Erk1 or total protein as the loading control and normalized as described under Materials and methods. Values are reported as mean±s.e.m. (n=3 for DMSO and LY294002; n=2 for control vector and S17N Ras). (C) MEK/Erk and JNK pathways contribute to feedback upregulation of MKP-1. PDGF stimulation was 1 nM for 60 min. MEK or/and JNK were inhibited by incubation with 50 μM PD098059 (PD) and 25 μM SP600125 (SP), respectively. The DMSO concentration was 0.25% in all cases. The blot is representative of two independent experiments. Source data is available for this figure at www.nature.com/msb. Download figure Download PowerPoint Parsing the magnitudes of PI3K-dependent cross-talk interactions in the PDGF receptor signaling network Synthesizing the data assembled, a conceptual model of the PDGF receptor signaling network is now clear (Figure 6). Yet, the unique dose–response and kinetic information in the data set allow for a more quantitative description through mathematical modeling and analysis. The relatively coarse granularity of our model, described in detail in the Supplementary information, reflects a careful balance between the level of molecular detail included and both the uncertainty of those details and the ability to specify model parameters. In the context of the model, the magnitudes of the Ras- and PI3K-dependent inputs converging on MEK/Erk determine the saturability of Erk phosphorylation with respect to PDGF dose and also the degree to which the response adapts, and conversely, the observed dynamics can be used to quantify the magnitudes of the inputs. Figure 6.Conceptual model of the PDGF receptor signaling network. Cross-talk interactions from PI3K lipid products (3′ PIs) affect Ras-specific GEF (e.g. Grb2–Sos complex) recruitment and activation of MEK kinases, which might or might not be the same as those activated by Ras. It is recognized that those cross-talk effects might entail multiple steps, and that a more refined model would account for the effect of JNK activation on the MKP negative feedback loop. Download figure Download PowerPoint A total of 34 unspecified parameter values were estimated using a Monte Carlo-based algorithm that directly and globally compares the model output to the experimental data (Supplementary information); thus, an ensemble of 10 000 parameter sets that fit the data almost equally well was assembled. This approach embraces the inherent ‘sloppiness’ of kinetic models, which prohibits the reliable identification of precise parameter values yet allows for predictions based on collective fits to data (Gutenkunst et al, 2007). The model output is expressed as an ensemble average (Brown and Sethna, 2003; Violin et al, 2008) and compared with the corresponding data (Figure 7). The remaining data used to constrain the algorithm indicate the degree of saturation in the MEK/Erk pathway (Supplementary Figure S2). Taken together, the data force the model to reconcile time- and PDGF dose-dependent features of the network observed under the various experimental conditions tested, including subtle differences between the two control experiments (DMSO vehicle only versus empty pBM-puro vector). Considering the global constraints imposed by the data and the necessarily simplified nature of the kinetic model, it is our assessment that the model performs quite well; however, one feature that it was not able to reconcile well is the sensitivity of the Erk phosphorylation response in S17N Ras-expressing cells stimulated with the lower doses of PDGF (Figure 7; bottom row, second plot from left). We speculate that the apparent sensitivity of the response, relative to the model output, is diminished by cell variability. It is known that variability in the cells’ sensitivity to stimulation (the EC50 of the dose–response curve) produces a flatter dose–response curve for the population (Altan-Bonnet and Germain, 2005). The model also does not capture the transient nature of the S17N Ras/30 pM PDGF curve, suggesting that ligand depletion or other negative feedback effects might need to be characterized and accounted for in future refinements of the model. Indeed, the transient nature of the Akt phosphorylation response at low PDGF concentrations (Figure 2) provides additional evidence for such effects affecting PI3K-dependent signaling. Figure 7.Computational model and algorithm for direct comparison to experimental data. A quantitative kinetic model of the network was formulated, and a Monte Carlo schem DA - 2009/1// PY - 2009/1// DO - 10.1038/msb.2009.4 VL - 5 IS - 1 SP - 246 J2 - Mol Syst Biol LA - en OP - SN - 1744-4292 1744-4292 UR - http://dx.doi.org/10.1038/msb.2009.4 DB - Crossref KW - kinetic model KW - mitogen-activated protein kinase KW - phosphatidylinositol 3-kinase KW - receptor tyrosine kinase KW - signal transduction ER - TY - JOUR TI - Role of vapBC toxin–antitoxin loci in the thermal stress response of Sulfolobus solfataricus AU - Cooper, Charlotte R. AU - Daugherty, Amanda J. AU - Tachdjian, Sabrina AU - Blum, Paul H. AU - Kelly, Robert M. T2 - Biochemical Society Transactions AB - TA (toxin–antitoxin) loci are ubiquitous in prokaryotic micro-organisms, including archaea, yet their physiological function is largely unknown. For example, preliminary reports have suggested that TA loci are microbial stress-response elements, although it was recently shown that knocking out all known chromosomally located TA loci in Escherichia coli did not have an impact on survival under certain types of stress. The hyperthermophilic crenarchaeon Sulfolobus solfataricus encodes at least 26 vapBC (where vap is virulence-associated protein) family TA loci in its genome. VapCs are PIN (PilT N-terminus) domain proteins with putative ribonuclease activity, while VapBs are proteolytically labile proteins, which purportedly function to silence VapCs when associated as a cognate pair. Global transcriptional analysis of S. solfataricus heat-shock-response dynamics (temperature shift from 80 to 90°C) revealed that several vapBC genes were triggered by the thermal shift, suggesting a role in heat-shock-response. Indeed, knocking out a specific vapBC locus in S. solfataricus substantially changed the transcriptome and, in one case, rendered the crenarchaeon heat-shock-labile. These findings indicate that more work needs to be done to determine the role of VapBCs in S. solfataricus and other thermophilic archaea, especially with respect to post-transcriptional regulation. DA - 2009/1/20/ PY - 2009/1/20/ DO - 10.1042/BST0370123 VL - 37 IS - 1 SP - 123-126 LA - en OP - SN - 0300-5127 1470-8752 UR - http://dx.doi.org/10.1042/BST0370123 DB - Crossref KW - archaeon KW - heat shock KW - hyperthermophile KW - stress response KW - Sulfolobus solfataricus KW - toxin-antioxin locus ER - TY - JOUR TI - Drug Delivery Technologies: The Way Forward in the New Decade AU - Martín del Valle, Eva M. AU - Galán, Miguel A. AU - Carbonell, Ruben G. T2 - Industrial & Engineering Chemistry Research AB - The design and development of drug delivery systems involves many different sciences that underpin the research. It is clear that significant advances will only be made through multidisciplinary teams that utilize the latest advances in the biological, chemical, physical, and engineering sciences. The underpinning sciences are also vital to the process of developing successful products. There are three key and interrelated areas of research. (i) Achieve a greater understanding of the biological fate and the targeting of drugs, particularly biopharmaceuticals, macromolecules and macromolecular delivery systems, at the molecular, membrane, and cellular level. (ii) Provide a greater understanding of the physicochemical properties of biopharmaceuticals, macromolecules, and macromolecular delivery systems and how these are modified within a biological environment affecting their activity. (iii) Promote the development of novel materials and delivery systems that will overcome these biological barriers. This article aims to provide a comprehensive review of the key issues to design an effective drug delivery system. DA - 2009/3/4/ PY - 2009/3/4/ DO - 10.1021/ie800886m VL - 48 IS - 5 SP - 2475-2486 J2 - Ind. Eng. Chem. Res. LA - en OP - SN - 0888-5885 1520-5045 UR - http://dx.doi.org/10.1021/ie800886m DB - Crossref ER - TY - JOUR TI - Binding site on human immunoglobulin G for the affinity ligand HWRGWV AU - Yang, Haiou AU - Gurgel, Patrick V. AU - Williams, D. Keith, Jr AU - Bobay, Benjamin G. AU - Cavanagh, John AU - Muddiman, David C. AU - Carbonell, Ruben G. T2 - Journal of Molecular Recognition AB - Abstract Affinity ligand HWRGWV has demonstrated the ability to isolate human immunoglobulin G (hIgG) from mammalian cell culture media. The ligand specifically binds hIgG through its Fc portion. This work shows that deglycosylation of hIgG has no influence on its binding to the HWRGWV ligand and the ligand does not compete with Protein A or Protein G in binding hIgG. It is suggested by the mass spectrometry (MS) data and docking simulation that HWRGWV binds to the pFc portion of hIgG and interacts with the amino acids in the loop Ser383–Asn389 (SNGQPEN) located in the C H 3 domain. Subsequent modeling has suggested a possible three‐dimensional minimized solution structure for the interaction of hIgG and the HWRGWV ligand. The results support the fact that a peptide as small as a hexamer can have specific interactions with large proteins such as hIgG. Copyright © 2009 John Wiley & Sons, Ltd. DA - 2009/// PY - 2009/// DO - 10.1002/jmr.967 SP - n/a-n/a J2 - J. Mol. Recognit. LA - en OP - SN - 0952-3499 1099-1352 UR - http://dx.doi.org/10.1002/jmr.967 DB - Crossref KW - hexamer ligand KW - immunoglobulin G KW - glycosylation KW - mass spectrometry KW - computational docking KW - binding site ER - TY - JOUR TI - Interactions between endothelial cells and electrospun methacrylic terpolymer fibers for engineered vascular replacements AU - Veleva, A. N. AU - Heath, D. E. AU - Johnson, J. K. AU - Nam, J. AU - Patterson, C. AU - Lannutti, J. J. AU - Cooper, S. L. T2 - Journal of Biomedical Materials Research Part A AB - Abstract A compliant terpolymer made of hexylmethacrylate (HMA), methylmethacrylate (MMA), and methacrylic acid (MAA) intended for use in small diameter vascular graft applications has been developed. The mechanical properties and in vitro biostability of this terpolymer have been previously characterized. The goal of this investigation was to examine the interactions between endothelial cells and the new terpolymer and to evaluate endothelial cell function. Electrospinning was used to produce both oriented and random terpolymer fiber scaffolds. Smooth solution cast films and tissue culture polystyrene were used as negative and positive controls, respectively. Human blood outgrowth endothelial cells and human umbilical vein endothelial cells were incubated with the test and control samples and characterized with respect to initial cell attachment, proliferation, viability, and maintenance of the endothelial cell phenotype. It was found that the terpolymer is cytocompatible allowing endothelial cell growth, with random fibers being more effective in promoting enhanced cellular activities than oriented fibers. In addition, endothelial cells cultured on these substrates appeared to maintain their phenotype. The results from this study demonstrate that electrospun HMA:MMA:MAA terpolymer has the potential to be used successfully in fabricating small diameter blood vessel replacements. © 2009 Wiley Periodicals, Inc. J Biomed Mater Res, 2009 DA - 2009/12/15/ PY - 2009/12/15/ DO - 10.1002/jbm.a.32276 VL - 91A IS - 4 SP - 1131-1139 J2 - J. Biomed. Mater. Res. LA - en OP - SN - 1549-3296 1552-4965 UR - http://dx.doi.org/10.1002/jbm.a.32276 DB - Crossref KW - methacrylic terpolymers KW - biocompatibility KW - electrospinning KW - endothelial cells KW - engineered vascular grafts ER - TY - JOUR TI - Synthesis and characterization of PAMPS-filled nylon nonwoven membranes T2 - Abstracts of Papers of the American Chemical Society DA - 2009/// PY - 2009/// UR - https://publons.com/publon/7178320/ ER - TY - JOUR TI - POLY 63-Polymer-filled nonwoven membranes for chemical protection T2 - Abstracts of Papers of the American Chemical Society DA - 2009/// PY - 2009/// UR - https://publons.com/publon/7178334/ ER - TY - JOUR TI - Energy-Related Applications of Electrospun Nanofibers T2 - PROCEEDINGS OF THE FIBER SOCIETY 2009 SPRING CONFERENCE, VOLS I AND II DA - 2009/// PY - 2009/// UR - https://publons.com/publon/6540076/ ER - TY - CONF TI - Green Chemistry and Engineering with Gas Expanded Liquids and Near-Critical Media AU - Du, L. AU - DeSimone, J.M. AU - Roberts, G.W. A2 - Hutchenson, K.W. A2 - Scurto, A.M. A2 - Subramaniam, B. C2 - 2009/// C3 - ACS Symposium Series DA - 2009/// VL - 90 SP - 259–273 M1 - 1006 ER - TY - JOUR TI - Photonic Crystal Geometry for Organic Solar Cells AU - Ko, Doo-Hyun AU - Tumbleston, John R. AU - Zhang, Lei AU - Williams, Stuart AU - DeSimone, Joseph M. AU - Lopez, Rene AU - Samulski, Edward T. T2 - Nano Letters AB - We report organic solar cells with a photonic crystal nanostructure embossed in the photoactive bulk heterojunction layer, a topography that exhibits a 3-fold enhancement of the absorption in specific regions of the solar spectrum in part through multiple excitation resonances. The photonic crystal geometry is fabricated using a materials-agnostic process called PRINT wherein highly ordered arrays of nanoscale features are readily made in a single processing step over wide areas (approximately 4 cm(2)) that is scalable. We show efficiency improvements of approximately 70% that result not only from greater absorption, but also from electrical enhancements. The methodology is generally applicable to organic solar cells and the experimental findings reported in our manuscript corroborate theoretical expectations. DA - 2009/7/8/ PY - 2009/7/8/ DO - 10.1021/nl901232p VL - 9 IS - 7 SP - 2742-2746 J2 - Nano Lett. LA - en OP - SN - 1530-6984 1530-6992 UR - http://dx.doi.org/10.1021/nl901232p DB - Crossref ER - TY - CONF TI - Hybrid Reverse Monte Carlo Simulations of Nano-Porous Carbons AU - Palmer, J.C. AU - Jain, S.K. AU - Gubbins, K.E. AU - Cohaut, N. AU - Fischer, J.E. AU - Dash, R.K. AU - Gogotsi, Y. T2 - 8th International Conference on Characterization of Porous Solids A2 - Kaskel, S. A2 - Llewellyn, P. A2 - Rodriguez-Reinsos, F. A2 - Seaton, N.A. C2 - 2009/// C3 - Characterization of Porous Solids VIII, Proceedings of the 8th International Conference on Characterization of Porous Solids DA - 2009/// PY - 2009/// VL - 318 SP - 56–63 PB - Royal Society of Chemistry ER - TY - JOUR TI - Multiscale Modeling of the Self-Assembly of Nonionic Poly(oxyethylene) Alkyl Ether Surfactants in Bulk and on Solid Surfaces AU - Moore, Joshua D. AU - Gubbins, Keith E. T2 - Abstracts of Papers of the American Chemical Society DA - 2009/// PY - 2009/// VL - 237 ER - TY - JOUR TI - Surface Nanostructure, Diffusion and Catalysis: The Role of Confinement and Surface Chemistry AU - Gubbins, Keith E. T2 - Abstracts of Papers of the American Chemical Society DA - 2009/// PY - 2009/// VL - 237 ER - TY - CONF TI - The prehistory of soot: Small rings from small molecules AU - Westmoreland, P.R. A2 - Bockhorn, Henning C2 - 2009/// C3 - Combustion Generated Fine Carbonaceous Particles: Proceedings of an International Workshop CY - Villa Orlandi, Anacapri DA - 2009/// PY - 2007/5/13/ SP - 30-47 PB - KIT Scientific Publishing ER - TY - JOUR TI - Particle-localized AC and DC manipulation and electrokinetics AU - Velev, O.D. AU - Gangwal, S. AU - Petsev, D.N. T2 - Annual Reports on the Progress of Chemistry - Section C AB - Colloidal particles suspended in water respond to direct (DC) or alternating current (AC) fields in a variety of ways, including directional motion along or across the field direction, field-gradient dependent response and induced particle–particle interaction. We review here some of these effects and their applications in new techniques for particle manipulation and assembly, making of novel biomaterials and designing of new self-propelling microdevices. The coupling of the counterionic layer mobility, fluid flows and the resulting particle motion are the basis not only of the classic electrophoretic effects, but also of the recent developments in AC electrohydrodynamics and induced charge electrophoresis of asymmetric particles. We also discuss how dielectrophoresis (particle interaction with external AC field gradients), could be used to manipulate and assemble objects on any size scale. We discuss the interactions leading to the assembly of such structures, ways to simulate the dynamics of the process and the effect of particle size and conductivity on the type of structure obtained. Finally, we demonstrate how an additional level of complexity can be engineered to turn miniature semiconductor diodes into prototypes of self-propelling micromachines and micropumps. The diodes suspended in water propel themselves electro-osmotically when a uniform alternating electric field is applied across the container. Semiconductor diodes embedded in channel walls could serve as distributed microfluidic pumps and mixers powered by a global external field. DA - 2009/// PY - 2009/// DO - 10.1039/b803015b VL - 105 SP - 213-246 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-65549108008&partnerID=MN8TOARS ER - TY - JOUR TI - Thermosensitive Nanocables Prepared by Surface-Initiated Atom Transfer Radical Polymerization AU - Wei, Q. S. AU - Zhou, W. B. AU - Ji, J. AU - Shen, J. C. T2 - Nanoscale Research Letters AB - Abstract Thermosensitive nanocables consisting of Au nanowire cores and poly( N -isopropylacrylamide) sheaths (denoted as Au/PNIPAAm) were synthesized by surface-initiated atom transfer radical polymerization (SI-ATRP). The formation of PNIPAAm sheath was verified by Fourier transform infrared (FTIR) and hydrogen nuclear magnetic resonance ( 1 H NMR) spectroscopy. Transmission electron microscope (TEM) results confirmed the core/shell structure of nanohybrids. The thickness and density of PNIPAAm sheaths can be adjusted by controlling the amount of cross-linker during the polymerization. Signature temperature response was observed from Au/cross-linked-PNIPAAm nanocables. Such smart nanocables show immense potentials as building blocks for novel thermosensitive nanodevices in future. DA - 2009/// PY - 2009/// DO - 10.1007/s11671-008-9206-5 VL - 4 IS - 1 SP - 84-89 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000262506500012&KeyUID=WOS:000262506500012 KW - Nanocables KW - Gold nanowires KW - Poly(N-isopropylacrylamide) KW - Surface-initiated atom transfer radical polymerization Thermoresponsive ER - TY - JOUR TI - Gyromagnetic Imaging: Dynamic Optical Contrast Using Gold Nanostars with Magnetic Cores AU - Wei, Q. S. AU - Song, H. M. AU - Leonov, A. P. AU - Hale, J. A. AU - Oh, D. M. AU - Ong, Q. K. AU - Ritchie, K. AU - Wei, A. T2 - Journal of the American Chemical Society AB - Plasmon-resonant nanoparticles with optical scattering in the near-infrared (NIR) are valuable contrast agents for biophotonic imaging and may be detected at the single-particle limit against a dark background, but their contrast is often limited in environments with high noise. Here we consider gyromagnetic imaging as a dynamic mode of optical contrast, using gold nanostars with superparamagnetic cores. The nanostars exhibit polarization-sensitive NIR scattering and can produce a frequency-modulated signal in response to a rotating magnetic field gradient. This periodic “twinkling” can be converted into Fourier-domain images with a dramatic reduction in background. We demonstrate gyromagnetic imaging of nanostars inside of tumor cells, using broadband excitation: while their time-domain signals are obscured by incoherent scattering, their Fourier-domain signals can be clearly resolved in less than a second. The gyromagnetically active nanostars do not cause a loss in viability, and can even have a mild stimulatory effect on cell growth. DA - 2009/// PY - 2009/// DO - 10.1021/ja901562j VL - 131 IS - 28 SP - 9728-9734 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000268399800034&KeyUID=WOS:000268399800034 ER - TY - JOUR TI - Gold Nanorods as Contrast Agents for Biological Imaging: Optical Properties, Surface Conjugation and Photothermal Effects AU - Tong, L. AU - Wei, Q. S. AU - Wei, A. AU - Cheng, J. X. T2 - Photochemistry and Photobiology AB - Abstract Gold nanorods (NRs) have plasmon‐resonant absorption and scattering in the near‐infrared (NIR) region, making them attractive probes for in vitro and in vivo imaging. In the cellular environment, NRs can provide scattering contrast for darkfield microscopy, or emit a strong two‐photon luminescence due to plasmon‐enhanced two‐photon absorption. NRs have also been employed in biomedical imaging modalities such as optical coherence tomography or photoacoustic tomography. Careful control over surface chemistry enhances the capacity of NRs as biological imaging agents by enabling cell‐specific targeting, and by increasing their dispersion stability and circulation lifetimes. NRs can also efficiently convert optical energy into heat, and inflict localized damage to tumor cells. Laser‐induced heating of NRs can disrupt cell membrane integrity and homeostasis, resulting in Ca 2+ influx and the depolymerization of the intracellular actin network. The combination of plasmon‐resonant optical properties, intense local photothermal effects and robust surface chemistry render gold NRs as promising theragnostic agents. DA - 2009/// PY - 2009/// DO - 10.1111/j.1751-1097.2008.00507.x VL - 85 IS - 1 SP - 21-32 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000262486800003&KeyUID=WOS:000262486800003 ER - TY - JOUR TI - COLL 347-Polarization-sensitive NIR imaging modalities based on gold nanorods and nanostars AU - Wei, Q. S. AU - Song, H. M. AU - Leonov, A. AU - Ritchie, K. AU - Wei, A. T2 - Abstracts of Papers of the American Chemical Society DA - 2009/// PY - 2009/// VL - 238 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000207861903202&KeyUID=WOS:000207861903202 ER - TY - JOUR TI - Synthesis and characterization of PAMPS-filled nylon nonwoven membranes AU - Jung, Kyung-Hye AU - Pourdeyhimi, Behnam AU - Zhang, Xiangwu T2 - Abstracts of Papers of the American Chemical Society DA - 2009/// PY - 2009/// VL - 237 ER - TY - CHAP TI - Processing-Structure Relationships of Electrospun Nanofibers AU - Zhang, Xiangwu T2 - Nanofibers: Fabrication, Performance, and Applications A2 - Chang, W.N. PY - 2009/// SP - 239-270, PB - Nova Science ER - TY - JOUR TI - POLY 63-Polymer-filled nonwoven membranes for chemical protection AU - Jung, Kyung-Hye AU - Pourdeyhimi, Behnam AU - Zhang, Xiangwu T2 - Abstracts of Papers of the American Chemical Society DA - 2009/// PY - 2009/// VL - 238 ER - TY - BOOK TI - Energy-Related Applications of Electrospun Nanofibers AU - Zhang, Xiangwu AU - Ji, Liwen AU - Lin, Zhan AU - Donghua, University DA - 2009/// PY - 2009/// PB - SE - 959-960 ER - TY - CONF TI - Synthesis and Characterization of PAMPS-Filled Nylon Nonwoven Membranes C2 - 2009/3// C3 - 237th American Chemical Society National Meeting DA - 2009/3// ER - TY - CONF TI - Pt-Carbon Nanofiber Composites for Use as Electrodes in DMFCs C2 - 2009/5// C3 - 215th Electrochemical Society Meeting DA - 2009/5// ER - TY - CONF TI - Pt-Carbon Nanofiber Composites for Use as Electrodes in DMFCs C2 - 2009/5// C3 - 215th Electrochemical Society Meeting DA - 2009/5// ER - TY - CONF TI - Nonwovens Containing Polymer Fillers C2 - 2009/4// C3 - Richard D. Gilbert Award Symposium for Students in Polymer Science DA - 2009/4// ER - TY - CONF TI - Nanofiber-Based Anode Materials for High-Performance Lithium-Ion Batteries C2 - 2009/4// C3 - 7th Annual Research Open House in the College of Textiles DA - 2009/4// ER - TY - CONF TI - Lithium-Ion Battery Pack Design C2 - 2009/5// C3 - Electrifying Trasportation Conference DA - 2009/5// ER - TY - JOUR TI - Electrocatalytic properties of Pt/carbon composite nanofibers AU - Lin, Zhan AU - Ji, Liwen AU - Zhang, Xiangwu T2 - Electrochimica Acta AB - Pt/carbon composite nanofibers were prepared by electrodepositing Pt nanoparticles directly onto electrospun carbon nanofibers. The morphology and size of Pt nanoparticles were controlled by the electrodeposition time. The resulting Pt/carbon composite nanofibers were characterized by running cyclic voltammograms in 0.20 M H2SO4 and 5.0 mM K4[Fe(CN)6] + 0.10 M KCl solutions. The electrocatalytic activities of Pt/carbon composite nanofibers were measured by the oxidation of methanol. Results show that Pt/carbon composite nanofibers possess the properties of high active surface area and fast electron transfer rate, which lead to a good performance towards the electrocatalytic oxidation of methanol. It is also found that the Pt/carbon nanofiber electrode with a Pt loading of 0.170 mg cm−2 has the highest activity. DA - 2009/// PY - 2009/// DO - 10.1016/j.electacta.2009.07.022 VL - 54 IS - 27 SP - 7042-7047 UR - https://publons.com/publon/6540064/ KW - Electrospinning KW - Electrodeposition KW - Pt nanoparticles KW - Carbon nanofibers KW - Methanol ER - TY - CONF TI - Design and Synthesis of Dyes for Dye-Sensitized Solar Cells (DSSCs) C2 - 2009/4// C3 - 7th Annual Research Open House in the College of Textiles DA - 2009/4// ER - TY - JOUR TI - A Review of Pt Alloys and Carbon Nanotube/Nanofiber Supported Catalysts for Direct Methanol Fuel Cells AU - Lin, Zhan AU - Ji, Liwen AU - Zhang, Xiangwu T2 - Journal of Energy Storage and Conversion DA - 2009/// PY - 2009/// VL - 1 SP - 101-115 ER - TY - CONF TI - Polymer-Filled Nonwoven Membranes for Chemical Protection C2 - 2009/8// C3 - 2009 Fall American Chemistry Society National Meeting DA - 2009/8// ER - TY - CONF TI - Fabrication of Composite Nanofiber Anodes for Rechargeable Lithium-Ion Batteries C2 - 2009/5// C3 - 215th Electrochemical Society Meeting DA - 2009/5// ER - TY - CONF TI - Fabrication of Composite Nanofiber Anodes for Rechargeable Lithium-Ion Batteries C2 - 2009/5// C3 - 215th Electrochemical Society Meeting DA - 2009/5// ER - TY - CONF TI - Fabrication of Anode Materials for Lithium-Ion Batteries Using Tin (IV) Acetate and the Electrospinning Method C2 - 2009/7// C3 - The 8th Annual NC State University Undergraduate Summer Research Symposium DA - 2009/7// ER - TY - CONF TI - Electrospun Composite Nanofibers for Lithium-Ion Batteries C2 - 2009/10// C3 - AATCC Innovations in Functional Materials, Sports and Defense Technologies, and Composites/NTC Forum DA - 2009/10// ER - TY - CONF TI - Effects of Carbon Black and Current Rate on LiFePO4 Cathodes and Lithium-Ion Batteries C2 - 2009/8// C3 - NCSU Summer Research Program Meeting DA - 2009/8// ER - TY - CONF TI - Challenges in Advanced Nanofiber Wound Dressings C2 - 2009/10// C3 - AATCC Innovations in Functional Materials, Sports and Defense Technologies, and Composites/NTC Forum DA - 2009/10// ER - TY - CONF TI - Application of Atmospheric Pressure Plasma on Electrospun Functional Nanofibers C2 - 2009/11// C3 - Chemical and Biological Defense Science and Technology (CBD S&T) Conference DA - 2009/11// ER - TY - CHAP TI - Ab initio simulations of chemical reactions in nanostructured carbon materials AU - Santiso, E. E. AU - Huang, L. AU - Gubbins, K. E. AU - Kostov, M. K. AU - George, A. M. AU - Nardelli, M. B. T2 - Quantum chemical calculations of surfaces and interfaces of materials A2 - V. A. Basiuk, A2 - Ugliengo, P. PY - 2009/// PB - Stevenson Ranch, Calif.: American Scientific Publishers, SN - 1588831388 ER - TY - JOUR TI - Enzymes for pharmaceutical applications-a cradle-to-gate life cycle assessment AU - Kim, Seungdo AU - Jimenez-Gonzalez, Concepcion AU - Dale, Bruce E. T2 - INTERNATIONAL JOURNAL OF LIFE CYCLE ASSESSMENT DA - 2009/7// PY - 2009/7// DO - 10.1007/s11367-009-0081-9 VL - 14 IS - 5 SP - 392-400 SN - 1614-7502 KW - Biocatalysis KW - Bioprocesses KW - Cradle-to-gate KW - Enzymes KW - LCA KW - Life cycle assessment KW - Life cycle inventories KW - Pharmaceuticals ER - TY - CHAP TI - Secondary batteries - lithium rechargeable systems - electrolytes: Ionic liquids AU - Passerini, S. AU - Henderson, W. A. T2 - Encyclopedia of Electrochemical Power Sources PY - 2009/// PB - Amsterdam : Elsevier SN - 9780444520937 ER - TY - CONF TI - Electrochemical and physicochemical properties of PYR14-FSI based electrolytes with LiFSI AU - Paillard, E. AU - Zhou, Q. AU - Henderson, W. A. AU - Appetecchi, G. B. AU - Montanino, M. AU - Passerini, S. C2 - 2009/// C3 - ECS Transactions DA - 2009/// SP - 51-57 ER - TY - JOUR TI - Viscoelastic properties of oxide-coated liquid metals AU - Larsen, Ryan J. AU - Dickey, Michael D. AU - Whitesides, George M. AU - Weitz, David A. T2 - JOURNAL OF RHEOLOGY 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 Ryan J. Larsen, Michael D. Dickey, George M. Whitesides, David A. Weitz; Viscoelastic properties of oxide-coated liquid metals. J. Rheol. 1 November 2009; 53 (6): 1305–1326. https://doi.org/10.1122/1.3236517 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 ContentThe Society of RheologyJournal of Rheology Search Advanced Search |Citation Search DA - 2009/// PY - 2009/// DO - 10.1122/1.3236517 VL - 53 IS - 6 SP - 1305-1326 SN - 0148-6055 ER - TY - JOUR TI - Optical Antenna Arrays on a Fiber Facet for in Situ Surface-Enhanced Raman Scattering Detection AU - Smythe, Elizabeth J. AU - Dickey, Michael D. AU - Bao, Jiming AU - Whitesides, George M. AU - Capasso, Federico T2 - NANO LETTERS AB - This paper reports a bidirectional fiber optic probe for the detection of surface-enhanced Raman scattering (SERS). One facet of the probe features an array of gold optical antennas designed to enhance Raman signals, while the other facet of the fiber is used for the input and collection of light. Simultaneous detection of benzenethiol and 2-[(E)-2-pyridin-4-ylethenyl]pyridine is demonstrated through a 35 cm long fiber. The array of nanoscale optical antennas was first defined by electron-beam lithography on a silicon wafer. The array was subsequently stripped from the wafer and then transferred to the facet of a fiber. Lithographic definition of the antennas provides a method for producing two-dimensional arrays with well-defined geometry, which allows (i) the optical response of the probe to be tuned and (ii) the density of "hot spots" generating the enhanced Raman signal to be controlled. It is difficult to determine the Raman signal enhancement factor (EF) of most fiber optic Raman sensors featuring hot spots because the geometry of the Raman enhancing nanostructures is poorly defined. The ability to control the size and spacing of the antennas enables the EF of the transferred array to be estimated. EF values estimated after focusing a laser directly onto the transferred array ranged from 2.6 x 10(5) to 5.1 x 10(5). DA - 2009/3// PY - 2009/3// DO - 10.1021/nl803668u VL - 9 IS - 3 SP - 1132-1138 SN - 1530-6992 ER - TY - JOUR TI - A Technique to Transfer Metallic Nanoscale Patterns to Small and Non-Planar Surfaces AU - Smythe, Elizabeth J. AU - Dickey, Michael D. AU - Whitesides, George M. AU - Capasso, Federico T2 - ACS NANO AB - Conventional lithographic methods (e.g., electron-beam lithography, photolithography) are capable of producing high-resolution structures over large areas but are generally limited to large (>1 cm(2)) planar substrates. Incorporation of these features on unconventional substrates (i.e., small (<1 mm(2)) and/or non-planar substrates) would open possibilities for many applications, including remote fiber-based sensing, nanoscale optical lithography, three-dimensional fabrication, and integration of compact optical elements on fiber and semiconductor lasers. Here we introduce a simple method in which a thin thiol-ene film strips arbitrary nanoscale metallic features from one substrate and is then transferred, along with the attached features, to a substrate that would be difficult or impossible to pattern with conventional lithographic techniques. An oxygen plasma removes the sacrificial film, leaving behind the metallic features. The transfer of dense and sparse patterns of isolated and connected gold features ranging from 30 nm to 1 mum, to both an optical fiber facet and a silica microsphere, demonstrates the versatility of the method. A distinguishing feature of this technique is the use of a thin, sacrificial film to strip and transfer metallic nanopatterns and its ability to directly transfer metallic structures produced by conventional lithography. DA - 2009/1// PY - 2009/1// DO - 10.1021/nn800720r VL - 3 IS - 1 SP - 59-65 SN - 1936-086X KW - pattern transfer KW - soft lithography KW - metal nanoparticles KW - nanofabrication KW - nanopatterning ER - TY - JOUR TI - Species identification in a laminar premixed low-pressure flame of morpholine as a model substance for oxygenated nitrogen-containing fuels AU - Lucassen, Arnas AU - Osswald, Patrick AU - Struckmeier, Ulf AU - Kohse-Hoeinghaus, Katharina AU - Kasper, Tina AU - Hansen, Nils AU - Cool, Terrill A. AU - Westmoreland, Phillip R. T2 - PROCEEDINGS OF THE COMBUSTION INSTITUTE AB - The combustion chemistry of morpholine (1-oxa-4-aza-cyclohexane) was investigated under laminar, premixed low-pressure conditions. Morpholine, as a heterocyclic secondary amine with numerous industrial applications, was studied as a model fuel which simultaneously contains oxygen and nitrogen heteroatoms. Stable and radical intermediates and products of the combustion process in a slightly fuel-rich Φ = 1.3 (C/O = 0.41) flat premixed morpholine–oxygen–argon flame at 40 mbar (4 kPa) were identified. A detailed fuel destruction scheme is proposed based on combined measurements using two different in situ molecular beam mass spectrometry (MBMS) techniques. The results are discussed with special attention to hydrocarbon, oxygenated and N-containing compounds important in pollutant emission. DA - 2009/// PY - 2009/// DO - 10.1016/j.proci.2008.06.053 VL - 32 IS - Pt.1 SP - 1269-1276 SN - 1873-2704 KW - Morpholine KW - Molecular beam mass spectrometry KW - Fuel-N KW - Biofuel combustion ER - TY - JOUR TI - Recent contributions of flame-sampling molecular-beam mass spectrometry to a fundamental understanding of combustion chemistry AU - Hansen, Nils AU - Cool, Terrill A. AU - Westmoreland, Phillip R. AU - Kohse-Höinghaus, Katharina T2 - Progress in Energy and Combustion Science AB - Flame-sampling molecular-beam mass spectrometry of premixed, laminar, low-pressure flat flames has been demonstrated to be an efficient tool to study combustion chemistry. In this technique, flame gases are sampled through a small opening in a quartz probe, and after formation of a molecular beam, all flame species are separated using mass spectrometry. The present review focuses on critical aspects of the experimental approach including probe sampling effects, different ionization processes, and mass separation procedures. The capability for isomer-resolved flame species measurements, achievable by employing tunable vacuum-ultraviolet radiation for single-photon ionization, has greatly benefited flame-sampling molecular-beam mass spectrometry. This review also offers an overview of recent combustion chemistry studies of flames fueled by hydrocarbons and oxygenates. The identity of a variety of intermediates in hydrocarbon flames, including resonantly stabilized radicals and closed-shell intermediates, is described, thus establishing a more detailed understanding of the fundamentals of molecular-weight growth processes. Finally, molecular-beam mass-spectrometric studies of reaction paths in flames of alcohols, ethers, and esters, which have been performed to support the development and validation of kinetic models for bio-derived alternative fuels, are reviewed. DA - 2009/4// PY - 2009/4// DO - 10.1016/j.pecs.2008.10.001 VL - 35 IS - 2 SP - 168-191 J2 - Progress in Energy and Combustion Science LA - en OP - SN - 0360-1285 UR - http://dx.doi.org/10.1016/j.pecs.2008.10.001 DB - Crossref KW - Low-pressure flame KW - Mass spectrometry KW - Combustion chemistry KW - Aromatic ring formation KW - Oxygenated fuel ER - TY - JOUR TI - Professor Jack Benny Howard (1937–2008), Massachusetts Institute of Technology AU - Westmoreland, Phillip R. T2 - Combustion and Flame DA - 2009/3// PY - 2009/3// DO - 10.1016/j.combustflame.2008.12.006 VL - 156 IS - 3 SP - 547-548 J2 - Combustion and Flame LA - en OP - SN - 0010-2180 UR - http://dx.doi.org/10.1016/j.combustflame.2008.12.006 DB - Crossref ER - TY - JOUR TI - Kinetics of enol formation from reaction of OH with propene AU - Huynh, L. K. AU - Zhang, H. R. AU - Zhang, S. AU - Eddings, E. AU - Sarofim, A. AU - Law, M. E. AU - Westmoreland, Phillip AU - Truong, T. N T2 - Journal of Physical Chemistry. A, Molecules, Spectroscopy, Kinetics, Environment & General Theory AB - Kinetics of enol generation from propene has been predicted in an effort to understand the presence of enols in flames. A potential energy surface for reaction of OH with propene was computed by CCSD(T)/cc-pVDZ//B3LYP/cc-pVTZ calculations. Rate constants of different product channels and branching ratios were then calculated using the Master Equation formulation (J. Phys. Chem. A 2006, 110, 10528). Of the two enol products, ethenol is dominant over propenol, and its pathway is also the dominant pathway for the OH + propene addition reactions to form bimolecular products. In the temperature range considered, hydrogen abstraction dominated propene + OH consumption by a branching ratio of more than 90%. Calculated rate constants of enol formation were included in the Utah Surrogate Mechanism to model the enol profile in a cyclohexane premixed flame. The extended model shows consistency with experimental data and gives 5% contribution of ethenol formation from OH + propene reaction, the rest coming from ethene + OH. DA - 2009/// PY - 2009/// DO - 10.1021/jp808050j VL - 113 IS - 13 SP - 3177–3185 ER - TY - JOUR TI - Kinetics and Mechanism of Cellulose Pyrolysis AU - Lin, Yu-Chuan AU - Cho, Joungmo AU - Tompsett, Geoffrey A. AU - Westmoreland, Phillip R. AU - Huber, George W. T2 - The Journal of Physical Chemistry C AB - In this paper we report the kinetics and chemistry of cellulose pyrolysis using both a Pyroprobe reactor and a thermogravimetric analyzer mass spectrometer (TGA-MS). We have identified more than 90% of the products from cellulose pyrolysis in a Pyroprobe reactor with a liquid nitrogen trap. The first step in the cellulose pyrolysis is the depolymerization of solid cellulose to form levoglucosan (LGA; 6,8-dioxabicyclo[3.2.1]octane-2,3,4-triol). LGA can undergo dehydration and isomerization reactions to form other anhydrosugars including levoglucosenone (LGO; 6,8-dioxabicyclo[3.2.1]oct-2-en-4-one), 1,4:3,6-dianhydro-β-d-glucopyranose (DGP) and 1,6-anhydro-β-d-glucofuranose (AGF; 2,8-dioxabicyclo[3.2.1]octane-4,6,7-triol). The anhydrosugars can react further to form furans, such as furfural (furan-2-carbaldehyde) and hydroxymethylfurfural (HMF; 5-(hydroxymethyl)furan-2-carbaldehyde) by dehydration reactions or hydroxyacetone (1-hydroxypropan-2-one), glycolaldehyde (2-hydroxyacetaldehyde), and glyceraldehyde (2,3-dihydroxypropanal) by fragmentation and retroaldol condensation reactions. Carbon monoxide and carbon dioxide are formed from decarbonylation and decarboxylation reactions. Char is formed from polymerization of the pyrolysis products. The pyrolytic conversion of cellulose was fitted to two different reaction models. The first model (Model I) combined the first-order kinetic model with a thermal-lag model that assumed the temperature difference between the thermocouple and specimen in TGA to be directly proportional to the heating rate. The second model (Model II) combined the first-order kinetic model with an energy balance that took into account the heat transfer at the sample boundary including the heat flow by endothermic pyrolysis reaction. Both models were able to adequately fit the empirical data. The kinetic parameters obtained from both models were similar. Cellulose pyrolysis had an activation energy of 198 kJ mol−1. Model I is computationally easier, however Model II is physically more realistic. Importantly, our results indicate that the intrinsic kinetics for cellulose pyrolysis are not a function of heating rate. During the pyrolysis of cellulose a thermal temperature gradient between the cellulose and heater can occur due to the endothermic pyrolysis reaction. A faster heating rate can magnify the thermal-lag, which leads kinetic derivations to artificial outcomes. DA - 2009/10/22/ PY - 2009/10/22/ DO - 10.1021/jp906702p VL - 113 IS - 46 SP - 20097-20107 J2 - J. Phys. Chem. C LA - en OP - SN - 1932-7447 1932-7455 UR - http://dx.doi.org/10.1021/jp906702p DB - Crossref ER - TY - JOUR TI - Isomer-specific combustion chemistry in allene and propyne flames AU - Hansen, Nils AU - Miller, James A. AU - Westmoreland, Phillip R. AU - Kasper, Tina AU - Kohse-Höinghaus, Katharina AU - Wang, Juan AU - Cool, Terrill A. T2 - Combustion and Flame AB - A combined experimental and modeling study is performed to clarify the isomer-specific combustion chemistry in flames fueled by the C3H4 isomers allene and propyne. To this end, mole fraction profiles of several flame species in stoichiometric allene (propyne)/O2/Ar flames are analyzed by means of a chemical kinetic model. The premixed flames are stabilized on a flat-flame burner under a reduced pressure of 25 Torr (=33.3 mbar). Quantitative species profiles are determined by flame-sampling molecular-beam mass spectrometry, and the isomer-specific flame compositions are unraveled by employing photoionization with tunable vacuum-ultraviolet synchrotron radiation. The temperature profiles are measured by OH laser-induced fluorescence. Experimental and modeled mole fraction profiles of selected flame species are discussed with respect to the isomer-specific combustion chemistry in both flames. The emphasis is put on main reaction pathways of fuel consumption, of allene and propyne isomerization, and of isomer-specific formation of C6 aromatic species. The present model includes the latest theoretical rate coefficients for reactions on a C3H5 potential [J.A. Miller, J.P. Senosiain, S.J. Klippenstein, Y. Georgievskii, J. Phys. Chem. A 112 (2008) 9429–9438] and for the propargyl recombination reactions [Y. Georgievskii, S.J. Klippenstein, J.A. Miller, Phys. Chem. Chem. Phys. 9 (2007) 4259–4268]. Larger peak mole fractions of propargyl, allyl, and benzene are observed in the allene flame than in the propyne flame. In these flames virtually all of the benzene is formed by the propargyl recombination reaction. DA - 2009/11// PY - 2009/11// DO - 10.1016/j.combustflame.2009.07.014 VL - 156 IS - 11 SP - 2153-2164 J2 - Combustion and Flame LA - en OP - SN - 0010-2180 UR - http://dx.doi.org/10.1016/j.combustflame.2009.07.014 DB - Crossref KW - Low-pressure flame KW - Allene KW - Propyne KW - Flame modeling KW - Benzene formation ER - TY - JOUR TI - Controlling the Kinetics of Contact Electrification with Patterned Surfaces AU - Thomas, Samuel W., III AU - Vella, Sarah J. AU - Dickey, Michael D. AU - Kaufman, George K. AU - Whitesides, George M. T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - This communication describes a new approach for controlling static charging (contact electrification), and resulting electrical discharging, that occurs when two contacting materials separate. The prevention of contact electrification is an important problem; unwanted adhesion between oppositely charged materials, spark-initiated explosions, and damage to microelectronic circuitry are some of the deleterious effects of static charging. Current strategies for controlling contact electrification rely upon dissipating an accumulated charge by making contacting surfaces conductive and, therefore, can be difficult to implement with electrically insulating materials. Specifically, using our understanding of the ion-transfer mechanism of contact electrification, we patterned glass slides with negatively charging areas (clean glass) and positively charging areas (glass silanized with a cationic siloxane terminated with a quaternary ammonium group). The rate of charge separation due to a steel sphere rolling on the patterned glass surface correlated linearly with the percentage of the glass surface that was silanized; the rate of charge transfer was minimal when 50% of the glass surface area was silanized. Patterned surfaces also prevented electrical discharges between electrically conducting (bare steel) or insulating (acrylate-coated steel) spheres rolling on the glass, because the rate of charging was sufficiently slow to prevent electric fields greater than the dielectric strength of air to develop. This strategy for preventing static charging therefore does not require one of the two contacting surfaces to be electrically conductive. More generally, these results show that our enhanced understanding of the ion-transfer mechanism of contact electrification enables the rational design of chemically tailored surfaces for functional electrets. DA - 2009/7/1/ PY - 2009/7/1/ DO - 10.1021/ja902862b VL - 131 IS - 25 SP - 8746-+ SN - 0002-7863 ER - TY - JOUR TI - Composition of reaction intermediates for stoichiometric and fuel-rich dimethyl ether flames: flame-sampling mass spectrometry and modeling studies AU - Wang, Juan AU - Chaos, Marcos AU - Yang, Bin AU - Cool, Terrill A. AU - Dryer, Fred L. AU - Kasper, Tina AU - Hansen, Nils AU - Oßwald, Patrick AU - Kohse-Höinghaus, Katharina AU - Westmoreland, Phillip AU - al. T2 - Physical Chemistry Chemical Physics AB - Molecular-beam synchrotron photoionization mass spectrometry and electron-ionization mass spectrometry are used for measurements of species mole fraction profiles for low-pressure premixed dimethyl ether (DME) flames with equivalence ratios ranging from near-stoichiometric conditions (Φ = 0.93) to fuel-rich flames near the limits of flat-flame stability (Φ = 1.86). The results are compared with predictions of a recently modified kinetic model for DME combustion [Zhao et al., Int. J. Chem. Kinet., 2008, 40, 1–18] that has been extensively tested against laminar flame speed measurements, jet-stirred reactor experiments, pyrolysis and oxidation experiments in flow reactors, species measurements for burner-stabilized flames and ignition delay measurements in shock tubes. The present comprehensive measurements of the composition of reaction intermediates over a broad range of equivalence ratios considerably extends the range of the previous experiments used for validation of this model and allows for an accurate determination of contributions of individual reactions to the formation or destruction of any given flame species. The excellent agreement between measurements and predictions found for all major and most intermediate species over the entire range of equivalence ratios provides a uniquely sensitive test of details of the kinetic model. The dependence on equivalence ratio of the characteristic reaction paths in DME flames is examined within the framework of reaction path analyses. DA - 2009/// PY - 2009/// DO - 10.1039/b815988b VL - 11 IS - 9 SP - 1328 J2 - Phys. Chem. Chem. Phys. LA - en OP - SN - 1463-9076 1463-9084 UR - http://dx.doi.org/10.1039/B815988B DB - Crossref ER - TY - JOUR TI - Combustion chemistry of the propanol isomers — investigated by electron ionization and VUV-photoionization molecular-beam mass spectrometry AU - Kasper, T. AU - Oßwald, P. AU - Struckmeier, U. AU - Kohse-Höinghaus, K. AU - Taatjes, C.A. AU - Wang, J. AU - Cool, T.A. AU - Law, M.E. AU - Morel, A. AU - Westmoreland, Phillip AU - al. T2 - Combustion and Flame AB - The combustion of 1-propanol and 2-propanol was studied in low-pressure, premixed flat flames using two independent molecular-beam mass spectrometry (MBMS) techniques. For each alcohol, a set of three flames with different stoichiometries was measured, providing an extensive data base with in total twelve conditions. Profiles of stable and intermediate species, including several radicals, were measured as a function of height above the burner. The major-species mole fraction profiles in the 1-propanol flames and the 2-propanol flames of corresponding stoichiometry are nearly identical, and only small quantitative variations in the intermediate species pool could be detected. Differences between flames of the isomeric fuels are most pronounced for oxygenated intermediates that can be formed directly from the fuel during the oxidation process. The analysis of the species pool in the set of flames was greatly facilitated by using two complementary MBMS techniques. One apparatus employs electron ionization (EI) and the other uses VUV light for single-photon ionization (VUV-PI). The photoionization technique offers a much higher energy resolution than electron ionization and as a consequence, near-threshold photoionization-efficiency measurements provide selective detection of individual isomers. The EI data are recorded with a higher mass resolution than the PI spectra, thus enabling separation of mass overlaps of species with similar ionization energies that may be difficult to distinguish in the photoionization data. The quantitative agreement between the EI- and PI-datasets is good. In addition, the information in the EI- and PI-datasets is complementary, aiding in the assessment of the quality of individual burner profiles. The species profiles are supplemented by flame temperature profiles. The considerable experimental efforts to unambiguously assign intermediate species and to provide reliable quantitative concentrations are thought to be valuable for improving the mechanisms for higher alcohol combustion. DA - 2009/6// PY - 2009/6// DO - 10.1016/j.combustflame.2009.01.023 VL - 156 IS - 6 SP - 1181-1201 J2 - Combustion and Flame LA - en OP - SN - 0010-2180 UR - http://dx.doi.org/10.1016/j.combustflame.2009.01.023 DB - Crossref KW - Propanol KW - Laminar flame KW - Molecular-beam mass spectrometry ER - TY - JOUR TI - Benzene formation in premixed fuel-rich 1,3-butadiene flames AU - Hansen, Nils AU - Miller, James A. AU - Kasper, Tina AU - Kohse-Hoeinghaus, Katharina AU - Westmoreland, Phillip R. AU - Wang, Juan AU - Cool, Terrill A. T2 - PROCEEDINGS OF THE COMBUSTION INSTITUTE AB - Detailed kinetic modeling and flame-sampling molecular-beam time-of-flight mass spectrometry are combined to unravel important pathways leading to the formation of benzene in a premixed laminar low-pressure 1,3-butadiene flame. The chemical kinetic model developed is compared with new experimental results obtained for a rich (ϕ = 1.8) 1,3-butadiene/O2/Ar flame at 30 Torr and with flame data for a similar but richer (ϕ = 2.4) flame reported by Cole et al. [Combust. Flame 56 (1) (1984) 51–70]. The newer experiment utilizes photoionization by tunable vacuum-ultraviolet synchrotron radiation, which allows for the identification and separation of combustion species by their characteristic ionization energies. Predictions of mole fractions as a function of distance from the burner of major combustion intermediates and products are in overall satisfactory agreement with experimentally observed profiles. The accurate predictions of the propargyl radical and benzene mole fractions permit an assessment of potential benzene formation pathways. The results indicate that C6H6 is formed mainly by the C3H3 + C3H3 and i-C4H5 + C2H2 reactions, which are roughly of equal importance. Smaller contributions arise from C3H3 + C3H5. However, given the experimental and modeling uncertainties, other pathways cannot be ruled out. DA - 2009/// PY - 2009/// DO - 10.1016/j.proci.2008.06.050 VL - 32 IS - Pt.1 SP - 623-630 SN - 1873-2704 KW - 1,3-Butadiene KW - Laminar flames KW - Modeling KW - Mass spectrometry KW - Benzene formation ER - TY - JOUR TI - A detailed chemical kinetic reaction mechanism for oxidation of four small alkyl esters in laminar premixed flames AU - Westbrook, C. K. AU - Pitz, W. J. AU - Westmoreland, P. R. AU - Dryer, F. L. AU - Chaos, M. AU - Osswald, P. AU - Kohse-Hoeinghaus, K. AU - Cool, T. A. AU - Wang, J. AU - Yang, B. AU - Hansen, N. AU - Kasper, T. T2 - PROCEEDINGS OF THE COMBUSTION INSTITUTE AB - A detailed chemical kinetic reaction mechanism has been developed for a group of four small alkyl ester fuels, consisting of methyl formate, methyl acetate, ethyl formate, and ethyl acetate. This mechanism is validated by comparisons between computed results and recently measured intermediate species mole fractions in fuel-rich, low-pressure, premixed laminar flames. The model development employs a principle of similarity of functional groups in constraining the H atom abstraction and unimolecular decomposition reactions for each of these fuels. As a result, the reaction mechanism and formalism for mechanism development are suitable for extension to larger oxygenated hydrocarbon fuels, together with an improved kinetic understanding of the structure and chemical kinetics of alkyl ester fuels that can be extended to biodiesel fuels. Variations in concentrations of intermediate species levels in these flames are traced to differences in the molecular structure of the fuel molecules. DA - 2009/// PY - 2009/// DO - 10.1016/j.proci.2008.06.106 VL - 32 IS - Pt.1 SP - 221-228 SN - 1540-7489 KW - Reaction mechanisms KW - Laminar flames KW - Oxygenates KW - Kinetic modeling ER - TY - JOUR TI - Non-Aqueous Electrolytes for Lithium Batteries AU - Jow, T. R. AU - Henderson, W. AU - Lucht, B. AU - Ue, M T2 - Electrochemical Society DA - 2009/// PY - 2009/// VL - 16 IS - 35 SP - 230 ER - TY - JOUR TI - Molecular aspects of cardiac differentiation in embryonic stem cells AU - Sarkar, P. AU - Rao, B. M. T2 - Critical Reviews in Biomedical Engineering AB - Embryonic stem cells (ESCs) are culture-adapted pluripotent cells derived from the inner cell mass of the blastocyst-stage embryo. ESCs provide unique opportunities to study the molecular basis of the process of differentiation that gives rise to all the somatic cell types of the body, including cells of the cardiac lineages. Many protocols have been established to obtain cells of the cardiac lineage from ESCs in vitro. More recently, a clearer picture of the regulatory networks governing cardiac differentiation has begun to emerge. Herein, we summarize the current methods to obtain cells of the cardiac lineages from ESCs and present a review of the signaling pathways, transcription factors, and target genes involved in cardiac differentiation. DA - 2009/// PY - 2009/// DO - 10.1615/critrevbiomedeng.v37.i4-5.10 VL - 37 IS - 4-5 SP - 283-320 ER - TY - JOUR TI - Exploring the influence of ionic liquid ion structure on cellulose solvation AU - Brown, K. AU - Geng, X. AU - McDanel, W. AU - Henderson, W. A. T2 - ECS Transactions DA - 2009/// PY - 2009/// VL - 16 IS - 49 SP - 107-110 ER - TY - JOUR TI - Design Principles for Riboswitch Function AU - Beisel, Chase L. AU - Smolke, Christina D. T2 - PLOS COMPUTATIONAL BIOLOGY AB - Scientific and technological advances that enable the tuning of integrated regulatory components to match network and system requirements are critical to reliably control the function of biological systems. RNA provides a promising building block for the construction of tunable regulatory components based on its rich regulatory capacity and our current understanding of the sequence-function relationship. One prominent example of RNA-based regulatory components is riboswitches, genetic elements that mediate ligand control of gene expression through diverse regulatory mechanisms. While characterization of natural and synthetic riboswitches has revealed that riboswitch function can be modulated through sequence alteration, no quantitative frameworks exist to investigate or guide riboswitch tuning. Here, we combined mathematical modeling and experimental approaches to investigate the relationship between riboswitch function and performance. Model results demonstrated that the competition between reversible and irreversible rate constants dictates performance for different regulatory mechanisms. We also found that practical system restrictions, such as an upper limit on ligand concentration, can significantly alter the requirements for riboswitch performance, necessitating alternative tuning strategies. Previous experimental data for natural and synthetic riboswitches as well as experiments conducted in this work support model predictions. From our results, we developed a set of general design principles for synthetic riboswitches. Our results also provide a foundation from which to investigate how natural riboswitches are tuned to meet systems-level regulatory demands. DA - 2009/4// PY - 2009/4// DO - 10.1371/journal.pcbi.1000363 VL - 5 IS - 4 SP - SN - 1553-7358 ER - TY - JOUR TI - Conformational analysis of gossypol and its derivatives by molecular mechanics AU - Bayer TS, Hoff KG AU - Beisel CL, Lee JJ AU - CD, Smolke T2 - Journal of Molecular Structure [including Theochem] DA - 2009/// PY - 2009/// VL - 3 IS - 1 ER - TY - JOUR TI - Quantitative imaging of the Dorsal nuclear gradient reveals limitations to threshold-dependent patterning in Drosophila AU - Liberman, Louisa M. AU - Reeves, Gregory T. AU - Stathopoulos, Angelike T2 - Proceedings of the National Academy of Sciences AB - The NF-κB-related transcription factor, Dorsal, forms a nuclear concentration gradient in the early Drosophila embryo, patterning the dorsal-ventral (DV) axis to specify mesoderm, neurogenic ectoderm, and dorsal ectoderm cell fates. The concentration of nuclear Dorsal is thought to determine these patterning events; however, the levels of nuclear Dorsal have not been quantified previously. Furthermore, existing models of Dorsal-dependent germ layer specification and patterning consider steady-state levels of Dorsal relative to target gene expression patterns, yet both Dorsal gradient formation and gene expression are dynamic. We devised a quantitative imaging method to measure the Dorsal nuclear gradient while simultaneously examining Dorsal target gene expression along the DV axis. Unlike observations from other insects such as Tribolium , we find the Dorsal gradient maintains a constant bell-shaped distribution during embryogenesis. We also find that some classical Dorsal target genes are located outside the region of graded Dorsal nuclear localization, raising the question of whether these genes are direct Dorsal targets. Additionally, we show that Dorsal levels change in time during embryogenesis such that a steady state is not reached. These results suggest that the multiple gene expression outputs observed along the DV axis do not simply reflect a steady-state Dorsal nuclear gradient. Instead, we propose that the Dorsal gradient supplies positional information throughout nuclear cycles 10-14, providing additional evidence for the idea that compensatory combinatorial interactions between Dorsal and other factors effect differential gene expression along the DV axis. DA - 2009/12/16/ PY - 2009/12/16/ DO - 10.1073/pnas.0906227106 VL - 106 IS - 52 SP - 22317–22322 SN - 0027-8424 1091-6490 UR - http://dx.doi.org/10.1073/pnas.0906227106 KW - development KW - gene expression ER - TY - JOUR TI - Graded dorsal and differential gene regulation in the Drosophila embryo AU - Reeves, G. T. AU - Stathopoulos, A. T2 - Cold Spring Harbor Perspectives in Biology DA - 2009/// PY - 2009/// VL - 1 IS - 4 SP - 566-577 ER - TY - JOUR TI - Biological systems from an engineer's point of view AU - Reeves, G. T. AU - Fraser, S. E. T2 - PLoS Biology DA - 2009/// PY - 2009/// VL - 7 IS - 1 SP - 0032-0035 ER - TY - BOOK TI - Chemical reactions and chemical reactors AU - Roberts, George W. DA - 2009/// PY - 2009/// PB - Hoboken, NJ: John Wiley & Sons ER - TY - JOUR TI - Top-down particle fabrication: control of size and shape for diagnostic imaging and drug delivery AU - Canelas, Dorian A. AU - Herlihy, Kevin P. AU - DeSimone, Joseph M. T2 - WILEY INTERDISCIPLINARY REVIEWS-NANOMEDICINE AND NANOBIOTECHNOLOGY AB - Abstract This review discusses rational design of particles for use as therapeutic vectors and diagnostic imaging agent carriers. The emerging importance of both particle size and shape is considered, and the adaptation and modification of soft lithography methods to produce nanoparticles are highlighted. To this end, studies utilizing particles made via a process called Particle Replication In Non‐wetting Templates are discussed. In addition, insights gained into therapeutic cargo and imaging agent delivery from related types of polymer‐based carriers are considered. Copyright © 2009 John Wiley & Sons, Inc. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies DA - 2009/// PY - 2009/// DO - 10.1002/wnan.40 VL - 1 IS - 4 SP - 391-404 SN - 1939-0041 ER - TY - CONF TI - BioDEAL: community generation of biological annotations AU - Breimyer, P. AU - Green, N. AU - Kumar, V. AU - Samatova, N. F. C2 - 2009/// C3 - BMC Medical Informatics and Decision Making DA - 2009/// VL - 9 ER - TY - CHAP TI - Tools to probe nanoscale surface phenomena in cellulose thin films: Applications in the area of adsorption and friction AU - Song, S. AU - Li, Y. AU - Hinestroza, J. P. AU - Rojas, O. J. T2 - The nanoscience and technology of renewable biomaterials A2 - Lucia, L. A. A2 - Rojas, O. J. AB - This chapter contains sections titled: Introduction Polyampholytes Applications in Fiber Modification Cellulose Thin Films Friction Phenomena in Cellulose Systems Lubrication Boundary Layer Lubrication Techniques to Study Adsorption and Friction Phenomena Surface Plasmon Resonance (SPR) Quartz Crystal Microbalance with Dissipation (QCM) Application of SPR and QCM to Probe Adsorbed Films Lateral Force Microscopy Summary Acknowledgements References PY - 2009/// DO - 10.1002/9781444307474.ch4 PB - Chichester, West Sussex, U.K.: Wiley-Blackwell SN - 9781405167864 ER - TY - JOUR TI - Reinforcing Poly(epsilon-caprolactone) Nanofibers with Cellulose Nanocrystals AU - Zoppe, Justin O. AU - Peresin, Maria S. AU - Habibi, Youssef AU - Venditti, Richard A. AU - Rojas, Orlando J. T2 - ACS APPLIED MATERIALS & INTERFACES AB - We studied the use of cellulose nanocrystals (CNXs) obtained after acid hydrolysis of ramie cellulose fibers to reinforce poly(ε-caprolactone) (PCL) nanofibers. Chemical grafting with low-molecular-weight PCL diol onto the CNXs was carried out in an attempt to improve the interfacial adhesion with the fiber matrix. Grafting was confirmed via infrared spectroscopy and thermogravimetric analyses. The polymer matrix consisted of electrospun nanofibers that were collected as nonwoven webs. The morphology as well as thermal and mechanical properties of filled and unfilled nanofibers were elucidated by scanning electron microscopy, differential scanning calorimetry, and dynamic mechanical analysis, respectively. The addition of CNXs into PCL produced minimal changes in the thermal behavior of the electrospun fibers. However, a significant improvement in the mechanical properties of the nanofibers after reinforcement with unmodified CNXs was confirmed. Fiber webs from PCL reinforced with 2.5% unmodified CNXs showed ca. 1.5-fold increase in Young’s modulus and the ultimate strength compared to PCL webs. Compared to the case of grafted nanocrystals, the unmodified ones imparted better morphological homogeneity to the nanofibrillar structure. The grafted nanocrystals had a negative effect on the morphology of nonwoven webs in which individual nanofibers became annealed during the electrospinning process and, therefore, could not be compared to neat PCL nonwoven webs. A rationalization for the different effects of grafted and unmodified CNXs in reinforcing PCL nanofibers is provided. DA - 2009/9// PY - 2009/9// DO - 10.1021/am9003705 VL - 1 IS - 9 SP - 1996-2004 SN - 1944-8252 KW - cellulose nanocrystals KW - nanocrystalline cellulose KW - cellulose whiskers KW - surface grafting KW - electrospinning KW - fiber reinforcement KW - nanofibers KW - nanocomposites KW - nanoparticles KW - poly(epsilon-caprolactone) ER - TY - JOUR TI - Polyampholytes: Their use in papermaking and their solution and adsorption behaviors AU - Silva, D. J AU - Rojas, O. J. AU - Hubbe, M. A AU - Park, S. W. AU - Yamaguchi, T. AU - Song, J. T2 - O Papel DA - 2009/// PY - 2009/// VL - 70 IS - 9 SP - 40-50 ER - TY - CONF TI - Investigation of adsorption behaviors of polyampholytes AU - Yamaguchi, T AU - Hubbe, M. A. AU - Rojas, O. J. C2 - 2009/// C3 - Kami Parupu Kenkyu? Happyo?kai: Ko?en yo?shishu? DA - 2009/// VL - 76 SP - 6-9 ER - TY - CHAP TI - Interfacial properties of sugar-based surfactants AU - Rojas, O. J. AU - Lucia, L. A. AU - Habibi, Y. AU - Stubenrauch, C. T2 - Bio-based surfactants and detergents: Synthesis, properties, and applications PY - 2009/// PB - Urbana, IL: AOCS Press SN - 9781893997677 ER - TY - CHAP TI - Evaluation of adsorbed polyampholyte layers by using quartz crystal microbalance AU - Silva, D. J. AU - Rojas, O. J. AU - Park, S. W. AU - Hubbe, M. A. T2 - 10th International Symposium on Process Systems Engineering -- (Computer-aided chemical engineering, 7) A2 - R. M. De Brito Alves, C. A. Oller do Nascimento A2 - Biscaia, E. C. PY - 2009/// PB - Amsterdam: Elsevier ER - TY - JOUR TI - Role of Gas Doping Sequence in Surface Reactions and Dopant Incorporation during Atomic Layer Deposition of Al-Doped ZnO AU - Na, Jeong-Seok AU - Peng, Qing AU - Scarel, Giovanna AU - Parsons, Gregory N. T2 - CHEMISTRY OF MATERIALS AB - Aluminum incorporation into ZnO films during atomic layer deposition (ALD) is investigated using in situ quartz crystal microbalance and electrical conductance analysis. Chemical interactions between Zn and Al species during ZnO:Al ALD depend on the order of metal precursor exposure. Exposing the growing ZnO surface to trimethyl aluminum (TMA) impedes the subsequent ∼4 monolayers of ZnO growth. However, the extent of interaction can be reduced by performing the TMA exposure immediately following a diethyl zinc step, without an intermediate water exposure step, consistent with increased surface mixing of Zn and Al species. Infrared spectroscopy analysis of heavily aluminum doped ZnO shows features consistent with the presence of amorphous ZnAl2O4 bonding units. For more lightly doped films, mass spectroscopic depth profiling confirms nonuniform aluminum distribution, even after annealing at 500 °C. Film conductance measured during growth shows complex trends that are highly repeatable over multiple doping cycles, and values for in situ conductance are consistent with postdeposition current vs. voltage characterization. Results are understood in terms of relative bonding energies of surface species, and expected reaction pathways for dopant atom incorporation. DA - 2009/12/8/ PY - 2009/12/8/ DO - 10.1021/cm901404p VL - 21 IS - 23 SP - 5585-5593 SN - 1520-5002 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000272084500009&KeyUID=WOS:000272084500009 ER - TY - JOUR TI - Reversibly Deformable and Mechanically Tunable Fluidic Antennas AU - So, Ju-Hee AU - Thelen, Jacob AU - Qusba, Amit AU - Hayes, Gerard J. AU - Lazzi, Gianluca AU - Dickey, Michael D. T2 - ADVANCED FUNCTIONAL MATERIALS AB - Abstract This paper describes the fabrication and characterization of fluidic dipole antennas that are reconfigurable, reversibly deformable, and mechanically tunable. The antennas consist of a fluid metal alloy injected into microfluidic channels comprising a silicone elastomer. By employing soft lithographic, rapid prototyping methods, the fluidic antennas are easier to fabricate than conventional copper antennas. The fluidic dipole radiates with ≈90% efficiency over a broad frequency range (1910–1990 MHz), which is equivalent to the expected efficiency for a similar dipole with solid metallic elements such as copper. The metal, eutectic gallium indium (EGaIn), is a low‐viscosity liquid at room temperature and possesses a thin oxide skin that provides mechanical stability to the fluid within the elastomeric channels. Because the conductive element of the antenna is a fluid, the mechanical properties and shape of the antenna are defined by the elastomeric channels, which are composed of polydimethylsiloxane (PDMS). The antennas can withstand mechanical deformation (stretching, bending, rolling, and twisting) and return to their original state after removal of an applied stress. The ability of the fluid metal to flow during deformation of the PDMS ensures electrical continuity. The shape and thus, the function of the antenna, is reconfigurable. The resonant frequency can be tuned mechanically by elongating the antenna via stretching without any hysteresis during strain relaxation, and the measured resonant frequency as a function of strain shows excellent agreement (±0.1–0.3% error) with that predicted by theoretical finite element modeling. The antennas are therefore sensors of strain. The fluid metal also facilitates self‐healing in response to sharp cuts through the antenna. DA - 2009/11/23/ PY - 2009/11/23/ DO - 10.1002/adfm.200900604 VL - 19 IS - 22 SP - 3632-3637 SN - 1616-3028 ER - TY - JOUR TI - Design of copolymers with tunable randomness using discontinuous molecular dynamics simulation AU - Strickland, L. A. AU - Hall, Carol AU - Genzer, Jan T2 - Macromolecules AB - We present the results of discontinuous molecular dynamics simulations of a “coloring” reaction performed on A-type homopolymers having length ranging from 100 to 300 units in implicit solvents. The transformation of selected A-type monomers to B-type units along the macromolecule produces A1−x-co-Bx random copolymers, where x is the mole fraction of B (= degree of “coloring”). We demonstrate that for a fixed A−B interaction strength the comonomer distribution of A and B units in A1−x-co-Bx can be tuned to range from “purely random” to “random−blocky” by adjusting both the degree of “coloring” and the solubility of the A and B segments with respect to the implicit solvent. In general, increasing the solubility of the A-type homopolymer or the degree of coloring results in a decrease in blockiness in the comonomer distribution. In addition, decreasing the solubility of the B species in the implicit solvent increases the tendency of the A1−xBx copolymer to form “random−blocky” sequences. DA - 2009/// PY - 2009/// DO - 10.1021/ma901605v VL - 42 IS - 22 SP - 9063–9071 ER - TY - JOUR TI - Carbohydrate Utilization Patterns for the Extremely Thermophilic Bacterium Caldicellulosiruptor saccharolyticus Reveal Broad Growth Substrate Preferences AU - VanFossen, Amy L. AU - Verhaart, Marcel R. A. AU - Kengen, Serve M. W. AU - Kelly, Robert M. T2 - APPLIED AND ENVIRONMENTAL MICROBIOLOGY AB - Coutilization of hexoses and pentoses derived from lignocellulose is an attractive trait in microorganisms considered for consolidated biomass processing to biofuels. This issue was examined for the H(2)-producing, extremely thermophilic bacterium Caldicellulosiruptor saccharolyticus growing on individual monosaccharides (arabinose, fructose, galactose, glucose, mannose, and xylose), mixtures of these sugars, as well as on xylan and xylogluco-oligosacchrides. C. saccharolyticus grew at approximately the same rate (t(d), approximately 95 min) and to the same final cell density (1 x 10(8) to 3 x 10(8) cells/ml) on all sugars and sugar mixtures tested. In the monosaccharide mixture, although simultaneous consumption of all monosaccharides was observed, not all were utilized to the same extent (fructose > xylose/arabinose > mannose/glucose/galactose). Transcriptome contrasts for monosaccharide growth revealed minimal changes in some cases (e.g., 32 open reading frames [ORFs] changed >/=2-fold for glucose versus galactose), while substantial changes occurred for cases involving mannose (e.g., 353 ORFs changed >/=2-fold for glucose versus mannose). Evidence for catabolite repression was not noted for either growth on multisugar mixtures or the corresponding transcriptomes. Based on the whole-genome transcriptional response analysis and comparative genomics, carbohydrate specificities for transport systems could be proposed for most of the 24 putative carbohydrate ATP-binding cassette transporters and single phosphotransferase system identified in C. saccharolyticus. Although most transporter genes responded to individual monosaccharides and polysaccharides, the genes Csac_0692 to Csac_0694 were upregulated only in the monosaccharide mixture. The results presented here affirm the broad growth substrate preferences of C. saccharolyticus on carbohydrates representative of lignocellulosic biomass and suggest that this bacterium holds promise for biofuel applications. DA - 2009/12/15/ PY - 2009/12/15/ DO - 10.1128/AEM.01959-09 VL - 75 IS - 24 SP - 7718-7724 SN - 1098-5336 ER - TY - JOUR TI - Plant Cell Calcium-Rich Environment Enhances Thermostability of Recombinantly Produced alpha-Amylase From the Hyperthermophilic Bacterium Thermotoga maritime AU - Santa-Maria, Monica C. AU - Chou, Chung-Jung AU - Yencho, G. Craig AU - Haigler, Candace H. AU - Thompson, William F. AU - Kelly, Robert M. AU - Sosinski, Bryon T2 - BIOTECHNOLOGY AND BIOENGINEERING AB - Abstract In the industrial processing of starch for sugar syrup and ethanol production, a liquefaction step is involved where starch is initially solubilized at high temperature and partially hydrolyzed with a thermostable and thermoactive α‐amylase. Most amylases require calcium as a cofactor for their activity and stability, therefore calcium, along with the thermostable enzyme, are typically added to the starch mixture during enzymatic liquefaction, thereby increasing process costs. An attractive alternative would be to produce the enzyme directly in the tissue to be treated. In a proof of concept study, tobacco cell cultures were used as model system to test in planta production of a hyperthermophilic α‐amylase from Thermotoga maritima . While comparable biochemical properties to recombinant production in Escherichia coli were observed, thermostability of the plant‐produced α‐amylase benefited significantly from high intrinsic calcium levels in the tobacco cells. The plant‐made enzyme retained 85% of its initial activity after 3 h incubation at 100°C, whereas the E. coli ‐produced enzyme was completely inactivated after 30 min under the same conditions. The addition of Ca 2+ or plant cell extracts from tobacco and sweetpotato to the E. coli ‐produced enzyme resulted in a similar stabilization, demonstrating the importance of a calcium‐rich environment for thermostability, as well as the advantage of producing this enzyme directly in plant cells where calcium is readily available. Biotechnol. Bioeng. 2009; 104: 947–956. © 2009 Wiley Periodicals, Inc. DA - 2009/12/1/ PY - 2009/12/1/ DO - 10.1002/bit.22468 VL - 104 IS - 5 SP - 947-956 SN - 1097-0290 KW - hyperthermophilic enzymes KW - starch processing KW - transgenic plants KW - tobacco NT1 Cell cultures KW - biofuel ER - TY - JOUR TI - Influence of Peptide Ligand Surface Density and Ethylene Oxide Spacer Arm on the Capture of Porcine Parvovirus AU - Heldt, Caryn L. AU - Gurgel, Patrick V. AU - Jaykus, Lee-Ann AU - Carbonell, Ruben G. T2 - BIOTECHNOLOGY PROGRESS AB - Abstract In previous work, we identified two trimeric peptide ligands (designated WRW and KYY), which bound specifically to porcine parvovirus (PPV) and demonstrated their ability to capture and remove the virus from solutions containing 7.5% human blood plasma. This article examines the influences of peptide density and the presence of an ethylene oxide spacer arm on the efficiency of virus capture using these two ligands. The WRW peptide bound the most virus from plasma solutions at the lowest peptide density tested (0.008 mmol/g dry resin), and binding was enhanced by the presence of the spacer arm. On the other hand, the KYY peptide bound the most viruses at the same low peptide density, but it performed better in the absence of the spacer arm. Of the two, the binding efficiency of the WRW peptide was more sensitive to peptide density and spacer arm presence. These results indicate that low peptide densities enhance binding selectivity, facilitating specific peptide‐virus binding even in the presence of plasma proteins which can theoretically bind nonspecifically. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 DA - 2009/// PY - 2009/// DO - 10.1002/btpr.236 VL - 25 IS - 5 SP - 1411-1418 SN - 1520-6033 KW - viral clearance KW - affinity resins KW - parvovirus KW - affinity ligands KW - combinatorial libraries ER - TY - JOUR TI - Determination of polystyrene-carbon dioxide-decahydronaphthalene solution properties by high pressure dynamic light scattering AU - Dong, Laura Beth AU - Carbonell, Ruben G. AU - Roberts, George W. AU - Kiserow, Douglas J. T2 - POLYMER AB - The diffusion coefficients of polystyrene (PS) in decahydronaphthalene (DHN) and in solutions of carbon dioxide (CO2) and DHN were measured for dilute PS solutions over a range of temperatures and CO2–DHN ratios using high pressure dynamic light scattering. Infinite dilution diffusion coefficients (D0) of PS and dynamic second virial coefficients (kD) were determined for essentially monodisperse 308 kDa PS. At a system pressure of 20.7 MPa, PS diffusion coefficients increased by a factor of 2.5, and the activation energy of diffusion decreased by approximately 16% when DHN was “expanded” with 44 mol% CO2. However, the hydrodynamic radius of PS at a given temperature was not particularly sensitive to the CO2 concentration. Solvent quality, as measured by kD, decreased at higher CO2 concentrations. The addition of CO2 to polymer solutions may offer a way to “tune” the properties of the solution to facilitate the heterogeneous catalytic hydrogenation of polymers. DA - 2009/11/16/ PY - 2009/11/16/ DO - 10.1016/j.polymer.2009.09.069 VL - 50 IS - 24 SP - 5728-5732 SN - 1873-2291 KW - Polystyrene KW - Diffusion KW - Dynamic light scattering ER - TY - JOUR TI - In-Situ Encapsulation of Nickel Particles in Electrospun Carbon Nanofibers and the Resultant Electrochemical Performance AU - Ji, Liwen AU - Lin, Zhan AU - Medford, Andrew J. AU - Zhang, Xiangwu T2 - CHEMISTRY-A EUROPEAN JOURNAL AB - Loaded nanofibers: Ni nanoparticle-loaded carbon nanofibers, which exhibit high reversible lithium-storage capacity, excellent cycling performance, and remarkably enhanced rate capability, are fabricated by using the electrospinning technique and the subsequent stabilization and carbonization processes (see figure). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article. DA - 2009/// PY - 2009/// DO - 10.1002/chem.200902012 VL - 15 IS - 41 SP - 10718-10722 SN - 1521-3765 UR - https://publons.com/publon/6540091/ KW - carbon nanofibers KW - electrospinning KW - nanoparticles KW - nickel KW - rechargeable lithium-ion batteries ER - TY - JOUR TI - In Situ Monitoring of Cellulase Activity by Microgravimetry with a Quartz Crystal Microbalance AU - Hu, Gang AU - Heitmann, John A., Jr. AU - Rojas, Orlando J. T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - Quartz crystal microgravimetry (QCM) was used to investigate the interactions between cellulase enzymes and model cellulose substrates. The substrates consisted of thin films of cellulose that were spin-coated onto polyvinylamine (PVAm) precoated quartz crystal sensors carrying conductive gold surfaces. In QCM the quartz crystals are piezoelectrically driven and the frequency and dissipation shifts allow monitoring of substrate hydrolysis at various temperatures and enzyme concentrations in situ and in real time. The changes in frequency of cellulose-coated quartz resonators during their incubation in cellulase solutions were related to contributions from the liquid phase properties, the adsorptions of cellulase enzymes, and the hydrolysis of the substrate. Cellulase adsorption was found to be nonspecific and irreversible on gold-, PVAm-, and cellulose-coated quartz crystal sensors. The contribution to frequency shifts due to the bulk fluid properties of the cellulase solutions (at concentrations lower than 0.5 mg/mL) was minimal compared to the frequency shifts produced by cellulase binding. The maximum frequency decreases were fitted to a Langmuir model. The adsorption constant and the maximum adsorption were estimated by the fitting parameters of this model. The hydrolysis process was modeled by using a dose-response model that was then used to estimate the maximum hydrolysis rate, to compare the relative effects of temperature on adsorption and hydrolysis rate, and to obtain the apparent activation energy of cellulose hydrolysis. The hydrolysis rate increased with incubation temperature while apparent adsorption decreased. The apparent activation energy for the hydrolysis of the cellulose films employed was calculated to be 37 kJ/mol. DA - 2009/11/5/ PY - 2009/11/5/ DO - 10.1021/jp907155v VL - 113 IS - 44 SP - 14761-14768 SN - 1520-6106 ER - TY - JOUR TI - Sorption strain as a packing phenomenon AU - Guenther, Gerrit AU - Schoen, Martin T2 - PHYSICAL CHEMISTRY CHEMICAL PHYSICS AB - We employ Monte Carlo simulations in a semi-grand canonical ensemble to analyze the relation between sorption strains and the thermodynamic state of a confined fluid composed of “simple” fluid molecules that possess only translational degrees of freedom. Fluid molecules are confined to a slit-pore whose walls are composed of individual atoms distributed across the plane of each substrate according to the (100) structure of the face-centered cubic lattice. The substrates can be deformed to a certain extent on account of their own thermal energy and due to the interaction with the fluid molecules. We determine the phase diagram in both the bulk and in confinement for both rigid and deformable solid substrates. By using finite-size scaling concepts the location of the critical point is determined accurately. Our results indicate for the first time that the previously observed variation of sorption strains with the amount of adsorbed fluid material [G. Günther et al., Phys. Rev. Lett., 2008, 101, 086104] is caused by packing effects (i.e. stratification of the confined fluid) but is largely independent of the precise nature of the thermodynamic state considered. DA - 2009/// PY - 2009/// DO - 10.1039/b903514a VL - 11 IS - 40 SP - 9082-9092 SN - 1463-9084 ER - TY - JOUR TI - Porous carbon nanofibers from electrospun polyacrylonitrile/SiO2 composites as an energy storage material AU - Ji, Liwen AU - Lin, Zhan AU - Medford, Andrew J. AU - Zhang, Xiangwu T2 - CARBON AB - Porous carbon nanofibers with large accessible surface areas and well-developed pore structures were prepared by electrospinning and subsequent thermal and chemical treatments. They were directly used as anodes in lithium-ion batteries without adding any non-active materials such as polymer binders or electronic conductors. The electrochemical performance results show that porous carbon nanofiber anodes have improved lithium-ion storage ability, enhanced charge–discharge kinetics, and better cyclic stability compared with non-porous counterparts. The unique structures and properties of these materials make them excellent candidates for use as anodes in high-performance rechargeable lithium-ion batteries. DA - 2009/11// PY - 2009/11// DO - 10.1016/j.carbon.2009.08.002 VL - 47 IS - 14 SP - 3346-3354 SN - 1873-3891 UR - https://publons.com/publon/6540062/ ER - TY - JOUR TI - Modification of PET surfaces with self-assembled monolayers of organosilane precursors AU - Ozcam, Ali E. AU - Efimenko, Kirill AU - Jaye, Cherno AU - Spontak, Richard J. AU - Fischer, Daniel A. AU - Genzer, Jan T2 - JOURNAL OF ELECTRON SPECTROSCOPY AND RELATED PHENOMENA AB - Abstract We report on a facile, robust and rapid method by which poly(ethylene terephthalate) (PET) surfaces can be chemically modified while avoiding chemical degradation. Specifically, we demonstrate that brief exposure of PET surfaces to ultraviolet/ozone (UVO) generates a large surface concentration of hydrophilic moieties that serve as points of chemical attachment, thereby facilitating subsequent chemisorption of organosilane precursors. The feasibility of this methodology is tested by decorating UVO-modified PET surfaces with semifluorinated organosilane (SFOS) molecules, which serve to alter the surface energy of PET without compromising its bulk characteristics. The physico-chemical properties of the SFOS layers attached to PET are studied with a palette of experimental probes, including near-edge X-ray absorption fine structure (NEXAFS) spectroscopy, X-ray photoelectron spectroscopy (XPS), contact angle, atomic force microscopy (AFM), and ellipsometry. Experimental results indicate that ≈2 min of UVO treatment is optimal for covering PET with dense self-assembled monolayers (SAMs) of SFOS. Longer UVO treatment times contaminate and correspondingly roughen PET surfaces with low-molecular-weight organic compounds (LMWOCs) generated from degradation of the topmost PET material. As a consequence, SFOS SAMs attached to the LMWOC layer readily wash off from UVO-treated PET. DA - 2009/5// PY - 2009/5// DO - 10.1016/j.elspec.2009.03.012 VL - 172 IS - 1-3 SP - 95-103 SN - 1873-2526 KW - Poly(ethylene terephthalate) (PET) KW - Ultraviolet/ozone (UVO) KW - Polymer surface modification KW - SAM KW - NEXAFS ER - TY - JOUR TI - Mechanism of Extreme Ultraviolet Photoresist Development with a Supercritical CO2 Compatible Salt AU - Zweber, Amy E. AU - Wagner, Mark AU - DeYoung, James AU - Carbonell, Ruben G. T2 - LANGMUIR AB - The mechanism of developing an extreme ultraviolet (EUV) commercial photoresist with supercritical carbon dioxide (scCO2) and a CO2 compatible salt (CCS) solution was studied. The cloud point of CCS in CO2 and the pressure at which the photoresist dissolves in CCS/scCO2 were determined for temperatures between 35 and 50 °C. For this temperature range, it was found that the CCS cloud point ranges between 11.2 and 16.1 MPa, while the photoresist dissolution point ranges from 15.5 to 21.3 MPa. The kinetics of the CCS/scCO2 development was modeled using a simplified rate equation, where the rate-limiting steps were photoresist dissolution and mass transfer. The effects of temperature, mass transfer, pressure, and CCS concentration on photoresist removal rate were further explored experimentally using a high-pressure quartz crystal microbalance (QCM). Increasing temperature (35−50 °C) at a constant fluid density of 0.896 g/mL was found to increase the removal rate following an Arrhenius behavior with a photoresist dissolution energy of activation, Ea, equal to 79.0 kJ/mol. The removal was zero order in CCS concentration, signifying photoresist phase transfer, photoresist mass transfer, or both were rate limiting. Mass transfer studies showed that circulation enhanced the photoresist removal rate, but that the mass transfer coefficient was independent of temperature from 35 °C to 50 °C. In pressure studies, increasing pressure (27.6−34.5 MPa) at a constant temperature of 40 °C increased the removal rate by enhancing the fluid density, but at 50 °C increasing pressure had little effect on the removal rate. When the total CCS concentration was in large global excess over the number of Brönsted acid groups in the polymer (2400:1 at 5 mM CCS concentration), the mass of photoresist removed varied linearly with time. At lower CCS concentrations but still in global excess of the number of Brönsted acid groups, the photoresist removal slowed (0.5 mm CCS, ∼240:1) or was prevented (0.03 Mm CCS, ∼15:1) due to partitioning of the CCS between the CO2-rich phase and the film. The CCS partitioning into the resist was found to decrease with increasing temperature, revealing an enthalpy-driven CCS absorption. DA - 2009/6/2/ PY - 2009/6/2/ DO - 10.1021/la8043158 VL - 25 IS - 11 SP - 6176-6190 SN - 0743-7463 ER - TY - JOUR TI - Materials of Controlled Shape and Stiffness with Photocurable Microfluidic Endoskeleton AU - Chang, Suk Tai AU - Ucar, Ahmet Burak AU - Swindlehurst, Garrett R. AU - Bradley, Robert O., IV AU - Renk, Frederick J. AU - Velev, Orlin D. T2 - ADVANCED MATERIALS AB - Photocurable microfluidic channel networks in thin layers of polydimethylsiloxane can act as on-demand endoskeletons to lock-in specific shapes. The light-induced solidification of photopolymer inside the microchannel networks leads to drastic increases in the elastic and bending moduli of the elastomeric material. DA - 2009/7/20/ PY - 2009/7/20/ DO - 10.1002/adma.200803638 VL - 21 IS - 27 SP - 2803-+ SN - 1521-4095 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-67651108709&partnerID=MN8TOARS ER - TY - JOUR TI - Energy stores are not altered by long-term partial sleep deprivation in Drosophila melanogaster AU - Harbison, S. T. AU - Sehgal, A. T2 - PLoS One DA - 2009/// PY - 2009/// VL - 4 IS - 7 ER - TY - JOUR TI - Electrospun polyacrylonitrile fibers with dispersed Si nanoparticles and their electrochemical behaviors after carbonization AU - Ji, Liwen AU - Jung, Kyung-Hye AU - Medford, Andrew J. AU - Zhang, Xiangwu T2 - JOURNAL OF MATERIALS CHEMISTRY AB - Si nanoparticle-incorporated polyacrylonitrile (PAN) fibers are prepared using the electrospinning method and Si-filled carbon (Si/C) fibers are obtained by the subsequent heat treatment of these Si/PAN fibers. Their microstructures are characterized by various analytical techniques. It is found that Si nanoparticles are distributed both inside and on the surface of PAN fibers and this is preserved after the formation of Si/C fibers. The crystal structure characterization indicates that, in Si/C fibers, Si nanoparticles exist in a crystalline state while carbon is in a predominantly amorphous or disordered form. Si/C fibers show high reversible capacity and good capacity retention when tested as anodes in lithium ion batteries (LIBs). The excellent electrochemical performance of these fibers can be ascribed to the combined contributions of carbon matrices and Si nanoparticles, and the favorable textures and surface properties of the Si/C fibers. DA - 2009/7/28/ PY - 2009/7/28/ DO - 10.1039/b903165k VL - 19 IS - 28 SP - 4992-4997 SN - 1364-5501 UR - https://publons.com/publon/7178352/ ER - TY - JOUR TI - Electrospun carbon nanofibers containing silicon particles as an energy-storage medium AU - Ji, Liwen AU - Zhang, Xiangwu T2 - CARBON AB - A new energy-storage material has been developed by embedding Si nanoparticles as an alloying medium in electrospun carbon nanofibers. Anodes made from these carbon/Si composite nanofibers combine the advantages of both carbon (long cycle life) and Si (high lithium-storage capacity). They exhibit good electrochemical performance in terms of large reversible capacity, relatively good capacity retention and excellent rate capability upon insertion/extraction of lithium. As a result, they are promising anode candidates for storing energy in high performance batteries. DA - 2009/11// PY - 2009/11// DO - 10.1016/j.carbon.2009.07.039 VL - 47 IS - 14 SP - 3219-3226 SN - 1873-3891 UR - https://publons.com/publon/7178314/ ER - TY - JOUR TI - Effect of Pressure on the Freezing of Pure Fluids and Mixtures Confined in Nanopores AU - Coasne, Benoit AU - Czwartos, J. AU - Sliwinska-Bartkowiak, M. AU - Gubbins, Keith E. T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - Monte Carlo simulations combined with the parallel tempering technique are used to study the freezing of Ar, CH4, and their mixtures in a slit graphite nanopore. For all systems, the solid/liquid coexistence line is located at higher temperature than that for the bulk phase, as expected for fluids for which the wall/fluid interaction is stronger than the fluid/fluid interaction. In the case of the mixtures, the phase diagram for the confined system is of the same type as that for the bulk (azeotropic). It is also found that the freezing temperatures for the confined fluids and mixture are much more affected by pressure than those for the bulk phase. By calculating the isothermal compressibility of the confined fluids and determining the slope of the solid/liquid coexistence line (T,P) from the Clapeyron equation, we show that such a strong effect of pressure is not related to reduced compressibility within the pores. On the other hand, the pressure dependence of the in-pore freezing temperature is correctly described in the frame of the model proposed by Miyahara et al. [Miyahara, M.; Kanda, H.; Shibao, M.; Higashitani, K. J. Chem. Phys. 2000, 112, 9909.], which is based on the pressure difference between the bulk and confined phases (capillary effect). In this model, a change in the in-pore freezing temperature with pressure is explained by a drastic change in the in-pore pressure, which varies very sharply with the bulk external pressure. We present an extended version of this model to confined systems for which an increase in the freezing temperature is observed. DA - 2009/10/22/ PY - 2009/10/22/ DO - 10.1021/jp9031699 VL - 113 IS - 42 SP - 13874-13881 SN - 1520-5207 ER - TY - CONF TI - Ductility of ultrafine-grained copper processed by equal-channel angular pressing AU - Zhao, Y. H. AU - Lia, Y. AU - Topping, T. D. AU - Liao, X. Z. AU - Zhu, Y. D. AU - Valiev, R. Z. AU - Lavernia, E. J. C2 - 2009/// C3 - International Journal of Materials Research DA - 2009/// VL - 100 SP - 1647-1652 M1 - 12 ER - TY - JOUR TI - Determination of the Electron Escape Depth for NEXAFS Spectroscopy AU - Sohn, K. E. AU - Dimitriou, M. D. AU - Genzer, J. AU - Fischer, D. A. AU - Hawker, C. J. AU - Kramer, E. J. T2 - LANGMUIR AB - A novel method was developed to determine carbon atom density as a function of depth by analyzing the postedge signal in near-edge X-ray absorption fine structure (NEXAFS) spectra. We show that the common assumption in the analysis of NEXAFS data from polymer films, namely, that the carbon atom density is constant as a function of depth, is not valid. This analysis method is then used to calculate the electron escape depth (EED) for NEXAFS in a model bilayer system that contains a perfluorinated polyether (PFPE) on top of a highly oriented pyrolitic graphite (HOPG) sample. Because the carbon atom densitites of both layers are known, in addition to the PFPE surface layer thickness, the EED is determined to be 1.95 nm. This EED is then used to measure the thickness of the perfluorinated surface layer of poly(4-(1H,1H,2H,2H-perfluorodecyl)oxymethylstyrene) (PFPS). DA - 2009/6/2/ PY - 2009/6/2/ DO - 10.1021/la803951y VL - 25 IS - 11 SP - 6341-6348 SN - 0743-7463 ER - TY - JOUR TI - Conductive oxide thin films: Model systems for understanding and controlling surface plasmon resonance AU - Losego, M. D. AU - Efremenko, A. Y. AU - Rhodes, C. L. AU - Cerruti, M. G. AU - Franzen, S. AU - Maria, J. P. T2 - Journal of Applied Physics DA - 2009/// PY - 2009/// VL - 106 IS - 2 ER - TY - JOUR TI - Asphaltene Adsorption onto Self-Assembled Monolayers of Mixed Aromatic and Aliphatic Trichlorosilanes AU - Turgman-Cohen, Salomon AU - Smith, Matthew B. AU - Fischer, Daniel A. AU - Kilpatrick, Peter K. AU - Genzer, Jan T2 - LANGMUIR AB - The adsorption of asphaltenes onto flat solid surfaces modified with mixed self-assembled monolayers (SAMs) of aliphatic and aromatic trichlorosilanes with varying wettabilities, aromaticities, and thicknesses is tested. The mixed SAMs are characterized by means of contact angle to assess hydrophobicity and molecular and chemical uniformity, spectroscopic ellipsometry to measure the thickness of the films, and near edge X-ray absorption fine structure (NEXAFS) spectroscopy to assess chemical and molecular composition. The molecular characteristics of the adsorbed asphaltene layer and the extent of asphaltene adsorption are determined using NEXAFS and spectroscopic ellipsometry, respectively. The SAMs are formed by depositing phenyl-, phenethyl-, butyl-, and octadecyl- trichlorosilanes from toluene solutions onto silica-coated substrates; the chemical composition and the wettability of the SAM surface is tuned systematically by varying the trichlorosilane composition in the deposition solutions. The adsorption of asphaltenes on the substrates does not correlate strongly with the SAM chemical composition. Instead, the extent of asphaltene adsorption decreases with increasing SAM thickness. This observation suggests that the leading interaction governing the adsorption of asphaltenes is their interaction with the polar silica substrate and that the chemical composition of the SAM is of secondary importance. DA - 2009/6/2/ PY - 2009/6/2/ DO - 10.1021/la9000895 VL - 25 IS - 11 SP - 6260-6269 SN - 0743-7463 ER - TY - JOUR TI - Adsorption and molecular rearrangement of amphoteric species at oil-water interfaces AU - Verruto, V. J. AU - Le, R. K. AU - Kilpatrick, P. K. T2 - Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces & Biophysical DA - 2009/// PY - 2009/// VL - 113 IS - 42 SP - 13788-13799 ER - TY - JOUR TI - A Light-Activated DNA Polymerase AU - Chou, Chungjung AU - Young, Douglas D. AU - Deiters, Alexander T2 - ANGEWANDTE CHEMIE-INTERNATIONAL EDITION AB - When the time is right: The widely applied Thermus aquaticus DNA polymerase was rendered light-activatable by incorporation of the photocaged amino acid ortho-nitrobenzyl tyrosine in place of a key tyrosine residue in the active site (see picture). As the modified enzyme was completely inactive until irradiated with UV light, temporal regulation of polymerase activity was possible. DA - 2009/// PY - 2009/// DO - 10.1002/anie.200901115 VL - 48 IS - 32 SP - 5950-5953 SN - 1521-3773 KW - DNA polymerases KW - mutagenesis KW - non-natural amino acids KW - photoactivation KW - polymerase chain reaction ER - TY - JOUR TI - Tuning Gold Nanoparticle-Poly(2-hydroxyethyl methacrylate) Brush Interactions: From Reversible Swelling to Capture and Release AU - Diamanti, Steve AU - Arifuzzaman, Shafi AU - Genzer, Jan AU - Vaia, Richard A. T2 - ACS NANO AB - Tailoring the interaction between surfaces and nanoparticles (NPs) affords great opportunities for a range of applications, including sensors, information storage, medical diagnostics, and filtration membranes. In addition to controlling local ordering and microscale patterning of the NPs, manipulating the temporal factors determining the strength of the interaction between NP and surface enables dynamic modulation of these structural characteristics. In this contribution we demonstrate robust polymer brush-NP hybrids that exhibit both reversible swelling and reversible NP adsorption/desorption. Polymer brush functionality is tailored through post-functionalization of poly(2-hydroxyethyl methacrylate) (PHEMA) brushes on flat solid substrates with alpha-amine conjugates ranging from perfluoro alkanes to poly(ethylene glycol) of varying molecular weights. The type of functionality controls NP affinity for the surfaces. In the case of poly(ethylene glycol) (PEG), the molecular weight (MW) of the PEG dictates adsorption and desorption phenomena. Higher MW PEG chains possess increased binding affinity toward NPs, which leads to higher relative Au-NP densities on the PHEMA-g-PEG brushes and concurrent sluggish desorption of NPs by thermal stimulus. Adsorption and desorption phenomena are further modulated by NP size yielding a system where adsorption and desorption are controlled by a delicate balance between the competitive energetics of polymer brush chelation versus solvation. DA - 2009/4// PY - 2009/4// DO - 10.1021/nn800822c VL - 3 IS - 4 SP - 807-818 SN - 1936-086X KW - nanoparticles KW - poly(2-hydroxyethyl methacrylate) (PHEMA) KW - polymer brush KW - poly(ethylene glycol) (PEG) KW - surface chemistry KW - reversible adsorption KW - thermoresponsive ER - TY - JOUR TI - Surface Polarity Shielding and Hierarchical ZnO Nano-Architectures Produced Using Sequential Hydrothermal Crystal Synthesis and Thin Film Atomic Layer Deposition AU - Na, Jeong-Seok AU - Gong, Bo AU - Scarel, Giovanna AU - Parsons, Gregory N. T2 - ACS NANO AB - Three-dimensional nanoscale constructs are finding applications in many emerging fields, including energy generation and storage, advanced water and air purification, and filtration strategies, as well as photocatalytic and biochemical separation systems. Progress in these important technologies will benefit from improved understanding of fundamental principles underlying nanostructure integration and bottom-up growth processes. While previous work has identified hydrothermal synthesis conditions to produce nanoscale ZnO rods, sheets, and plates, strategies to systematically integrate these elements into more complex nano-architectures are not previously described. This article illustrates that amorphous nanoscale coatings formed by atomic layer deposition (ALD) are a viable means to modulate and screen the surface polarity of ZnO crystal faces and thereby regulate the growth morphology during successive hydrothermal nanocrystal synthesis. Using this new strategy, this work demonstrates direct integration and sequential assembly of nanocrystalline rods and sheets to produce complex three-dimensional geometric forms, where structure evolution is achieved by modifying the surface growth condition, keeping the hydrothermal growth chemistry unchanged. Therefore, rational planning of seed layer and feature spacing geometries may allow researchers to engineer, at the nanoscale, complex three-dimensional crystalline and semicrystalline constructs for a wide range of future applications. DA - 2009/10// PY - 2009/10// DO - 10.1021/nn900702e VL - 3 IS - 10 SP - 3191-3199 SN - 1936-086X UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000271106100043&KeyUID=WOS:000271106100043 KW - ZnO KW - nanorods KW - nanosheets KW - morphology KW - atomic layer deposition KW - hydrothermal ER - TY - JOUR TI - Porous carbon nanofibers loaded with manganese oxide particles: Formation mechanism and electrochemical performance as energy-storage materials AU - Ji, Liwen AU - Medford, Andrew J. AU - Zhang, Xiangwu T2 - JOURNAL OF MATERIALS CHEMISTRY AB - Mn oxide-loaded porous carbon nanofibers are prepared by electrospinning polyacrylonitrile nanofibers containing different amounts of Mn(CH3COO)2, followed by thermal treatments in different environments. It is found that the manganese salt may transform into γ-Mn(OOH)2 or other Mn compounds during the thermal oxidation in air environment, while further thermal treatment in argon atmosphere results in MnO and Mn3O4 particles confined to a nanoporous carbon structure. Surface morphology, thermal properties and crystal structures are characterized using various analytical techniques to provide insight into the formation mechanism of the porous structure. These Mn oxide-loaded porous carbon composite nanofibers exhibit high reversible capacity, improved cycling performance, and elevated rate capability even at high current rates when used as anodes for rechargeable lithium-ion batteries without adding any polymer binder or electronic conductor. DA - 2009/// PY - 2009/// DO - 10.1039/b905755b VL - 19 IS - 31 SP - 5593-5601 SN - 1364-5501 UR - https://publons.com/publon/7178331/ ER - TY - JOUR TI - Molecular design of photoactive acenes for organic photovoltaics AU - Huang, Liping AU - Rocca, Dario AU - Baroni, Stefano AU - Gubbins, Keith E. AU - Nardelli, Marco Buongiorno T2 - JOURNAL OF CHEMICAL PHYSICS AB - Absorption spectra of n-acenes (n from 2 to 6, for naphthalene, anthracene, tetracene, pentacene, and hexacene, respectively) have been calculated using a newly developed code based on time-dependent density-functional theory. Our calculations show that absorption spectra and charge carrier mobility of acenes not only depend on the molecular identity but also on the molecular packing. By designing the interaction between metal substrates and the first layer of acene molecules, they can be packed in a face-to-face fashion instead of the conventional herringbone (face-to-edge) arrangement. Acenes in the cofacial packing would increase the pi-orbital overlap and thus enhance the charge mobility by maximizing electronic coupling between adjacent molecules. Absorption spectra of cofacially packed acenes have a better overlap with the solar spectrum, which allows harvesting more of the solar energy from red photons. DA - 2009/5/21/ PY - 2009/5/21/ DO - 10.1063/1.3133361 VL - 130 IS - 19 SP - SN - 1089-7690 KW - carrier mobility KW - density functional theory KW - infrared spectra KW - organic semiconductors KW - photovoltaic effects KW - ultraviolet spectra KW - visible spectra ER - TY - JOUR TI - Microviscoelasticity of adhesive hard sphere dispersions: Tracer particle microrheology of aqueous Pluronic L64 solutions AU - Kloxin, C. J. AU - Zanten, J. H. T2 - Journal of Chemical Physics DA - 2009/// PY - 2009/// VL - 131 IS - 13 ER - TY - JOUR TI - Electrospun hydrophilic fumed silica/polyacrylonitrile nanofiber-based composite electrolyte membranes AU - Jung, Hong-Ryun AU - Ju, Dong-Hyuk AU - Lee, Wan-Jin AU - Zhang, Xiangwu AU - Kotek, Richard T2 - ELECTROCHIMICA ACTA AB - Hydrophilic fumed silica (SiO2)/polyacrylonitrile (PAN) composite electrolyte membranes were prepared by electrospinning composite solutions of SiO2 and PAN in N,N-dimethylformamide (DMF). Among electrospinning solutions with various SiO2 contents, the 12 wt% SiO2 in PAN solution has highest zeta potential (−40.82 mV), and exhibits the best dispersibility of SiO2 particles. The resultant 12 wt% SiO2/PAN nanofiber membrane has the smallest average fiber diameter, highest porosity, and largest specific surface area. In addition, this membrane has a three-dimensional network structure, which is fully interconnected with combined mesopores and macropores because of a good SiO2 dispersion. Composite electrolyte membranes were prepared by soaking these porous nanofiber membranes in 1 M lithium hexafluorophosphate (LiPF6) in ethylene carbonate (EC)/dimethyl carbonate (DMC) (1:1 vol%). It is found that 12 wt% SiO2/PAN electrolyte membrane has the highest conductivity (1.1 × 10−2 S cm−1) due to the large liquid electrolyte uptake (about 490%). In addition, the electrochemical performance of composite electrolyte membranes is also improved after the introduction of SiO2. For initial cycle, 12 wt% SiO2/PAN composite electrolyte membrane delivers the discharge capacity of 139 mAh g−1 as 98% of theoretical value, and still retains a high value of 127 mAh g−1 as 89% at 150th cycle, which is significantly higher that of pure PAN nanofiber-based electrolyte membranes. DA - 2009/5/1/ PY - 2009/5/1/ DO - 10.1016/j.electacta.2009.01.039 VL - 54 IS - 13 SP - 3630-3637 SN - 1873-3859 UR - https://publons.com/publon/7178329/ KW - Composite polymer electrolyte KW - Electrospinning KW - Polyacrylonitrile KW - Fumed silica ER - TY - JOUR TI - Durable Hydrophobic Textile Fabric Finishing Using Silica Nanoparticles and Mixed Silanes AU - Roe, Barry AU - Zhang, Xiangwu T2 - TEXTILE RESEARCH JOURNAL AB - Cotton fabric surface was treated with combinations of silica nanoparticles, silane hydrophobes, and silane crosslinkers to obtain durable hydrophobicity. Performance analysis was done by measuring the contact angle of water on the treated fabric surface. To evaluate the durability of the surface hydrophobicity, AATCC crocking and laundering tests were performed. Cotton fabrics with good hydrophobicity (contact angle = 139.1°) and excellent durability (e.g. 95% recovery of contact angle after laundering) were obtained when treated with Aerosil ® 90 nanoparticles, n-octyltrimethoxysilane, and bis(triethoxysilyl)ethane. This study demonstrated that the surface treatment using silica nanoparticles and mixed silanes is a promising alternative to fluoropolymer chemistry for achieving durable hydrophobic fabrics. DA - 2009/8// PY - 2009/8// DO - 10.1177/0040517508100184 VL - 79 IS - 12 SP - 1115-1122 SN - 1746-7748 UR - https://publons.com/publon/7178317/ KW - fabric finishing KW - hydrophobicity KW - nanotechnology KW - silane KW - silica ER - TY - JOUR TI - Development and Testing of Hierarchically Wrinkled Coatings for Marine Antifouling AU - Efimenko, Kirill AU - Finlay, John AU - Callow, Maureen E. AU - Callow, James A. AU - Genzer, Jan T2 - ACS APPLIED MATERIALS & INTERFACES AB - We report on the formation and testing of novel marine coatings comprising hierarchically wrinkled surface topographies (HWTS) having wrinkles of different length scales (generations) ranging from tens of nanometers to a fraction of a millimeter. The individual wrinkle generations are arranged in nested patterns, where each larger wrinkle resides underneath and represents a scaled-up version of the smaller wrinkle. We present and discuss results from field tests in seawater and laboratory experiments. The results of our field tests reveal that while coatings with flat topographies foul after relatively short time periods (4−15 weeks), the HWST coatings with the same chemistries as flat coatings remain relatively free of biofouling even after prolonged exposure to seawater (18 months). In contrast to flat coatings, the HWST substrates are not colonized by barnacles. These observations suggest that surface topography plays a dominant role in governing the coating defense against barnacle fouling even without fine-tuning the chemical composition of the overcoat. Laboratory experiments indicate that settlement of zoospores of the green alga Ulva and the strength of attachment of sporelings (young plants) depend on the chemical composition of the coating as well as surface topography. DA - 2009/5// PY - 2009/5// DO - 10.1021/am9000562 VL - 1 IS - 5 SP - 1031-1040 SN - 1944-8252 KW - marine fouling KW - buckling KW - wrinkling KW - topographically corrugated substrate KW - Ulva settlement KW - barnacle settlement ER - TY - JOUR TI - Analysis of Reaction-Diffusion Systems with Anomalous Subdiffusion AU - Haugh, Jason M. T2 - BIOPHYSICAL JOURNAL AB -

Abstract

Reaction-diffusion equations are the cornerstone of modeling biochemical systems with spatial gradients, which are relevant to biological processes such as signal transduction. Implicit in the formulation of these equations is the assumption of Fick's law, which states that the local diffusive flux of species i is proportional to its concentration gradient; however, in the context of complex fluids such as cytoplasm and cell membranes, the use of Fick's law is based on empiricism, whereas evidence has been mounting that such media foster anomalous subdiffusion (with mean-squared displacement increasing less than linearly with time) over certain length scales. Particularly when modeling diffusion-controlled reactions and other systems where the spatial domain is considered semi-infinite, assuming Fickian diffusion might not be appropriate. In this article, two simple, conceptually extreme models of anomalous subdiffusion are used in the framework of Green's functions to demonstrate the solution of four reaction-diffusion problems that are well known in the biophysical context of signal transduction: fluorescence recovery after photobleaching, the Smolochowski limit for diffusion-controlled reactions in solution, the spatial range of a diffusing molecule with finite lifetime, and the collision coupling mechanism of diffusion-controlled reactions in two dimensions. In each case, there are only subtle differences between the two subdiffusion models, suggesting how measurements of mean-squared displacement versus time might generally inform models of reactive systems with partial diffusion control. DA - 2009/7/22/ PY - 2009/7/22/ DO - 10.1016/j.bpj.2009.05.014 VL - 97 IS - 2 SP - 435-442 SN - 0006-3495 ER - TY - JOUR TI - Sorption of CO2 and a CO2 Compatible Salt into an Extreme Ultraviolet Photoresist Film on a SiO2 Substrate AU - Zweber, Amy E. AU - Wagner, Mark AU - Carbonell, Ruben G. T2 - JOURNAL OF PHYSICAL CHEMISTRY B AB - The development of standard extreme ultraviolet (EUV) lithography photoresists with a CO2 compatible salt (CCS) and supercritical carbon dioxide (scCO2) solution has several advantages over typical trimethylammonium hydroxide development, including reduced image collapse and line width roughness in the resulting microchip features. The mechanism and characteristics of the CCS/scCO2 development process are currently being examined. In this paper, the sorption behavior of CO2 and the CCS onto a bare SiO2 surface and into the photoresist was studied using a quartz crystal microbalance (QCM). From the adsorption studies of CO2 and CCS/CO2 onto a bare SiO2 surface, it was found that the CCS begins to adsorb at 8.0 MPa at a temperature of 35 °C and at 9.4 MPa at a temperature of 50 °C. The adsorption of the CCS was favored and driven by entropy changes. The absorption of CO2 into the glassy photoresist resin was also measured with QCM and found comparable to CO2 absorption in glassy polystyrene for 35 and 50 °C up to a pressure where the photoresist is believed to dewet from the substrate. The diffusion behavior during CO2 absorption was found to be comparable to that of small fluorescent molecule diffusion in a CO2 swollen polystyrene. DA - 2009/7/23/ PY - 2009/7/23/ DO - 10.1021/jp900481j VL - 113 IS - 29 SP - 9687-9693 SN - 1520-6106 ER - TY - JOUR TI - Plasmonic phenomena in indium tin oxide and ITO-Au hybrid films AU - Franzen, Stefan AU - Rhodes, Crissy AU - Cerruti, Marta AU - Gerber, Ralph W. AU - Losego, Mark AU - Maria, Jon-Paul AU - Aspnes, D. E. T2 - OPTICS LETTERS AB - The observation of surface-plasmon resonances in indium tin oxide (ITO) thin films is complemented with the effects of hybrid ITO/Au conducting layers where charge densities can be tuned. Where carrier densities are similar (ITO and nanoparticle Au), the plasmonic behavior is that of a monolithic ITO thin film. Where the carrier density of one layer is much greater than that of the other (ITO and Au metal), boundary conditions lead to cancelation of the surface plasmon. In the latter case a capacitivelike plasmon resonance is observed for sufficiently thin films. DA - 2009/9/15/ PY - 2009/9/15/ DO - 10.1364/OL.34.002867 VL - 34 IS - 18 SP - 2867-2869 SN - 1539-4794 ER - TY - JOUR TI - Photochemically Cross-Linked Perfluoropolyether-Based Elastomers: Synthesis, Physical Characterization, and Biofouling Evaluation AU - Hu, Zhaokang AU - Finlay, John A. AU - Chen, Liang AU - Betts, Douglas E. AU - Hillmyer, Marc A. AU - Callow, Maureen E. AU - Callow, James A. AU - DeSimone, Joseph M. T2 - MACROMOLECULES AB - A series of reactive liquid perfluoropolyether (PFPE) precursors were synthesized which can be photochemically cross-linked (UV-cured) into high-performance PFPE elastomers in one step. To investigate how fundamental changes in the PFPE molecular structure correlate to bulk and surface properties, the variable functional end group, molecular weight, and the copolymer content were systematically explored in relation to thermal stability, contact angle/surface tension, modulus, and biofouling behavior. The morphologies of these PFPE materials were studied using differential scanning calorimetry, dynamic mechanical thermal analysis, and small-angle X-ray scattering. From these studies, it was determined that clusters of polymerized functional end groups were found to be nanophase separated within the PFPE matrix. By varying the cross-link density, the Young’s modulus of the fully cross-linked PFPE elastomeric film could be tuned from 1.5 to 90 MPa with a critical surface tension of 8.6−16 mN/m. The marine antifouling and fouling-release properties of the cross-linked PFPE elastomeric coatings were evaluated by settlement and release assays involving zoospores and sporelings (young plants), respectively, of green fouling alga Ulva. DA - 2009/9/22/ PY - 2009/9/22/ DO - 10.1021/ma901227k VL - 42 IS - 18 SP - 6999-7007 SN - 1520-5835 ER - TY - JOUR TI - Modeling Micelle-Templated Mesoporous Material SBA-15: Atomistic Model and Gas Adsorption Studies AU - Bhattacharya, Supriyo AU - Coasne, Benoit AU - Hung, Francisco R. AU - Gubbins, Keith E. T2 - LANGMUIR AB - We report the development of a realistic molecular model for mesoporous silica SBA-15, which includes both the large cylindrical mesopores and the smaller micropores in the pore walls. The methodology for modeling the SBA-15 structure involves molecular and mesoscale simulations combined with geometrical interpolation techniques. First, a mesoscale model is prepared by mimicking the synthesis process using lattice Monte Carlo simulations. The main physical features of this mesoscale pore model are then carved out of an atomistic silica block; both the mesopores and the micropores are incorporated from the mimetic simulations. The calculated pore size distribution, surface area, and simulated TEM images of the model structure are in good agreement with those obtained from experimental samples of SBA-15. We then investigate the adsorption of argon in this structure using Grand Canonical Monte Carlo (GCMC) simulations. The adsorption results for our SBA-15 model are compared with those for a similar model that does not include the micropores; we also compare with results obtained in a regular cylindrical pore. The simulated adsorption isotherm for the SBA-15 model shows semiquantitative agreement with the experimental isotherm for a SBA-15 sample having a similar pore size. We observe that the presence of the micropores leads to increased adsorption at low pressure compared to the case of a model without micropores in the pore walls. At higher pressures, for all models, the filling proceeds via the monolayer-multilayer adsorption on the mesopore surface followed by capillary condensation, which is mainly controlled by the mesopore diameter and is not influenced by the presence of the micropores. DA - 2009/5/19/ PY - 2009/5/19/ DO - 10.1021/la801560e VL - 25 IS - 10 SP - 5802-5813 SN - 0743-7463 ER - TY - JOUR TI - Melting of mixtures in silica nanopores AU - Czwartos, Joanna AU - Sliwinska-Bartkowiak, Malgorzata AU - Coasne, Benoit AU - Gubbins, Keith E. T2 - PURE AND APPLIED CHEMISTRY AB - Abstract We report experimental measurements of the melting of mixtures confined in nanoporous materials. Dielectric relaxation spectroscopy (DRS) was used to determine the solid–liquid phase diagram of bromobenzene/carbon tetrachloride (C 6 H 5 Br /CCl 4 ) mixtures confined in controlled pore glasses (CPGs) with an average pore diameter H = 7.5 nm. Our results 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 different temperatures. These results are compared with those previously obtained for CCl 4 /C 6 H 6 mixtures in activated carbon fibers (ACFs). DA - 2009/10// PY - 2009/10// DO - 10.1351/PAC-CON-09-01-15 VL - 81 IS - 10 SP - 1953-1959 SN - 1365-3075 KW - confinement mixture KW - controlled pore glasses KW - freezing KW - melting KW - solid-liquid phase diagrams ER - TY - JOUR TI - Materials Fabricated by Micro- and Nanoparticle Assembly - The Challenging Path from Science to Engineering AU - Velev, Orlin D. AU - Gupta, Shalini T2 - ADVANCED MATERIALS AB - Abstract We classify the strategies for colloidal assembly and review the diverse potential applications of micro‐ and nanoparticle structures in materials and device prototypes. The useful properties of the particle assemblies, such as high surface‐to‐volume ratio, periodicity at mesoscale, large packing density, and long‐range ordering, can be harnessed in optical, electronic, and biosensing devices. We discuss the present and future trends in the colloidal‐ assembly field, focusing on the challenges of developing fabrication procedures that are rapid and efficiently controlled. We speculate on how the issues of scalability, control, and precision could be addressed, and how the functionality of the assemblies can be increased to better match the needs of technology. DA - 2009/5/18/ PY - 2009/5/18/ DO - 10.1002/adma.200801837 VL - 21 IS - 19 SP - 1897-1905 SN - 0935-9648 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-66249132369&partnerID=MN8TOARS ER - TY - JOUR TI - Intense and selective coloration of foams stabilized with functionalized particles AU - Kim, Sejong AU - Barraza, Harry AU - Velev, Orlin D. T2 - JOURNAL OF MATERIALS CHEMISTRY AB - We report a new method for intense and selective coloring of foams stabilized by particles from cellulose derivatives. The addition of pH-sensitive dyes during the process of formation of hydrophobically modified cellulose (HMC) particles by a pH-jump leads to co-precipitation and strong adsorption of the pH-sensitive dyes on the cellulose particle surfaces at low pH. These strongly colored HMC particles not only act as strong stabilizers of the foams, but also allow their intense and selective coloration without any coloring of the solution medium. We characterized quantitatively the color intensity of these foams, analyzed the adsorption behavior of pH-sensitive dyes on the cellulose particles and showed that it follows well the Langmuir isotherm model. Lower pH of the media leads to stronger adsorption of the pH-sensitive dyes on the HMC particles due to the hydrophobic attraction under reduced electrostatic repulsion. The results illustrate how particle stabilizers can be used to impart additional functionality to foams and prepare dispersion systems of unusual properties. DA - 2009/// PY - 2009/// DO - 10.1039/b908054f VL - 19 IS - 38 SP - 7043-7049 SN - 1364-5501 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-70349345796&partnerID=MN8TOARS ER - TY - JOUR TI - Hydrogen storage enhanced in Li-doped carbon replica of zeolites: A possible route to achieve fuel cell demand AU - Roussel, Thomas AU - Bichara, Christophe AU - Gubbins, Keith E. AU - Pellenq, Roland J. -M. T2 - JOURNAL OF CHEMICAL PHYSICS AB - We first report the atomistic grand canonical Monte Carlo simulations of the synthesis of two realistic ordered microporous carbon replica in two siliceous forms of faujasite zeolite (cubic Y-FAU and hexagonal EMT). Atomistic simulations of hydrogen adsorption isotherms in these two carbon structures and their Li-doped composites were carried out to determine their storage capacities at 77 and 298 K. We found that these new forms of carbon solids and their Li-doped versions show very attractive hydrogen storage capacities at 77 and 298 K, respectively. However, for a filling pressure of 300 bars and at room temperature, bare carbons do not show advantageous performances compared to a classical gas cylinder despite of their crystalline micropore network. In comparison, Li-doped nanostructures provide reversible gravimetric and volumetric hydrogen storage capacities twice larger (3.75 wt % and 33.7 kg/m3). The extreme lattice stiffness of their skeleton will prevent them from collapsing under large external applied pressure, an interesting skill compared to bundle of carbon nanotubes, and metal organic frameworks (MOFs). These new ordered composites are thus very promising materials for hydrogen storage issues by contrast with MOFs. DA - 2009/5/7/ PY - 2009/5/7/ DO - 10.1063/1.3122382 VL - 130 IS - 17 SP - SN - 0021-9606 KW - adsorption KW - carbon nanotubes KW - doping KW - fuel cells KW - hydrogen storage KW - lithium KW - Monte Carlo methods KW - nanocomposites KW - nanoporous materials KW - nanotechnology KW - zeolites ER - TY - JOUR TI - Electrodeposition of platinum nanoparticles onto carbon nanofibers for electrocatalytic oxidation of methanol AU - Lin, Zhan AU - Ji, Liwen AU - Zhang, Xiangwu T2 - MATERIALS LETTERS AB - Pt/carbon composite nanofibers were prepared by electrodepositing Pt nanoparticles onto electrospun carbon nanofibers and were used as catalysts towards the oxidation of methanol. The morphology and size of Pt nanoparticles were controlled by selectively adjusting the electrodeposition potential and time. SEM and TEM results show that the composite nanofibers were successfully obtained and Pt particle diameters were between 10 and 55 nm. The electrocatalytic activity of the composite nanofibers expressed by current density per Pt particle mass was found to depend on the particle size, showing an increasing activity when the catalyst diameter decreased. DA - 2009/10/15/ PY - 2009/10/15/ DO - 10.1016/j.matlet.2009.07.005 VL - 63 IS - 24-25 SP - 2115-2118 SN - 1873-4979 UR - https://publons.com/publon/6540063/ KW - Electrodeposition KW - Electrospinning KW - Pt nanoparticles KW - Carbon nanofibers KW - Methanol ER - TY - JOUR TI - Electrochemical and Physicochemical Properties of PY(14)FSI-Based Electrolytes with LiFSI AU - Paillard, Elie AU - Zhou, Qian AU - Henderson, Wesley A. AU - Appetecchi, Giovanni B. AU - Montanino, Maria AU - Passerini, Stefano T2 - JOURNAL OF THE ELECTROCHEMICAL SOCIETY AB - We report here the characterization of Li battery electrolytes based upon the -butyl--methylpyrrolidinium bis(fluorosulfonyl)imide ionic liquid with lithium bis(fluorosulfonyl)imide (LiFSI) as a support salt. These electrolytes show low viscosity relative to other pyrrolidinium-based ionic liquids (ILs) and corresponding higher conductivity at subambient temperatures. The melting point of the IL decreases with the addition of LiFSI and concentrated samples remain totally amorphous. The electrolytes exhibit decreased thermal stability and increased parasitic cathodic reactions with increasing LiFSI fraction relative to the pure IL, probably due to a higher impurity level for the commercial LiFSI. Despite this, the electrolytes have excellent lithium cycling behavior at . DA - 2009/// PY - 2009/// DO - 10.1149/1.3208048 VL - 156 IS - 11 SP - A891-A895 SN - 0013-4651 ER - TY - JOUR TI - Dispersion of Cellulose Crystallites by Nonionic Surfactants in a Hydrophobic Polymer Matrix AU - Kim, Jooyoun AU - Montero, Gerardo AU - Habibi, Youssef AU - Hinestroza, Juan P. AU - Genzer, Jan AU - Argyropoulos, Dimitris S. AU - Rojas, Orlando J. T2 - POLYMER ENGINEERING AND SCIENCE AB - Abstract Cellulose nanoparticles obtained by acid hydrolysis of cellulose paper were used to reinforce polystyrene composite films. The nonionic surfactant sorbitan monostearate was utilized to improve the dispersion properties of the hydrophilic cellulose in hydrophobic matrix and to prevent the formation of aggregates. Turbidity tests were used to measure dispersion stability of the cellulose crystallites in the hydrophobic solvent used in the composite manufacture. A correlation was found between the dispersion stability in solvent and the formation of aggregates in the polymeric composites. Nanocomposite films were processed using a casting/evaporation technique. Thermal and mechanical properties of processed composites were studied by differential scanning calorimetry (DSC) and dynamical mechanical analyses (DMA), respectively. The results showed that the optimum addition of surfactant produced better dispersion of the cellulose particles in the polystyrene matrix and improved the mechanical properties of the resulting composite due to an enhanced compatibility. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers DA - 2009/10// PY - 2009/10// DO - 10.1002/pen.21417 VL - 49 IS - 10 SP - 2054-2061 SN - 1548-2634 ER - TY - JOUR TI - Discriminating Among Co-monomer Sequence Distributions in Random Copolymers Using Interaction Chromatography AU - Han, Junwon AU - Jeon, Byung Ho AU - Ryu, Chang Y. AU - Semler, James J. AU - Jhon, Young K. AU - Genzer, Jan T2 - MACROMOLECULAR RAPID COMMUNICATIONS AB - Abstract Interaction chromatography has been employed to validate that adsorption of poly[styrene‐ co ‐(4‐bromostyrene)] (PBr x S) random copolymers, where x denotes the mole fraction of 4‐bromostyrene (4–BrS) in PBr x S in solution depends on the average number of adsorptive segments, the type of adsorbing substrate, and on the co‐monomer sequence distribution in PBr x S. magnified image DA - 2009/9/17/ PY - 2009/9/17/ DO - 10.1002/marc.200900282 VL - 30 IS - 18 SP - 1543-1548 SN - 1521-3927 KW - co-monomer sequence distribution KW - interaction chromatography KW - monomers KW - polystyrene KW - poly(styrene-co-4-bromostyrene) KW - PBrxS KW - random copolymer adsorption ER - TY - JOUR TI - Deposition of Coatings from Live Yeast Cells and Large Particles by "Convective-Sedimentation" Assembly AU - Jerrim, Lindsey B. AU - Velev, Orlin D. T2 - LANGMUIR AB - Convective assembly at high volume fraction was used for the rapid deposition of uniform, close-packed coatings of Saccharomyces cerevisiae yeast cells onto glass slides. A computational model was developed to calculate the thickness profiles of such coatings for different set of conditions. Both the experiments and the numerical simulations demonstrated that the deposition process is strongly affected by the presence of sedimentation. The deposition device was inclined to increase the uniformity of the coatings by causing the cells to sediment toward the three-phase contact line. In accordance with the simulation, the experiments showed that both increasing the angle of the device and decreasing the angle between the slides increased the uniformity of the deposited coatings. Finally, the "convective-sedimentation" assembly method was used to deposit mixed layers of live cells and large latex particles as an example of immobilized biologically active composite coatings. DA - 2009/5/19/ PY - 2009/5/19/ DO - 10.1021/la900519p VL - 25 IS - 10 SP - 5692-5702 SN - 0743-7463 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-66249112167&partnerID=MN8TOARS ER - TY - JOUR TI - A Bipolar Clamp Mechanism for Activation of Jak-Family Protein Tyrosine Kinases AU - Barua, Dipak AU - Faeder, James R. AU - Haugh, Jason M. T2 - PLOS COMPUTATIONAL BIOLOGY AB - Most cell surface receptors for growth factors and cytokines dimerize in order to mediate signal transduction. For many such receptors, the Janus kinase (Jak) family of non-receptor protein tyrosine kinases are recruited in pairs and juxtaposed by dimerized receptor complexes in order to activate one another by trans-phosphorylation. An alternative mechanism for Jak trans-phosphorylation has been proposed in which the phosphorylated kinase interacts with the Src homology 2 (SH2) domain of SH2-B, a unique adaptor protein with the capacity to homo-dimerize. Building on a rule-based kinetic modeling approach that considers the concerted nature and combinatorial complexity of modular protein domain interactions, we examine these mechanisms in detail, focusing on the growth hormone (GH) receptor/Jak2/SH2-Bbeta system. The modeling results suggest that, whereas Jak2-(SH2-Bbeta)(2)-Jak2 heterotetramers are scarcely expected to affect Jak2 phosphorylation, SH2-Bbeta and dimerized receptors synergistically promote Jak2 trans-activation in the context of intracellular signaling. Analysis of the results revealed a unique mechanism whereby SH2-B and receptor dimers constitute a bipolar 'clamp' that stabilizes the active configuration of two Jak2 molecules in the same macro-complex. DA - 2009/4// PY - 2009/4// DO - 10.1371/journal.pcbi.1000364 VL - 5 IS - 4 SP - SN - 1553-7358 ER - TY - JOUR TI - Sequestration and selective oxidation of carbon monoxide on graphene edges AU - Paul, Sujata AU - Santiso, Erik E. AU - Nardelli, Marco Buongiorno T2 - JOURNAL OF PHYSICS-CONDENSED MATTER AB - The versatility of carbon nanostructures makes them attractive as possible catalytic materials, as they can be synthesized in various shapes and chemically modified by doping, functionalization, and the creation of defects in the nanostructure. Recent research has shown how the properties of carbon nanostructures can be exploited to enhance the yield of chemical reactions such as the thermal decomposition of water (Kostov et al 2005 Phys. Rev. Lett. 95) and the dissociation of methane into carbon and hydrogen (Huang et al 2008 J. Chem. Phys. at press). In this work, we consider the carbon-mediated partial sequestration and selective oxidation of carbon monoxide (CO), both in the presence and absence of hydrogen. Using first-principles calculations we study several reactions of CO with carbon nanostructures, where the active sites can be regenerated by the deposition of carbon decomposed from the reactant (CO) to make the reactions self-sustained. Using statistical mechanics, we also study the conditions under which the conversion of CO to graphene and carbon dioxide is thermodynamically favorable, both in the presence and in the absence of hydrogen. These results are a first step toward the development of processes for the carbon-mediated partial sequestration and selective oxidation of CO in a hydrogen atmosphere. DA - 2009/9/2/ PY - 2009/9/2/ DO - 10.1088/0953-8984/21/35/355008 VL - 21 IS - 35 SP - SN - 1361-648X ER - TY - JOUR TI - Microcapsules containing suspensions of carbon nanotubes AU - Caruso, Mary M. AU - Schelkopf, Stuart R. AU - Jackson, Aaron C. AU - Landry, Alexandra M. AU - Braun, Paul V. AU - Moore, Jeffrey S. T2 - JOURNAL OF MATERIALS CHEMISTRY AB - Single-walled nanotubes (SWNTs) suspended in chlorobenzene (PhCl) and ethyl phenylacetate (EPA) were incorporated into microcapsules using an in situemulsification polymerization of urea-formaldehyde; the capsules release the SWNTs upon mechanical rupture. DA - 2009/// PY - 2009/// DO - 10.1039/b910673a VL - 19 IS - 34 SP - 6093-6096 SN - 1364-5501 ER - TY - JOUR TI - Electrospun Nanocomposites from Polystyrene Loaded with Cellulose Nanowhiskers AU - Rojas, Orlando J. AU - Montero, Gerardo A. AU - Habibi, Youssef T2 - JOURNAL OF APPLIED POLYMER SCIENCE AB - Abstract Composite microfibers from polystyrene and cellulose nanowhiskers were produced by electrospinning. The morphology of the microfibers was examined by using scanning and transmission electron microscopies. Surface porosity, unique ribbon‐shapes, and the presence of twists along the fiber axis were observed in the composite microfibers. Thermomechanical properties of processed nanocomposites were studied by differential scanning calorimetry and dynamical mechanical analyses. The reinforcing effect of cellulose nanowhiskers was confirmed as the glassy modulus of electrospun microfibers increased with nanowhisker load. This effect is explained to be the result of mechanical percolation of cellulose nanowhiskers forming a stiff and continuous network held by hydrogen bonding. It is demonstrated that cellulose nanoparticles can be used effectively to reinforce hydrophobic matrices and to produce unique structural properties, enabling new functionalities and properties. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 DA - 2009/7/15/ PY - 2009/7/15/ DO - 10.1002/app.30011 VL - 113 IS - 2 SP - 927-935 SN - 1097-4628 KW - cellulose KW - electrospinning KW - mechanical properties KW - microfibers KW - nanocomposites KW - nanoparticles ER - TY - JOUR TI - Adsorption and Structure of Benzene on Silica Surfaces and in Nanopores AU - Coasne, Benoit AU - Alba-Simionesco, Christiane AU - Audonnet, Fabrice AU - Dosseh, Gilberte AU - Gubbins, Keith E. T2 - LANGMUIR AB - Grand canonical Monte Carlo simulations are used to study the adsorption of benzene on atomistic silica surfaces and in cylindrical nanopores. The effect of temperature and surface chemistry is addressed by studying the adsorption of benzene at 293 and 323 K on both fully and partially hydroxylated silica surfaces or nanopores. We also consider the adsorption of benzene in a cylindrical nanopore of diameter D=3.6 nm and compare our results with those obtained for planar surfaces. The structure of benzene in the vicinity of the planar surface and confined in the cylindrical nanopore is determined by calculating orientational order parameters and examining positional pair correlation functions. The density profiles of adsorbed benzene reveal the strong layering of the adsorbate, which decays with the distance from the silica surface. At a given temperature and at low pressures, the film adsorbed at the fully hydroxylated silica surface is larger than that for the partially hydroxylated silica surface. This result is due to an increase in the density of silanol groups that induces an increase in the polarity of the silica surface, which becomes more attractive for the adsorbate. Our results also suggest that the benzene molecules prefer an orientation in which their ring is nearly perpendicular to the surface when fully hydroxylated surfaces are considered. When partially hydroxylated surfaces are considered, a second preferential orientation is observed where the benzene ring forms an angle of approximately 50 degrees with the silica surface. In this case, the average orientation of the benzene molecules appears disordered as in the bulk phase. These results suggest that determining the experimental orientation of benzene in the vicinity of a silica surface is a difficult task even when the surface chemistry is known. Capillary condensation in the nanopores involves a transition from a partially filled pore (a thin film adsorbed at the pore surface) to a completely filled pore configuration where the confined liquid coexists at equilibrium with the external gas phase. The disordered orientation of the adsorbed benzene molecules in the case of the partially hydroxylated surface favors the condensation of benzene molecules (the condensation pressure for this substrate is lower than that for the fully hydroxylated surface). Finally, these results are consistent with the structural analysis, showing that (1) benzene tends to relax its liquid structure a little in order to optimize its molecular arrangement near the pore wall and (2) the disordering of the liquid structure induced by the surface becomes stronger as the interaction with the pore wall increases. DA - 2009/9/15/ PY - 2009/9/15/ DO - 10.1021/la900984z VL - 25 IS - 18 SP - 10648-10659 SN - 0743-7463 ER - TY - JOUR TI - Quantitative photocatalyzed soot oxidation on titanium dioxide AU - Chin, Paul AU - Grant, Christine S. AU - Ollis, David F. T2 - APPLIED CATALYSIS B-ENVIRONMENTAL AB - Abstract We report here the titanium dioxide (TiO 2 ) photocatalyzed oxidation of deposited hurricane lamp soot. Sol–gel derived TiO 2 was coated on quartz crystal microbalance (QCM) elements. Characterization by spectroscopic ellipsometry ( SE ) and atomic force microscopy (AFM) revealed low surface roughness of 0–17%, and SE showed a linear variation of the TiO 2 thickness versus the number of sol–gel spin coats. Soot was deposited on the calcined TiO 2 film using an analytical rotor passing through a hurricane lamp flame, and subsequently irradiated with near-UV light. Varying the soot mass on the TiO 2 -coated QCM crystals revealed behaviors over 20,000 min ranging from total soot destruction of a single pass soot layer to minimal oxidation of an eight pass soot layer, the latter caused by soot screening of the incident UV light. A series/parallel reaction mechanism [P. Chin, G.W. Roberts, D.F. Ollis, Industrial & Engineering Chemistry Research 46 (2007) 7598] developed to describe previous literature data on TiO 2 -catalyzed soot photooxidation was successfully employed to capture the longer time changes in presumably graphitic soot mass as a function of UV illumination time from 1000 to 20,000 min and of soot layer thickness. Short time soot mass loss is attributed to oxidation of organic carbons deposited on the graphitic soot components. This kinetic model can be used to predict the rate of TiO 2 -catalyzed soot destruction as a function of near-UV illumination time and initial soot layer thickness. DA - 2009/4/7/ PY - 2009/4/7/ DO - 10.1016/j.apcatb.2008.09.020 VL - 87 IS - 3-4 SP - 220-229 SN - 1873-3883 KW - Titania KW - Photocatalysis KW - Soot KW - Kinetic model KW - Oxidation KW - Formal quantum efficiency ER - TY - JOUR TI - Formation of surface-grafted polymeric amphiphilic coatings comprising ethylene glycol and fluorinated groups and their response to protein adsorption AU - Arifuzzaman, Shafi AU - Oezcam, Ali E. AU - Efimenko, Kirill AU - Fischer, Daniel A. AU - Genzer, Jan T2 - BIOINTERPHASES AB - Amphiphilic polymer coatings were prepared by first generating surface-anchored polymer layers of poly(2-hydroxyethyl methacrylate) (PHEMA) on top of flat solid substrates followed by postpolymerization reaction on the hydroxyl terminus of HEMA's pendent group using three classes of fluorinating agents, including organosilanes, acylchlorides, and trifluoroacetic anhydride (TFAA). The distribution of the fluorinated groups inside the polymer brushes was assessed by means of a suite of analytical probes, including contact angle, ellipsometry, infrared spectroscopy, atomic force microscopy, and near-edge x-ray absorption fine structure spectroscopy. While organosilane modifiers were found to reside primarily close to the tip of the brush, acylchlorides penetrated deep inside PHEMA thus forming random copolymers P(HEMA-co-fHEMA). The reaction of TFAA with the PHEMA brush led to the formation of amphiphilic diblocks, PHEMA-b-P(HEMA-co-fHEMA), whose bottom block comprised unmodified PHEMA and the top block was made of P(HEMA-co-fHEMA) rich in the fluorinated segments. This distribution of the fluorinated groups endowed PHEMA-b-P(HEMA-co-fHEMA) with responsive properties; while in hydrophobic environment P(HEMA-co-fHEMA) segregated to the surface, when in contact with a hydrophilic medium, PHEMA partitioned at the brush surface. The surface activity of the amphiphilic coatings was tested by studying the adsorption of fibrinogen (FIB). While some FIB adsorption occurred on most coatings, the ones made by TFAA modification of PHEMA remained relatively free of FIB. DA - 2009/6// PY - 2009/6// DO - 10.1116/1.3114502 VL - 4 IS - 2 SP - FA33-FA44 SN - 1559-4106 KW - adsorption KW - atomic force microscopy KW - biomedical materials KW - contact angle KW - ellipsometry KW - hydrophilicity KW - hydrophobicity KW - infrared spectra KW - polymer blends KW - polymer films KW - polymerisation KW - proteins KW - surface chemistry KW - X-ray absorption ER - TY - JOUR TI - Fabrication of porous carbon/Si composite nanofibers as high-capacity battery electrodes AU - Ji, Liwen AU - Zhang, Xiangwu T2 - ELECTROCHEMISTRY COMMUNICATIONS AB - Carbon/Si composite nanofibers with porous structures are prepared by electrospinning and subsequent carbonization processes. It is found that these porous composite nanofibers can be used as anode materials for rechargeable lithium-ion batteries (LIBs) without adding any binding or conducting additive. The resultant anodes exhibit good electrochemical performance; for example, a large discharge capacity of 1100 mAh g−1 at a high current density of 200 mA g−1. DA - 2009/6// PY - 2009/6// DO - 10.1016/j.elecom.2009.03.042 VL - 11 IS - 6 SP - 1146-1149 SN - 1873-1902 UR - https://publons.com/publon/7178318/ KW - Electrospinning KW - Porous carbon nanofibers KW - Si nanoparticles KW - Lithium-ion batteries ER - TY - JOUR TI - Fabrication of multiphasic and regio-specifically functionalized PRINT (R) particles of controlled size and shape AU - Zhang, H. AU - Nunes, J. K. AU - Gratton, S. E. A. AU - Herlihy, K. P. AU - Pohlhaus, P. D. AU - DeSimone, J. M. T2 - NEW JOURNAL OF PHYSICS AB - Using Particle Replication In Nonwetting Templates (PRINT®) technology, multiphasic and regio-specifically functionalized shape-controlled particles have been fabricated that include end-labeled particles via post-functionalization; biphasic Janus particles that integrate two compositionally different chemistries into a single particle; and more complex multiphasic shape-specific particles. Controlling the anisotropic distribution of matter within a particle creates an extra parameter in the colloidal particle design, providing opportunities to generate advanced particles with versatile and tunable compositions, properties, and thus functionalities. Owing to their robust characteristics, these multiphasic and regio-specifically functionalized PRINT particles should be promising platforms for applications in life science and materials science. DA - 2009/7/31/ PY - 2009/7/31/ DO - 10.1088/1367-2630/11/7/075018 VL - 11 SP - SN - 1367-2630 ER - TY - JOUR TI - Energetics investigation on encapsulation of protein/peptide drugs in carbon nanotubes AU - Chen, Qu AU - Wang, Qi AU - Liu, Ying-Chun AU - Wu, Tao AU - Kang, Yu AU - Moore, Joshua D. AU - Gubbins, Keith E. T2 - JOURNAL OF CHEMICAL PHYSICS AB - This work focuses on the dynamic properties and energetics of the protein/peptide drug during its transport through carbon nanotubes (CNTs). A systematic study was performed on the interaction between the peptide and the CNTs. In the molecular dynamics (MD) simulations, the protein/peptide molecule Zadaxin® is observed to be encapsulated inside the nanotube after its spontaneous insertion and oscillates around the center of the tube, where the van der Waals interaction energy is observed to be a minimum. Furthermore, it is found by performing steered MD simulations that the pulling force applied to the peptide reaches a maximum value, which demonstrates the ability of the CNTs to trap protein/peptide drugs. Such effects, attributed to van der Waals interactions, can be influenced by varying the lengths and diameters of the CNTs. Longer nanotubes provide a broader area to trap the peptide, while smaller nanotubes are able to encapsulate the peptide with a deeper interaction energy well. This investigation provides insights into nanoscale pharmaceutical drug delivery devices. DA - 2009/7/7/ PY - 2009/7/7/ DO - 10.1063/1.3148025 VL - 131 IS - 1 SP - SN - 1089-7690 KW - biomedical materials KW - carbon nanotubes KW - drug delivery systems KW - drugs KW - encapsulation KW - molecular biophysics KW - molecular dynamics method KW - nanobiotechnology KW - proteins KW - van der Waals forces ER - TY - JOUR TI - Effect of Comonomer Sequence Distribution on the Adsorption of Random Copolymers onto Impenetrable Flat Surfaces AU - Jhon, Young K. AU - Semler, James J. AU - Genzer, Jan AU - Beevers, Martin AU - Gus'kova, Olga A. AU - Khalatur, Pavel G. AU - Khokhlov, Alexei R. T2 - MACROMOLECULES AB - We study the effect of comonomer sequence distributions in random copolymers (RCPs) on RCP adsorption on flat impenetrable surfaces. RCP poly(styrene-co-4-bromostyrene) (PBrxS), where x denotes the mole fraction of 4-bromostryrene (4-BrS), is prepared by bromination of parent homopolystyrene. By varying the solvent quality during the bromination, either “truly random” (good solvent) or “random-blocky” (poor solvent) PBrxS RCPs are prepared. Adsorption studies of PBrxS from various solvents at silica surfaces reveal that the adsorption of PBrxS increases with (1) increasing blockiness of the macromolecule, (2) increasing content of 4-BrS in PBrxS, and (3) decreasing solvent quality. Additionally, the effect of comonomer sequence distribution on RCP adsorption is modeled in detail using a coarse-grained statistical mechanical model and fully atomistic simulations based on configurational-biased grand-canonical Monte Carlo (CB-GCMC) technique. The main result from the simulations can be summarized as follows: (1) Increasing the degree of “blockiness” in comonomer distribution enhances the adsorption of macromolecules dissolved in a good solvent. (2) Near the adsorption transition, the amount of adsorbed segments in “random-blocky” copolymers is larger relative to their regular multiblock counterparts. (3) Lowering the solvent quality facilitates copolymer adsorption. Overall, the findings from computer modeling are found to be in a good agreement with the experimental data. DA - 2009/4/14/ PY - 2009/4/14/ DO - 10.1021/ma8027936 VL - 42 IS - 7 SP - 2843-2853 SN - 1520-5835 ER - TY - JOUR TI - Development and characterization of thin polymer films relevant to fiber processing AU - Song, Junlong AU - Liang, Jing AU - Liu, Xiaomeng AU - Krause, Wendy E. AU - Hinestroza, Juan P. AU - Rojas, Orlando J. T2 - THIN SOLID FILMS AB - Dilute solutions of cellulose, polypropylene, polyethylene, nylon and polyester were spun cast onto gold and silica wafers to generate thin films of these polymers, which are commonly used in the manufacture of synthetic fibers. The thin films were used as substrates in the quartz crystal microbalance and nano-indentation techniques to monitor adsorption and friction behaviors after treatment with a polymer solution (as a mimic of a textile finish). The spin coating conditions were optimized in terms of the resulting film morphology, thickness and surface energy. Atomic force microscopy, X-ray photoelectron spectrometry, ellipsometry and contact angle were used to probe the physical and surface properties of the resulting films. Overall, we developed thin films that are helpful to inquire, at the molecular level, phenomena relevant to fiber and textile processing including swelling, degradation, and adsorption of polymers and surfactants. DA - 2009/6/1/ PY - 2009/6/1/ DO - 10.1016/j.tsf.2009.03.015 VL - 517 IS - 15 SP - 4348-4354 SN - 0040-6090 KW - Polymers KW - Textiles KW - Adsorption KW - Tribology ER - TY - JOUR TI - Detailed structural models for activated carbons from molecular simulation AU - Palmer, J. C. AU - Brennan, J. K. AU - Hurley, M. M. AU - Balboa, A. AU - Gubbins, K. E. T2 - CARBON AB - A detailed atomistic model of Calgon Co.’s bituminous coal-based activated carbon (BPL) was developed using an adaptation of the Hybrid Reverse Monte Carlo method. The resulting model was a highly heterogeneous carbon structure that had features consistent with experimental X-ray diffraction measurements. The microstructure of the model was characterized and Grand Canonical Monte Carlo simulations were used to examine the adsorptive properties of the model. These findings were compared with experimental measurements taken on samples of the real material. The results showed that the model provides a realistic description of the BPL’s microstructure and accurately predicts adsorptive behavior over a wide range of state conditions. DA - 2009/10// PY - 2009/10// DO - 10.1016/j.carbon.2009.06.037 VL - 47 IS - 12 SP - 2904-2913 SN - 0008-6223 ER - TY - JOUR TI - Complex Effects of the Sweep Fluid on Solid-State Polymerization: Poly(bisphenol A carbonate) in Supercritical Carbon Dioxide AU - Kim, Jaehoon AU - Dong, Laura Beth AU - Kiserow, Douglas J. AU - Roberts, George W. T2 - MACROMOLECULES AB - The effects of the sweep fluid on solid-state polymerization (SSP) of poly(bisphenol A carbonate) (BPA-PC) were investigated. Prepolymers with two different number-average molecular weights, PCP6C (Mn = 3800 g/mol) and PCP9C (Mn = 2400 g/mol), were synthesized using melt transesterification. Solid-state polymerization of these prepolymers was carried out at temperatures in the range of 150−190 °C with supercritical carbon dioxide (scCO2) and N2 as the sweep fluids. It was found that scCO2 at 207 bar could either increase or decrease the rate of SSP relative to the rate in atmospheric N2, depending on the prepolymer molecular weight. At 190 °C, the molecular weights of the polymers synthesized from the higher-molecular-weight prepolymer (PCP6C) were higher with scCO2 as the sweep fluid compared to those of the polymers synthesized with N2. In contrast, at the same temperature of 190 °C, the molecular weights of the polymers synthesized from the lower-molecular-weight prepolymer (PCP9C) were lower with scCO2 compared to those of the polymers synthesized with N2. This apparently contradictory effect can be understood in terms of competition between rate-increasing effects of scCO2, such as greater chain mobility and a higher byproduct diffusion coefficient caused by plasticizing of the polymer by scCO2, and rate-diminishing effects associated with scCO2, such as lamellar thickening, higher crystallinity, and perhaps increased occlusion of end groups in crystalline regions. DA - 2009/4/14/ PY - 2009/4/14/ DO - 10.1021/ma802193q VL - 42 IS - 7 SP - 2472-2479 SN - 1520-5835 ER - TY - JOUR TI - Asphaltene Adsorption onto Self-Assembled Monolayers of Alkyltrichlorosilanes of Varying Chain Length AU - Turgman-Cohen, Salomon AU - Fischer, Daniel A. AU - Kilpatrick, Peter K. AU - Genzer, Jan T2 - ACS APPLIED MATERIALS & INTERFACES AB - The adsorption of asphaltenes onto flat silica surfaces modified with self-assembled monolayers (SAMs) of alkyltrichlorosilanes of varying thickness due to a variable number of carbon atoms (N(C)) has been studied by means of contact angle measurements, spectroscopic ellipsometry, and near-edge X-ray absorption fine structure spectroscopy. The extent of asphaltene adsorption was found to depend primarily on the ability of the SAM layer to shield the underlying silicon substrate from interacting with the asphaltenes present in solution. Specifically, asphaltene adsorption decreased with an increase in N(C) and/or an increase in SAM grafting density, sigma(SAM), (i.e., number of SAM molecules per unit area). The effect of the solvent quality on the extent of asphaltene adsorption was gauged by adsorbing asphaltenes from toluene, 1-methylnaphthalene, tetralin, decalin, and toluene-heptanes mixtures. The extent of asphaltene adsorption was found to increase proportionally with a decrease in the Hildebrand solubility parameter of the solvent. DA - 2009/6// PY - 2009/6// DO - 10.1021/am900203u VL - 1 IS - 6 SP - 1347-1357 SN - 1944-8244 KW - asphaltenes KW - self-assembled monolayers KW - alklyltrichlorosilanes KW - NEXAFS KW - ellipsometry KW - wettability ER - TY - JOUR TI - Temperature, not LuxS, mediates AI-2 formation in hydrothermal habitats AU - Nichols, Jason D. AU - Johnson, Matthew R. AU - Chou, Chung-Jung AU - Kelly, Robert M. T2 - FEMS MICROBIOLOGY ECOLOGY AB - Quorum sensing provides the basis for coordinating community-wide, microbial behaviors in many mesophilic bacteria. However, little attention has been directed toward the possibility that such phenomena occur in extremely thermal microbial environments. Despite the absence of luxS in hyperthermophile genomes, autoinducer-2 (AI-2), a boronated furanone and proposed 'universal' interspecies mesophilic bacterial communication signal, could be formed by Thermotoga maritima and Pyrococcus furiosus through a combination of biotic and abiotic reaction steps. AI-2 did not, however, induce any detectable quorum-sensing phenotypes in these organisms, although transcriptome-based evidence of an AI-2-induced stress response was observed in T. maritima. The significance, if any, of AI-2 in hydrothermal habitats is not yet clear. Nevertheless, these results show the importance of considering environmental factors, in this case high temperatures, as abiotic causative agents of biochemical and microbiological phenomena. DA - 2009/4// PY - 2009/4// DO - 10.1111/j.1574-6941.2009.00662.x VL - 68 IS - 2 SP - 173-181 SN - 1574-6941 KW - autoinducer-2 KW - AI-2 KW - hyperthermophiles KW - hydrothermal environments KW - Thermotoga maritima KW - Pyrococcus furiosus ER - TY - JOUR TI - Modeling Sorption Kinetics of Carbon Dioxide in Glassy Polymeric Films Using the Nonequilibrium Thermodynamics Approach AU - Carla, Vito AU - Hussain, Yazan AU - Grant, Christine AU - Sarti, Giulio C. AU - Carbonell, Ruben G. AU - Doghieri, Ferruccio T2 - INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH AB - The nonequilibrium thermodynamics of glassy polymers (NET-GP) approach (Macromolecules 2005, 38, 10299.) has been applied to the development of a one-dimensional transport model aimed at describing the kinetics of sorption and dilation of polymeric films in supercritical carbon dioxide. The NET-GP model was combined with a simple rheological constitutive equation to build a sorption−diffusion−relaxation model able to describe mass uptake and swelling kinetics of polymeric films in contact with carbon dioxide over a wide range of pressures and temperatures. The model calculations are compared with data on mass sorption kinetics for CO2 in supported glassy poly(methyl methacrylate) (PMMA) films, measured in a high-pressure quartz crystal microbalance (QCM). DA - 2009/4/15/ PY - 2009/4/15/ DO - 10.1021/ie800655w VL - 48 IS - 8 SP - 3844-3854 SN - 0888-5885 ER - TY - JOUR TI - Generation of activated carbon nanofibers from electrospun polyacrylonitrile-zinc chloride composites for use as anodes in lithium-ion batteries AU - Ji, Liwen AU - Zhang, Xiangwu T2 - ELECTROCHEMISTRY COMMUNICATIONS AB - Activated carbon nanofibers (CNFs) with large surface areas and small pores were prepared by electrospinning and subsequent thermal and chemical treatments. These activated CNFs were examined as anodes for lithium-ion batteries (LIBs) without adding any non-active material. Their electrochemical behaviors show improved lithium-ion storage capability and better cyclic stability compared with unactivated counterparts. The results demonstrate that the unique structures and properties of these materials make them promising candidates as anodes in LIBs. DA - 2009/3// PY - 2009/3// DO - 10.1016/j.elecom.2009.01.018 VL - 11 IS - 3 SP - 684-687 SN - 1873-1902 UR - https://publons.com/publon/7178330/ KW - Carbon nanofibers KW - Lithium-ion batteries KW - Electrospinning ER - TY - JOUR TI - Epitaxial Ba0.5Sr0.5TiO3-GaN heterostructures with abrupt interfaces AU - Losego, M. D. AU - Kourkoutis, L. Fitting AU - Mita, S. AU - Craft, H. S. AU - Muller, D. A. AU - Collazo, R. AU - Sitar, Z. AU - Maria, J. -P. T2 - JOURNAL OF CRYSTAL GROWTH AB - Abstract Epitaxial heterostructures incorporating the complex ferroelectric oxide Ba 0.5 Sr 0.5 TiO 3 (BST) and GaN were prepared using a combination of RF magnetron sputtering and metalorganic chemical vapor deposition for the respective layers. The heterostructures were grown on c -plane sapphire substrates and were characterized using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning transmission electron microscopy (STEM). This analysis showed that at substrate temperatures of 650 °C, BST films grow epitaxially on GaN with a {1 1 1} orientation and that the GaN–BST interface is smooth and abrupt, with disorder confined to grain boundaries and the interface plane. The film morphology is grainy indicating a 3-D growth mode. High-temperature post-deposition annealing studies suggest no interface reactions up to 900 °C. These results demonstrate that complex oxides like BST can be integrated with wide bandgap semiconductors like GaN and open exciting possibilities for new multifunctional devices. DA - 2009/2/1/ PY - 2009/2/1/ DO - 10.1016/j.jcrysgro.2008.11.085 VL - 311 IS - 4 SP - 1106-1109 SN - 1873-5002 KW - Physical vapor deposition processes KW - Nitrides KW - Perovskites KW - Ferroelectric materials ER - TY - JOUR TI - Mechanical and actuation behavior of electroactive nanostructured polymers AU - Shankar, Ravi AU - Ghosh, Tushar K. AU - Spontak, Richard J. T2 - SENSORS AND ACTUATORS A-PHYSICAL AB - Electroactive polymers (EAPs) can exhibit relatively large actuation strain responses upon electrical stimulation. For this reason, in conjunction with their light weight, robust properties, low cost and facile processability, EAPs are of considerable interest in the development of next-generation organic actuators. Within this class of materials, dielectric electroactive polymers (D-EAPs) have repeatedly exhibited the most promising and versatile properties. A new family of D-EAPs derived from swollen poly[styrene-b-(ethylene-co-butylene)-b-styrene] triblock copolymers has been recently found to undergo ultrahigh displacement at relatively low electric fields compared to previously reported D-EAPs. The present work examines the mechanical and actuation response of these electroactive nanostructured polymer (ENP) systems under quasi-static, and electromechanical loading conditions. Careful measurement of the quasi-static properties under tensile and compressive loading yield similar results that are significantly influenced by the introduction of in-plane strain, as well as by copolymer concentration or molecular weight. Blocking stress measurements reveal that the actuation effectiveness achieved by some of the ENPs is comparable to that of the VHB 4910 acrylic D-EAP, thus providing a novel and efficient avenue to designer D-EAPs for advanced engineering, biomimetic and biomedical applications. DA - 2009/4/8/ PY - 2009/4/8/ DO - 10.1016/j.sna.2009.01.002 VL - 151 IS - 1 SP - 46-52 SN - 0924-4247 KW - Electroactive nanostructured polymer KW - Compressive modulus KW - Blocking stress ER - TY - JOUR TI - Manganese oxide nanoparticle-loaded porous carbon nanofibers as anode materials for high-performance lithium-ion batteries AU - Ji, Liwen AU - Zhang, Xiangwu T2 - ELECTROCHEMISTRY COMMUNICATIONS AB - Mn-based oxide-loaded porous carbon nanofiber anodes, exhibiting large reversible capacity, excellent capacity retention, and good rate capability, are fabricated by carbonizing electrospun polymer/Mn(CH3COO)2 composite nanofibers without adding any polymer binder or electronic conductor. The excellent electrochemical performance of these organic/inorganic nanocomposites is a result of the unique combinative effects of nano-sized Mn-based oxides and carbon matrices as well as the highly-developed porous composite nanofiber structure, which make them promising anode candidates for high-performance rechargeable lithium-ion batteries. DA - 2009/4// PY - 2009/4// DO - 10.1016/j.elecom.2009.01.039 VL - 11 IS - 4 SP - 795-798 SN - 1873-1902 UR - https://publons.com/publon/7178338/ KW - Porous carbon nanofibers KW - Lithium-ion batteries KW - Electrospinning ER - TY - JOUR TI - Sugar surfactants in paper recycling AU - Spence, K. AU - Venditti, R. AU - Rojas, O. J. T2 - Nordic Pulp & Paper Research Journal DA - 2009/// PY - 2009/// DO - 10.3183/npprj-2009-24-01-p107-111 VL - 24 IS - 1 SP - 107–111 KW - Sugar surfactants KW - Natural surfactants KW - Protein surfactants KW - Paper recycling KW - Flotation deinking KW - Quartz crystal microbalance KW - Alkyl phenol ethoxylates KW - Copy paper KW - model inks ER - TY - JOUR TI - Rapid Removal of Organics and Oil Spills from Waters Using Silicone Rubber "Sponges" AU - Park, Insun AU - Efimenko, Kirill AU - Sjoblom, Johan AU - Genzer, Jan T2 - JOURNAL OF DISPERSION SCIENCE AND TECHNOLOGY AB - We have developed a simple, robust, and efficient technology utilizing cheap and recoverable materials based on commercially available silicone elastomer networks for removing organic solvents and crude oil from waters. Hydrophobic and oleophilic properties of silicone elastomers endow poly(dimethyl siloxane) (PDMS) with the capacity to absorb a large variety of organics, including benzene (B), toluene (T), ethylbenzene (E), and xylene (X), commonly referred to as BTEX, and also crude oils, while at the same time enabling the organic “sponges” to float on waters, which facilitates straightforward handling. We developed a method for generating PDMS particles with variable sizes (ranging from hundreds nanometers to few millimeters) by drop-wise depositing siloxane/cross-linker mixtures into warm water, a process which leads to the cross-linking of the PDMS components. We have tested the capability of the PDMS particles to remove toluene and benzene from water. We also performed similar experiments by utilizing PDMS sheets. In both instances we observed a rapid sorption of the organic phase into PDMS; the amount of absorbed organic solvent depended on the concentration in water and the total mass (volume) of PDMS and did not depend on the geometry of the PDMS “sponge.” In addition, we have examined the uptake of toluene and benzene from toluene/benzene (T/B) mixtures dissolved in water. Our results indicate that the amount of benzene absorbed from the T/B mixtures into PDMS increases relative to the uptake from pure benzene/water solutions. This behavior is associated with toluene acting as a “surfactant” that effectively replaces the more unfavorable PDMS/B contacts with less costly T/B ones. Finally, a simple experiment demonstrates qualitatively that PDMS is also capable of removing crude oils from oil-contaminated waters. DA - 2009/// PY - 2009/// DO - 10.1080/01932690802540384 VL - 30 IS - 3 SP - 318-327 SN - 1532-2351 KW - Water purification KW - removal of organic from water KW - BTEX KW - PDMS KW - sylgard-184 ER - TY - JOUR TI - Quantification of Cellulase Activity Using the Quartz Crystal Microbalance Technique AU - Hu, Gang AU - Heitmann, John A., Jr. AU - Rojas, Orlando J. T2 - ANALYTICAL CHEMISTRY AB - The development of more efficient utilization of biomass has received increased attention in recent years. Cellulases play an important role in processing biomass through advanced biotechnological approaches. Both the development and the application of cellulases require an understanding of the activities of these enzymes. A new method to determine the activity of cellulase has been developed using a quartz crystal microbalance (QCM) technique. We compare the results from this technique with those from the IUPAC (International Union of Pure and Applied Chemistry) dinitrosalicylic acid (DNS) standard method and also from biccinchoninic acid and ion chromatography methods. It is shown that the QCM technique provides results closer to those obtained by measuring the actual reducing sugars. The elimination of the use of color development in the standard redox methods makes the QCM platform easier to implement; it also allows more flexibility in terms of the nature of the substrate. Finally, validation of the proposed method was carried out by relating the crystallinity of different substrates to the cellulase activity. Numerical values of cellulase activities measured with the QCM method showed that celluloses with higher crystallinity indices were hydrolyzed slower and to a lower extent than those of lower crystallinity indices for the cellulase mixtures examined. DA - 2009/3/1/ PY - 2009/3/1/ DO - 10.1021/ac802318t VL - 81 IS - 5 SP - 1872-1880 SN - 1520-6882 ER - TY - JOUR TI - Formation and Properties of Responsive Siloxane-Based Polymeric Surfaces with Tunable Surface Reconstruction Kinetics AU - Crowe-Willoughby, Julie Ann AU - Genzer, Jan T2 - ADVANCED FUNCTIONAL MATERIALS AB - Abstract Here, the formation of responsive polymeric materials with tunable response time is reported. These structures are fabricated by chemically modifying poly(vinylmethyl siloxane) (PVMS) networks with alkanethiols bearing a hydrophilic end‐group (COOH or OH). The response time is facilitated by the liquid nature of the PVMS backbone and increases with increase in length of the methylene spacer (CH 2 ) n  in the alkanethiol pendent group. While for n = 2 and 6, the surface reconstructs almost instantaneously, specimens with n = 11 resist reconstruction because of strong van der Waals forces, leading to the formation of semi‐crystalline regions. It is demonstrated that the responsive nature of PVMSS(CH 2 ) 11 OH can be fine‐tuned by varying the temperature; it possesses a faster response at temperatures above the melting point of the S(CH 2 ) 11 OH moiety. DA - 2009/2/10/ PY - 2009/2/10/ DO - 10.1002/adfm.200800622 VL - 19 IS - 3 SP - 460-469 SN - 1616-3028 ER - TY - JOUR TI - Fabrication of porous carbon nanofibers and their application as anode materials for rechargeable lithium-ion batteries AU - Ji, Liwen AU - Zhang, Xiangwu T2 - NANOTECHNOLOGY AB - Porous carbon nanofibers were prepared by the electrospinning of a bicomponent polymer solution, followed by thermal treatments under different atmospheres. The surface morphology, thermal properties, and crystalline features of these nanofibers were characterized using various analytic techniques, and it was found that they were formed with turbostratically disordered graphene sheets and had small pores and large surface areas. The unique structure of these porous carbon nanofibers resulted in good electrochemical performance such as high reversible capacity and good cycle stability when they were used as anodes for rechargeable lithium-ion batteries. DA - 2009/4/15/ PY - 2009/4/15/ DO - 10.1088/0957-4484/20/15/155705 VL - 20 IS - 15 SP - SN - 1361-6528 UR - https://publons.com/publon/6110280/ ER - TY - JOUR TI - Bi-directional Kirkendall Effect in Coaxial Microtuble Nanolaminate Assemblies Fabricated by Atomic Layer Deposition AU - Peng, Qing AU - Sun, Xiao-Yu AU - Spagnola, Joseph C. AU - Saquing, Carl AU - Khan, Saad A. AU - Spontak, Richard J. AU - Parsons, Gregory N. T2 - ACS NANO AB - The solid-state reaction within a coaxial Al2O3/ZnO/Al2O3 multilayered microtubular structure can be used to prepare discrete microtube-in-microtube ZnAl2O4 spinel assemblies through a Kirkendall void production mechanism at 700 degrees C. In contrast with previous studies of the nanoscale Kirkendall effect, the reaction observed here proceeds through a bi-directional vacancy diffusion mechanism wherein ZnO species diffuse into inner- and outer-Al2O3 concentric layers, thereby resulting in vacancy supersaturation and void production between two isolated spinel microtubes. Low-temperature atomic layer deposition (ALD) of Al2O3 and ZnO enables the fabrication of complex coaxial multilayered microtubes with precise control of the starting film thicknesses and relative composition. When a molar excess of ZnO is present between two Al2O3 layers, electron microscopy images reveal incomplete ZnO consumption after annealing at 700 degrees C. At higher initial Al2O3 concentrations, however, complete reaction with ZnO is observed, and the size of the Kirkendall gap between isolated spinel microtubes appears to be directly influenced by the thickness of the intermediate ZnO layer. DA - 2009/3// PY - 2009/3// DO - 10.1021/nn8006543 VL - 3 IS - 3 SP - 546-554 SN - 1936-086X UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000264535200010&KeyUID=WOS:000264535200010 KW - atomic layer deposition KW - electrospinning KW - aluminum oxide KW - zinc oxide KW - Kirkendall effect KW - tube-in-tube KW - microtube ER - TY - JOUR TI - Atomic layer deposition and biocompatibility of titanium nitride nano-coatings on cellulose fiber substrates AU - Hyde, G. K. AU - McCullen, S. D. AU - Jeon, S. AU - Stewart, S. M. AU - Jeon, H. AU - Loboa, E. G. AU - Parsons, G. N. T2 - BIOMEDICAL MATERIALS AB - Atomic layer deposition (ALD) is investigated as a process to produce inorganic metallic bio-adhesive coatings on cellulosic fiber substrates. The atomic layer deposition technique is known to be capable of forming highly conformal and uniform inorganic thin film coatings on a variety of complex surfaces, and this work presents an initial investigation of ALD on porous substrate materials to produce high-precision biocompatible titanium oxynitride coatings. X-ray photoelectron spectroscopy (XPS) confirmed TiNOx composition, and transmission electron microscopy (TEM) analysis showed the coatings to be uniform and conformal on the fiber surfaces. Biocompatibility of the modified structures was determined as a function of coating layer thickness by fluorescent live/dead staining of human adipose-derived adult stem cells (hADSC) at 6, 12 and 24 h. Cell adhesion showed that thin TiNOx coatings yielded the highest number of cells after 24 h with a sample coated with a 20 Å coating having approximately 28.4 ± 3.50 ng DNA. By altering the thickness of the deposited film, it was possible to control the amount of cells adhered to the samples. This work demonstrates the potential of low temperature ALD as a surface modification technique to produce biocompatible cellulose and other implant materials. DA - 2009/4// PY - 2009/4// DO - 10.1088/1748-6041/4/2/025001 VL - 4 IS - 2 SP - SN - 1748-605X UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000264935500003&KeyUID=WOS:000264935500003 ER - TY - JOUR TI - Deposition of Copper Particles and Films by the Displacement of Two Immiscible Supercritical Phases and Subsequent Reaction AU - Kim, Jaehoon AU - Taylor, Douglas AU - DeYoung, James AU - McClain, James B. AU - DeSimone, Joseph M. AU - Carbonell, Ruben G. T2 - Chemistry of Materials AB - Copper (Cu) particles and films were produced by forming Cu(II) compound (Cu(hfac)2·H2O) films on substrates using a displacement from two immiscible supercritical phases (DISP) technique followed by reducing the copper(II) compound films in hydrogen at 200 °C. Various surfaces including native oxide of silicon (SiOx), titanium nitride (TiN), tungsten (W), and low-k dielectric materials such as Coral, JSR5109, and Silox were used as substrates. The nucleation and growth behavior of the Cu DISP process was evaluated over a range of reduction times (from 5 to 60 min) and copper(II) compound concentrations (0.5−3 wt %). At short reduction periods (5−15 min) or low Cu(II) compound concentrations (∼ 0.5 wt %), Cu particles ranging from 60 to 95 nm in diameter were produced. In contrast, at long reduction periods (45−60 min) and high concentrations (∼3 wt %), continuous Cu films with 220−450 nm in thickness were deposited on the substrates. A morphology transition from particle to film was observed at medium reduction period (∼30 min) or medium concentration range (∼1 wt %). High affinity of TiN to Cu nucleation and film formation leads to more dense and smooth films than Cu films deposited under similar conditions on SiOx. However, nucleation of Cu DISP is not very sensitive to the surface conditions of the substrates compared with Cu CVD (chemical vapor deposition). Chemical composition analysis of the Cu film on TiN and SiOx by X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) revealed that highly pure Cu films were obtained from Cu DISP. DA - 2009/3/10/ PY - 2009/3/10/ DO - 10.1021/cm802659j VL - 21 IS - 5 SP - 913-924 J2 - Chem. Mater. LA - en OP - SN - 0897-4756 1520-5002 UR - http://dx.doi.org/10.1021/cm802659j DB - Crossref ER - TY - JOUR TI - "Zincone" Zinc Oxide-Organic Hybrid Polymer Thin Films Formed by Molecular Layer Deposition AU - Peng, Qing AU - Gong, Bo AU - VanGundy, Ryan M. AU - Parsons, Gregory N. T2 - CHEMISTRY OF MATERIALS AB - Hybrid organic−inorganic polymer thin films of the form (−O−Zn−O−C2H4−)n have been deposited from diethyl zinc and ethylene glycol using molecular layer deposition (MLD) over a range of substrate temperatures between 100 and 170 °C. Infrared transmission confirms that the films consist of Zn−O and ethylene-oxide units. In analogy with known alucone polymers of the form (−O−Al−O−R−)n, the zinc-based hybrid material is an example of a “zincone” polymer. In situ quartz crystal microbalance analysis indicated that the sequential surface reactions of diethyl zinc and ethylene glycol are sufficiently self-limiting and saturating to enable well-controlled MLD growth. Quantitative analysis of in situ quartz crystal microbalance and film thickness results indicate that ethylene glycol molecules can undergo a “double reaction” where the OH groups on both ends of the diol react with available Zn−C2H5 surface sites to produce a relatively inert bridging alkane. The mass uptake per MLD cycle during Zn−hybrid film deposition decreases with increasing reaction temperature. Infrared transmission spectroscopy also shows that Zn−organic hybrid films are stable in dry air. However, the as-deposited ZnO−hybrid material could be hydrolyzed by H2O (for example, in ambient) resulting in films consisting of zinc oxide and zinc hydroxide with some carbon remnants. Spectroscopic ellipsometry indicates the thickness of hydrolyzed films increases linearly with reaction cycles, and scanning probe and transmission electron microscopy images show the hydrolyzed ZnO−hybrid film coating is uniform and conformal. The transmission electron micrographs also show the hydrolyzed Zn−hybrid films contain nanoscale porosity. These results suggest new pathways to fabricate organic−inorganic hybrid materials, including metal-organic framework structures. DA - 2009/3/10/ PY - 2009/3/10/ DO - 10.1021/cm8020403 VL - 21 IS - 5 SP - 820-830 SN - 1520-5002 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000263891700009&KeyUID=WOS:000263891700009 ER - TY - JOUR TI - Reconfigurable responsive structures assembled from magnetic Janus particles AU - Smoukov, Stoyan K. AU - Gangwal, Sumit AU - Marquez, Manuel AU - Velev, Orlin D. T2 - SOFT MATTER AB - Magnetic Janus particles are assembled into novel staggered chain structures under the action of magnetic and electric fields. The magnetic assembly can result in permanent structures, which could be disassembled on demand by remote demagnetization. DA - 2009/// PY - 2009/// DO - 10.1039/b814304h VL - 5 IS - 6 SP - 1285-1292 SN - 1744-6848 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-62249108648&partnerID=MN8TOARS ER - TY - JOUR TI - Fabrication of Carbon Fibers with Nanoporous Morphologies from Electrospun Polyacrylonitrile/Poly(L-lactide) Blends AU - Ji, Liwen AU - Medford, Andrew J. AU - Zhang, Xiangwu T2 - JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS AB - Abstract Porous carbon nanofibers were prepared through electrospinning a blend solution of polyacrylonitrile and poly( L ‐lactide), followed by carbonization at different temperatures and in different atmospheres. Structural features of these porous carbon nanofibers were characterized using scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, X‐ray powder diffraction, and Raman spectroscopy. Surface area and pore structure were evaluated using the nitrogen adsorption technique. It was found that carbon fibers prepared by this scalable and relatively economical method exhibited a porous surface morphology with high specific surface area and large pore volume. The fiber diameter, surface area, pore volume, bulky crystalline structure, and surface crystalline structure of these carbon nanofibers showed a strong dependence on the polymer precursor composition and carbonization condition. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 493–503, 2009 DA - 2009/3/1/ PY - 2009/3/1/ DO - 10.1002/polb.21654 VL - 47 IS - 5 SP - 493-503 SN - 1099-0488 UR - https://publons.com/publon/7178332/ KW - blends KW - carbonization KW - electrospinning KW - fibers KW - phase separation KW - polyacrylonitrile KW - poly(L-lactide) KW - porous carbon nanofibers ER - TY - JOUR TI - Transmission electron microtomography in polymer research AU - Jinnai, Hiroshi AU - Spontal, Richard J. T2 - POLYMER AB - This feature article summarizes recent advances in an emerging three-dimensional (3D) imaging technique, transmission electron microtomography (TEMT), and its applications to polymer-related materials, such as nanocomposites and block copolymer morphologies. With the recent developments made in TEMT, it is now possible to obtain truly quantitative 3D data with sub-nanometer resolution. A great deal of new structural information, which has never been obtained by conventional microscopy or various scattering methods, can be directly evaluated from the 3D volume data. It has also been demonstrated that, with the combination of TEMT and scattering methods, it becomes possible to study structures that have not yet been characterized. The structural information obtained from such 3D imaging provides a good opportunity not only to gain essential insight into the physics of self-assembling processes and the statistical mechanics of long chain molecules, but also to establish the “structure–property” relationship in polymeric materials. DA - 2009/2/23/ PY - 2009/2/23/ DO - 10.1016/j.polymer.2008.12.023 VL - 50 IS - 5 SP - 1067-1087 SN - 1873-2291 KW - 3D imaging KW - Transmission electron microtomography KW - 3D digital image analysis KW - Block copolymers KW - Microphase-separated structures KW - Bicontinuous structures ER - TY - JOUR TI - Porous Nylon-6 Fibers via a Novel Salt-Induced Electrospinning Method AU - Gupta, Amit AU - Saquing, Carl D. AU - Afshari, Mehdi AU - Tonelli, Alan E. AU - Khan, Saad A. AU - Kotek, Richard T2 - MACROMOLECULES AB - Porous nylon-6 fibers are obtained from Lewis acid−base complexation of gallium trichloride (GaCl3) and nylon-6 using electrospinning followed by GaCl3 removal. DSC and FTIR results reveal that the electrospun fibers, prior to GaCl3 removal, are amorphous with no hydrogen bonds present between nylon-6 chains. GaCl3 being a Lewis acid interacts with the Lewis base sites (C═O groups) on the nylon-6 chains, thereby preventing the chains to crystallize via intermolecular hydrogen bonding. Subsequent removal of GaCl3 from the as-spun fibers by soaking the electrospun web in water for 24 h leads to the formation of pores throughout the fibers. While the average fiber diameter remains effectively the same after salt removal, the average surface area increases by more than a factor of 6 for the regenerated fibers. The dual use of a metal salt (Lewis acid) to (a) facilitate fiber formation by temporary removal of polymer interchain interactions and (b) act as a porogen provides a facile approach to obtain porous fibers via electrospinning. DA - 2009/2/10/ PY - 2009/2/10/ DO - 10.1021/ma801918c VL - 42 IS - 3 SP - 709-715 SN - 1520-5835 ER - TY - JOUR TI - Inhibition of Acinetobacter baumannii, Staphylococcus aureus and Pseudomonas aeruginosa biofilm formation with a class of TAGE-triazole conjugates AU - Huigens, Robert W., III AU - Rogers, Steven A. AU - Steinhauer, Andrew T. AU - Melander, Christian T2 - ORGANIC & BIOMOLECULAR CHEMISTRY AB - A chemically diverse library of TAGE-triazole conjugates was synthesized utilizing click chemistry on the TAGE scaffold. This library of small molecules was screened for anti-biofilm activity and found to possess the ability of inhibiting biofilm formation against Acinetobacter baumannii, Staphylococcus aureus and Pseudomonas aeruginosa. One such compound in this library demonstrated the most potent inhibitory effect against Staphylococcus aureus biofilm formation that has been displayed by any 2-aminoimidazole derivative. DA - 2009/// PY - 2009/// DO - 10.1039/b817926c VL - 7 IS - 4 SP - 794-802 SN - 1477-0539 ER - TY - JOUR TI - Fluoropolymer synthesis in supercritical carbon dioxide AU - Du, Libin AU - Kelly, Jennifer Y. AU - Roberts, George W. AU - DeSimone, Joseph M. T2 - JOURNAL OF SUPERCRITICAL FLUIDS AB - Herein we review the environmentally friendly synthesis of fluorinated polymers in supercritical carbon dioxide (scCO2). Historically, many high-performance fluorinated materials are commercially synthesized in aqueous media using fluorinated surfactants or in non-aqueous conditions using fluorinated solvents. Our group has pioneered both the homogeneous and heterogeneous polymerization of fluorinated monomers in scCO2. This review includes discussions on the synthesis of main-chain and side-chain fluoropolymers conducted via a chain-growth or continuous process. Specific materials consist of acrylate- and styrene-based systems, poly(vinyl ether)s, tetrafluoroethylene- and vinylidenefluoride-based, as well as novel fluorinated elastomers and thermoplastics. DA - 2009/1// PY - 2009/1// DO - 10.1016/j.supflu.2008.11.011 VL - 47 IS - 3 SP - 447-457 SN - 1872-8162 KW - Supercritical carbon dioxide KW - Fluoropolymer ER - TY - JOUR TI - Competitive hydrogen-bonding in polymer solutions with mixed solvents AU - Shankar, Ravi AU - Klossner, Rebecca R. AU - Weaver, Juan T. AU - Koga, Tsuyoshi AU - Zanten, John H. AU - Krause, Wendy E. AU - Colina, Coray M. AU - Tanaka, Fumihiko AU - Spontak, Richard J. T2 - SOFT MATTER AB - Poly(ethylene oxide) (PEO) coil size is investigated in a binary mixture of solvent molecules capable of cooperatively hydrogen-bonding with each other, as well as with the PEO chains. Viscometry reveals a minimum in zero shear rate solution viscosity at a molar ratio of ∼2:1 water:methanol. This viscosity coincides with a minimum in PEO gyration radius and occurs near the conditions where water/methanol mixtures deviate most markedly from ideal solution behavior. A minimum in polymer mean square end-to-end distance is predicted for polymer solutions composed of two hydrogen-bonding solvents. DA - 2009/// PY - 2009/// DO - 10.1039/b808479c VL - 5 IS - 2 SP - 304-307 SN - 1744-683X ER - TY - JOUR TI - Purification of human immunoglobulin G via Fc-specific small peptide ligand affinity chromatography AU - Yang, Haiou AU - Gurgel, Patrick V. AU - Carbonell, Ruben G. T2 - JOURNAL OF CHROMATOGRAPHY A AB - Chromatographic resins of a family of linear Fc-binding hexamer peptides (HWRGWV, HYFKFD, and HFRRHL) exhibited the ability to selectively adsorb and isolate human IgG (hIgG) from complete mammalian cell culture medium (cMEM). Among them, the HWRGWV resin with a peptide density of 0.08 mequiv./g of resin was able to purify hIgG from cMEM with both purity and yield as high as 95%, comparable to Protein A and A2P agarose gels. The influences of N-terminal acetylation of the HWRGWV resin, ligand density on the resin, initial hIgG concentration, and temperature on IgG isolation were also investigated. The results indicate that these small peptide ligands, especially HWRGWV, offer a potential alternative to the use of Protein A or Protein G for large scale affinity chromatography. DA - 2009/2/6/ PY - 2009/2/6/ DO - 10.1016/j.chroma.2008.12.004 VL - 1216 IS - 6 SP - 910-918 SN - 1873-3778 KW - Human immunoglobulin G KW - Fc fragment KW - Hexamer peptide ligand KW - Affinity chromatography KW - Ligand density ER - TY - JOUR TI - Spontaneous phosphoinositide 3-kinase signaling dynamics drive spreading and random migration of fibroblasts AU - Weiger, Michael C. AU - Wang, Chun-Chao AU - Krajcovic, Matej AU - Melvin, Adam T. AU - Rhoden, John J. AU - Haugh, Jason M. T2 - JOURNAL OF CELL SCIENCE AB - During directed cell migration (chemotaxis), cytoskeletal dynamics are stimulated and spatially biased by phosphoinositide 3-kinase (PI3K) and other signal transduction pathways. Live-cell imaging using total internal reflection fluorescence (TIRF) microscopy revealed that, in the absence of soluble cues, 3'-phosphoinositides are enriched in a localized and dynamic fashion during active spreading and random migration of mouse fibroblasts on adhesive surfaces. Surprisingly, we found that PI3K activation is uncoupled from classical integrin-mediated pathways and feedback from the actin cytoskeleton. Inhibiting PI3K significantly impairs cell motility, both in the context of normal spreading and when microtubules are dissociated, which induces a dynamic protrusion phenotype as seen by TIRF in our cells. Accordingly, during random migration, 3'-phosphoinositides are frequently localized to regions of membrane protrusion and correlate quantitatively with the direction and persistence of cell movement. These results underscore the importance of localized PI3K signaling not only in chemotaxis but also in basal motility/migration of fibroblasts. DA - 2009/2/1/ PY - 2009/2/1/ DO - 10.1242/jcs.037564 VL - 122 IS - 3 SP - 313-323 SN - 1477-9137 KW - Cell migration KW - Phosphoinositide 3-kinase KW - Integrin KW - Fibronectin KW - Adhesion ER - TY - JOUR TI - Surfactant-Mediated Modulation of Hydrophobic Interactions in Associative Polymer Solutions Containing Cyclodextrin AU - Talwar, Sachin AU - Harding, Jonathon AU - Oleson, Keith R. AU - Khan, Saad A. T2 - LANGMUIR AB - The ability of nonionic surfactants to modulate the rheological characteristics of comblike hydrophobically modified associative polymer solutions containing cyclodextrin (CD) is examined. Addition of either alpha- or beta-CD to these polymers results in a marked decrease in solution viscosity and viscoelastic properties because of the encapsulation of the polymer hydrophobes by CD. Nonionic surfactants, introduced to such a system, alter the hydrophobic interactions by competing with the polymer hydrophobes for complexation with the CDs. In this regard, nonylphenol ethoxylates (NPe) with different ethylene oxide chain lengths, which determine the hydrophilic-lipophilic balance (HLB) of the surfactant, are used. Our results reveal that the extent and rate of recovery of zero shear viscosity as well as dynamic moduli are strongly influenced by the type of CD (alpha versus beta) as well as the HLB of the surfactant. For polymer solutions containing alpha-CD, recovery is observed solely in the presence of a low-HLB surfactant (NP6 and NP8). Additionally, in the case of NP6, the viscosity increases monotonically above the original hydrophobically modified alkali-soluble emulsion viscosity with surfactant addition, whereas for that of a higher HLB surfactant (NP15), the viscosity shows no appreciable change. In the case of beta-CD, on the other hand, a complete recovery as well as further enhancement of rheological properties is achieved using the above surfactants. However, the trends of viscosity modulation are dissimilar for different surfactants as we witness a monotonous increase in the case of NP6 while a maximum in viscosity is observed in the presence of NP8 and NP15. The contrasting observations can be explained in terms of varying affinities of alpha- and beta-CDs to bind with NP surfactants and the existence of different micellar structures in solution as governed by surfactant HLB. These results are further confirmed by UV/vis spectroscopy and cloud point measurements. DA - 2009/1/20/ PY - 2009/1/20/ DO - 10.1021/la803056e VL - 25 IS - 2 SP - 794-802 SN - 0743-7463 ER - TY - JOUR TI - Kinetics of the Homopolymerization of Vinylidene Fluoride and Its Copolymerization with Hexafluoropropylene in Supercritical Carbon Dioxide: The Locus of Polymerization AU - Ahmed, Tamer S. AU - DeSimone, Joseph M. AU - Roberts, George W. T2 - Macromolecules AB - In previous studies, the continuous polymerization of vinylidene fluoride (VF2) and mixtures of VF2 with hexafluoropropylene (HFP) was carried out in supercritical carbon dioxide (scCO2) using a continuous stirred-tank reactor (CSTR). Most of the polymerizations were heterogeneous; i.e., polymer particles precipitated during the reaction. However, some were homogeneous, especially at higher HFP concentrations. In this study, the data from the earlier experiments have been tested against three kinetic models to determine the primary locus of the heterogeneous polymerizations. The first model, the “solution polymerization” model, is based on the assumption that all of the polymerization reactions take place in the continuous, CO2-rich phase, with no reaction in the polymer phase. In the second model, the “surface polymerization” model, chain initiation occurs in the continuous phase, while chain propagation and termination occur in a thin zone on the surface of the polymer particles. The third model, the “interior polymerization” model, is similar to the “surface polymerization” model, except that propagation and termination take place uniformly throughout the polymer particles. For all polymer compositions, the solution polymerization model is able to describe the experimental data for both the rate of polymerization and the number-average molecular weight quite well. On the other hand, both the surface and the interior polymerization models consistently fail to fit the experimental results. This analysis suggests that the CO2-rich continuous phase is the main locus of polymerization in the precipitation polymerization of VF2 and VF2/HFP mixtures in scCO2 over the current range of the experimental data. DA - 2009/1/13/ PY - 2009/1/13/ DO - 10.1021/ma801911j VL - 42 IS - 1 SP - 148-155 J2 - Macromolecules LA - en OP - SN - 0024-9297 1520-5835 UR - http://dx.doi.org/10.1021/ma801911j DB - Crossref ER - TY - JOUR TI - Electrospun polyacrylonitrile/zinc chloride composite nanofibers and their response to hydrogen sulfide AU - Ji, Liwen AU - Medford, Andrew J. AU - Zhang, Xiangwu T2 - POLYMER AB - In this work, we explore the electrospinning of polyacrylonitrile (PAN)/zinc(II) chloride (ZnCl2) composite nanofibers and the response of these nanofibers to hydrogen sulfide (H2S). Solution properties, including surface tension, viscosity, and conductivity, have been measured and integrated with the results of a variety of other analytical techniques to investigate the effects of ZnCl2 salt on the structure and thermal properties of electrospun nanofibers. It is found that the addition of ZnCl2 reduces the diameter and inhibits the instantaneous cyclization reaction of these nanofibers. Additionally, exposing PAN/ZnCl2 fibers to H2S leads to the formation of PAN/zinc sulfide (ZnS) composite nanofibers that contain ZnS crystals on the surface. These results indicate that PAN/ZnCl2 composite nanofibers could find applications in H2S sensing and removal, or as precursors for semiconductor ZnS-coated polymer nanofibers. DA - 2009/1/16/ PY - 2009/1/16/ DO - 10.1016/j.polymer.2008.11.016 VL - 50 IS - 2 SP - 605-612 SN - 1873-2291 UR - https://publons.com/publon/7178383/ KW - Electrospinning KW - Polyacrylonitrile KW - Zinc(II) chloride ER -