TY - CHAP TI - Interface reactions during oxygen plasma assisted chemical vapor deposition of yttrium oxide on silicon AU - Niu, D AU - Ashcraft, RW AU - Stemmer, S AU - Parsons, GN AU - Huff, HR AU - Fabry, L AU - Kishino, S T2 - Semiconductor Silicon 2002, Vols 1 and 2 PY - 2002/// VL - 2002 SP - 429-439 PB - SE - UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000180812100038&KeyUID=WOS:000180812100038 ER - TY - RPRT TI - Saccharification enzymes from hyperthermophilic bacteria and processes for their production AU - Kelly, R.M. AU - Brown, S.H. AU - Costantino, H.R. AU - Anfinsen, C.B. DA - 2002/3// PY - 2002/3// M1 - 6,355,467 M3 - U.S. Patent SN - 6,355,467 ER - TY - CONF TI - Graft polymerization and other methods to reduce the hygroscopic nature of cellulose insulation AU - Oommen, T.V. AU - Andrady, T.L. T2 - 1996 IEEE International Symposium on Electrical Insulation AB - Cellulosic insulation materials are widely used in power transformers and other high voltage devices, but require intensive drying out to remove all moisture. This paper describes three methods used to modify cellulose to reduce its hygroscopicity, of which graft polymerization was the most successful method. The modified paper sheets, however, lost some mechanical strength properties, and showed a tendency to be thicker than the starting material. C2 - 2002/12/24/ C3 - Conference Record of the 1996 IEEE International Symposium on Electrical Insulation CY - Montreal, Quebec, Canada DA - 2002/12/24/ PY - 1996/6/16/ DO - 10.1109/elinsl.1996.549401 PB - IEEE SN - 0780335317 UR - http://dx.doi.org/10.1109/elinsl.1996.549401 ER - TY - CHAP TI - Enzymatic Modification of Guar Solutions AU - Tayal, Akash AU - Pai, Vandita AU - Kelly, Robert M. AU - Khan, Saad A. T2 - Water Soluble Polymers A2 - Amjad, Z. PY - 2002/// DO - 10.1007/0-306-46915-4_4 SP - 41–49 PB - Springer US SN - 9780306459313 9780306469152 UR - http://dx.doi.org/10.1007/0-306-46915-4_4 ER - TY - JOUR TI - Proteolysis in hyperthermophilic microorganisms AU - Ward, Donald E. AU - Shockley, Keith R. AU - Chang, Lara S. AU - Levy, Ryan D. AU - Michel, Joshua K. AU - Conners, Shannon B. AU - Kelly, Robert M. T2 - Archaea AB - Proteases are found in every cell, where they recognize and break down unneeded or abnormal polypeptides or peptide-based nutrients within or outside the cell. Genome sequence data can be used to compare proteolytic enzyme inventories of different organisms as they relate to physiological needs for protein modification and hydrolysis. In this review, we exploit genome sequence data to compare hyperthermophilic microorganisms from the euryarchaeotal genus Pyrococcus , the crenarchaeote Sulfolobus solfataricus , and the bacterium Thermotoga maritima . An overview of the proteases in these organisms is given based on those proteases that have been characterized and on putative proteases that have been identified from genomic sequences, but have yet to be characterized. The analysis revealed both similarities and differences in the mechanisms utilized for proteolysis by each of these hyperthermophiles and indicated how these mechanisms relate to proteolysis in less thermophilic cells and organisms. DA - 2002/// PY - 2002/// DO - 10.1155/2002/503191 VL - 1 IS - 1 SP - 63-74 J2 - Archaea LA - en OP - SN - 1472-3646 1472-3654 UR - http://dx.doi.org/10.1155/2002/503191 DB - Crossref ER - TY - JOUR TI - Investigation of Enhanced Free Volume in Nanosilica-Filled Poly(1-trimethylsilyl-1-propyne) by 129Xe NMR Spectroscopy AU - Merkel, T. C. AU - Toy, L. G. AU - Andrady, A. L. AU - Gracz, H. AU - Stejskal, E. O. T2 - Macromolecules AB - The gas permeability of poly[1-(trimethylsilyl)-1-propyne] (PTMSP) containing nanoparticulate fumed silica increases with increasing filler content. This unusual phenomenon is explored using 129Xe NMR spectroscopy to examine the effect of filler on the free volume of the PTMSP host matrix. The 129Xe NMR chemical shift decreases regularly with increasing fumed silica concentration, consistent with an increase in the average size of free volume elements or cavities through which molecular transport can occur. A relationship between the chemical shift and gas permeability in the filled polymer is reported. DA - 2002/12/20/ PY - 2002/12/20/ DO - 10.1021/ma0256690 VL - 36 IS - 2 SP - 353-358 J2 - Macromolecules LA - en OP - SN - 0024-9297 1520-5835 UR - http://dx.doi.org/10.1021/ma0256690 DB - Crossref ER - TY - JOUR TI - Active EGF receptors have limited access to PtdIns(4,5)P2 in endosomes: implications for phospholipase C and PI 3-kinase signaling T2 - Journal of Cell Science DA - 2002/1/15/ PY - 2002/1/15/ ER - TY - JOUR TI - Localization of Receptor-Mediated Signal Transduction Pathways: The Inside Story AU - Haugh, J. M. T2 - Molecular Interventions AB - Receptor tyrosine kinases such as the epidermal growth factor receptor (EGFR) elicit proliferation, migration, and differentiation in a wide spectrum of cell types through various signal transduction pathways. These activities are attenuated by receptor internalization, intracellular trafficking through endosomes, and degradation in lysosomes, resulting in decreased receptor expression. However, there is now considerable evidence that EGFRs continue to signal in endosomes, forcing us to reevaluate the outcomes of receptor trafficking. An exciting revelation is that internalized receptors extend some signaling activities but not others, suggesting that certain responses, such as cell motility, must be mediated at the cell surface. Still, only when the effects of decreased receptor populations and signaling compartmentalization are integrated can we hope to understand and manipulate receptor function at the molecular level. DA - 2002/9/1/ PY - 2002/9/1/ DO - 10.1124/mi.2.5.292 VL - 2 IS - 5 SP - 292-307 ER - TY - CONF TI - Molecular Simulation of Confined Nano-Phases AU - Gubbins, K.E. T2 - 7th International Conference on Fundamentals of Adsorption A2 - Kaneko, K. A2 - Kanoh, H. A2 - Hanzawa, Y. C2 - 2002/// C3 - Fundamentals of Adsorption 7: Proceedings of the 7th International Conference on Fundamentals of Asorption, Nagasaki, May, 20-25, 2001 CY - Nagasaki, Japan DA - 2002/// PY - 2001/5/20/ SP - 13 PB - International Adsorption Society (IK International Pub.) SN - 9784902479003 ER - TY - CONF TI - A New Molecular Model for Activated Carbons AU - Pikunic, J. AU - Thomson, K.T. AU - Gubbins, K.E. T2 - 7th International Conference on Fundamentals of Adsorption A2 - Kaneko, K. A2 - Kanoh, H. A2 - Hanzawa, Y. C2 - 2002/// C3 - Fundamentals of Adsorption 7: Proceedings of the 7th International Conference on Fundamentals of Adsorption, Nagasaki, May, 20-25, 2001 CY - Nagasaki, Japan DA - 2002/// PY - 2001/5/20/ SP - 377 PB - International Adsorption Society (IK International Pub. ER - TY - CONF TI - Molecular Simulation of Capillary Phenomena in Controlled Pore Glasses AU - Gelb, L.D. AU - Gubbins, K.E. T2 - 7th International Conference on Fundamentals of Adsorption A2 - Kaneko, K. A2 - Kanoh, H. A2 - Hanzawa, Y. C2 - 2002/// C3 - Fundamentals of Adsorption 7: Proceedings of the 7th International Conference on Fundamentals of Adsorption, Nagasaki, May, 20-25, 2001 CY - Nagasaki, Japan DA - 2002/// PY - 2001/5/20/ SP - 333 PB - International Adsorption Society (IK International Pub.) SN - 9784902479003 ER - TY - CONF TI - Mimetic Synthesis of Templated Mesoporous Materials Using Molecular Simulation AU - Siperstein, F.R. AU - Gubbins, K.E. T2 - 7th International Conference on Fundamentals of Adsorption A2 - Kaneko, K. A2 - Kanoh, H. A2 - Hanzawa, Y. C2 - 2002/// C3 - Fundamentals of Adsorption 7: Proceedings of the 7th International Conference on Fundamentals of Adsorption, Nagasaki, May, 20-25, 2001 CY - Nagasaki, Japan DA - 2002/// PY - 2001/5/20/ SP - 434 PB - International Adsorption Society (IK International Pub.) SN - 9784902479003 ER - TY - CONF TI - Understanding Freezing Behavior in Porous Materials AU - Radhakrishnan, R. AU - Gubbins, K.E. AU - Sliwinska-Bartkowiak, M. AU - Kaneko, K. T2 - 7th International Conference on Fundamentals of Adsorption A2 - Kaneko, K. A2 - Kanoh, H. A2 - Hanzawa, Y. C2 - 2002/// C3 - Fundamentals of Adsorption 7: Proceedings of the 7th International Conference on Fundamentals of Adsorption, Nagasaki, May, 20-25, 2001 CY - Nagasaki, Japan DA - 2002/// PY - 2001/5/20/ SP - 341 PB - International Adsorption Society (IK International Pub.) SN - 9784902479003 ER - TY - CONF TI - Water in Porous Carbons: A Simulation Study AU - Brennan, John K. AU - Thomson, Kendall T. AU - Gubbins, Keith E. T2 - 7th International Conference on Fundamentals of Adsorption (FOA7) A2 - Kaneko, K. A2 - Kanoh, H. A2 - Hanzawa, Y. C2 - 2002/// C3 - Fundamentals of Adsorption 7: Proceedings of the 7th International Conference on Fundamentals of Adsorption, Nagasaki, May, 20-25, 2001 CY - Nagasaki, Japan DA - 2002/// PY - 2001/5/20/ SP - 426 PB - International Adsorption Society (IK International Pub.) SN - 9784902479003 ER - TY - JOUR TI - Designing Photoresist Systems for Microlithography in Carbon Dioxide AU - Flowers, D. AU - Hoggan, E. AU - DeSimone, J.M. AU - Carbonell, R. T2 - Materials Research Society Symposium Proceedings DA - 2002/// PY - 2002/// VL - 705 SP - 81–87 ER - TY - CHAP TI - Synthesis of Fluoropolymers in Liquid and Supercritical Carbon Dioxide Solvent Systems AU - DeYoung, James P. AU - Romack, Timothy J. AU - DeSimone, Joseph M. T2 - Fluoropolymers 1: Synthesis A2 - Hougham, G. A2 - Cassidy, P.E. A2 - Johns, K. A2 - Davidson, T. T3 - Topics in Applied Chemistry AB - Unlike a large portion of the many billions of pounds of organic and halogenated solvents used in industry every year, CO2 is inexpensive, of low toxicity, and environmentally and chemically benign. The prime factors inhibiting the widespread use of this attractive solvent replacement have been the disappointingly low solubility of most materials in CO2 in both liquid and supercritical states, and a less than complete understanding of its physical properties. Discoveries made over the past decade identifying the solubility of siloxanes and many amorphous fluoropolymers in CO2 have facilitated a greater understanding of the solvency properties of this uniquely “tunable” solvent. The subsequent development of amphiphilic surfactants incorporating lyophilic fluorocarbon or siloxane segments with lipophilic or hydrophilic moieties opens the door for the synthesis of a broad range of hydrocarbons. Carbon dioxide technology is of particular significance with respect to the manufacture of many fluoropolymers that require nonaqueous synthesis. Reduction of unwanted side reactions such as β-scission and opportunities for unique separation and purification processes demonstrate that CO2 is not only an adequate replacement for chlorofluorocarbons, but in many cases a superior one. PY - 2002/// DO - 10.1007/0-306-46918-9_13 SP - 191–205 PB - Kluwer Academic Publishers SN - 0306460602 UR - http://dx.doi.org/10.1007/0-306-46918-9_13 ER - TY - JOUR TI - Kinetics of block-copolymer aggregation in super critical CO2 AU - Triolo, A. AU - Lo Celso, F. AU - Triolo, F. AU - Amenitsch, H. AU - Steinhart, M. AU - Thiyagarajan, P. AU - Wells, S. AU - DeSimone, J.M. AU - Triolo, R. T2 - Journal of Non-Crystalline Solids AB - Small angle X-ray and neutron scattering (SAXS and SANS) are used to obtain structural information on the aggregation behavior of block-copolymers dissolved in supercritical CO2. The SANS technique is used to provide a detailed structural model for the micellar aggregates, which form below the critical micellization density (CMD), that we defined in our previous work. The SAXS technique (with a synchrotron source) is used to provide the first experimental information concerning the kinetic features of both formation and decomposition of such aggregates as soon as pressure jumps are applied to the solutions across the CMD. 2002 Elsevier Science B.V. All rights reserved. DA - 2002/9// PY - 2002/9// DO - 10.1016/s0022-3093(02)01553-3 VL - 307-310 SP - 725-730 J2 - Journal of Non-Crystalline Solids LA - en OP - SN - 0022-3093 UR - http://dx.doi.org/10.1016/s0022-3093(02)01553-3 DB - Crossref ER - TY - JOUR TI - Structure of Phosphate Fluorosurfactant Based Reverse Micelles in Supercritical Carbon Dioxide AU - Senapati, Sanjib AU - Keiper, Jason S. AU - DeSimone, Joseph M. AU - Wignall, George D. AU - Melnichenko, Yuri B. AU - Frielinghaus, Henrich AU - Berkowitz, Max L. T2 - Langmuir AB - The existence of microemulsions in the system composed of phosphate-based fluorosurfactant, water, and supercritical CO2 is demonstrated by small-angle neutron scattering experiments. A computer simulation study performed on a reverse micelle created in this system shows that the micelle remains stable over a 4 ns time period of the simulation. While the data obtained from the experiments provide information about the size of the reverse micelle, the data obtained from the simulations provide additional information about the shape and structure of such a micelle. DA - 2002/10// PY - 2002/10// DO - 10.1021/la025952s VL - 18 IS - 20 SP - 7371-7376 J2 - Langmuir LA - en OP - SN - 0743-7463 1520-5827 UR - http://dx.doi.org/10.1021/la025952s DB - Crossref ER - TY - JOUR TI - Industrial applications of the aggregation of block copolymers in supercritical CO 2 : a SANS study AU - Lo Celso, F. AU - Triolo, A. AU - Triolo, F. AU - McClain, J. AU - Desimone, J.M. AU - Heenan, R.K. AU - Amenitsch, H. AU - Triolo, R. T2 - Applied Physics A: Materials Science & Processing DA - 2002/12/1/ PY - 2002/12/1/ DO - 10.1007/s003390101240 VL - 74 IS - 0 SP - s1427-s1429 J2 - Applied Physics A: Materials Science & Processing OP - SN - 0947-8396 1432-0630 UR - http://dx.doi.org/10.1007/s003390101240 DB - Crossref ER - TY - JOUR TI - Electrospinning of polymer nanofibers with specific surface chemistry AU - Deitzel, J.M. AU - Kosik, W. AU - McKnight, S.H. AU - Beck Tan, N.C. AU - DeSimone, J.M. AU - Crette, S. T2 - Polymer AB - Electrospinning is a process by which sub-micron polymer fibers can be produced using an electrostatically driven jet of polymer solution (or polymer melt). Electrospun textiles are of interest in a wide variety of applications including semi-permeable membranes, filters, composite applications, and as scaffolding for tissue engineering. The goal of the research presented here is to demonstrate that it is possible to produce sub-micron fibers with a specific surface chemistry through electrospinning. This has been accomplished by electrospinning a series of random copolymers of PMMA-r-TAN from a mixed solvent of toluene and dimethyl formamide. X-ray Photoelectron Spectroscopy (XPS) analysis shows that the atomic percentage of fluorine in the near surface region of the electrospun fibers is about double the atomic percentage of fluorine found in a bulk sample of the random copolymer, as determined by elemental analysis. These results are in good agreement with XPS and water contact angle results obtained from thin films of the same copolymer materials. DA - 2002/2// PY - 2002/2// DO - 10.1016/s0032-3861(01)00594-8 VL - 43 IS - 3 SP - 1025-1029 SN - 0032-3861 UR - http://dx.doi.org/10.1016/s0032-3861(01)00594-8 KW - electrospinning KW - random copolymer KW - surface segregation ER - TY - JOUR TI - Electron and Mass Transport in Hybrid Redox Polyether Melts Contacted with Carbon Dioxide AU - Lee, Dongil AU - Hutchison, John C. AU - Leone, Anthony M. AU - DeSimone, Joseph M. AU - Murray, Royce W. T2 - Journal of the American Chemical Society AB - Films of neat metal salts with covalently attached oligoether side chains ([Co(bpy(CO(2)MePEG-350)(2))(3)](ClO(4))(2); bpy is 2,2'-bipyridine, and MePEG-350 is methyl-terminated oligomeric ethylene oxide with an average molecular weight of 350 Da) undergo marked changes in physical and electrochemical properties upon contact with CO(2). Electrochemical measurements indicate that the physical diffusion coefficient (D(PHYS)) of the Co(II) species, the observed rate constant for Co(II/I) self-exchange (k(EX)), and the physical diffusion coefficient of the perchlorate counterion (D(ClO4)) increase from 2.4 x 10(-11) to 7.0 x 10(-10) cm(2)/s, 6.8 x 10(5) to 4.5 x 10(6) M(-1) s(-1), and 3.4 x 10(-10) to 4.3 x 10(-9) cm(2)/s, respectively, as CO(2) pressure is increased from 0 to 2000 psi at 23 degrees C. A reduction in activation energy accompanies the enhancement of each of these properties over this pressure range. Increasing CO(2) pressure from ambient to 1000 psi causes the films to swell 13%, and free-volume theory explains the enhanced mass transport properties of the films. The origin of increases in electron-transfer kinetics is considered. Plots of log(k(EX)) versus log(D(PHYS)) and log(k(EX)) versus log(D(ClO4)) are both linear. This suggests that electron self-exchange is controlled by factors that also affect log(D(PHYS)) or log(D(ClO4)). One explanation is based on plasticization of the oligoether side-chain motions by CO(2) that affect ether dipole repolarization and Co complex diffusion rates. A second explanation for the changes in k(EX) is based on control of electron transfer by relaxation of counterions neighbor to the Co complexes, which is measured by D(ClO4). Both explanations represent a kind of solvent dynamics control of k(EX). DA - 2002/8// PY - 2002/8// DO - 10.1021/ja026209p VL - 124 IS - 31 SP - 9310-9317 J2 - J. Am. Chem. Soc. LA - en OP - SN - 0002-7863 1520-5126 UR - http://dx.doi.org/10.1021/ja026209p DB - Crossref ER - TY - JOUR TI - Novel Electronic Coatings Using Liquid CO2 AU - Hoggan, E.N. AU - Novick, B.J. AU - DeSimone, J.M. AU - Carbonell, R.G. T2 - Semiconductor Fabtech DA - 2002/// PY - 2002/// VL - 16 SP - 169–173 ER - TY - CONF TI - Chemical Reaction Equilibria in Carbon Micropores from Monte Carlo Simulation: 2NO = (NO)2 and N2 +3H2 = 2NH3 AU - Turner, C.H. AU - Gubbins, K.E. T2 - 7th International Conference on Fundamentals of Adsorption A2 - Kaneko, K. A2 - Kanoh, H. A2 - Hanzawa, Y. C2 - 2002/// C3 - Fundamentals of Adsorption 7: Proceedings of the 7th International Conference on Fundamentals of Adsorption, Nagasaki, May, 20-25, 2001 CY - Nagasaki, Japan DA - 2002/// PY - 2001/5/20/ SP - 489 PB - International Adsorption Society (IK International Pub.) SN - 9784902479003 ER - TY - JOUR TI - Molecular Self-Organization and Gelation of Dibenzylidene Sorbital: An Overview AU - Wilder, E.A. AU - Hall, C.K. AU - Khan, S.A. AU - Spontak, R.J. T2 - Recent Research Developments in Materials Science DA - 2002/// PY - 2002/// VL - 3 SP - 93 ER - TY - JOUR TI - A reactive molecular dynamics model of thermal decomposition in polymers: I. Poly(methyl methacrylate) AU - Stoliarov, S. I. AU - Westmoreland, Phillip AU - Nyden, M. R. AU - Forney, G. P. T2 - Polymer AB - The theory and implementation of reactive molecular dynamics (RMD) are presented. The capabilities of RMD and its potential use as a tool for investigating the mechanisms of thermal transformations in materials are demonstrated by presenting results from simulations of the thermal degradation of poly(methyl methacrylate) (PMMA). While it is known that depolymerization must be the major decomposition channel for PMMA, there are unanswered questions about the nature of the initiation reaction and the relative reactivities of the tertiary and primary radicals formed in the degradation process. The results of our RMD simulations, performed directly in the condensed phase, are consistent with available experimental information. They also provide new insights into the mechanism of the thermally induced conversion of this polymer into its constituent monomers. DA - 2002/// PY - 2002/// DO - 10.1016/s0032-3861(02)00761-9 VL - 44 IS - 3 SP - 883–894 KW - reactive molecular dynamics KW - poly(methyl methacrylate) KW - thermal decomposition ER - TY - BOOK TI - Applying Molecular and Materials Modeling: An International Comparative Study AU - Westmoreland, P.R. AU - Kollman, P.A. AU - Chaka, A.M. AU - Cummings, P.T. AU - Morokuma, K. AU - Neurock, M. AU - Stechel, E.B. AU - Vashishta, P. DA - 2002/// PY - 2002/// SP - 430 PB - Kluwer Academic SN - 1-4020-0906-2 UR - http://www.wtec.org/loyola/molmodel/mm_final.pdf ER - TY - JOUR TI - Synthesis of UV-sensitive and fire-resistant polyarylates AU - Plichta, A. AU - Brzozowski, Z.K. AU - Zhang, H. AU - Coughlin, E.B. AU - Westmoreland, P.R. AU - Farris, R.J. T2 - Polymer DA - 2002/// PY - 2002/// VL - 43 IS - 20 SP - 5463–5472 ER - TY - JOUR TI - Modeling ethylene combustion from low to high pressure AU - Carriere, T. AU - Westmoreland, P.R. AU - Kazakov, A. AU - Stein, Y.S. AU - Dryer, F.L. T2 - Proceedings of the Combustion Institute AB - With the same reaction set, data have been modeled successfully from two ethylene-oxygen combustion systems at greatly different pressures. New data are from the Princeton flow reactor, a lower temperature (850–950 K) and high-pressure (5–10 atm) data set (=2.5). The second set is for a high-temperature (<2000 K) and low-pressure (20 torr), premixed laminar fuel-rich flame (=1.9) studied by Bhargava and Westmoreland. Several reaction sets were tested, but only the present set demonstrated good agreement in both cases. A key difference between this set and previous ones lies in the modeling of the complex C2H3+O2 reaction. New rate constants were calculated based on recent findings regarding the potential energy surface of the C2H3+O2 system. In the 850–1600 K range that is crucial in these experiments, the product set CH2CHO+O was found to contribute much less than reported in earlier studies, and the HCO+CH2O channel dominated. The present reaction set predicted the species profiles in both cases with reasonable accuracy, allowing us to interpret and compare the reaction pathways over a wide range of conditions. In the low-pressure flame, C2H4 is mainly consumed by abstraction, while in the high-pressure system, abstraction (mainly by OH instead of H) competes with H addition that forms C2H5. In both cases, abstraction forms C2H3 that reacts with O2 to make HCO and CH2O and eventually CO and CO2 However, higher levels of C2H5 and HO2 at the high-pressure, lower temperature flow reactor condition drive distinct pathway differences. The key role of HO2 chemistry is particularly emphasized through the reaction CH2O+HO2. Model comparisons support a lower value of the rate constant for this reaction, consistent with that recommended by Hochgreb and Dryer. DA - 2002/1// PY - 2002/1// DO - 10.1016/s1540-7489(02)80155-9 VL - 29 IS - 1 SP - 1257-1266 J2 - Proceedings of the Combustion Institute LA - en OP - SN - 1540-7489 UR - http://dx.doi.org/10.1016/s1540-7489(02)80155-9 DB - Crossref ER - TY - JOUR TI - Dense packing of binary and polydisperse hard spheres AU - Santiso, E AU - Müller, EA T2 - Molecular Physics AB - The packing of binary and polydisperse unimodal and bimodal ensembles of hard spheres in the limit of high pressure is studied using a sequential addition algorithm. Upon fixing the number of particles, and their size distribution, the average (maximum) packing fraction is determined for systems of up to 20 000 particles. The structures obtained correspond to amorphous states close to the dense random close packing density. Binary distributions obtained are denser than the equivalent monodisperse distribution and agree with the theoretical prediction for an infinite size ratio limit. Unimodal normal and lognormal polydisperse distributions obtained compare favourably with available simulation and experimental data. Results for bimodal lognormal distributions are presented. In all cases it is seen how an increase in polydispersity increases the packing fraction of the system. The results can be employed to gain insight into optimal formulations for dense emulsions. DA - 2002/8/10/ PY - 2002/8/10/ DO - 10.1080/00268970210125313 VL - 100 IS - 15 SP - 2461-2469 SN - 0026-8976 1362-3028 UR - http://dx.doi.org/10.1080/00268970210125313 ER - TY - JOUR TI - Effect of pH and Ca2+-induced associations of soybean proteins AU - Yuan, Y.J. AU - Velev, O.D. AU - Chen, K. AU - Campbell, B.E. AU - Kaler, E.W. AU - Lenhoff, A.M. T2 - Journal of Agricultural and Food Chemistry AB - An experimental procedure was developed to characterize the solubility of the soybean protein fractions close to the isoelectric point. The results show that the 7S fraction is precipitated in a much narrower range of pH values than the 11S fraction. Surprisingly, the addition of salt to the solutions leads to increased solubility of proteins, unlike the common "salting out" effect generally expected for proteins in solution in this range of salt concentrations. The precipitation equilibria of both soybean fractions in the presence of calcium ions and electrolyte were characterized. The amount of calcium ions required to precipitate a mole of the 7S fraction is much larger than that required for the 11S fractions. The precipitation pattern can be correlated to the charge density per surface area of the proteins. DA - 2002/// PY - 2002/// DO - 10.1021/jf025582d VL - 50 IS - 17 SP - 4953-4958 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0037077361&partnerID=MN8TOARS KW - soybean proteins KW - precipitation KW - equilibrium KW - pH KW - calcium KW - electric charge ER - TY - CONF TI - Dielectrophoretic assembly of switchable two-dimensional photonic crystals with specific orientation AU - Lumsdon, S.O. AU - Williams, J.P. AU - Kaler, E.W. AU - Velev, O.D. C2 - 2002/// C3 - American Chemical Society, Polymer Preprints, Division of Polymer Chemistry DA - 2002/// VL - 43 SP - 21-22 M1 - 1 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84899709236&partnerID=MN8TOARS ER - TY - JOUR TI - Self-discharge of secondary lithium-ion graphite anodes AU - Wang, C. AU - Zhang, X. AU - Appleby, A. J. AU - Chen, X. AU - Little, F. E. T2 - Journal of Power Sources AB - A new method for measuring self-discharge of lithium-ion graphite anodes is reported. First, the anode lithium content is calculated from the open-circuit potential as a function of open-circuit time (OCP versus OCT) using equilibrium potential–composition isotherms. Then, the self-discharge rate is obtained from the differential of lithium content with respect to time on open circuit. The self-discharge rate measured by this means after the first charge–discharge cycle to 0.0 V versus Li/Li+ is largely controlled by the growth of the solid electrolyte interphase (SEI) film, with some influence from stage transformation. DA - 2002/// PY - 2002/// DO - https://doi.org/10.1016/s0378-7753(02)00359-2 VL - 112 ER - TY - JOUR TI - Polystyrene/Sn-Pb alloy blends. II: Effect of alloy particle surface treatment on dynamic rheological behavior AU - Zhang, X. AU - Pan, Y. AU - Zheng, Q. AU - Yi, X. S. T2 - Journal of Applied Polymer Science AB - Abstract The effect of filler surface treatment on the dynamic rheological behaviors of polystyrene filled with Sn–Pb alloy particles was tested below and above the melting temperature ( T m ) of the alloy. The mechanical relaxation relevant to the T m of the alloy in the composite was diminished by the filler surface pretreatment. In the whole temperature range of interest, there existed a secondary plateau of the storage modulus at low frequencies. The effect of alloy particle surface treatment on the plateau was related to the matter‐state change (from solid to liquid) of the alloy. Above the T m of the alloy, the surface treatment of the alloy affected the secondary plateau, but below the T m , it did not. The analyses of Cole–Cole diagrams of the systems suggested that untreated and pretreated alloy fillers all retarded the relaxation processes in the molten state of polystyrene below the T m of the alloy and that the relaxation process was separated into the high‐frequency relaxation of the phases and the low‐frequency relaxation of the droplets above the T m . The surface treatments of the alloy filler further enhanced this action. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3173–3179, 2002 DA - 2002/// PY - 2002/// DO - https://doi.org/10.1002/app.11352 VL - 86 ER - TY - JOUR TI - Polystyrene/Sn-Pb alloy blends. I: Dynamic rheological behavior AU - Zheng, Q. AU - Zhang, X. AU - Pan, Y. AU - Yi, X. S. T2 - Journal of Applied Polymer Science AB - Abstract The dynamic rheological behavior of polystyrene filled with low‐melting‐point ( T m ) Sn–Pb was investigated at temperatures below and above the T m of the alloy, 183°C. In the whole temperature range of interest, there existed a secondary plateau in the plot of the dynamic storage modulus versus frequency (ω) at low ωs, and the influences of alloy content and temperature on the plateau were related to the matter state (liquid or solid) of the alloy. We believe that the secondary plateau observed below the alloy T m was due to the network‐type structure formed by the agglomeration of solid filler particles, whereas the plateau above T m was due to the deformability and relaxation of the liquid alloy droplets. By analyzing the Cole–Cole diagrams, we suggest that the alloy fillers retarded the relaxation processes for polystyrene melt when the temperature was lower than the T m . However, there existed two separated relaxation processes when the temperature was higher than the T m , that is, the high‐ω relaxation of the phases and low‐ω relaxation of the droplets. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3166–3172, 2002 DA - 2002/// PY - 2002/// DO - https://doi.org/10.1002/app.11353 VL - 86 ER - TY - JOUR TI - PTC Characteristic of Sn-Pb Alloy-Loaded Polymer Composites AU - Liu, Jing AU - Pan, Yi AU - Zhang, Xiang-Wu T2 - Acta Mater. Comp. Sinica DA - 2002/// PY - 2002/// VL - 19 SP - 116-119 ER - TY - JOUR TI - Influence of ionic conductive ceramic fillers on the electrochemical performance of nano-tin anodes in lithium-ion batteries AU - Zhang, X. AU - Wang, C. AU - Appleby, A.J. AU - Little, F.E. T2 - DA - 2002/// PY - 2002/// VL - ER - TY - JOUR TI - Improvement in electrochemical properties of nano-tin-polyaniline lithium-ion composite anodes by control of electrode microstructure AU - Zhang, X. AU - Wang, C. AU - Appleby, A. J. AU - Little, F. E. T2 - Journal of Power Sources AB - Four different types of nano-tin-polyaniline (nano-Sn-PAni) lithium-ion composite anode microstructures have been examined to investigate the relationship between this parameter and anode characteristics. Scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) show that the electrochemical properties of nano-tin composite electrodes can be significantly affected by microstructure variation. To simultaneously obtain high capacity and long cycle life, the active materials should be encased in a polymer matrix to accommodate volume changes during cycling, and porosity is required to offer low interfacial lithium insertion/extraction impedance. The polymer matrix should have a high binding strength to prevent the anode cracking. DA - 2002/// PY - 2002/// DO - https://doi.org/10.1016/s0378-7753(02)00091-5 VL - 109 ER - TY - JOUR TI - Composite doped emeraldine-polyethylene oxide-bonded lithium-ion nano-tin anodes with electronic-ionic mixed conduction AU - Zhang, X. AU - Wang, C. AU - Appleby, A.J. AU - Little, F.E. T2 - Solid State Ionics AB - Mixed-conducting lithium-ion doped emeraldine polyaniline (PAni)–polyethylene oxide (PEO) blends have been developed to achieve an optimal electronic–ionic conductivity balance in nano-tin composite anodes. Electrochemical evaluation was performed on the anodes with differing electrode preparation procedures, doping methods and PEO contents. Results indicate that both good electronic and ionic conductivity in the binder are required for rapid lithium insertion/extraction and low polarization. This doped PAni–PEO polymer blend is an attractive binder for high capacity composite anodes with low polarization. DA - 2002/// PY - 2002/// DO - https://doi.org/10.1016/s0167-2738(02)00522-2 VL - 150 ER - TY - JOUR TI - Characteristics of lithium-ion conducting composite polymer-glass secondary cell electrolytes AU - Zhang, X. AU - Wang, C. AU - Appleby, A. J. AU - Little, F. E. T2 - Journal of Power Sources AB - A family of lithium-ion-conducting composite polymer-glass electrolytes containing the glass composition 14Li2O–9Al2O3–38TiO2–39P2O5 (abbreviated as (LiAlTiP)xOy) with high ionic conductivity, an excellent electrochemical stability range, and high compatibility with lithium insertion anodes is described. An optimized composition has a room temperature conductivity of 1.7×10−4 S cm−1, an Li+ transference number of 0.39, and an electrochemical stability window to +5.1 V versus Li/Li+. It also has good interfacial stability under both open-circuit and lithium metal plating–stripping conditions and provides good shelf-life. DA - 2002/// PY - 2002/// DO - https://doi.org/10.1016/s0378-7753(02)00365-8 VL - 112 ER - TY - JOUR TI - Thermal decomposition and flammability of fire-resistant, UV/visible-sensitive polyarylates, copolymers and blends AU - Zhang, H AU - Westmoreland, PR AU - Farris, RJ AU - Coughlin, EB AU - Plichta, A AU - Brzozowski, ZK T2 - POLYMER AB - Thermal decomposition behavior and flammability of three polyarylates based on bisphenol A (BPA), 1,1-dichloro-2,2-bis(4-hydroxy-phenyl)ethylene (BPC II) and 4,4′-dihydroxy-3-ethoxy-benzylidenoacetophenone (Chalcon II), their copolymers and blends were investigated by pyrolysis GC/MS, simultaneous thermal analysis and pyrolysis-combustion flow calorimetry (PCFC). The relationships between flammability and structure/composition of these polymers have also been explored. It is found that BPC II-polyarylate is an extremely fire-resistant thermoplastic that can be used as an efficient flame-retardant agent to be blended with the other polymers. Chalcon II-polyarylate is of interest as a UV/visible-sensitive polymer with a relatively low heat-release rate and a high char yield. PCFC results show that the total heat of combustion of the copolymers or blends changes linearly with the composition, but the change of maximum heat-release rate and char yield depends greatly on the chemical structure of the components. DA - 2002/9// PY - 2002/9// DO - 10.1016/s0032-3861(02)00427-5 VL - 43 IS - 20 SP - 5463-5472 SN - 0032-3861 KW - polyarylate KW - thermal decomposition KW - flammability ER - TY - JOUR TI - Polymeric [Li(NO3)(monoglyme)]n AU - Henderson, W. A. AU - Brooks, N. R. AU - Smyrl, W. H T2 - Acta Crystallographica DA - 2002/// PY - 2002/// VL - E58 IS - 9 SP - m500-m501 ER - TY - JOUR TI - Lithium trifluoro-methanesulfonate acetonitrile adduct AU - Brooks, N. R. AU - Henderson, W. A. AU - Smyrl, W. H. T2 - Acta Crystallographica DA - 2002/// PY - 2002/// VL - E58 IS - 5 SP - m176-m177 ER - TY - JOUR TI - Li+ cation coordination in [Li2(CF3SO3)2(diglyme)] and [Li3(C2F3O2)3(diglyme)] AU - Henderson, W. A. AU - Young, V. G., Jr. AU - Brooks, N. R. AU - Smyrl, W. H. T2 - Acta Crystallographica DA - 2002/// PY - 2002/// VL - C58 IS - 10 SP - m501-m503 ER - TY - CONF TI - Influence of ionic conductive ceramic fillers on the electrochemical performance of nano-tin anodes in lithium-ion batteries AU - Zhang, X. AU - Wang, C. AU - Appleby, A.J. AU - Little, F.E. C2 - 2002/// C3 - Selected papers presented at the 11th Internaional Meeting on Lithium Batteries, Monterey, CA, USA, 22-28 June 2002 DA - 2002/// PB - Amsterdam : Elsevier ER - TY - JOUR TI - Composite doped emeraldine-polyethylene oxide-bonded lithium-ion nano-tin anodes with electronic-ionic mixed conduction AU - Zhang, XW AU - Wang, CS AU - Appleby, AJ AU - Little, FE T2 - SOLID STATE IONICS AB - Mixed-conducting lithium-ion doped emeraldine polyaniline (PAni)–polyethylene oxide (PEO) blends have been developed to achieve an optimal electronic–ionic conductivity balance in nano-tin composite anodes. Electrochemical evaluation was performed on the anodes with differing electrode preparation procedures, doping methods and PEO contents. Results indicate that both good electronic and ionic conductivity in the binder are required for rapid lithium insertion/extraction and low polarization. This doped PAni–PEO polymer blend is an attractive binder for high capacity composite anodes with low polarization. DA - 2002/10// PY - 2002/10// DO - 10.1016/s0167-2738(02)00522-2 VL - 150 IS - 3-4 SP - 383-389 SN - 0167-2738 UR - https://publons.com/publon/7178370/ KW - nano-tin KW - polyaniline KW - polyethylene oxide KW - polymer blend KW - composite electrode KW - mixed conductivity ER - TY - JOUR TI - Self-discharge of secondary lithium-ion graphite anodes AU - Wang, CS AU - Zhang, XW AU - Appleby, AJ AU - Chen, XL AU - Little, FE T2 - JOURNAL OF POWER SOURCES AB - A new method for measuring self-discharge of lithium-ion graphite anodes is reported. First, the anode lithium content is calculated from the open-circuit potential as a function of open-circuit time (OCP versus OCT) using equilibrium potential–composition isotherms. Then, the self-discharge rate is obtained from the differential of lithium content with respect to time on open circuit. The self-discharge rate measured by this means after the first charge–discharge cycle to 0.0 V versus Li/Li+ is largely controlled by the growth of the solid electrolyte interphase (SEI) film, with some influence from stage transformation. DA - 2002/10/24/ PY - 2002/10/24/ DO - 10.1016/S0378-7753(02)00359-2 VL - 112 IS - 1 SP - 98-104 SN - 1873-2755 UR - https://publons.com/publon/7178378/ KW - self-discharge KW - graphite anode KW - Li-ion batteries KW - solid electrolyte interphase ER - TY - JOUR TI - Polystyrene/Sn-Pb alloy blends. II. Effect of alloy particle surface treatment on dynamic rheological behavior AU - Zhang, XW AU - Pan, Y AU - Zheng, Q AU - Yi, XS T2 - JOURNAL OF APPLIED POLYMER SCIENCE AB - Abstract The effect of filler surface treatment on the dynamic rheological behaviors of polystyrene filled with Sn–Pb alloy particles was tested below and above the melting temperature ( T m ) of the alloy. The mechanical relaxation relevant to the T m of the alloy in the composite was diminished by the filler surface pretreatment. In the whole temperature range of interest, there existed a secondary plateau of the storage modulus at low frequencies. The effect of alloy particle surface treatment on the plateau was related to the matter‐state change (from solid to liquid) of the alloy. Above the T m of the alloy, the surface treatment of the alloy affected the secondary plateau, but below the T m , it did not. The analyses of Cole–Cole diagrams of the systems suggested that untreated and pretreated alloy fillers all retarded the relaxation processes in the molten state of polystyrene below the T m of the alloy and that the relaxation process was separated into the high‐frequency relaxation of the phases and the low‐frequency relaxation of the droplets above the T m . The surface treatments of the alloy filler further enhanced this action. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3173–3179, 2002 DA - 2002/12/13/ PY - 2002/12/13/ DO - 10.1002/app.11352 VL - 86 IS - 12 SP - 3173-3179 SN - 1097-4628 UR - https://publons.com/publon/7178381/ KW - surfaces KW - rheology KW - composites KW - alloys KW - melting point ER - TY - JOUR TI - Polystyrene/Sn-Pb alloy blends. I. Dynamic rheological behavior AU - Zheng, Q AU - Zhang, XW AU - Pan, Y AU - Yi, XS T2 - JOURNAL OF APPLIED POLYMER SCIENCE AB - Abstract The dynamic rheological behavior of polystyrene filled with low‐melting‐point ( T m ) Sn–Pb was investigated at temperatures below and above the T m of the alloy, 183°C. In the whole temperature range of interest, there existed a secondary plateau in the plot of the dynamic storage modulus versus frequency (ω) at low ωs, and the influences of alloy content and temperature on the plateau were related to the matter state (liquid or solid) of the alloy. We believe that the secondary plateau observed below the alloy T m was due to the network‐type structure formed by the agglomeration of solid filler particles, whereas the plateau above T m was due to the deformability and relaxation of the liquid alloy droplets. By analyzing the Cole–Cole diagrams, we suggest that the alloy fillers retarded the relaxation processes for polystyrene melt when the temperature was lower than the T m . However, there existed two separated relaxation processes when the temperature was higher than the T m , that is, the high‐ω relaxation of the phases and low‐ω relaxation of the droplets. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3166–3172, 2002 DA - 2002/12/13/ PY - 2002/12/13/ DO - 10.1002/app.11353 VL - 86 IS - 12 SP - 3166-3172 SN - 0021-8995 UR - https://publons.com/publon/7178382/ KW - rheology KW - polystyrene KW - composites KW - melting point KW - alloys ER - TY - JOUR TI - Improvement in electrochemical properties of nano-tin-polyaniline lithium-ion composite anodes by control of electrode microstructure AU - Zhang, XW AU - Wang, CS AU - Appleby, AJ AU - Little, FE T2 - JOURNAL OF POWER SOURCES AB - Four different types of nano-tin-polyaniline (nano-Sn-PAni) lithium-ion composite anode microstructures have been examined to investigate the relationship between this parameter and anode characteristics. Scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) show that the electrochemical properties of nano-tin composite electrodes can be significantly affected by microstructure variation. To simultaneously obtain high capacity and long cycle life, the active materials should be encased in a polymer matrix to accommodate volume changes during cycling, and porosity is required to offer low interfacial lithium insertion/extraction impedance. The polymer matrix should have a high binding strength to prevent the anode cracking. DA - 2002/6/15/ PY - 2002/6/15/ DO - 10.1016/S0378-7753(02)00091-5 VL - 109 IS - 1 SP - 136-141 SN - 0378-7753 UR - https://publons.com/publon/7178369/ KW - nano-tin KW - polyaniline KW - composite electrode KW - charge-discharge KW - cycle life ER - TY - JOUR TI - Characteristics of lithium-ion-conducting composite polymer-glass secondary cell electrolytes AU - Zhang, XW AU - Wang, CS AU - Appleby, AJ AU - Little, FE T2 - JOURNAL OF POWER SOURCES AB - A family of lithium-ion-conducting composite polymer-glass electrolytes containing the glass composition 14Li2O–9Al2O3–38TiO2–39P2O5 (abbreviated as (LiAlTiP)xOy) with high ionic conductivity, an excellent electrochemical stability range, and high compatibility with lithium insertion anodes is described. An optimized composition has a room temperature conductivity of 1.7×10−4 S cm−1, an Li+ transference number of 0.39, and an electrochemical stability window to +5.1 V versus Li/Li+. It also has good interfacial stability under both open-circuit and lithium metal plating–stripping conditions and provides good shelf-life. DA - 2002/10/24/ PY - 2002/10/24/ DO - 10.1016/S0378-7753(02)00365-8 VL - 112 IS - 1 SP - 209-215 SN - 1873-2755 UR - https://publons.com/publon/7178377/ KW - composite electrolyte KW - Li+-conducting glasses KW - conductivity KW - stability KW - interfacial properties ER - TY - PAT TI - LPCVD coated reflector AU - Israel, R. AU - Gunter, C. AU - Chowdhury, A. C2 - 2002/// DA - 2002/// PY - 2002/// ER - TY - JOUR TI - Sequential extraction and photocatalytic recovery of lead from model contaminated soils AU - Borrell-Damian, L. AU - Ollis, D. F. T2 - Journal of Advanced Oxidation Technologies AB - Abstract This work explores the technical feasibility of a two-step process for the treatment of lead contaminated soils. The first step is an extraction by chelation of lead from soil. The second step is the photocatalytic treatment of the metal-chelate extract with UV radiation and particulate TiO DA - 2002/// PY - 2002/// DO - 10.1515/jaots-2002-0106 VL - 5 IS - 1 SP - 41-57 ER - TY - JOUR TI - Effects of TiO2 pretreatments on the photocatalytic oxidation of gas-phase aromatic contaminants AU - Lewandowski, M. AU - Ollis, D. F. T2 - Journal of Advanced Oxidation Technologies AB - Abstract The effects of various halide salt and inorganic acid pretreatments on the photocatalytic destruction of toluene were examined to determine the source of activity enhancements seen previously with HCl pretreatments. Pretreatments with chloride salts (NaCl, KCl) are found to have little influence on photocatalyst activity, suggesting that the presence of an acid is needed. Acid pretreatments either increase (sulfuric, nitric, phosphoric) or decrease (hydrobromic, hydroiodic, and perchloric) the catalyst activity. These results indicate that acidification alone is not responsible for the observed changes in catalyst activity and that both protons and anions influence photocatalyst behavior. DA - 2002/// PY - 2002/// DO - 10.1515/jaots-2002-0105 VL - 5 IS - 1 SP - 33-40 ER - TY - JOUR TI - Vel block copolymers as nanofiltration materials AU - DiGiano, FA AU - Roudman, A AU - Arnold, M AU - Freeman, B T2 - ENVIRONMENTAL ENGINEERING SCIENCE AB - The overarching goal of this research was to forge a link between materials science and engineering that may eventually lead to development of new membranes with decreased fouling tendency. Polymer structure influences water transport rates, solute partitioning, and fouling resistance. This article presents the results of testing the first generation of a novel class of nonporous block copolymers for use in nanofiltration (NF) membranes. The block copolymers comprised low surface energy fluoropolymers and highly hydrophilic hydrocarbon-based polymers. The very low surface energy of the fluoropolymer block was intended to resist adhesion of natural organic matter (NOM), a common foulant in drinking water applications of nanofiltration technology. The hydrophilic block was intended to provide channels for water permeation. Thin-film composite membrane tests with a coagulated, settled, and cartridge-filtered drinking water sample showed that the experimental membrane produced comparable water flux to a commercial NF membrane. However, flux decline was also similar to that of the commercial NF membrane. Despite the failure to resist fouling, the data suggest that NOM may be more easily removed from the experimental membrane surface than the commercial membrane surface. Dense film testing of the experimental materials provided measurements of NOM partitioning and diffusion. DA - 2002/// PY - 2002/// DO - 10.1089/109287502320963463 VL - 19 IS - 6 SP - 497-511 SN - 1092-8758 KW - materials science KW - engineering KW - novel block copolymers KW - fouling ER - TY - JOUR TI - Topological similarity of sponge-like bicontinuous morphologies differing in length scale AU - Jinnai, H AU - Nishikawa, Y AU - Ito, M AU - Smith, SD AU - Agard, DA AU - Spontak, RJ T2 - ADVANCED MATERIALS AB - Sponge-like bicontinuous morphologies (see Figure and also cover) are ubiquitous in the physical and biological sciences, but are only qualitatively understood in terms of their structure. Here, 3D imaging techniques are used to explore the characteristics of such morphologies at the nanoscale, microscale, and macroscale. Comparison of local and global topology metrics provides quantitative evidence of similarities between these morphologies. DA - 2002/11/18/ PY - 2002/11/18/ DO - 10.1002/1521-4095(20021118)14:22<1615::AID-ADMA1615>3.0.CO;2-S VL - 14 IS - 22 SP - 1615-1618 SN - 1521-4095 ER - TY - JOUR TI - Photocatalytic powder layer reactor: A uniformly mixed gas phase occurring in a catalytic fixed-bed flow reactor AU - Ollis, DF T2 - INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH AB - Integral conversion photocatalysis rate data in gas−solid studies have often been obtained through the use of a powder layer downflow laboratory reactor illuminated from above. The photocatalyst particles, characteristically 20−40 nm in primary particle size and ∼1 μm in agglomerate size, are illuminated to a characteristic depth of the reciprocal of the absorption coefficient, resulting in opacity at 30−50 μm in a loose-packed powder layer. We establish here that this photocatalytic membrane reactor behaves as a well-mixed system; thus, reaction kinetic models can be directly tested for any degree of reactant conversion, without prior need for rate integration. DA - 2002/12/11/ PY - 2002/12/11/ DO - 10.1021/ie020038f VL - 41 IS - 25 SP - 6409-6412 SN - 0888-5885 ER - TY - JOUR TI - Hydrophobically modified associative polymer solutions: Rheology and microstructure in the presence of nonionic surfactants AU - English, RJ AU - Laurer, JH AU - Spontak, RJ AU - Khan, SA T2 - INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH AB - We report on the rheology and morphology of a hydrophobically modified alkali-swellable emulsion (HASE) polymer solubilized in alkaline media containing nonionic surfactants. The HASE polymer consists of complex alkylaryl hydrophobes composed of oligomeric nonylphenol condensates attached to a poly(ethyl acrylate-co-methacrylic acid) backbone. The complex linear viscoelastic response of the polymer in alkaline solution suggests an unentangled network with an appreciable fraction of microgel. The concentration and hydrophile−lipophile balance (HLB) of nonionic surfactants profoundly affect the solution rheology. A surfactant of high HLB inhibits the dynamic network connectivity of the HASE polymer, as demonstrated by reductions of both the steady-shear viscosity and the dynamic storage modulus. The shear-induced structuring previously reported for this polymer is also progressively diminished as the surfactant concentration is increased. In contrast, the addition of a low-HLB surfactant promotes system structuring, as evidenced by (i) increases in the shear viscosity and the high-frequency plateau modulus and (ii) retention of the ability to undergo shear-induced structuring. We also employ cryofracture-replication transmission electron microscopy for the first time with regard to HASE associative polymers to examine the morphological characteristics of selected systems. The morphology of the HASE polymer in both latex and solubilized form appears more complex than previously anticipated, and a reasonable interpretation of these new data is provided. DA - 2002/12/11/ PY - 2002/12/11/ DO - 10.1021/ie020409s VL - 41 IS - 25 SP - 6425-6435 SN - 0888-5885 ER - TY - JOUR TI - Generation of microcellular foams of PVDF and its blends using supercritical carbon dioxide in a continuous process AU - Siripurapu, S AU - Gay, YJ AU - Royer, , JR AU - DeSimone, JM AU - Spontak, RJ AU - Khan, SA T2 - POLYMER AB - Use of supercritical carbon dioxide (scCO2) as a blowing agent to generate microcellular polymer foams (MPFs) has recently received considerable attention due to environmental concerns associated with conventional organic blowing agents. While such foams derived from amorphous thermoplastics have been previously realized, semicrystalline MPFs have not yet been produced in a continuous scCO2 process. This work describes the foaming of highly crystalline poly(vinylidene fluoride) (PVDF) and its blends with amorphous polymers during extrusion. Foams composed of neat PVDF and immiscible blends of PVDF with polystyrene exhibit poor cell characteristics, whereas miscible blends of PVDF with poly(methyl methacrylate) (PMMA) yield foams possessing vastly improved morphologies. The results reported herein illustrate the effects of blend composition and scCO2 solubility on PVDF/PMMA melt viscosity, which decreases markedly with increasing PMMA content and scCO2 concentration. Morphological characterization of microcellular PVDF/PMMA foams reveals that the cell density increases as the PMMA fraction is increased and the foaming temperature is decreased. This study confirms that novel MPFs derived continuously from semicrystalline polymers in the presence of scCO2 can be achieved through judicious polymer blending. DA - 2002/9// PY - 2002/9// DO - 10.1016/S0032-3861(02)00407-X VL - 43 IS - 20 SP - 5511-5520 SN - 1873-2291 KW - supercritical carbon dioxide KW - microcellular foam KW - polymer blends ER - TY - JOUR TI - Rheology of concentrated solutions of hyperbranched polyesters AU - Andrady, Anthony L. AU - Nunez, Carlos M. AU - Chiou, Bor-Sen AU - Khan, Saad A. T2 - Polymer Engineering & Science AB - Abstract The solution rheology of different generations of hyperbranched polyesters in N‐methyl‐2‐pyrrolidinone (NMP) solvent was examined in this study. The solutions exhibited Newtonian behavior over a wide range of polyester concentrations. Also, the relative viscosities of poly(amidoamine) (PAMAM) dendrimers in ethylenediamine were compared with those of the hyperbranched polyesters in NMP. Both types of dendritic polymers have relative viscosities that are exponential functions of their molar fraction in solution. The slopes of these relative viscosity curves show a linear relationship with respect to the generation number. PAMAM dendrimers have the greater slopes for each generation, reflecting their relatively larger intrinsic viscosity values. DA - 2002/11// PY - 2002/11// DO - 10.1002/pen.11097 VL - 42 IS - 11 SP - 2065-2071 J2 - Polym. Eng. Sci. LA - en OP - SN - 0032-3888 1548-2634 UR - http://dx.doi.org/10.1002/pen.11097 DB - Crossref ER - TY - JOUR TI - Reactions of Y2O3 films with (001) Si substrates and with polycrystalline Si capping layers AU - Stemmer, S AU - Klenov, DO AU - Chen, ZQ AU - Niu, D AU - Ashcraft, RW AU - Parsons, GN T2 - APPLIED PHYSICS LETTERS AB - We use electron energy-loss spectroscopy in scanning transmission electron microscopy to investigate interfacial reactions of chemical vapor deposited Y2O3 films with the Si substrate and with in situ polycrystalline Si (“poly-Si”) capping layers after postdeposition annealing. We find that in situ capping layers significantly reduce the formation of SiO2 at the interface with the substrate, but silicates form at the substrate and the capping layer interfaces. Predeposition nitridation of the Si surface can impede the reaction at the substrate interface, resulting in crystallization of Y2O3 in the film interior. Possible mechanisms of the silicate formation are discussed. DA - 2002/7/22/ PY - 2002/7/22/ DO - 10.1063/1.1496500 VL - 81 IS - 4 SP - 712-714 SN - 1077-3118 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000176871600048&KeyUID=WOS:000176871600048 ER - TY - JOUR TI - Molecular orientation and grafting density in semifluorinated self-assembled monolayers of mono-, di-, and trichloro silanes on silica substrates AU - Genzer, J AU - Efimenko, K AU - Fischer, DA T2 - LANGMUIR AB - Near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is used to measure the molecular orientation in semifluorinated self-assembled monolayers (SAMs) prepared by vapor deposition of mono- (F3C(CF2)8(CH2)2Si(CH3)2Cl, m-F8H2), di- (F3C(CF2)8(CH2)2Si(CH3)Cl2, d-F8H2), and trichloroorganosilanes (F3C(CF2)8(CH2)2SiCl3, t-F8H2) on flat silica-covered substrates. The average tilt angles (from the sample normal) of the fluorocarbon part, F(CF2)8-, of t-F8H2, d-F8H2, and m-F8H2 measured by carbon K-edge NEXAFS are 10 ± 2°, 35 ± 2°, and 45 ± 3°, respectively. We show that the increase of the tilt angle is associated with the steric hindrance of the methyl groups attached to silicon close to the bonding substrate. We also show that the molecular orientation obtained from the NEXAFS measurements can be used to estimate the grafting densities of the F8H2 molecules on the substrates. We present a simple one-dimensional geometric model to show that the grafting density of m-F8H2 is approximately one-half of that corresponding to the t-F8H2 SAM. Finally, we show that the results of this simple model are in accord with estimates of the two-dimensional fluorine areal density obtained from the fluorine K-edge NEXAFS spectra. DA - 2002/11/26/ PY - 2002/11/26/ DO - 10.1021/la025921x VL - 18 IS - 24 SP - 9307-9311 SN - 0743-7463 ER - TY - JOUR TI - Gas and vapor sorption, permeation, and diffusion in glassy amorphous teflon AF1600 AU - Alentiev, AY AU - Shantarovich, VP AU - Merkel, TC AU - Bondar, , VI AU - Freeman, BD AU - Yampolskii, YP T2 - MACROMOLECULES AB - Sorption and permeation parameters of light gases, C1−C12 hydrocarbons, and C1−C7 perfluorocarbons were determined in a random, amorphous, glassy copolymer containing 65 mol % 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole (BDD) and 35 mol % tetrafluoroethylene (TFE) (TFE/BDD65 or AF1600). AF1600 results were compared to those of another copolymer, AF2400, which contains 87 mol % BDD. As the amount of bulky, packing-disrupting BDD increases, solubility coefficients increase systematically, primarily due to increases in the nonequilibrium excess volume of the glassy polymer. Permeability and diffusivity also increase with increasing BDD content. AF1600 is easily plasticized by larger, more soluble penetrants and is susceptible to penetrant-induced conditioning. As penetrant size increases, permeability and diffusion coefficients decrease. The rates of decrease of permeability and diffusivity with increasing penetrant size, which characterize permeability and diffusivity selectivity, are intermediate between those of conventional glassy polymers and exceptionally high free volume glassy materials such as poly(1-trimethylsilyl-1-propyne) (PTMSP). Positron annihilation lifetime spectroscopy (PALS) results suggest unusually large free volume elements and a bimodal distribution of free volume element size: this is consistent with similar results obtained earlier for other high free volume glassy polymers such as AF2400 and PTMSP. Inverse gas chromatography and PALS estimates of free volume element size distributions were consistent. DA - 2002/12/3/ PY - 2002/12/3/ DO - 10.1021/ma020494f VL - 35 IS - 25 SP - 9513-9522 SN - 0024-9297 ER - TY - JOUR TI - Accounting for Auger yield energy loss for improved determination of molecular orientation using soft x-ray absorption spectroscopy AU - Genzer, J AU - Kramer, EJ AU - Fischer, DA T2 - JOURNAL OF APPLIED PHYSICS AB - Partial (Auger) yield near edge x-ray absorption fine structure (NEXAFS) is a structural analytical technique that has been primarily used to measure the spatial orientation and chemical bonding of small molecules on solid (i.e., inorganic or semiconductor) surfaces. In this article we demonstrate that the building block (BB) scheme proposed by Outka and co-workers [Phys. Rev. Lett. 59, 1321 (1987)] for analyzing NEXAFS spectra can be applied to model the molecular orientation of larger molecules, provided one accounts properly for kinetic energy losses of the Auger electrons traversing through the sample and hence the attenuation in measured Auger yield. We test the applicability of the proposed “modified” BB (MBB) model by measuring the orientation of a self-assembled monolayer (SAM) of –O1.5Si–(CH2)2–(CF2)8F, SF–SAM (SiOx), deposited on top of SiOx-covered silicon wafer as a function of the entrance grid bias (EGB) of the channeltron photoelectron detector. Our measurements of the EGB-dependent electron escape depth reveal that a crude depth profiling within the top ≈5 nm of the sample is possible by increasing the negative EGB on the channeltron detector, at the highest bias thus selecting only the Auger electrons, which have suffered negligible energy loss. In addition, we discuss how the order parameter method introduced recently by Stöhr and Samant [J. Electron Spectrosc. Relat. Phenom. 98–99, 189 (1989)] can be used to determine the molecular orientation of large organic molecules on surfaces. We also show that by accounting for energy losses of the NEXAFS Auger electrons (attenuation of measured Auger yield), the corrected order parameter (COP) approach gives good estimates of the orientation of molecules. We present a comparison between the MBB and COP models using experimental data collected from NEXAFS experiments from semifluorinated (SF) mesogens, –(CH2)x(CF2)yF, which are attached to: (1) the isoprene backbone of polyisoprene or a styrene–isoprene diblock copolymer and (2) a SiOx-covered solid substrate. We show that on both surfaces, the SF groups are oriented and on average are tilted by an angle 〈τF-helix〉 from the sample normal. We show that at higher 〈τF-helix〉 the results from the COP approach agree almost quantitatively with those extracted using the MBB model. DA - 2002/12/15/ PY - 2002/12/15/ DO - 10.1063/1.1516258 VL - 92 IS - 12 SP - 7070-7079 SN - 0021-8979 ER - TY - JOUR TI - Structural and catalytic response to temperature and cosolvents of carboxylesterase EST1 from the extremely thermoacidophilic archaeon Sulfolobus solfataricus P1 AU - Sehgal, AC AU - Tompson, R AU - Cavanagh, J AU - Kelly, RM T2 - BIOTECHNOLOGY AND BIOENGINEERING AB - The interactive effects of temperature and cosolvents on the kinetic and structural features of a carboxylesterase from the extremely thermoacidophilic archaeon Sulfolobus solfataricus P1 (Sso EST1) were examined. While dimethylformamide, acetonitrile, and dioxane were all found to be deleterious to enzyme function, dimethyl sulfoxide (DMSO) activated Sso EST1 to various extents. This was particularly true at 3.5% (v/v) DMSO, where k(cat) was 20-30% higher than at 1.2% DMSO, over the temperature range of 50-85 degrees C. DMSO compensated for thermal activation in some cases; for example, k(cat) at 60 degrees C in 3.5% DMSO was comparable to k(cat) at 85 degrees C in 1.2% DMSO. The relationship between DMSO activation and enzyme structural characteristics was also investigated. Nuclear magnetic resonance spectroscopy and circular dichroism showed no gross change in enzyme conformation with 3.5% DMSO between 50 and 80 degrees C. However, low levels of DMSO were shown to have a small yet significant change in enzyme conformation. This was evident through the reduction of Sso EST1's melting temperature and changes in the microenvironment of the enzyme's tyrosine and tryptophan residues at 3.5% versus 1.2% (v/v) solvent. Finally, activation parameter analysis based on kinetic data, at 1.2% and 3.5% DMSO, implied an increase in conformational flexibility with additional cosolvent. These results suggest the activating effect of DMSO was related to small changes in the enzyme's structure resulting in an increase in its conformational flexibility. Thus, in addition to their use for solubilizing hydrophobic substrates in water, cosolvents may also serve as activators in applications involving thermostable biocatalysts at sub-optimal temperatures. DA - 2002/12/30/ PY - 2002/12/30/ DO - 10.1002/bit.10433 VL - 80 IS - 7 SP - 784-793 SN - 0006-3592 KW - DMSO KW - conformational flexibility KW - enzyme activation KW - thermostable ER - TY - JOUR TI - Simulation of chemical reaction equilibria and kinetics in heterogeneous carbon micropores AU - Turner, CH AU - Brennan, JK AU - Pikunic, J AU - Gubbins, KE T2 - APPLIED SURFACE SCIENCE AB - We present a simulation study which shows how the equilibrium yield and kinetics of chemical reactions can be enhanced by tailoring the structure and surface chemistry of the catalyst support material. Equilibrium results are presented for the ammonia synthesis reaction, N2+3H2↔2NH3, occurring within various carbon supports, representing a range of chemical and physical surface heterogeneity. Using a simulation technique known as Reactive Monte Carlo (RxMC), we find that surface activation and pore width are primary factors in determining the conversion of the ammonia synthesis reaction while effects of surface corrugation are small. We probe the kinetic effects of physical confinement within microporous carbons by studying the bimolecular hydrogen iodide decomposition reaction, 2HI→H2+I2, in carbon slit-pores and nanotubes. The rate constant of this reaction is measured by combining the quasi-equilibrium hypothesis of transition-state theory (TST) with the RxMC simulation technique. The kinetic simulations represent a new method for probing reaction kinetics in non-ideal environments and show accurate results when applied to the hydrogen iodide decomposition reaction. DA - 2002/8/15/ PY - 2002/8/15/ DO - 10.1016/S0169-4332(02)00074-0 VL - 196 IS - 1-4 SP - 366-374 SN - 0169-4332 KW - reaction KW - kinetics KW - equilibrium KW - carbon KW - pores KW - simulation ER - TY - JOUR TI - Realistic molecular models for saccharose-based carbons AU - Pikunic, J AU - Gubbins, KE AU - Pellenq, RJM AU - Cohaut, N AU - Rannou, I AU - Gueth, JM AU - Clinard, C AU - Rouzaud, JN T2 - APPLIED SURFACE SCIENCE AB - We used a simulation protocol based on reverse Monte Carlo that we had developed in a previous work to build models for three carbons produced by the pyrolysis of saccharose and subsequent heat treatment at three different temperatures. In order to characterize the resulting models, we calculated the radial distribution function and the pore size distribution of the three structures. From this analysis, we found that the size of the graphene layers increases with the treatment temperature and that the carbons treated at higher temperatures present longer-range correlations. The short-range structural properties are in excellent agreement with HRTEM image analysis results. We performed grand canonical Monte Carlo (GCMC) simulations of nitrogen at 77 K in the resulting structural models to show how our models can be used to predict the effects of heterogeneity on the adsorption properties of carbons. DA - 2002/8/15/ PY - 2002/8/15/ DO - 10.1016/S0169-4332(02)00039-9 VL - 196 IS - 1-4 SP - 98-104 SN - 1873-5584 KW - carbons KW - adsorbent structure KW - reverse Monte Carlo ER - TY - JOUR TI - Polymer self-assembly in carbon dioxide AU - Taylor, DK AU - Keiper, JS AU - DeSimone, JM T2 - INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH AB - The foreseeable future should find carbon dioxide used in an ever-increasing number of industrial applications, from materials production to lithography. Many such processes will involve the use of amphiphilic compounds, which have greatly enhanced the versatility and potential of CO2 as a solvent. In a relatively short period of time, research on the self-assembly of amphiphilic polymers in CO2 has undergone remarkable maturation. The growth is largely due to strong fundamental and practical interest, as well as a cache of techniques available to characterize the self-assembly process. This article serves to summarize what has thus far been discovered about polymer self-assembly in CO2, what needs further examination, and where the field is headed. DA - 2002/9/4/ PY - 2002/9/4/ DO - 10.1021/ie010715q VL - 41 IS - 18 SP - 4451-4459 SN - 0888-5885 ER - TY - JOUR TI - Glucose-to-fructose conversion at high temperatures with xylose (glucose) isomerases from Streptomyces murinus and two hyperthermophilic Thermotoga species AU - Bandlish, RK AU - Hess, JM AU - Epting, KL AU - Vieille, C AU - Kelly, RM T2 - BIOTECHNOLOGY AND BIOENGINEERING AB - Abstract The conversion of glucose to fructose at elevated temperatures, as catalyzed by soluble and immobilized xylose (glucose) isomerases from the hyperthermophiles Thermotoga maritima (TMGI) and Thermotoga neapolitana 5068 (TNGI) and from the mesophile Streptomyces murinus (SMGI), was examined. At pH 7.0 in the presence of Mg 2+ , the temperature optima for the three soluble enzymes were 85°C (SMGI), 95° to 100°C (TNGI), and >100°C (TMGI). Under certain conditions, soluble forms of the three enzymes exhibited an unusual, multiphasic inactivation behavior in which the decay rate slowed considerably after an initial rapid decline. However, the inactivation of the enzymes covalently immobilized to glass beads, monophasic in most cases, was characterized by a first‐order decay rate intermediate between those of the initial rapid and slower phases for the soluble enzymes. Enzyme productivities for the three immobilized GIs were determined experimentally in the presence of Mg 2+ . The highest productivities measured were 750 and 760 kg fructose per kilogram SMGI at 60°C and 70°C, respectively. The highest productivity for both TMGI and TNGI in the presence of Mg 2+ occurred at 70°C, pH 7.0, with approximately 230 and 200 kg fructose per kilogram enzyme for TNGI and TMGI, respectively. At 80°C and in the presence of Mg 2+ , productivities for the three enzymes ranged from 31 to 273. A simple mathematical model, which accounted for thermal effects on kinetics, glucose–fructose equilibrium, and enzyme inactivation, was used to examine the potential for high‐fructose corn syrup (HFCS) production at 80°C and above using TNGI and SMGI under optimal conditions, which included the presence of both Co 2+ and Mg 2+ . In the presence of both cations, these enzymes showed the potential to catalyze glucose‐to‐fructose conversion at 80°C with estimated lifetime productivities on the order of 2000 kg fructose per kilogram enzyme, a value competitive with enzymes currently used at 55° to 65°C, but with the additional advantage of higher fructose concentrations. At 90°C, the estimated productivity for SMGI dropped to 200, whereas, for TNGI, lifetime productivities on the order of 1000 were estimated. Assuming that the most favorable biocatalytic and thermostability features of these enzymes can be captured in immobilized form and the chemical lability of substrates and products can be minimized, HFCS production at high temperatures could be used to achieve higher fructose concentrations as well as create alternative processing strategies. © 2002 Wiley Periodicals, Inc. Biotechnol Bioeng 80: 185–194, 2002. DA - 2002/10/20/ PY - 2002/10/20/ DO - 10.1002/bit.10362 VL - 80 IS - 2 SP - 185-194 SN - 0006-3592 KW - Thermotoga KW - xylose isomerase KW - Streptomyces murinus KW - hyperthermophile ER - TY - PCOMM TI - Fabricating planar nanoparticle assemblies with number density gradients AU - Bhat, RR AU - Fischer, DA AU - Genzer, J AB - We report on preparing assemblies of gold nanoparticles with continuous gradients in number density on flat silica-covered substrates. The methodology consists of (i) first forming a one-dimensional molecular gradient of amino groups (−NH2) on the substrate by vapor deposition of amine-terminated silane molecules, followed by (ii) attachment of gold nanoparticles to −NH2 functional groups by immersing the substrate in a colloidal gold solution. Experiments using atomic force microscopy reveal that the number density of nanoparticles on the substrate varies continuously as a function of the position on the substrate. Near-edge X-ray absorption fine structure studies confirm that the nanoparticle number density gradient is closely correlated with the concentration gradient of −NH2 groups anchored to the substrate. We demonstrate that the number density of nanoparticles within the gradient and the length of the gradient can be tuned by controlling the vapor diffusion of silane molecules. In addition we show that this simple methodology can be further extended to create double gradients, thus producing “a valley in nanoparticle concentration”. DA - 2002/7/23/ PY - 2002/7/23/ DO - 10.1021/la025524m SP - 5640-5643 ER - TY - JOUR TI - Enantiomeric resolution of 2-aryl propionic esters with hyperthermophilic and mesophilic esterases: Contrasting thermodynamic mechanisms AU - Sehgal, AC AU - Kelly, RM T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - The enantiomeric resolution of 2-aryl propionic esters by hyperthermophilic and mesophilic esterases was found to be governed by contrasting thermodynamic mechanisms. Entropic contributions predominated for mesophilic esterases from Candida rugosa and Rhizomucor miehei, while enthalpic forces controlled this resolution by the esterase from the extremely thermoacidophilic archaeon, Sulfolobus solfataricus P1. This disparity in thermodynamic mechanism can be attributed to the differences in conformational flexibility of mesophilic and thermophilic enzymes as they relate to the temperature range (4-70 degrees C) examined. DA - 2002/7/17/ PY - 2002/7/17/ DO - 10.1021/ja026512q VL - 124 IS - 28 SP - 8190-8191 SN - 0002-7863 ER - TY - JOUR TI - Effect of rate of chemical or thermal renaturation on refolding and aggregation of a simple lattice protein AU - Nguyen, HD AU - Hall, CK T2 - BIOTECHNOLOGY AND BIOENGINEERING AB - We used dynamic Monte Carlo simulation to investigate how changing the rate of chemical or thermal renaturation affects the folding and aggregation behavior of a system of simple, two-dimensional lattice protein molecules. Four renaturation methods were simulated: infinitely slow cooling; slow but finite cooling; quenching; and pulse renaturation. The infinitely slow cooling method, which is equivalent to dialysis or diafiltration, provides refolding yields that are relatively high and aggregates that are relatively small (mostly dimers or trimers). The slow but finite cooling method, which is equivalent to multiple-step dilution, provides refolding yields that are almost as high as those observed in the infinitely slow cooling case, but in a relatively short period of time. Quenching, which is equivalent to one-step dilution or quick quenching, is extremely slow and has low re- folding yields. A maximum appears in the refolding yield as a function of denaturant concentration in the simulation but disappears after a very long duration. Finally, the pulse renaturation method provides refolding yields that are substantially higher than those observed in the other three methods, even at high packing fractions. As in the early stages of quenching, there is a maximum in the refolding yield as a function of denaturant concentration when relatively large numbers of denatured chains are added to the refolding solution at each step. DA - 2002/12/30/ PY - 2002/12/30/ DO - 10.1002/bit.10448 VL - 80 IS - 7 SP - 823-834 SN - 1097-0290 KW - protein folding KW - protein aggregation KW - renaturation KW - Monte Carlo KW - computer simulation ER - TY - JOUR TI - Effect of poly(aspartic acid) on the removal rates of brushite deposits from stainless steel tubing in turbulent flow AU - Littlejohn, F AU - Grant, CS AU - Wong, YL AU - Saez, AE T2 - INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH AB - This research investigates the effect of poly(aspartic acid) (PASP) and its sodium salt on the removal of brushite (dicalcium phosphate dihydrate, DCPD) deposits from stainless steel tubing in turbulent flows. In the absence of PASP, DCPD removal is dominated by the abrasion of solid particles from the deposit by fluid shear and is influenced by the kinetics of the interfacial dissolution process. The presence of PASP promotes DCPD removal for pHs between 4 and 10, with an optimum enhancement at pH 5. A decrease in the sensitivity of the removal rate to shear forces indicates that PASP inhibits solids detachment from the deposit for pH < 5. At higher pHs, PASP appears to reduce the shear stress required to remove particles from the deposit. A model for the interfacial dissolution process that includes mass transfer, adsorption equilibria, and the kinetics of acid dissolution and surface complexation is used to explain the trends of the experimental data on removal rates. DA - 2002/9/4/ PY - 2002/9/4/ DO - 10.1021/ie0201011 VL - 41 IS - 18 SP - 4576-4584 SN - 0888-5885 ER - TY - JOUR TI - Copolymer adsorption on planar chemically heterogeneous substrates: The interplay between the monomer sequence distribution and interaction energies AU - Genzer, J T2 - MACROMOLECULAR THEORY AND SIMULATIONS AB - We use a three-dimensional self-consistent field model to study the adsorption of A-B copolymers from A-B copolymer/A homopolymer blends on planar substrates comprising two chemically distinct regions C and D. The interplay between the spatial distribution of the surface chemical heterogeneities and the monomer sequence distribution in the copolymer is examined for diblock (A-B), triblock (A-B-A), inverted triblock (B-A-B), and alternating (A-alt-B) copolymers. Our results demonstrate that when the chemically heterogeneous motifs on the substrate are detected by the copolymer adsorbing segments, the copolymers can transcribe them with high fidelity into three dimensions. The way the surface pattern gets transferred is dictated by the monomer sequence distribution. We show that relative to alternating copolymers, block copolymers are generally better at capturing the chemical pattern shape and transcribing it into the polymer mixture. Moreover, block copolymers with shorter adsorbing blocks are capable of better recognizing the substrate motifs. In order to address the interplay between the monomer sequence distribution in the copolymer and the interaction energies, we systematically vary the repulsion between A and B, and the attraction between B and D. Our calculations reveal that increasing i) the interaction between the copolymer adsorbing segments (B) and the “sticky” points at the substrate (D), and/or ii) the repulsion between the copolymer segments (A and B) increases the total amount of the copolymer adsorbed at the mixture/substrate interface, and decreases (increases) the fidelity of the substrate chemical pattern recognition by compositionally symmetric (asymmetric) copolymers. DA - 2002/6/28/ PY - 2002/6/28/ DO - 10.1002/1521-3919(20020601)11:5<481::AID-MATS481>3.0.CO;2-G VL - 11 IS - 5 SP - 481-493 SN - 1521-3919 KW - adsorption KW - interfaces KW - mean-field KW - molecular recognition KW - surfaces ER - TY - PAT TI - Compositions for fracturing subterranean formations AU - Kelly, R. M. AU - Khan, S. A. AU - Leduc, P. AU - Tayal, A. AU - Prud'homme, R. K. C2 - 2002/// DA - 2002/// PY - 2002/// ER - TY - JOUR TI - The effects of inorganic solid particles on water and crude oil emulsion stability AU - Sullivan, AP AU - Kilpatrick, PK T2 - INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH AB - Small inorganic particles strongly enhance water−crude oil emulsion stability when interactions with asphaltenes promote particle adsorption at the oil−water interface. A variety of particle types have been studied to investigate the controlling factors for particle-stabilization effectiveness. Emulsion stabilities were determined by the extent of water resolved after centrifugation and the electric field required for emulsion breakdown. All particles used were hydrophilic and stabilized oil-in-water emulsions if small enough to be interfacially active. When dried and exposed to asphaltene-containing oil phases, the particles stabilized water-in-oil emulsions. Decreased extents of preadsorbed water, decreased particle sizes, and increased particle concentrations enhanced water-in-oil emulsion stability. Investigations with model emulsions showed that an intermediate state of asphaltene aggregation, near the point of incipient precipitation, is required for particle modification and emulsion stabilization. Increased asphaltene−particle interactions increased emulsion stabilization effectiveness. DA - 2002/7/10/ PY - 2002/7/10/ DO - 10.1021/ie010927n VL - 41 IS - 14 SP - 3389-3404 SN - 0888-5885 ER - TY - JOUR TI - Reduction in dislocation density and strain in GaN thin films grown via maskless pendeo-epitaxy AU - Roskowski, A. M. AU - Preble, E. A. AU - Einfeldt, S. AU - Miraglia, P. M. AU - Schuck, J. AU - Grober, R. AU - Davis, R. F. T2 - Opto-electronics Review DA - 2002/// PY - 2002/// VL - 10 IS - 4 SP - 261-270 ER - TY - CHAP TI - Reconstruction Method for the Characterization of Porous Carbons AU - Pikunic, J. AU - Clinard, C. AU - Cohaut, N. AU - Gubbins, K.E. AU - Guet, J.-M. AU - Pellenq, R.J.-M. AU - Rannou, I. AU - Rouzaud, J.-N. T2 - Characterization of Porous Solids VI, Proceedings of the 6th International Symposium on the Characterization of Porous Solids (COPS-VI) CN - TA418.9 .P6 I96 2002 PY - 2002/// DO - 10.1016/s0167-2991(02)80215-4 SP - 19-26 OP - PB - Elsevier SN - 9780444512611 UR - http://dx.doi.org/10.1016/s0167-2991(02)80215-4 DB - Crossref ER - TY - JOUR TI - Protein folding pathways and kinetics: Molecular dynamics simulations of beta-strand motifs AU - Jang, H AU - Hall, CK AU - Zhou, YQ T2 - BIOPHYSICAL JOURNAL AB - The folding pathways and the kinetic properties for three different types of off-lattice four-strand antiparallel beta-strand protein models interacting via a hybrid Go-type potential have been investigated using discontinuous molecular dynamics simulations. The kinetic study of protein folding was conducted by temperature quenching from a denatured or random coil state to a native state. The progress parameters used in the kinetic study include the squared radius of gyration R(2)(g), the fraction of native contacts within the protein as a whole Q, and between specific strands Q(ab). In the time series of folding, the denatured proteins undergo a conformational change toward the native state. The model proteins exhibit a variety of kinetic folding pathways that include a fast-track folding pathway without passing through an intermediate and multiple pathways with trapping into more than one intermediate. The kinetic folding behavior of the beta-strand proteins strongly depends on the native-state geometry of the model proteins and the size of the bias gap g, an artificial measure of a model protein's preference for its native state. DA - 2002/8// PY - 2002/8// DO - 10.1016/S0006-3495(02)75211-9 VL - 83 IS - 2 SP - 819-835 SN - 0006-3495 ER - TY - PAT TI - Method of making foamed materialsUSing surfactants and carbon dioxide AU - DeSimone, J. M. AU - Khan, S. A. AU - Royer, J. R. AU - Spontak, R. J. AU - Walker, T. A. C2 - 2002/// DA - 2002/// PY - 2002/// ER - TY - JOUR TI - Investigations regarding the maskless pendeo-epitaxial growth of GaN films prior to coalescence AU - Roskowski, AM AU - Preble, EA AU - Einfeldt, S AU - Miraglia, PM AU - Davis, RF T2 - IEEE JOURNAL OF QUANTUM ELECTRONICS AB - Pendeo-epitaxy employs lateral growth from etched seed forms to achieve a marked reduction in dislocation density in a material. In this research, high-resolution X-ray diffraction and atomic force microscopy of GaN stripes and the laterally grown wings confirmed transmission electron microscopy results regarding the reduction in dislocations in the latter regions. Micro-Raman and X-ray diffraction measurements showed the wings to be tilted /spl les/0.15/spl deg/ due to tensile stresses in the stripes induced primarily by the mismatch in the coefficients of thermal expansion between the GaN stripe and the SiC substrate. A strong, low-temperature D/spl deg/X peak at /spl ap/3.466 eV with a FWHM of /spl les/300 /spl mu/eV was measured in the wing material by micro-photoluminescence. Films grown at 1020/spl deg/C exhibited similar vertical [0001] and lateral [112~0] growth rates. Increasing the growth temperature increased the latter due to the higher thermal stability of the (112~0) GaN and initiated growth of spiral hillocks on the (0001) surface of the stripes. The latter were due to adatom diffusion to heterogeneous steps previously nucleated at the intersections of pure screw or mixed dislocations. The (112~0) surface was atomically smooth under all growth conditions with a root mean square roughness value of 0.17 nm. DA - 2002/8// PY - 2002/8// DO - 10.1109/JQE.2002.801005 VL - 38 IS - 8 SP - 1006-1016 SN - 0018-9197 KW - chemical vapor deposition KW - semiconductor growth KW - thin films KW - topography ER - TY - CHAP TI - Influence of synthesis conditions on surface heterogeneity of M41 type materials studied with lattice Monte Carlo AU - Siperstein, Flor R. AU - Gubbins, Keith E. T2 - Characterization of Porous Solids VI, Proceedings of the 6th International Symposium on the Characterization of Porous Solids (COPS-VI) AB - The synthesis of mesoporous silica materials using surfactants as structure-directing agents is studied using lattice Monte Carlo simulations. The surfactant HmTn is modeled as a sequence of m hydrophilic segments or heads (H) followed by n hydrophobic segments or tails (T). Favorable interactions between the surfactant heads and the silica result in the formation of a surfactant-rich silica-rich phase in equilibrium with a dilute phase. Liquid crystal behavior is observed in the phase containing high-surfactant and high-silica concentration, with different structures depending on the overall system composition that are similar to the M41 family. The formation of a silica hexagonal phase is observed at low surfactant/silica ratios and lamellar or perforated lamellar phases are formed at high surfactant/silica ratios. The structure of the silica materials depends on the surfactant chemistry, the surfactant/silica ratios and the temperature. Heats of adsorption of simple gases on model MCM-41 type materials are calculated using Grand Canonical Monte Carlo simulations. Adsorption properties on model materials that were generated through a mimetic synthesis using lattice Monte Carlo simulations are compared with those on smooth cylindrical pores. Energetic heterogeneity in the materials studied is due to surface roughness and structural defects and not to the presence of areas with different chemical composition. This is in agreement with experimentally measured heats of adsorption of simple gases. At low coverage, heats of adsorption of argon and krypton on MCM-41 decrease with coverage, indicating that MCM-41 is not a homogeneous adsorbent even for non-polar spherical gas molecules, where the presence of polar groups in the adsorbent surface should have little effect. CN - TA418.9 .P6 I96 2002 PY - 2002/// DO - 10.1016/s0167-2991(02)80192-6 SP - 647-654 OP - PB - Elsevier SN - 9780444512611 UR - http://dx.doi.org/10.1016/s0167-2991(02)80192-6 DB - Crossref ER - TY - CHAP TI - Freezing in Mesopores: Aniline in Silica Glasses and MCM-41 AU - Sliwinska-Bartkowiak, M. AU - Dudziak, G. AU - Radhakrishnan, R. AU - Gubbins, K.E. T2 - Characterization of Porous Solids VI, Proceedings of the 6th International Symposium on the Characterization of Porous Solids (COPS-VI) AB - We report a study of the freezing of aniline in silica porous materials, using dielectric relaxation spectroscopy and light transmission measurements. The porous materials include controlled pore glasses with pore sizes H in the range 7.5 to 50 nm, Vycor glass (H = 4.1 nm) and MCM-41 (H = 2.8 nm). The freezing temperature is lowered due to the confinement, and in the larger pores crystallization occurs. In the MCM-41 material no crystallization is observed; instead a glassy phase is formed at low temperatures. In Vycor the experiments indicate a mixture of microscopic domains of crystal and glass at low temperature. The results are consistent with recent molecular simulation results. CN - TA418.9 .P6 I96 2002 PY - 2002/// DO - 10.1016/s0167-2991(02)80169-0 SP - 467-474 OP - PB - Elsevier SN - 9780444512611 UR - http://dx.doi.org/10.1016/s0167-2991(02)80169-0 DB - Crossref ER - TY - JOUR TI - Entanglement relaxation and release in hard chain fluids during molecular dynamics simulations AU - McCormick, JA AU - Hall, CK AU - Khan, SA T2 - MACROMOLECULES AB - Discontinuous molecular dynamics simulations are performed on systems containing 32 hard chains of length 192 at three volume fractions, φ = 0.40, 0.45, and 0.50, to investigate entanglement relaxation and release in model polymer melts. The relaxation behavior of the systems is compared to that predicted by the tube model and to that suggested for the release of interchain entanglements, or knots. The mean squared displacement of the chain center of mass, the mean squared displacements of inner, outer, and intermediate segments along the chain, the end-to-end vector autocorrelation function, and the apparent self-diffusion coefficient are calculated over the course of the simulations. The three relaxation times (τe, τR, and τd) predicted by the tube model are estimated in order to determine the extent to which the results exhibit tube confinement. The initial relaxation of chain segments occurs from the ends toward the middle as the tube model predicts. However, different methods for predicting the longest relaxation time, τd, provide inconsistent results. An analysis of the mean squared displacement behavior of chain segments at various positions along the chain reveals when final relaxation occurs and suggests that the final relaxation is occurring at the chain ends, inconsistent with the tube model but compatible with the release of interchain entanglements or knots. A combined analysis of the end-to-end vector autocorrelation function, the outer segment mean squared displacement, and the apparent diffusion coefficient suggests that knot release behavior is occurring in the systems. The results provide support for a proposed mechanism of interchain entanglement relaxation consisting of initial relaxation, followed by memory and final release from a chain end; however, the uncertainty is large at these long times. DA - 2002/7/16/ PY - 2002/7/16/ DO - 10.1021/ma011134f VL - 35 IS - 15 SP - 6005-6019 SN - 1520-5835 ER - TY - JOUR TI - Electron energy-loss spectroscopy analysis of interface structure of yttrium oxide gate dielectrics on silicon AU - Niu, D AU - Ashcraft, RW AU - Chen, Z AU - Stemmer, S AU - Parsons, GN T2 - APPLIED PHYSICS LETTERS AB - Interface stability of high dielectric constant gate insulators on silicon is an important issue for advanced gate stack engineering. In this article, we analyze the silicon/dielectric interface structure for thin Y2O3 and Y silicate films deposited by chemical vapor deposition on clean and prenitrided Si(100) using high-resolution transmission electron microscopy, electron energy-loss spectroscopy, and x-ray photoelectron spectroscopy. The analysis shows the films to be stoichiometric Y2O3 on top and Y-silicate/SiO2 at the dielectric/Si interface. Prenitridation of the silicon surface impedes the reaction between the depositing film and the substrate, promoting a Si-free Y2O3 structure. Possible mechanisms leading to the observed Y2O3 and Y silicate structures are discussed. DA - 2002/7/22/ PY - 2002/7/22/ DO - 10.1063/1.1496138 VL - 81 IS - 4 SP - 676-678 SN - 1077-3118 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000176871600036&KeyUID=WOS:000176871600036 ER - TY - JOUR TI - Continuous precipitation polymerization of vinylidene fluoride in supercritical carbon dioxide: Molecular weight distribution AU - Saraf, MK AU - Wojcinski, LM AU - Kennedy, KA AU - Gerard, S AU - Charpentier, PA AU - DeSimone, J AU - Roberts, GW T2 - MACROMOLECULAR SYMPOSIA AB - The surfactant-free precipitation polymerization of vinylidene fluoride (VF2) in supercritical carbon dioxide was studied in a continuous stirred autoclave. The polymerization temperature ranged from 65 to 85°C, the average residence time in the reactor varied from 10 to 50 min., and the pressure was between 210 and 305 bar. Diethyl peroxydicarbonate was used as the initiator. The fractional conversion of monomer varied from 7 to 26%, the number-average molecular weight of the polymer was between about 14,000 and 79,000, and the weight-average molecular weight was between about 21,000 and 700,000. In many cases, the polymer exhibited a bimodal molecular-weight distribution, especially at high monomer concentrations. DA - 2002/6// PY - 2002/6// DO - 10.1002/1521-3900(200206)182:1<119::AID-MASY119>3.0.CO;2-P VL - 182 SP - 119-129 SN - 1521-3900 ER - TY - JOUR TI - The role of the OH species in high-k/polycrystalline silicon gate electrode interface reactions AU - Gougousi, T AU - Kelly, MJ AU - Parsons, GN T2 - APPLIED PHYSICS LETTERS AB - In this letter, reactions occurring at the interface between polycrystalline silicon (poly-Si) and LaSiOx high-dielectric-constant (high-k) insulating layers are characterized using x-ray photoelectron spectroscopy. Dielectrics were formed by sputter deposition of metal on silicon, followed by oxidation at 900 °C. Amorphous silicon was deposited on top by plasma-enhanced chemical vapor deposition from silane, followed by anneal at 650–1050 °C. We show that if the dielectric layer is exposed to sufficient water vapor before polysilicon deposition, annealing at 1050 °C for 10 s is sufficient to completely oxidize ∼25 Å of deposited silicon. Minimal reaction is observed without deliberate water exposure. This demonstrates the importance of the dielectric surface condition in determining reactivity of high-k/polysilicon interfaces. DA - 2002/6/10/ PY - 2002/6/10/ DO - 10.1063/1.1485122 VL - 80 IS - 23 SP - 4419-4421 SN - 1077-3118 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000175904600044&KeyUID=WOS:000175904600044 ER - TY - JOUR TI - The effects of personality type on engineering student performance and attitudes AU - Felder, R. M. AU - Felder, G. N. AU - Dietz, E.J. T2 - Journal of Engineering Education AB - Abstract The Myers‐Briggs Type Indicator® (MBTI) was administered to a group of 116 students taking the introductory chemical engineering course at North Carolina State University. That course and four subsequent chemical engineering courses were taught in a manner that emphasized active and cooperative learning and inductive presentation of course material. Type differences in various academic performance measures and attitudes were noted as the students progressed through the curriculum. The observations were generally consistent with the predictions of type theory, and the experimental instructional approach appeared to improve the performance of MBTI types (extraverts, sensors, and feelers) found in previous studies to be disadvantaged in the engineering curriculum. The conclusion is that the MBTI is a useful tool for helping engineering instructors and advisors to understand their students and to design instruction that can benefit all of them. DA - 2002/// PY - 2002/// DO - 10.1002/j.2168-9830.2002.tb00667.x VL - 91 IS - 1 SP - 3-17 ER - TY - JOUR TI - So you want to win a CAREER award AU - Felder, R. M. T2 - CEE, Chemical Engineering Education DA - 2002/// PY - 2002/// VL - 36 IS - 1 SP - 32-33 ER - TY - JOUR TI - Predicted inversion curve and third virial coefficients of carbon dioxide at high temperatures AU - Colina, CM AU - Olivera-Fuentes, C T2 - INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH AB - The shape of the Joule−Thomson inversion curve of a fluid at high temperatures is shown to be directly related to its second and third virial coefficients. Experimental values and empirical correlations of the third virial coefficient of carbon dioxide are used to resolve a previously observed conflict between inversion curves obtained from different equations of state for this fluid. In particular, third virial coefficients predicted from the Pitzer−Sterner equation of state are shown to be in error, resulting therefore in an incorrect inversion curve. DA - 2002/3/6/ PY - 2002/3/6/ DO - 10.1021/ie010367s VL - 41 IS - 5 SP - 1064-1068 SN - 0888-5885 ER - TY - JOUR TI - Polymeric nanogels produced via inverse microemulsion polymerization as potential gene and antisense delivery agents AU - McAllister, K AU - Sazani, P AU - Adam, M AU - Cho, MJ AU - Rubinstein, M AU - Samulski, RJ AU - DeSimone, JM T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - Polymeric nanogel vectors were developed for cellular gene and antisense delivery. Inverse microemulsion polymerization was utilized to synthesize biocompatible nanogels with controlled size, morphology, and composition. The chemical composition, size, polydispersity, stability, and swelling behavior of the nanogels were investigated by NMR, light scattering, transmission electron microscopy, and atomic force microscopy. The cell viability, uptake, and physical stability of nanogel-DNA complexes were evaluated under physiological conditions. Monodisperse nonionic and cationic nanogels were produced with controllable sizes ranging from 40 to 200 nm in diameter. The nanogels demonstrated extended stability in aqueous media and exhibited low toxicity in cell culture. Cationic nanogels formed monodisperse complexes with oligonucleotides and showed enhanced oligonucleotide uptake in cell culture. The nanogels synthesized in this study demonstrate potential utility as carriers of oligonucleotides and DNA for antisense and gene delivery. DA - 2002/12/25/ PY - 2002/12/25/ DO - 10.1021/ja027759q VL - 124 IS - 51 SP - 15198-15207 SN - 1520-5126 ER - TY - JOUR TI - On-line spectroscopic characterization of sodium cyanide with nanostructured gold surface-enhanced Raman spectroscopy substrates AU - Tessier, PM AU - Christesen, SD AU - Ong, KK AU - Clemente, EM AU - Lenhoff, AM AU - Kaler, EW AU - Velev, OD T2 - APPLIED SPECTROSCOPY AB - To implement surface-enhanced Raman spectroscopy as a practical detection method, highly enhancing, stable, and reproducible substrates need to be fabricated in an efficient manner, and their performance in different solution environments should be well characterized. In this work structured porous gold films have been fabricated using colloidal crystals to template gold nanoparticles. These films were integrated into an on-line flow chamber and used to study the effects of pH and other additives on the detection of sodium cyanide. The gold films proved to be highly enhancing and were used to detect cyanide over a wide range of pH values in the concentration range of ∼2 to 200 ppb. The Raman signal intensity could be increased by lowering the pH after the adsorption of cyanide, which was likely due to both a change in the ionization state and a conformational change of the bound molecules. The peak intensity could also be enhanced multifold by treating the substrate with silver nitrate. Cyanide could be removed from the substrates using hydrochloric acid, although this also passivated the structures, and the activity could only be restored partially with tannic acid. These results provide a rational method to optimize the online detection of cyanide in water. DA - 2002/12// PY - 2002/12// DO - 10.1366/000370202321115968 VL - 56 IS - 12 SP - 1524-1530 SN - 1943-3530 UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-0036971668&partnerID=MN8TOARS KW - surface-enhanced Raman spectroscopy KW - structured gold films KW - cyanide detection KW - colloidal crystal templating KW - nanoparticles ER - TY - JOUR TI - Maskless pendeo-epitaxial growth of GaN films AU - Roskowski, AM AU - Preble, EA AU - Einfeldt, S AU - Miraglia, PM AU - Davis, RF T2 - JOURNAL OF ELECTRONIC MATERIALS DA - 2002/5// PY - 2002/5// DO - 10.1007/s11664-002-0095-6 VL - 31 IS - 5 SP - 421-428 SN - 1543-186X KW - pendeo-epitaxy (PE) KW - gallium nitride (GaN) KW - metalorganic vapor phase epitaxy (MOVPE) KW - atomic force microscopy (AFM) KW - x-ray diffraction (XRD) KW - photoluminescence (PL) ER - TY - CONF TI - Introducing new faculty to multidisciplinary research collaboration AU - Ollis, D. F. AU - Felder, R. M. AU - Brent, R. C2 - 2002/// C3 - 2002 ASEE Annual Conference Proceedings, ASEE, June 2002 DA - 2002/// M1 - 2002 June PB - Washington, D.C.: American Society for Engineering Education ER - TY - CONF TI - How important is effective teaching to engineering faculty and administrators AU - Brawner, C. E. AU - Felder, R. M. AU - Allen, R.H. AU - Brent, R. C2 - 2002/// C3 - 2002 ASEE Annual Conference Proceedings, ASEE, June 2002 DA - 2002/// M1 - 2002 June PB - Washington, D.C.: American Society for Engineering Education ER - TY - JOUR TI - Ab initio analysis of silyl precursor physisorption and hydrogen abstraction during low temperature silicon deposition AU - Gupta, A AU - Yang, H AU - Parsons, GN T2 - SURFACE SCIENCE AB - Abstract The energetics of silyl (SiH 3 ) precursor surface adsorption and hydrogen abstraction on a monohydride terminated silicon surface are described. The abstraction of surface hydrogen by H radicals is more exothermic, and proceeds with a smaller kinetic barrier than H abstraction by silyl. Surface adsorption and abstraction were analyzed using both multi-parent configuration interaction (CI) and several density functional approaches using the Si 4 H 10 cluster representing a monohydride terminated silicon (1 1 1) surfaces, and results from the two techniques are critically compared and evaluated. Hydrogen abstraction by H is found to proceed through a kinetic barrier that is between 0 kcal/mol predicted by DFT and 7.2 kcal/mol determined from CI, consistent with experimental values of ∼2 kcal/mol. The barrier height for H abstraction by silyl (without zero point and H tunneling corrections) is determined to be between 4.1 kcal/mol calculated using DFT, and 14.2 kcal/mol determined from the multi-parent CI. These calculations indicate that during typical low temperature silicon deposition processes, H abstraction by impinging hydrogen atoms dominates H abstraction by SiH 3 and plays an important role in creation of surface dangling bonds. None of the Si–H/silyl potential energy surfaces obtained from CI and DFT methods show evidence for stable physisorbed three-center Si–H–(SiH 3 ) p bond, which is commonly presumed in several models of silicon thin film deposition. We discuss these results in relation to experimental analysis of surface diffusion kinetics in film deposition, and suggest alternate growth models, including H-mediated Si–Si bond breaking and/or direct silyl insertion, to describe activated low temperature silicon-based film deposition. DA - 2002/1/10/ PY - 2002/1/10/ DO - 10.1016/S0039-6028(01)01467-4 VL - 496 IS - 3 SP - 307-317 SN - 0039-6028 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000173286100016&KeyUID=WOS:000173286100016 KW - ab initio quantum chemical methods and calculations KW - density functional calculations KW - models of surface chemical reactions ER - TY - JOUR TI - The evolution of US pollution prevention, 1976-2001: a unique chemical engineering contribution to the environment - a review AU - Overcash, M T2 - JOURNAL OF CHEMICAL TECHNOLOGY AND BIOTECHNOLOGY AB - Abstract The importance of pollution prevention or cleaner production has been substantial in changing the environmental approach within advanced industrialized countries. Since the critical factors for pollution prevention success relate to fundamental understanding of diverse industrial processes, chemical engineering has had a major and unique role in this environmental field. Expanding this new and evolutionary topic into the undergraduate curriculum of chemical engineering has also been vital to improving the sustainability of cleaner production. This article describes the fundamental concepts that led to active pollution prevention progress and then the historical progress toward this new paradigm. © 2002 Society of Chemical Industry DA - 2002/11// PY - 2002/11// DO - 10.1002/jctb.701 VL - 77 IS - 11 SP - 1197-1205 SN - 0268-2575 KW - pollution prevention KW - cleaner production KW - environment ER - TY - JOUR TI - Surface modification of Sylgard-184 poly(dimethyl siloxane) networks by ultraviolet and ultraviolet/ozone treatment AU - Efimenko, Kirill AU - Wallace, W. E. AU - Genzer, Jan T2 - Journal of Colloid and Interface Science DA - 2002/// PY - 2002/// DO - 10.1006/jcis.202.8594 VL - 254 IS - 2 SP - 306–315 ER - TY - JOUR TI - Staphylococcus aureus adhesion to self-assembled monolayers: effect of surface chemistry and fibrinogen presence AU - Tegoulia, V. A. AU - Cooper, S. L. T2 - Colloids and Surfaces. B, Biointerfaces DA - 2002/// PY - 2002/// VL - 24 IS - 3-4 SP - 217-228 ER - TY - JOUR TI - Self-assembly of surfactants in a supercritical solvent from lattice Monte Carlo simulations AU - Lisal, M AU - Hall, CK AU - Gubbins, KE AU - Panagiotopoulos, AZ T2 - JOURNAL OF CHEMICAL PHYSICS AB - We modify Larson’s lattice model [J. Chem. Phys. 83, 2411 (1985)] and use it to study self-assembly of surfactants in a supercritical solvent by large-scale Monte Carlo simulations. Carbon dioxide and perfluoroalkylpoly(ethylene oxide) serve as prototypes for the solvent and surfactant, respectively. Larson-model type parameters for carbon dioxide and perfluoroalkylpoly(ethylene oxide) are obtained using experimental values of critical parameters and solubility along with a modified Berthelot combining rule. We perform canonical Monte Carlo simulations at a supercritical temperature, varying the number of surfactant head and tail segments, the solvent density and the surfactant concentration. Various properties such as the critical micelle concentration, the aggregate size distribution, and the size and shape of the micelles are evaluated and pseudophase diagrams are constructed. We further investigate the ability of the surfactant solutions to dissolve more solute than solutions without surfactants by calculating the partition coefficient. Water serves as a prototype for the solute and Larson-model type parameters for water are obtained in the same way as for carbon dioxide and perfluoroalkylpoly(ethylene oxide). DA - 2002/1/15/ PY - 2002/1/15/ DO - 10.1063/1.1428347 VL - 116 IS - 3 SP - 1171-1184 SN - 0021-9606 ER - TY - JOUR TI - Pd growth and subsequent Schottky barrier formation on chemical vapor cleaned p-type GaN surfaces AU - Hartlieb, PJ AU - Roskowski, A AU - Davis, RF AU - Platow, W AU - Nemanich, RJ T2 - JOURNAL OF APPLIED PHYSICS AB - Characterization of chemical vapor cleaned, Mg-doped, p-type GaN(0001) surfaces and Pd contacts sequentially deposited on these surfaces has been conducted using x-ray and ultraviolet photoelectron spectroscopies and low-energy electron diffraction. The band bending and the electron affinity at the cleaned p-GaN surface were 1.4±0.1 eV and 3.1±0.1 eV, respectively. A previously unidentified band of surface states was observed at ∼1.0 eV below the Fermi level on this surface. The Pd grew epitaxially on the cleaned surface in a layer-by-layer mode and formed an abrupt, unreacted metal–semiconductor interface. The induced Fermi level movement with Pd deposition has been attributed to a complex interaction between extrinsic and intrinsic surface states as well as metal induced gap states. The final Schottky barrier height at the Pd/p-GaN interface was 1.3±0.1 eV; the interface dipole contribution was 0.4±0.1 eV. DA - 2002/1/15/ PY - 2002/1/15/ DO - 10.1063/1.1424060 VL - 91 IS - 2 SP - 732-738 SN - 1089-7550 ER - TY - JOUR TI - Multiscale dewetting of low-molecular-weight block copolymer ultrathin films AU - Leonard, DN AU - Russell, PE AU - Smith, SD AU - Spontak, RJ T2 - MACROMOLECULAR RAPID COMMUNICATIONS AB - Ultrathin films of a low-molecular-weight block copolymer spontaneously dewet after several days at ambient temperature. Film rupture produces macroscopic holes and a residual pancake brush layer ≈ 2 nm thick with intermittent mounds measuring up to 25 nm in thickness. Multiscale dewetting likewise occurs when the films are heated and returned to ambient temperature. Regardless of the surface pattern that forms during heating, submicron mounds develop on the dewetted copolymer film, and fine holes emerge along the substrate surface, after cooling. DA - 2002/2/19/ PY - 2002/2/19/ DO - 10.1002/1521-3927(20020201)23:3<205::AID-MARC205>3.0.CO;2-X VL - 23 IS - 3 SP - 205-209 SN - 1022-1336 KW - block copolymers KW - surface dewetting KW - surface patterns KW - thin films ER - TY - JOUR TI - Global phase diagrams for freezing in porous media AU - Radhakrishnan, R AU - Gubbins, KE AU - Sliwinska-Bartkowiak, M T2 - JOURNAL OF CHEMICAL PHYSICS AB - Using molecular simulations and free energy calculations based on Landau theory, we show that freezing/melting behavior of fluids of small molecules in pores of simple geometry can be understood in terms of two main parameters: the pore width H* (expressed as a multiple of the diameter of the fluid molecule) and a parameter α that measures the ratio of the fluid-wall to the fluid–fluid attractive interaction. The value of the α parameter determines the qualitative nature of the freezing behavior, for example, the direction of change in the freezing temperature and the presence or absence of new phases. For slit-shaped pores, larger α values lead to an increase in the freezing temperature of the confined fluid, and to the presence of a hexatic phase. For pores that accommodate three or more layers of adsorbate molecules several kinds of contact layer phase (inhomogeneous phases in which the contact layer has a different structure than the inner layers) are observed. Smaller α values lead to a decrease in the freezing temperature. The parameter H* determines the magnitude of shift in the freezing temperature, and can also affect the presence of some of the new phases. Results are presented as plots of transition temperature vs α for a particular pore width. Experimental results are also presented for a variety of adsorbates in activated carbon fibers (ACF) covering a wide range of α values; the ACF have slit-shaped pores with average pore width 1.2 nm. The experimental and simulation results show qualitative agreement. DA - 2002/1/15/ PY - 2002/1/15/ DO - 10.1063/1.1426412 VL - 116 IS - 3 SP - 1147-1155 SN - 0021-9606 ER - TY - JOUR TI - Effect of polydispersity on viscoelasticity and shear thickening in aqueous solutions of hydrocarbon end-capped poly(ethylene oxide) AU - Ma, SX AU - Cooper, SL T2 - MACROMOLECULES AB - The linear viscoelastic and shear thickening behavior in aqueous solutions of model hydrophobically end-capped poly(ethylene oxide) were examined. Comparisons are made between monodisperse samples, unimodal polydisperse samples, and bimodal polydisperse samples. While the linear viscoelastic behavior is qualitatively similar for both polydisperse and monodisperse systems, the steady shear response displayed a marked dependence on the type of polydispersity, especially in the shear thickening behavior. No significant shear thickening was observed in unimodal polydisperse samples, and one possible explanation for this lack of significant shear thickening could be due to a lack of cooperative non-Gaussian chain stretching.1 Samples with bimodal molecular weight distribution exhibit similar shear thickening behavior as monodisperse samples. Furthermore, the characteristics of shear thickening of the bimodal system were found to be the same as in the monodisperse polymer with the lower molecular weight (10K), instead of that of the monodisperse polymer with the same average molecular weight (20K). The mechanism of shear thickening is due to the non-Gaussian chain stretching of the shorter polymer chain. DA - 2002/3/12/ PY - 2002/3/12/ DO - 10.1021/ma010390p VL - 35 IS - 6 SP - 2024-2029 SN - 1520-5835 ER - TY - JOUR TI - Effect of hydrogen on adsorbed precursor diffusion kinetics during hydrogenated amorphous silicon deposition AU - Bray, KR AU - Gupta, A AU - Parsons, Gregory T2 - Applied Physics Letters AB - Fractal analysis of the surface topography is used to study the effects of hydrogen dilution on the surface transport kinetics during the plasma deposition of hydrogenated amorphous silicon. Images obtained from atomic force microscopy are examined using dimensional fractal analysis, and surface diffusion lengths of growth precursors are estimated from the measured correlation lengths. The addition of small amounts of hydrogen (H2/SiH4 ratios &lt;10/1) during deposition leads to a decrease in the diffusion length, but larger hydrogen dilutions result in increased diffusion length. Moreover, the measured surface diffusion activation barrier is reduced from 0.20 eV for deposition from pure SiH4 to 0.13 eV with high hydrogen dilution. Results are consistent with recent models for precursor surface transport during low-temperature deposition, and give insight into critical processes for low-temperature silicon crystallization. DA - 2002/// PY - 2002/// DO - 10.1063/1.1467616 VL - 80 IS - 13 SP - 2356-2358 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000174623300040&KeyUID=WOS:000174623300040 ER - TY - JOUR TI - Effect of confinement by porous materials on chemical reaction kinetics AU - Turner, CH AU - Brennan, JK AU - Johnson, JK AU - Gubbins, KE T2 - JOURNAL OF CHEMICAL PHYSICS AB - A methodology for including the effects of nonidealities, such as confinement in a porous solid or solvation, into the calculation of bimolecular reaction rate constants is presented. The method combines the transition-state theory formalism with the Reactive Monte Carlo simulation method. The approach is computationally efficient and accurate, within the approximations imposed by transition-state theory and the intermolecular potentials. Several applications of the method are presented for the decomposition reaction, 2HI→H2+I2, including effects due to confinement within carbon micropores and due to inert solvents. The method can be readily extended to other chemical reaction rate calculations in which the structure and the activation energy of the transition state is known a priori. DA - 2002/2/1/ PY - 2002/2/1/ DO - 10.1063/1.1431590 VL - 116 IS - 5 SP - 2138-2148 SN - 0021-9606 ER - TY - JOUR TI - Continuous precipitation polymerization of vinylidene fluoride in supercritical carbon dioxide: Formation of polymers with bimodal molecular weight distributions AU - Saraf, MK AU - Gerard, S AU - Wojcinski, LM AU - Charpentier, PA AU - DeSimone, JM AU - Roberts, GW T2 - MACROMOLECULES AB - The polymerization of vinylidene fluoride in supercritical carbon dioxide was studied in a continuous stirred tank reactor using diethylperoxydicarbonate as the free radical initiator. Experiments were carried out to investigate the effect of inlet monomer concentration, temperature, average residence time, and agitation on the polymerization rate, the average molecular weights, and the molecular weight distribution of the poly(vinylidene fluoride). A homogeneous kinetic model that includes inhibition due to chain transfer to monomer predicted the polymerization rates reasonably well. However, imperfect mixing, rather than a chemical effect, may have caused the apparent inhibition observed at high monomer concentrations. At inlet monomer concentrations greater than about 1.5 M, broad and bimodal molecular weight distributions were observed. An extended homogeneous kinetic model that includes chain transfer to polymer predicted the polydispersities reasonably well. This model also predicted a region of inoperability that matched the experimental results. However, the extended homogeneous model could not account for the bimodal distributions. DA - 2002/10/8/ PY - 2002/10/8/ DO - 10.1021/ma0203602 VL - 35 IS - 21 SP - 7976-7985 SN - 1520-5835 ER - TY - JOUR TI - Biochemical characterization of Thermotoga maritima endoglucanase Ce174 with and without a carbohydrate binding module (CBM) AU - Chhabra, , SR AU - Kelly, RM T2 - FEBS LETTERS AB - The genome of the hyperthermophilic bacterium Thermotoga maritima (Tm) encodes at least eight glycoside hydrolases with putative signal peptides; the biochemical characteristics of seven of these have been reported previously. The eighth, Tm Cel74, is encoded by an open reading frame of 2124 bp corresponding to a polypeptide of 79 kDa with a signal peptide at the amino-terminus. The gene (lacking the signal peptide) encoding Tm Cel74 was expressed as a 77 kDa monomeric polypeptide in Escherichia coli and found to be optimally active at pH 6, 90 degrees C, with a melting temperature of approximately 105 degrees C. The cel74 gene was previously found to be induced during T. maritima growth on a variety of polysaccharides, including barley glucan, carboxymethyl cellulose (CMC), glucomannan, galactomannan and starch. However, while Tm Cel74 was most active towards barley glucan and to a lesser extent CMC, glucomannan and tamarind (xyloglucan), no activity was detected on other glycans, including galactomannan, laminarin and starch. Also, Tm Cel74 did not contain a carbohydrate binding module (CBM), versions of which have been identified in the amino acid sequences of other family 74 enzymes. As such, a CBM associated with a chitinase in another hyperthermophile, Pyrococcus furiosus, was used to create a fusion protein that was active on crystalline cellulose; Tm Cel74 lacked activity on this substrate. Based on the cleavage pattern determined for Tm Cel74 on glucan-based substrates, this enzyme likely initiates recruitment of carbohydrate carbon and energy sources by creating oligosaccharides that are transported into the cell for further processing. DA - 2002/11/6/ PY - 2002/11/6/ DO - 10.1016/S0014-5793(02)03493-2 VL - 531 IS - 2 SP - 375-380 SN - 1873-3468 ER - TY - JOUR TI - ABA triblock copolymer gels modified with an A-compatible semicrystalline homopolymer AU - Walker, TA AU - Semler, JJ AU - Leonard, DN AU - Maanen, GJ AU - Bukovnik, RR AU - Spontak, RJ T2 - LANGMUIR AB - In the presence of a midblock-selective solvent, ABA triblock copolymers form physical gels in which bridged and entangled B-chains establish a swollen network stabilized by A-microdomains. Here, we seek to improve the properties of an ABA gel through the addition of an A-compatible, high-molecular-weight semicrystalline homopolymer (shA). Dynamic rheology indicates that the elastic modulus increases substantially, and far beyond that achievable with an inert filler, with increasing shA content at constant solvent concentration. Transmission electron micrographs reveal the existence of nanoscale shA filaments and sheets dispersed in a micelle-stabilized gel network. The shape of the nanoscale shA objects, which are partially crystalline according to differential scanning calorimetry, and their apparent interaction with the A-rich micelles enhance network development and are responsible for the pronounced modulus increase. DA - 2002/10/29/ PY - 2002/10/29/ DO - 10.1021/la026117d VL - 18 IS - 22 SP - 8266-8270 SN - 0743-7463 ER - TY - JOUR TI - Transport properties of lithium hectorite-based composite electrolytes AU - Riley, M AU - Fedkiw, PS AU - Khan, SA T2 - JOURNAL OF THE ELECTROCHEMICAL SOCIETY AB - Conductivity and lithium-ion transference numbers are reported for physically gelled composite electrolytes using lithium hectorite clay as the charge carrier and carbonate solvents (ethylene carbonate, propylene carbonate, and dimethyl carbonate). Results are compared with those of typical lithium-ion battery electrolytes based on lithium hexafluorophosphate and carbonate solvents. Room-temperature conductivities of the composite electrolytes as high as S/cm were measured. Because of the nature of the anionic clay particulates creating the gel structure, near-unity lithium-ion transference numbers are expected and were observed as high as 0.98, as measured by the dc polarization method using lithium-metal electrodes. Since the carbonates react with lithium and create mobile ionic species that significantly reduce the observed lithium-ion transference number, care must be taken to minimize or eliminate the presence of the reaction-formed ionic species. These hectorite-based composite systems are possible electrolytes for rechargeable lithium-ion batteries requiring high discharge rates. © 2002 The Electrochemical Society. All rights reserved. DA - 2002/6// PY - 2002/6// DO - 10.1149/1.1470652 VL - 149 IS - 6 SP - A667-A674 SN - 1945-7111 ER - TY - JOUR TI - Topological coarsening of low-molecular-weight block copolymer ultrathin films by environmental AFM AU - Leonard, DN AU - Spontak, RJ AU - Smith, SD AU - Russell, PE T2 - POLYMER AB - Topological coarsening of block copolymer ultrathin films is well-understood for copolymers exhibiting intermediate or strong segregation and differing in film thickness or molecular weight at temperatures above the upper glass transition temperature (Tg), but below the order–disorder transition (TODT), of the copolymers. More recent studies suggest that the stability and topology of such films differ at temperatures above TODT. In this work, we use environmental atomic force microscopy to examine the effect of temperature on the coarsening of block copolymer ultrathin films in situ. Films measuring ca. 25 nm thick consist of a low-molecular-weight poly(styrene-b-isoprene) diblock copolymer for which the upper Tg and TODT in the bulk are about 42 and 70 °C, respectively. Time-resolved image sequences illustrating surface reorganization are obtained at temperatures below, above and near 70 °C. At temperatures very close to 70 °C, coarsening is found to slow markedly, by almost an order of magnitude relative to what is observed at higher and lower temperatures, suggesting that thermal factors may provide a means by which to inhibit the dewetting of block copolymer ultrathin films. DA - 2002/12// PY - 2002/12// DO - 10.1016/S0032-3861(02)00640-7 VL - 43 IS - 25 SP - 6719-6726 SN - 0032-3861 KW - block copolymer KW - polymer dewetting KW - order-disorder transition ER - TY - JOUR TI - Toluene bioconversion to p-hydroxybenzoate by fed-batch cultures of recombinant Pseudomonas putida AU - Miller, ES AU - Peretti, SW T2 - BIOTECHNOLOGY AND BIOENGINEERING AB - A microbial oxidation process for the production of p-hydroxybenzoate (HBA) from toluene is reported. The oxidation reaction was studied in fed-batch fermentations using a recombinant Pseudomonas putida grown on glutamate as the sole carbon and energy source with salicylate and IPTG induction of tmoABCDE, and pchCF and phbz pathway genes, respectively. An average volumetric HBA productivity of 13.4 mg HBA x L(-1) x h(-1) was obtained under rapid growth conditions (glutamate excess), giving an HBA titer of 132 mg x L(-1) after 9.8 h of fermentation. This corresponded to an average specific HBA productivity of 7.2 microg HBA (mg total protein)(-1) x h(-1). In contrast, maximum HBA titers of 35 mg HBA x L(-1) were achieved in 27 h in comparative studies employing glutumate limited fed-batch cultures. A specific productivity of 4.1 microg HBA (mg total protein)(-1) x h(-1) and volumetric productivity of 1.3 mg HBA x L(-1) x h(-1) were calculated for the growth-rate restricted cultures. The differences in HBA production between the two cultures could be correlated to the levels of specific toluene-4-monooxygenase (T4MO) polypeptides. T4MO catalyzes the rate-limiting step in the pathway. Using experimental data, the half-life value of TmoA was calculated to be approximately 28 h. Assuming linear, monomolecular decay of TmoA, a specific degradation constant of 0.025 x h(-1) was calculated, which placed the stability of recombinant TmoA in the range of relatively stable proteins, even in the absence of co-expression of tmoF, the terminal oxidoreductase subunit of T4MO. DA - 2002/2/5/ PY - 2002/2/5/ DO - 10.1002/bit.10071 VL - 77 IS - 3 SP - 340-351 SN - 1097-0290 KW - bioconversion KW - p-hydroxybenzoate KW - fed-batch fermentation KW - toluene-4-monooxygenase KW - protein stability KW - toluene ER - TY - JOUR TI - Synthesis of metal-loaded poly(aminohexyl)(aminopropyl)silsesquioxane colloids and their self-organization into dendrites AU - Bronstein, LM AU - Linton, C AU - Karlinsey, R AU - Stein, B AU - Svergun, DI AU - Zwanziger, JW AU - Spontak, RJ T2 - NANO LETTERS AB - Hydrolytic condensation of N-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS) in water results in the formation of spherical colloids measuring 40 to 190 nm in diameter and composed of a nearly fully condensed poly(aminohexyl)(aminopropyl)silsesquioxane (PAHAPS) nanostructure containing C−SiO3/2 species. Interaction of Pt and Pd salts with these PAHAPS colloids, followed by chemical reduction, results in the formation of discrete metal nanoparticles measuring ca. 1−2 nm in diameter stabilized within the colloids. Dendrites differing in size and shape are observed to form from aqueous solutions containing PAHAPS colloids loaded with metal salts or metal nanoparticles. DA - 2002/8// PY - 2002/8// DO - 10.1021/nl025543g VL - 2 IS - 8 SP - 873-876 SN - 1530-6992 ER - TY - JOUR TI - Strain and crystallographic tilt in uncoalesced GaN layers grown by maskless pendeoepitaxy AU - Einfeldt, S AU - Roskowski, AM AU - Preble, EA AU - Davis, RF T2 - APPLIED PHYSICS LETTERS AB - The strain in thin GaN layers grown by maskless pendeoepitaxy has been investigated using high-resolution x-ray diffraction and finite-element simulations. The crystallographic tilt of the free-hanging wings was determined to result from the strain relaxation of the seed stripes along [0001]. The impact of the dimensions of the pendeostructure and of the formation of crystal defects on the expected wing tilt is discussed. DA - 2002/2/11/ PY - 2002/2/11/ DO - 10.1063/1.1448145 VL - 80 IS - 6 SP - 953-955 SN - 0003-6951 ER - TY - JOUR TI - Lithium/V6O13 cells using silica nanoparticle-based composite electrolyte AU - Li, YX AU - Fedkiw, PS AU - Khan, SA T2 - ELECTROCHIMICA ACTA AB - The electrochemical behavior of Li/V6O13 cells is investigated at room temperature (22 °C) both in liquid electrolyte consisting of oligomeric poly(ethyleneglycol)dimethylether+lithium bis(trifluoromethylsulfonylimide) and composite electrolytes formed by blending the liquid electrolyte with silica nanoparticles (fumed silica). The addition of fumed silica yields a gel-like electrolyte that demonstrates the desirable property of suppressing lithium dendrite growth due to the rigidity and immobility of the electrolyte structure. The lithium/electrolyte interfacial resistance for composite gel electrolytes is less than that for the corresponding base-liquid electrolyte, and the charge–discharge cycle performance and electrochemical efficiency for the Li/V6O13 cell is significantly improved. The effect of fumed silica surface group on the electrochemical performance is discussed; the native hydrophilic silanol surface group appears better than fumed silica that is modified with a hydrophobic octyl surface moiety. DA - 2002/9/12/ PY - 2002/9/12/ DO - 10.1016/S0013-4686(02)00326-2 VL - 47 IS - 24 SP - 3853-3861 SN - 1873-3859 KW - lithium cell KW - composite gel electrolyte KW - silica nanoparticle KW - lithium dendrite KW - vanadium oxide ER - TY - JOUR TI - Langmuir films of naphthenic acids at different pH and electrolyte concentrations AU - Havre, T. E. AU - Ese, M. H. AU - Sjoblom, J. AU - Blokhus, A. M. T2 - Colloid & Polymer Science DA - 2002/// PY - 2002/// VL - 280 IS - 7 SP - 647-652 ER - TY - JOUR TI - Gelation and rheology of xanthan/enzyme-modified guar blends AU - Pai, VB AU - Khan, SA T2 - CARBOHYDRATE POLYMERS AB - The rheological behavior and synergistic character of mixed polysaccharide systems are examined for blends of xanthan with enzymatically-modified guar. In particular, the enzyme α-galactosidase is used to selectively cleave off the galactose side chains of guar in order to obtain galactomannans with tailored molecular architecture: EMG1 with a relatively high galactose content of 33.6% and a mannose (M) to galactose (G) ratio of 1.85, and EMG2 with a lower galactose content (25.2%) and an M/G ratio of 2.86. Blends of xanthan with enzymatically-modified guar gum samples are examined in terms of their dynamic rheological properties and compared to those of xanthan — locust bean gum blends. The extent of synergism, illustrated by the gel elastic modulus G′ and yield stress τc, is found to increase with increasing extent of enzymatic modification. At constant ionic strength, the EMG2 and locust bean blends behave similarly, with increasing extent of synergy as the temperature of mixing is increased. Additionally, at a fixed mixing temperature, the blends made in water have a higher elastic modulus than those made in salt. In contrast, the EMG1 blends are weaker and the dynamic moduli are unaffected by changes in the mixing temperature or ionic strength. These results are consistent with those of other researchers and are directly related to both the level of disorder in the xanthan molecule as well as the galactose content and fine structure of the galactomannan. DA - 2002/8// PY - 2002/8// DO - 10.1016/S0144-8617(01)00328-9 VL - 49 IS - 2 SP - 207-216 SN - 0144-8617 KW - rheology KW - modulus KW - yield stress KW - guar KW - xanthan KW - mixed polysaccharide ER - TY - JOUR TI - Formation of self-assembled monolayers of semifluorinated and hydrocarbon chlorosilane precursors on silica surfaces from liquid carbon dioxide AU - Efimenko, K AU - Novick, B AU - Carbonell, RG AU - DeSimone, JM AU - Genzer, J T2 - LANGMUIR AB - We report on the formation and properties of self-assembled monolayers (SAMs) prepared by depositing semifluorinated and hydrocarbon trichlorosilane precursors, F(CF2)8(CH2)2SiCl3 (F8H2) and H(CH2)18SiCl3 (H18), respectively, from vapor, organic solvent, and liquid CO2 (l-CO2). Contact angle measurements of the SAM deposition kinetics reveal that regardless of the molecule type, the deposition rates from l-CO2 exceed those from vapor or organic solvents by several orders of magnitude. We derive two different transport models describing the formation of SAMs. We show that while the diffusion-limited model is not capable of describing the experimental data, the adsorption-limited model captures the major features of the adsorption kinetics quite well. We apply the results of the adsorption-limited model to conclude that the observed behavior is a consequence of (i) a relatively high bulk concentration (l-CO2 vs vapor) and (ii) higher solution diffusivity (l-CO2 vs organic solvent) of the silanes in l-CO2. Near-edge X-ray absorption fine structure (NEXAFS) is used to monitor the orientation of the F8H2 and H18 molecules in their corresponding SAMs as a function of time. Our NEXAFS data show that the F8H2 molecules adsorb initially from l-CO2 without any molecular order in the monolayer. As more F8H2 molecules partition at the silicon oxide surface, they start to organize and orient. A complete monolayer order is achieved after ≈30 min exposure to F8H2/l-CO2 solutions. The deposition kinetics and molecular behavior of the H18 moieties in the SAMs are found to be different, however. After a brief exposure (<2 s) of the silica substrate to the H18/l-CO2 solution, the molecules adsorb and form an organized monolayer. Similar to the case of the semifluorinated species, the order in the H18 SAM increases with increasing time and saturates after ≈5 min exposure to H18/l-CO2 solution. We attribute the difference in the orientation kinetics to the different solubilities of F8H2 and H18 in l-CO2. DA - 2002/8/6/ PY - 2002/8/6/ DO - 10.1021/la011813j VL - 18 IS - 16 SP - 6170-6179 SN - 0743-7463 ER - TY - JOUR TI - Folding thermodynamics of model four-strand antiparallel beta-sheet proteins AU - Jang, H AU - Hall, CK AU - Zhou, YQ T2 - BIOPHYSICAL JOURNAL AB - The thermodynamic properties for three different types of off-lattice four-strand antiparallel β-strand protein models interacting via a hybrid Go-type potential have been investigated. Discontinuous molecular dynamic simulations have been performed for different sizes of the bias gap g, an artificial measure of a model protein’s preference for its native state. The thermodynamic transition temperatures are obtained by calculating the squared radius of gyration Rg2, the root-mean-squared pair separation fluctuation ΔB, the specific heat Cv, the internal energy of the system E, and the Lindemann disorder parameter ΔL. Despite these models’ simplicity, they exhibit a complex set of protein transitions, consistent with those observed in experimental studies on real proteins. Starting from high temperature, these transitions include a collapse transition, a disordered-to-ordered globule transition, a folding transition, and a liquid-to-solid transition. The high temperature transitions, i.e., the collapse transition and the disordered-to-ordered globule transition, exist for all three β-strand proteins, although the native-state geometry of the three model proteins is different. However the low temperature transitions, i.e., the folding transition and the liquid-to-solid transition, strongly depend on the native-state geometry of the model proteins and the size of the bias gap. DA - 2002/2// PY - 2002/2// DO - 10.1016/S0006-3495(02)75428-3 VL - 82 IS - 2 SP - 646-659 SN - 0006-3495 ER - TY - JOUR TI - Extraction of 4-nitrophenol from 1-octanol into aqueous solution in a hollow fiber liquid contactor AU - Peretti, SW AU - Tompkins, CJ AU - Goodall, JL AU - Michaels, AS T2 - JOURNAL OF MEMBRANE SCIENCE AB - p-Nitrophenol (PNP) was extracted from 1-octanol into an aqueous buffered solution using membrane-supported extraction in hollow fiber liquid contactors (HFLCs) containing hydrophobic, microporous polypropylene fibers. PNP is a weak acid and in aqueous solution may dissociate to form nitrophenolate ion (PNP−), that has negligible solubility in 1-octanol. The ratio of the two species in aqueous solution is governed by pH; therefore, the overall mass transfer coefficient based on solvent phase concentrations was determined as a function of pH. The extraction of PNP is a four-step process, consisting of diffusion across the solvent boundary layer, diffusion through the solvent-filled membrane, reaction (dissociation) at the solvent/aqueous interface, and diffusion across the aqueous boundary layer. The reaction step is assumed much faster than the others; a model of the mass transfer capabilities of the system is presented based on this assumption. The overall mass transfer coefficients were determined experimentally by recirculating the solvent phase through the shell space of a HFLC and the aqueous phase through the fibers. The model closely predicts the experimentally measured trends of the overall mass transfer coefficient. DA - 2002/1/31/ PY - 2002/1/31/ DO - 10.1016/S0376-7388(01)00566-X VL - 195 IS - 2 SP - 193-202 SN - 1873-3123 KW - hollow fiber KW - membrane transport KW - supported liquid membrane KW - pH-swing extraction ER - TY - JOUR TI - Evidence of lipoplex dissociation in liquid formulations AU - Lai, E AU - Zanten, JH T2 - JOURNAL OF PHARMACEUTICAL SCIENCES AB - Aggregation is typically cited as the root cause of lipoplex transfection efficacy loss in liquid formulations. Typically, this conclusion is based on observed increases in lipoplex hydrodynamic size. A more detailed physical characterization of the lipoplex transfection efficacy diminution has previously never been conducted. As a result, most research has focused on either methods of forming more stable lipoplex formulations or preservation methods such as lyophilization. These studies typically consider the use of stabilizing additives, such as polymer and sugar molecules, to enhance the efficacy of lipoplex dispersions. This report details a recent multiangle laser light scattering study of the temporal evolution of lipoplex geometric size (i.e., radius of gyration) and molar mass in liquid-based formulations over several months. The results indicate that for the lipoplex systems considered, the primary factor underlying the long-term loss of lipoplex transfection efficiency is actually lipoplex dissociation caused by a decrease in the observed molar mass of some lipoplex formulations. The increasing geometric sizes observed are actually the result of lipoplex dissociation combined with an increase in volume. That is, the lipoplexes lose mass and expand in volume, leading to a less dense lipoplex structure over time. © 2002 Wiley-Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 91: 1225–1232, 2002 DA - 2002/5// PY - 2002/5// DO - 10.1002/jps.10108 VL - 91 IS - 5 SP - 1225-1232 SN - 0022-3549 KW - gene therapy KW - light scattering KW - lipoplex KW - liposome KW - stability ER - TY - JOUR TI - Effect of polymer coatings from CO2 on water-vapor transport in porous media AU - Henon, FE AU - Carbonell, RG AU - DeSimone, JM T2 - AICHE JOURNAL AB - Abstract A variety of perfluorinated polyethers were coated onto surfaces of marble, sandstone and limestone samples from solutions in supercritical carbon dioxide. These polymers make ideal protectants for civil infrastructure by making stone surfaces hydrophobic and preventing penetration and deterioration of the stone by acid rain. The effective diffusivities of water vapor through coated and uncoated stones were measured as a function of polymer applied per unit area of sample. An analysis of the diffusive transport of water through the stones led to estimates of the penetration depths of the polymers and the percentages of blockage of the pores in the coated layers as a function of polymer surface coverage. Penetration depths were seen to strongly depend on the mean size and porosity of the stones. It is important for water‐vapor diffusion to occur through the samples to prevent water condensation inside polymer‐coated structural materials. DA - 2002/5// PY - 2002/5// DO - 10.1002/aic.690480504 VL - 48 IS - 5 SP - 941-952 SN - 1547-5905 ER - TY - JOUR TI - Cross-sectional imaging of pendeo-epitaxial GaN using continuous-wave two-photon microphotoluminescence AU - Schuck, PJ AU - Grober, RD AU - Roskowski, AM AU - Einfeldt, S AU - Davis, RF T2 - APPLIED PHYSICS LETTERS AB - A technique utilizing continuous-wave two-photon absorption has been developed for optically sectioning and imaging deep into GaN structures. Imaging at depths greater than 20 μm below the surface of a coalesced pendeo-epitaxial GaN sample is demonstrated. Free and donor-bound excitonic emission in this sample appears to originate at the surface, acceptor-bound exciton transitions are strongest in the top bulk portion of the sample, and subgap luminescence is most intense deep in the sample. The depth resolution of the imaging system is measured to be 1.75 μm near the GaN surface. DA - 2002/9/9/ PY - 2002/9/9/ DO - 10.1063/1.1506948 VL - 81 IS - 11 SP - 1984-1986 SN - 0003-6951 ER - TY - JOUR TI - Combinatorial study of the mushroom-to-brush crossover in surface anchored polyacrylamide AU - Wu, T AU - Efimenko, K AU - Genzer, J T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - We present a method for fabricating anchored polymers with a gradual variation of grafting densities on solid substrates. The technique for generating such structures comprises (i) formation of a molecular gradient of polymerization initiator on the solid substrate and (ii) polymerization from the substrate-bound initiator centers ("grafting from"). We measure the mushroom-to-brush transition in grafted polyacrylamides and show that the mushroom and brush behavior can be described using existing scaling theories. DA - 2002/8/14/ PY - 2002/8/14/ DO - 10.1021/ja027412n VL - 124 IS - 32 SP - 9394-9395 SN - 0002-7863 ER - TY - JOUR TI - Chemical, electrical, and structural properties of Ni/Au contacts on chemical vapor cleaned p-type GaN AU - Hartlieb, PJ AU - Roskowski, A AU - Davis, RF AU - Nemanich, RJ T2 - JOURNAL OF APPLIED PHYSICS AB - Chemical vapor cleaned, Mg-doped, p-type GaN(0001) surfaces and Ni/Au contacts deposited on these surfaces have been studied using several characterization techniques. Stoichiometric surfaces without detectable carbon and an 87% reduction in the surface oxygen to 2±1 at. % were achieved. The binding energies of the Ga 3d and N 1s core level photoelectron peaks were reduced by 0.5±0.1 eV following the chemical vapor clean. The band bending at the clean surface was measured to be 0.8±0.1 eV. As-deposited Ni/Au contacts on chemical vapor cleaned surfaces exhibited significantly less rectification in the low voltage region (&lt;2 V) compared to identical contact structures on conventional HCl treated surfaces. The specific contact resistance of these contacts deposited on chemical vapor cleaned surfaces and subsequently annealed at 450 °C for 30 seconds was 3±2 Ω cm2. Improved ohmic behavior and a specific contact resistance of 4±2 Ω cm2 was obtained for contacts deposited on HCl treated surfaces and annealed using the same schedule. The formation of Au:Ga and Au:Ni solid solutions was observed for contacts on HCl treated surfaces following the 450 °C anneal. There were significantly less interfacial reactions for annealed contacts on chemical vapor cleaned surfaces. The values of specific contact resistance, sheet resistance, and transfer length of the annealed contacts deposited on both chemical vapor cleaned and HCl treated surfaces and measured from room temperature to 140 °C did not change during three successive thermal cycles within this range. DA - 2002/6/1/ PY - 2002/6/1/ DO - 10.1063/1.1471578 VL - 91 IS - 11 SP - 9151-9160 SN - 1089-7550 ER - TY - JOUR TI - Affinity purification of fibrinogen using a ligand from a peptide library AU - Kaufman, DB AU - Hentsch, ME AU - Baumbach, GA AU - Buettner, JA AU - Dadd, CA AU - Huang, PY AU - Hammond, DJ AU - Carbonell, RG T2 - BIOTECHNOLOGY AND BIOENGINEERING AB - An affinity resin containing the peptide ligand Phe-Leu-Leu-Val-Pro-Leu (FLLVPL) has been developed for the purification of fibrinogen. The ligand was identified by screening a solid-phase combinatorial peptide library using an immunostaining technique. The specific binding of fibrinogen to the ligand has been characterized by isothermal calorimetry and adsorption isotherms and is dominated by both hydrophobic interactions and ionic interactions with the N-terminal free amino group. The effective association constant of fibrinogen was substantially higher when the peptide was immobilized on the resin than in solution; moreover, it increased with increasing peptide density, suggesting a cooperative binding effect. A low ionic strength buffer at pH 4 was used successfully to elute adsorbed fibrinogen from the column with high purity, retention of factor XIII crosslinking activity, and minimal, if any, loss of biological function. This general approach to ligand selection and characterization can be used to develop peptide ligands for the affinity purification of diverse proteins on a large scale. DA - 2002/2/5/ PY - 2002/2/5/ DO - 10.1002/bit.10120 VL - 77 IS - 3 SP - 278-289 SN - 0006-3592 KW - fibrinogen KW - peptide affinity chromatography KW - protein purification ER - TY - CHAP TI - The Scholarship of Teaching and Learning in Engineering AU - Wankat, P.C. AU - Felder, R. M. AU - Smith, K. A. AU - Oreovicz, F. S. T2 - Disciplinary styles in the scholarship of teaching and learning: Exploring common ground A2 - M. T. Huber, A2 - Morreale, S. PY - 2002/// PB - Washington: AAHE/Carnegie Foundation for the Advancement of Teaching ER - TY - JOUR TI - Student Use (and Non-Use) of Instructional Technology AU - Roskowski, A. M. AU - Felder, R. M. AU - Bullard, L. T2 - Journal of SMET Education: Innovations and Research DA - 2002/// PY - 2002/// VL - 2 IS - 2002 SP - 41-45 ER - TY - JOUR TI - Rheology of protein gels synthesized through a combined enzymatic and heat treatment method AU - Burke, MD AU - Ha, SY AU - Pysz, MA AU - Khan, SA T2 - INTERNATIONAL JOURNAL OF BIOLOGICAL MACROMOLECULES AB - Whey protein gels prepared under acidic conditions (pH<4.6) remain largely unutilized because of their weak and brittle nature in contrast to the favorable elastic gels produced at neutral or basic conditions. However, such usage is important, as low pH food products are desirable due to their shelf stability and less stringent sterilization processes. In this study, we use a two-step process involving enzyme followed by heat treatment to produce whey protein gels at low pH (4.0). Dynamic rheological measurements reveal that the gel elastic modulus and yield stress increase substantially when heat treatment is supplemented with enzyme treatment. Both the elastic modulus and yield stress increase with increasing enzyme concentration or treatment time. In contrast, the dynamic yield strain decreases with enzyme concentration but increases with time of enzyme treatment. These results are explained in terms of the enzyme treatment time affecting the diffusion of the enzyme within the gel. This in turn leads to two types of gel microstructure at short and long enzyme treatment times, with the extent of enzyme diffusion modulating the structure at intermediate times. DA - 2002/12/20/ PY - 2002/12/20/ DO - 10.1016/S0141-8130(02)00043-0 VL - 31 IS - 1-3 SP - 37-44 SN - 0141-8130 KW - whey protein KW - rheology KW - gels KW - enzyme KW - low pH ER - TY - JOUR TI - Predictions of the Joule-Thomson inversion curve for the n-alkane series and carbon dioxide from the Soft-SAFT equation of state AU - Colina, CM AU - Turrens, LF AU - Gubbins, KE AU - Olivera-Fuentes, C AU - Vega, LF T2 - INDUSTRIAL & ENGINEERING CHEMISTRY RESEARCH AB - In this work, we use a molecular based equation of state, the Soft-SAFT equation, to predict complete Joule−Thomson inversion curves for carbon dioxide and the n-alkane series, including heavy n-alkanes up to octatetracontane (n-C48H98). Comparisons with available experimental and correlation data, for carbon dioxide and the lighter n-alkanes, show good quantitative agreement. We observe a strong dependence of the inversion curve on the set of molecular parameters used in the calculations, especially near the inversion point and in the high-temperature region. The equation is able to predict the general trend of inversion curves even for extreme conditions, with reduced pressure, Pr = P/Pc, values up to 40, and reduced temperatures, Tr = T/Tc, of almost 5. DA - 2002/3/6/ PY - 2002/3/6/ DO - 10.1021/ie010382x VL - 41 IS - 5 SP - 1069-1075 SN - 0888-5885 ER - TY - JOUR TI - Liquid/catalyst interactions in slurry reactors: changes in tetrahydroquinoline composition during methanol synthesis over zinc chromite AU - Sun, XL AU - Jones, NW AU - Gesick, JC AU - Xu, LL AU - Roberts, GW T2 - APPLIED CATALYSIS A-GENERAL AB - The excellent thermal stability of tetrahydroquinoline (THQ) under reducing conditions [1] has led to its use as a slurry liquid for several catalytic reactions: the synthesis of methanol over “zinc chromite” catalyst [2], the synthesis of higher alcohols over promoted “zinc chromite” [3], and the dehydrogenation of methanol to formaldehyde over various copper-containing catalysts [4], [5]. However, the rate and selectivity of alcohol synthesis over zinc chromite catalyst was much different with THQ as the slurry liquid than with several similar compounds. It also was found that THQ was alkylated during both alcohol synthesis and methanol dehydrogenation. To understand the behavior of THQ-derived slurry liquids, various analyses were carried out on a sample of this liquid that was obtained after 240 h of continuous operation under methanol synthesis conditions. Silica gel liquid chromatography (LC) and high performance LC (HPLC) were used to fractionate the “spent” slurry liquid, while gas chromatography/mass spectroscopy (GC/MS), Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy were applied to identify the major compounds. Methyl-, dimethyl-, and trimethyl-THQ comprised more than 80% of the “spent” slurry liquid. The balance primarily was various methylated indoles. A methyl group always was attached to the N atom in the ring structure. There was no evidence of further alkylation of methyl groups. These results appear to eliminate the possibility that the observed differences between THQ and similar hydrocarbon slurry liquids result from the nucleophilicity of secondary amines in the liquid. They also suggest that alkylation of THQ will eventually stop as the ring positions in THQ become saturated. A mechanism for the alkylation of THQ is proposed. DA - 2002/5/10/ PY - 2002/5/10/ DO - 10.1016/S0926-860X(02)00069-8 VL - 231 IS - 1-2 SP - 269-280 SN - 1873-3875 KW - tetrahydroquinoline KW - methanol KW - slurry reactor KW - alkylation KW - zinc chromite ER - TY - JOUR TI - Factors contributing to petroleum foaming. 2. Synthetic crude oil systems AU - Zaki, NN AU - Poindexter, MK AU - Kilpatrick, PK T2 - ENERGY & FUELS AB - The influence of petroleum asphaltenes and resins on stabilizing model oil foams comprised of light mineral oil mixed with toluene (minerol) was investigated. Two factors contribute significantly to foam volume and stability: bulk viscosity and asphaltene state of aggregation. An increase in bulk viscosity was found to increase foam stability as gauged by the total time required for a foam to collapse. Asphaltene aggregation is governed primarily by the solvent aromaticity and resin/asphaltene (R/A) ratio. There is a threshold size in the state of asphaltene aggregation above which the ability of these aggregates to stabilize foams is markedly reduced. This appears to be closely related to asphaltene flocculation and precipitation at compositions beyond the solubility limit of the asphaltenes. Solvent systems generating the highest foam volume were found to reduce the air-oil surface tension to the greatest extent. Addition of an asphaltene dispersant increased the foamability of asphaltenes in minerol and seems to indicate that asphaltenes enhance foam stability when they are well dispersed or dissolved and in solvent mixtures in which they are highly surface active. By analogy to the role of asphaltenes in stabilizing emulsions, the highest foam stability was observed for asphaltenes near their solubility limit, the thermodynamic state at which asphaltenic aggregates are most surface-active. Addition of resins, similar to addition of dispersants, increased foam stability, presumably by decreasing the size of asphaltene aggregates. DA - 2002/// PY - 2002/// DO - 10.1021/ef010225a VL - 16 IS - 3 SP - 711-717 SN - 0887-0624 ER - TY - JOUR TI - Factors contributing to petroleum foaming. 1. Crude oil systems AU - Poindexter, MK AU - Zaki, NN AU - Kilpatrick, PK AU - Marsh, SC AU - Emmons, DH T2 - ENERGY & FUELS AB - Gas/oil separation can often be accompanied by unwanted foaming. To study this phenomenon, 20 crude oils were subjected to low-pressure foaming experiments. Eleven of the crudes were from offshore platforms where foaming occurs regularly. Two foaming parameters, foam volume (or foamability) and collapse slope (i.e. the rate of foam collapse in the absence of sparge gas), were compared with several crude oil properties, namely, density, bulk viscosity, surface tension, asphaltene and resin content, asphaltene and resin molecular weight, and asphaltene and resin heteroatom content. For asphaltenic crudes, collapse slope was found to correlate with asphaltene content as well as several other crude oil properties: density, viscosity, and surface tension. Foam volume did not relate to any asphaltenic crude oil property. However, for crudes having little to no asphaltenes, foam volume, not collapse slope, strongly related to crude oil surface tension. For low asphaltenic crudes, results further indicate that resin chemical composition plays a key role in determining foam volume and that larger foam volumes were associated with higher crude densities and viscosities. Finally, viscosity was found to play a major role in determining whether a crude oil will foam under the experimental conditions. DA - 2002/// PY - 2002/// DO - 10.1021/ef010224i VL - 16 IS - 3 SP - 700-710 SN - 1520-5029 ER - TY - JOUR TI - Existence of a Hexatic Phase in Confined Systems AU - Radhakrishnan, R. AU - Gubbins, K.E. AU - Śliwinska-Bartkowiak, M. T2 - Physical Review Letters AB - Molecular simulations for simple fluids in narrow slit-shaped carbon pores exhibit crystal-hexatic and hexatic-liquid transitions that are consistent with Kosterlitz-Thouless-Halperin-Nelson-Young theory. The temperature range over which the hexatic phase is stable is dramatically widened under confinement. Remarkably, the transitions, which are continuous for a single adsorbed layer, become weakly first order when the pore can accommodate two molecular layers. Nonlinear dielectric effect measurements for CCl4 and aniline in activated carbon fibers (pore width 1.4 nm) show divergence at these transitions, confirming the hexatic phase. DA - 2002/// PY - 2002/// DO - 10.1103/physrevlett.89.076101 VL - 89 IS - 7 SP - SN - 0031-9007 ER - TY - JOUR TI - Effect of chelation chemistry of sodium polyaspartate on the dissolution of calcite AU - Wu, Y. T. AU - Grant, Christine T2 - Langmuir DA - 2002/// PY - 2002/// DO - 10.1021/la0118939a VL - 18 IS - 18 SP - 6813–6820 ER - TY - JOUR TI - Bridged double percolation in conductive polymer composites: an electrical conductivity, morphology and mechanical property study AU - Thongruang, W AU - Spontak, RJ AU - Balik, CM T2 - POLYMER AB - Conductive polymer composites are ubiquitous in technological applications and constitute an ongoing topic of tremendous commercial interest. Strategies developed to improve the level of electrical conductivity achieved at a given filler concentration have relied on double-percolated networks induced by immiscible polymer blends, as well as mixtures of fillers in a single polymer matrix, to enhance interparticle connectivity. In this work, we combine these two strategies by examining quaternary composites consisting of high-density polyethylene (HDPE), ultrahigh molecular weight polyethylene (UHMWPE), graphite (G) and carbon fiber (CF). On the basis of our previous findings, we examine the electrical conductivity, morphology, thermal signature and mechanical properties of HDPE/UHMWPE/G systems that show evidence of double percolation. Upon addition of CF, tremendous increases in conductivity are realized. The mechanism by which this increase occurs is termed bridged double percolation to reflect the role of CF in spanning non-conductive regions and enhancing the continuity of conductive pathways. At CF concentrations above the percolation threshold concentration, addition of G promotes increases in conductivity and dynamic storage modulus in which the conductivity increases exponentially with increasing modulus. DA - 2002/6// PY - 2002/6// DO - 10.1016/S0032-3861(02)00180-5 VL - 43 IS - 13 SP - 3717-3725 SN - 0032-3861 KW - polyethylene KW - conductive polymer composites KW - graphite ER - TY - JOUR TI - Block copolymer/homopolymer mesoblends: Preparation and characterization AU - Roberge, RL AU - Patel, NP AU - White, SA AU - Thongruang, W AU - Smith, SD AU - Spontak, RJ T2 - MACROMOLECULES AB - Miscible block copolymer/homopolymer blends are typically prepared from homogeneous solutions in a nonselective solvent. During solvent removal and subsequent annealing, the molecular species comprising such blends organize in such fashion as to lower the system free energy and ideally attain thermodynamic equilibrium. In this work, we investigate nonequilibrium triblock copolymer/homopolymer (ABA/hB) blends generated by diffusing hB molecules from a hB-selective solvent into a lamellar ABA copolymer. Since the copolymer is already microphase-ordered during homopolymer incorporation, we refer to such blends as mesoblends. The mass uptake of hB is found to be strongly dependent on homopolymer molecular weight (MhB), with the maximum solubility scaling as MhB-1. An induction period that scales as MhB1/2 is also observed. Transmission electron microscopy reveals that the morphology of these mesoblends appears to be perforated lamellar, which, in some cases, transforms to cylindrical upon annealing. Dynamic mechanical analysis and differential scanning calorimetry confirm that the A-rich microdomains in the mesoblends are plasticized. The mechanical properties of these mesoblends can be improved upon annealing, but nonetheless differ from those of composition-matched conventional blends. DA - 2002/3/12/ PY - 2002/3/12/ DO - 10.1021/ma0115747 VL - 35 IS - 6 SP - 2268-2276 SN - 1520-5835 ER - TY - JOUR TI - Attrition resistance of spray-dried iron F-T catalysts: effect of activation conditions AU - Zhao, R AU - Sudsakorn, K AU - Goodwin, JG AU - Jothimurugesan, K AU - Gangwal, SK AU - Spivey, JJ T2 - CATALYSIS TODAY AB - The focus of the research reported herein was to investigate the effects of phase changes, as occur during Fe catalyst activation and Fischer–Tropsch synthesis, on Fe catalyst attrition resistance. Different activation conditions (CO, H2 or syngas) were applied prior to attrition testing to a selected spray-dried Fe catalyst containing 9.1 wt.% binder SiO2, which had been shown to have the highest attrition resistance in our early study of calcined catalysts. Although, XRD indicated that different Fe phase compositions resulted in the differently activated catalyst samples, chemical attrition was not observed for any of the samples. The BET surface areas of the activated samples were smaller than that of the calcined precursor but no significant changes in pore volume and particle size were found. The attrition resistances of the differently activated catalyst samples were found to be similar to that of the calcined catalyst for this spray-dried Fe catalyst. Attrition resistance was found previously to be governed by catalyst particle density, which has been shown earlier to relate to the SiO2 network in catalysts. It is therefore suggested that the type and concentration of SiO2 that is incorporated during the preparation of spray-dried Fe catalysts have a much more significant impact on catalyst attrition than Fe phase change during activation in the presence of CO, H2 or H2+CO. DA - 2002/1/15/ PY - 2002/1/15/ DO - 10.1016/S0920-5861(01)00458-8 VL - 71 IS - 3-4 SP - 319-326 SN - 0920-5861 KW - attrition resistance KW - Fischer-Tropsch synthesis KW - activation conditions KW - BET surface area KW - spray-dried Fe catalysts ER - TY - JOUR TI - Aggregation rate measurements by zero-angle time-resolved multiangle laser light scattering AU - Wang, K AU - Singh, AK AU - Zanten, JH T2 - LANGMUIR AB - A new method for determining second-order aggregation rate constants via time-resolved multiangle laser light scattering is introduced. A major advantage of this approach is that second-order aggregation rate constants are determined without any assumptions regarding the dimer intraparticle interference or form factor. The second-order aggregation rate constants are calculated from the temporal variation of the zero-angle excess Rayleigh ratio within the context of von Smoluchowski's well-established model of colloidal aggregation. The new method is illustrated with two systems: (1) GM1-bearing liposomes aggregated in the presence of the cholera toxin B subunit and (2) sulfonated polystyrene latex aggregated in the presence of CaCl2. Whereas the method is demonstrated to be particularly well-suited for investigating slow aggregation processes, rapid aggregation processes are also accessible if proper precautions are taken. DA - 2002/3/19/ PY - 2002/3/19/ DO - 10.1021/la011207o VL - 18 IS - 6 SP - 2421-2425 SN - 0743-7463 ER - TY - JOUR TI - New phosphate fluorosurfactants for carbon dioxide AU - Keiper, JS AU - Simhan, R AU - DeSimone, JM AU - Wignall, GD AU - Melnichenko, YB AU - Frielinghaus, H T2 - JOURNAL OF THE AMERICAN CHEMICAL SOCIETY AB - Anionic phosphate fluorosurfactants were shown to self-assemble into water-in-carbon dioxide microemulsions. The surfactants, having either two fluorinated chains or one fluorinated chain and one hydrocarbon chain, facilitated significant water uptake in CO2. Small angle neutron scattering (SANS) measurements of surfactant/water/CO2 solutions confirmed the presence of nanometer-scale aggregates, indicative of microemulsion formation. DA - 2002/3/6/ PY - 2002/3/6/ DO - 10.1021/ja0122142 VL - 124 IS - 9 SP - 1834-1835 SN - 1520-5126 ER - TY - JOUR TI - Determination of the equilibrium constant for the reaction between bisphenol A and diphenyl carbonate AU - Gross, SM AU - Bunyard, WC AU - Erford, K AU - Roberts, GW AU - Kiserow, DJ AU - DeSimone, JM T2 - JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY AB - Abstract Despite the industrial significance of poly(bisphenol A carbonate), there is a scarcity of open literature on the equilibrium of the melt‐phase process. In fact, the equilibrium constant ( K eq ) for this reaction has never been measured directly. This article describes a process on the basis of NMR for the measurement of K eq for the reaction between bisphenol A and diphenyl carbonate in the presence and absence of a catalyst. The apparent enthalpy and entropy were calculated using a van't Hoff plot. Decomposition of bisphenol A is a common side reaction in the melt‐phase reaction performed at high temperatures in the presence of catalyst. The effect of these side reactions on the K eq in the presence of catalyst is determined. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 171–178, 2002 DA - 2002/1/1/ PY - 2002/1/1/ DO - 10.1002/pola.10098 VL - 40 IS - 1 SP - 171-178 SN - 1099-0518 KW - bisphenol A KW - diphenyl carbonate KW - equilibrium constant KW - polycarbonates KW - thermodynamics KW - step growth polymerizations ER - TY - JOUR TI - Correlated electrical conductivity and mechanical property analysis of high-density polyethylene filled with graphite and carbon fiber AU - Thongruang, W AU - Spontak, RJ AU - Balik, CM T2 - POLYMER AB - The development of conductive polymer composites remains an important endeavor in light of growing energy concerns. In the present work, graphite (G), carbon fiber (CF) and G/CF mixtures are added to high-density polyethylene (HDPE) to discern if mixed fillers afford appreciable advantages over single fillers. The effects of filler type and composition on electrical conductivity, composite morphology and mechanical properties have been examined and correlated to establish structure–property relationships. The threshold loading levels required for G and CF to achieve measurable conductivity in HDPE have been identified. Addition of CF to HDPE/G composites is found to increase the conductivity relative to that of HDPE/G composites at the same filler concentration. This observed increase depends on CF length and becomes more pronounced at and beyond the threshold loading of the HDPE/G composite. Scanning electron microscopy is employed to elucidate the morphology of these multicomponent composites, whereas dynamic mechanical analysis reveals that filler concentration, composition and CF length impact both the magnitude and temperature dependence of the dynamic storage modulus. DA - 2002/4// PY - 2002/4// DO - 10.1016/S0032-3861(02)00043-5 VL - 43 IS - 8 SP - 2279-2286 SN - 0032-3861 KW - high-density polyethylene KW - polymer composite KW - electrical conductivity ER - TY - JOUR TI - Surface instability and associated roughness during conventional and pendeo-epitaxial growth of GaN(0001) films via MOVPE AU - Roskowski, AM AU - Miraglia, PQ AU - Preble, EA AU - Einfeldt, S AU - Davis, RF T2 - JOURNAL OF CRYSTAL GROWTH AB - Investigations of the origins of surface roughening in GaN(0 0 0 1) have resulted in the development of a growth process route having an optimum temperature of 1020°C and a film thickness beyond 2.5 μm which results in films with the smoothest surface morphology. Atomic force microscopy (AFM) revealed uncoalesced GaN islands and hillocks for non-optimum temperatures below and above 1020°C, respectively. Uncoalesced islands were a result of insufficient lateral growth. Hillocks were a result of the rotation of heterogeneous steps formed at pure screw or mixed dislocations which terminated on the (0 0 0 1) surface. Growth of the latter features was controlled kinetically by temperature through adatom diffusion. The 106 cm−2 density of hillocks was reduced through growth on thick GaN templates and regions of pendeo-epitaxy (PE) overgrowth with lower pure screw or mixed dislocations. Smooth PE surfaces were obtained at temperatures that reduced the lateral to vertical growth rate but also retarded hillock growth that originated in the stripe regions. The (112̄0) PE sidewall surface was atomically smooth, with a root mean square roughness value of 0.17 nm, which was the noise limited resolution of the AFM measurements. DA - 2002/5// PY - 2002/5// DO - 10.1016/S0022-0248(02)00943-0 VL - 241 IS - 1-2 SP - 141-150 SN - 0022-0248 KW - characterization KW - defects KW - surface structure KW - metalorganic vapor phase epitaxy KW - pendeoepitaxy KW - semiconducting gallium compounds ER - TY - JOUR TI - Catalysis and plasma technology - Preface AU - Jang, BWL AU - Reynolds, JG AU - Boutonnet, M AU - Spivey, JJ T2 - CATALYSIS TODAY DA - 2002/3/15/ PY - 2002/3/15/ DO - 10.1016/S0920-5861(01)00490-4 VL - 72 IS - 3-4 SP - 171-171 SN - 0920-5861 ER - TY - JOUR TI - Volume-exclusion effects in polyethylene blends filled with carbon black, graphite, or carbon fiber AU - Thongruang, W AU - Balik, CM AU - Spontak, RJ T2 - JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS AB - Abstract Conductive polymer composites possessing a low percolation‐threshold concentration as a result of double percolation of a conductive filler and its host phase in an immiscible polymer blend afford a desirable alternative to conventional composites. In this work, blends of high‐density polyethylene (HDPE) and ultrahigh molecular weight polyethylene (UHMWPE) were used to produce ternary composites containing either carbon black (CB), graphite (G), or carbon fiber (CF). Blend composition had a synergistic effect on electrical conductivity, with pronounced conductivity maxima observed at about 70–80 wt % UHMWPE in the CB and G composites. A much broader maximum occurred at about 25 wt % UHMWPE in composites prepared with CF. Optical and electron microscopies were used to ascertain the extent to which the polymers, and hence filler particles, are segregated. Differential scanning calorimetry of the composites confirmed that the constituent polymers are indistinguishable in terms of their thermal signatures and virtually unaffected by the presence of any of the fillers examined here. Dynamic mechanical analysis revealed that CF imparts the greatest stiffness and thermal stability to the composites. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1013–1023, 2002 DA - 2002/5/15/ PY - 2002/5/15/ DO - 10.1002/polb.10157 VL - 40 IS - 10 SP - 1013-1025 SN - 0887-6266 KW - high-density polyethylene (HDPE) KW - ultrahigh molecular weight polyethylene KW - (UHMWPE) KW - polymer composite KW - percolation threshold KW - conductivity KW - viscoelasticity KW - blends KW - composites KW - fillers KW - mechanical properties KW - polyethylene (PE) KW - thermal properties ER - TY - JOUR TI - Ultrapermeable, reverse-selective nanocomposite membranes AU - Merkel, TC AU - Freeman, BD AU - Spontak, RJ AU - He, Z AU - Pinnau, I AU - Meakin, P AU - Hill, AJ T2 - SCIENCE AB - Polymer nanocomposites continue to receive tremendous attention for application in areas such as microelectronics, organic batteries, optics, and catalysis. We have discovered that physical dispersion of nonporous, nanoscale, fumed silica particles in glassy amorphous poly(4-methyl-2-pentyne) simultaneously and surprisingly enhances both membrane permeability and selectivity for large organic molecules over small permanent gases. These highly unusual property enhancements, in contrast to results obtained in conventional filled polymer systems, reflect fumed silica-induced disruption of polymer chain packing and an accompanying subtle increase in the size of free volume elements through which molecular transport occurs, as discerned by positron annihilation lifetime spectroscopy. Such nanoscale hybridization represents an innovative means to tune the separation properties of glassy polymeric media through systematic manipulation of molecular packing. DA - 2002/4/19/ PY - 2002/4/19/ DO - 10.1126/science.1069580 VL - 296 IS - 5567 SP - 519-522 SN - 0036-8075 ER - TY - JOUR TI - Surface transport kinetics in low-temperature silicon deposition determined from topography evolution AU - Bray, KR AU - Parsons, GN T2 - PHYSICAL REVIEW B AB - In this article, surface transport kinetics during low-temperature silicon thin film deposition are characterized using time dependent surface topography and dynamic scaling models. Analysis of surface morphology indicates that diffusion of adsorbed species dominates surface transport, with a characteristic diffusion length that increases with surface temperature. A diffusion activation barrier of $\ensuremath{\sim}0.2 \mathrm{eV}$ is obtained, consistent with hydrogen-mediated adspecies diffusion on the growth silicon surface. Samples are compared over a range of deposition temperatures (25 to $350\ifmmode^\circ\else\textdegree\fi{}\mathrm{C})$ and film thickness (20 to $5000 \AA{})$ deposited using silane with helium or argon dilution, on glass and silicon substrates. Self-similar surface structure is found to depend on detailed film growth conditions, but is independent of film thickness after nuclei coalescence. For films deposited using helium dilution, static and dynamic scaling parameters are consistent with self-similar fractal geometry scaling, and the lateral correlation length increases from 45 to 150 nm as temperature increases from 25 to $150\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ These results are discussed in relation to current silicon deposition models and with topography evolution observed during low temperature growth of other amorphous material systems. DA - 2002/1/15/ PY - 2002/1/15/ DO - 10.1103/physrevb.65.035311 VL - 65 IS - 3 SP - SN - 2469-9969 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000173448900070&KeyUID=WOS:000173448900070 ER - TY - JOUR TI - Phase behavior of PVAC-PTAN block copolymer in supercritical carbon dioxide using SAFT AU - Colina, CM AU - Hall, CK AU - Gubbins, KE T2 - FLUID PHASE EQUILIBRIA AB - Statistical associating fluid theory (SAFT) is an equation of state that can be used to calculate the phase behavior of mixtures comprised of components that exhibit wide disparities in molecular size, such as solvent–polymer mixtures. In this paper, we model the phase behavior of a PVAC-PTAN block copolymer composed of a CO2–phobic polyvinyl acetate (PVAC) and a CO2–philic poly(1,1,2,2-tetrahydroperfluorooctyl acrylate) (PTAN) in supercritical carbon dioxide (scCO2) using SAFT. SAFT is a molecular-based equation that is designed to account for effects of molecular association, chain flexibility, repulsive and dispersion interactions. The group contribution approach of Lora et al. was used to obtain the physical SAFT parameters for PVAC and PTAN polymers. PTAN was modeled as a non-associating polymer while PVAC was modeled with two association sites per molecule. Cloud curves of CO2–PVAC, CO2–PTAN and of the PVAC-b-PTAN–CO2 system were predicted, and good agreement was obtained with the experimental data available. Additionally, critical micellar densities (CMD) appear to be successfully predicted for the PVAC-b-PTAN–CO2 system using a criteria based in the variation of osmotic pressure with surfactant concentration. This was made possible by the ability of SAFT to handle long chain and association interactions. DA - 2002/3/30/ PY - 2002/3/30/ DO - 10.1016/S0378-3812(01)00789-0 VL - 194 IS - 2002 Mar 30 SP - 553-565 SN - 1879-0224 KW - copolymer KW - cloud curves KW - critical micellar concentration KW - model KW - equation of state KW - SAFT ER - TY - JOUR TI - Microphase-Separated Block Copolymers Comprising Low Surface Energy Fluorinated Blocks and Hydrophilic Blocks:  Synthesis and Characterization AU - Arnold, M. E. AU - Nagai, K. AU - Spontak, Richard AU - Freeman, B. D. AU - Leroux, D. AU - Betts, D. E. AU - Desimone, J. M. AU - Digiano, F. A. AU - Stebbins, C. K. AU - Linton, R. W. AU - al. T2 - Macromolecules AB - The synthesis and characterization of diblock and triblock copolymers produced by a two-component iniferter system is reported. These materials, designed for possible water treatment applications, consist of a hydrophilic poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) block and a very low surface energy poly(1,1‘-dihydroperfluorooctyl methacrylate) (PFOMA) or poly(1,1,2,2-tetrahydroperfluorooctyl acrylate) (PTAN) block. Angle-dependent X-ray spectroscopy results and water contact angle measurements indicate that the surfaces of PDMAEMA-b-PFOMA diblock copolymers consist primarily of PFOMA. Transmission electron microscopy reveals that the block copolymers are microphase-separated, exhibiting either cylindrical or layered morphologies that do not change appreciably upon exposure to water. Both water uptake and water flux increase with increasing PDMAEMA content. DA - 2002/4// PY - 2002/4// DO - 10.1021/ma0119631 VL - 35 IS - 9 SP - 3697-3707 J2 - Macromolecules LA - en OP - SN - 0024-9297 1520-5835 UR - http://dx.doi.org/10.1021/ma0119631 DB - Crossref ER - TY - JOUR TI - Micellar behavior in supercritical solvent-surfactant systems from lattice Monte Carlo simulations AU - Lisal, M. AU - Hall, Carol AU - Gubbins, Keith AU - Panagiotopoulos, A. Z. T2 - Fluid Phase Equilibria AB - We modify Larson’s lattice model [J. Chem. Phys. 83 (1985) 2411] and use it to study micellar behavior in supercritical solvent–surfactant systems by large-scale Monte Carlo (MC) simulations. Carbon dioxide and perfluoroalkylpoly(ethylene oxide) serve as prototypes for the solvent and surfactant, respectively. Larson-model type parameters for carbon dioxide and perfluoroalkylpoly(ethylene oxide) are obtained using experimental values for critical parameters and solubility along with a modified Berthelot mixing rule. We perform canonical MC simulations at a supercritical temperature varying the structure of the surfactant, the solvent density and the surfactant concentration. Various properties such as the critical micelle concentration, the overlap concentration, the aggregate size distribution, and the size and shape of the micelles are calculated. The implications of these results for the thermodynamics of micellar formation in supercritical solvents are examined. DA - 2002/// PY - 2002/// DO - 10.1016/S0378-3812(01)00721-X VL - 194 IS - 2002 Mar 30 SP - 233–247 ER - TY - JOUR TI - Gas sorption and dilation in poly(2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole-co-tetrafluoroethylene): Comparison of experimental data with predictions of the nonequilibrium lattice fluid model AU - De Angelis, MG AU - Merkel, TC AU - Bondar, , VI AU - Freeman, BD AU - Doghieri, F AU - Sarti, GC T2 - MACROMOLECULES AB - The sorption and dilation properties of a series of n-alkanes and the corresponding perfluorinated compounds have been examined in two amorphous copolymers of tetrafluoroethylene (TFE) and 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole (BDD), commercially available under the names Teflon AF1600 and AF2400. The analysis was made at three different temperatures: 25, 35, and 45 °C, to test the effect of temperature on solubility and to evaluate the sorption enthalpies. The partial molar volumes of most penetrants have also been determined in both copolymers. The experimental data have been satisfactorily compared with the sorption isotherms predicted or correlated using the nonequilibrium lattice fluid model. DA - 2002/2/12/ PY - 2002/2/12/ DO - 10.1021/ma0106090 VL - 35 IS - 4 SP - 1276-1288 SN - 0024-9297 ER - TY - JOUR TI - Evolution of microstructure and rheology in mixed polysaccharide systems AU - Pai, V AU - Srinivasarao, M AU - Khan, SA T2 - MACROMOLECULES AB - Synergistic biopolymer blends composed of xanthan and enzymatically modified guar galactomannan are investigated in terms of their time-dependent properties. In particular, a side-chain cleaving enzyme, α-galactosidase, is used to cleave off galactose sugar units from guar to produce modified galactomannans with varying galactose contents of 25.2 and 16.2%. Laser scanning confocal microscopy and dynamic rheology are used to monitor the properties of each of these two modified guar gum in solution as well as in blends with xanthan as they are allowed to age over a period of 3 weeks. Our results indicate that solutions of guar with a higher galactose (25.2%) content undergo no rheological change over the period of observation and show a constant gel elastic modulus (G‘) in blends with xanthan. Confocal images of the solutions and the blends also indicate that the systems are stable over a period of 3 weeks. In contrast, guar gum with a lower galactose content (16.2%) forms interchain associations in solution, developing aggregates that convert it from a macromolecular solution to a gel. This is reflected in its dynamic moduli which increase significantly with time and show a transition from frequency-dependent behavior with G‘ ‘ (viscous modulus) > G‘ (elastic modulus) to a frequency-independent character with G‘ > G‘ ‘. This process of association and phase separation is directly observed in confocal images of the modified guar as well as in its blend, though not to the same extent in the latter. The presence of a second component thus seems to retard the association process. Interestingly, the blend moduli remain unchanged in magnitude and show gellike features even though the mode of association and concomitant microstructure changes. DA - 2002/2/26/ PY - 2002/2/26/ DO - 10.1021/ma0115545 VL - 35 IS - 5 SP - 1699-1707 SN - 1520-5835 ER - TY - JOUR TI - Elementary reaction schemes for physical and chemical vapor deposition of transition metal oxides on silicon for high-k gate dielectric applications AU - Niu, D AU - Ashcraft, RW AU - Kelly, MJ AU - Chambers, JJ AU - Klein, TM AU - Parsons, GN T2 - JOURNAL OF APPLIED PHYSICS AB - This article describes the kinetics of reactions that result in substrate consumption during formation of ultrathin transition metal oxides on silicon. Yttrium silicate films (∼40 Å) with an equivalent silicon dioxide thickness of ∼11 Å are demonstrated by physical vapor deposition (PVD) routes. Interface reactions that occur during deposition and during postdeposition treatment are observed and compared for PVD and chemical vapor deposition (CVD) yttrium oxides and CVD aluminum-oxide systems. Silicon diffusion, metal-silicon bond formation, and reactions involving hydroxides are proposed as critical processes in interface layer formation. For PVD of yttrium silicate, oxidation is thermally activated with an effective barrier of 0.3 eV, consistent with the oxidation of silicide being the rate-limited step. For CVD aluminum oxide, interface oxidation is consistent with a process limited by silicon diffusion into the deposited oxide layer. DA - 2002/5/1/ PY - 2002/5/1/ DO - 10.1063/1.1468253 VL - 91 IS - 9 SP - 6173-6180 SN - 0021-8979 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000175069000098&KeyUID=WOS:000175069000098 ER - TY - JOUR TI - Application of ion scattering techniques to characterize polymer surfaces and interfaces AU - Composto, RJ AU - Walters, RM AU - Genzer, J T2 - MATERIALS SCIENCE & ENGINEERING R-REPORTS AB - Ion beam analysis techniques, particularly elastic recoil detection (ERD) also known as forward recoil spectrometry (Frcs) has proven to be a value tool to investigate polymer surfaces and interfaces. A review of ERD, related techniques and their impact on the field of polymer science is presented. The physics of the technique is described as well as the underlying principles of the interaction of ions with matter. Methods for optimization of ERD for polymer systems are also introduced, specifically techniques to improve the depth resolution and sensitivity. Details of the experimental setup and requirements are also laid out. After a discussion of ERD, strategies for the subsequent data analysis are described. The review ends with the breakthroughs in polymer science that ERD enabled in polymer diffusion, surfaces, interfaces, critical phenomena, and polymer modification. DA - 2002/7/1/ PY - 2002/7/1/ DO - 10.1016/S0927-796X(02)00009-8 VL - 38 IS - 3-4 SP - 107-180 SN - 1879-212X KW - ion scattering KW - polymer surface KW - polymer interface KW - elastic recoil detection KW - forward recoil spectrometry KW - depth profiling ER - TY - JOUR TI - Adsorption of water in activated carbons: Effects of pore blocking and connectivity AU - Brennan, JK AU - Thomson, KT AU - Gubbins, KE T2 - LANGMUIR AB - We present a simulation study of the adsorption mechanism of water in a realistic carbon structure. Water molecules are modeled using a recently developed fixed-point charge water model optimized to the vapor−liquid coexistence properties.1 Reverse Monte Carlo techniques2 are used to generate a realistic porous carbon model composed of graphitic microcrystals consisting of rigid basal plates. Arrangements of the carbon plates are driven by a systematic refinement of simulated carbon−carbon radial distribution functions to match experimentally measured radial distribution functions. The adsorption of water in activated (having oxygenated surface groups) and nonactivated (graphitic) carbon is investigated using the grand canonical Monte Carlo simulation method. The adsorption behavior is found to be strongly dependent on the presence of activated sites. No appreciable adsorption occurs in the graphitic carbon until the pressure approaches the bulk gas saturation pressure. Effects of the surface site density, surface site position, and the magnitude of the surface site electrostatic charge on the adsorption behavior are investigated. Water adsorption is found to increase as the activated site density increases. The presence of water vapor in porous carbons is shown to dramatically affect the connectivity of the available pore space. Finally, cluster calculations are performed to investigate the growth mechanism of water clusters in activated carbons. DA - 2002/7/9/ PY - 2002/7/9/ DO - 10.1021/la0118560 VL - 18 IS - 14 SP - 5438-5447 SN - 0743-7463 ER - TY - JOUR TI - Active EGF receptors have limited access to Ptdlns(4,5)P-2 in endosomes: implications for phospholipase C and PI 3-kinase signaling AU - Haugh, J. M. AU - Meyer, T. T2 - Journal of Cell Science DA - 2002/// PY - 2002/// VL - 115 IS - 2 SP - 303-310 ER - TY - JOUR TI - Regulation of endo-acting glycosyl hydrolases in the hyperthermophilic bacterium Thermotoga maritima grown on glucan- and mannan-based polysaccharides AU - Chhabra, , SR AU - Shockley, KR AU - Ward, DE AU - Kelly, RM T2 - APPLIED AND ENVIRONMENTAL MICROBIOLOGY AB - ABSTRACT The genome sequence of the hyperthermophilic bacterium Thermotoga maritima encodes a number of glycosyl hydrolases. Many of these enzymes have been shown in vitro to degrade specific glycosides that presumably serve as carbon and energy sources for the organism. However, because of the broad substrate specificity of many glycosyl hydrolases, it is difficult to determine the physiological substrate preferences for specific enzymes from biochemical information. In this study, T. maritima was grown on a range of polysaccharides, including barley β-glucan, carboxymethyl cellulose, carob galactomannan, konjac glucomannan, and potato starch. In all cases, significant growth was observed, and cell densities reached 10 9 cells/ml. Northern blot analyses revealed different substrate-dependent expression patterns for genes encoding the various endo-acting β-glycosidases; these patterns ranged from strong expression to no expression under the conditions tested. For example, cel74 (TM0305), a gene encoding a putative β-specific endoglucananse, was strongly expressed on all substrates tested, including starch, while no evidence of expression was observed on any substrate for lam16 (TM0024), xyl10A (TM0061), xyl10B (TM0070), and cel12A (TM1524), which are genes that encode a laminarinase, two xylanases, and an endoglucanase, respectively. The cel12B (TM1525) gene, which encodes an endoglucanase, was expressed only on carboxymethyl cellulose. An extracellular mannanase encoded by man5 (TM1227) was expressed on carob galactomannan and konjac glucomannan and to a lesser extent on carboxymethyl cellulose. An unexpected result was the finding that the cel5A (TM1751) and cel5B (TM1752) genes, which encode putative intracellular, β-specific endoglucanases, were induced only when T. maritima was grown on konjac glucomannan. To investigate the biochemical basis of this finding, the recombinant forms of Man5 ( M r , 76,900) and Cel5A ( M r , 37,400) were expressed in Escherichia coli and characterized. Man5, a T. maritima extracellular enzyme, had a melting temperature of 99°C and an optimun temperature of 90°C, compared to 90 and 80°C, respectively, for the intracellular enzyme Cel5A. While Man5 hydrolyzed both galactomannan and glucomannan, no activity was detected on glucans or xylans. Cel5A, however, not only hydrolyzed barley β-glucan, carboxymethyl cellulose, xyloglucan, and lichenin but also had activity comparable to that of Man5 on galactomannan and higher activity than Man5 on glucomannan. The biochemical characteristics of Cel5A, the fact that Cel5A was induced only when T. maritima was grown on glucomannan, and the intracellular localization of Cel5A suggest that the physiological role of this enzyme includes hydrolysis of glucomannan oligosaccharides that are transported following initial hydrolysis by extracellular glycosidases, such as Man5. DA - 2002/2// PY - 2002/2// DO - 10.1128/AEM.68.2.545-554.2002 VL - 68 IS - 2 SP - 545-554 SN - 0099-2240 ER - TY - JOUR TI - A commentary on "Carbon dioxide-poly(vinylidene fluoride) interactions at high pressure" AU - Kennedy, KA AU - Desimone, JM AU - Roberts, GW T2 - JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS AB - Journal of Polymer Science Part B: Polymer PhysicsVolume 40, Issue 6 p. 602-604 Rapid Communication A commentary on “Carbon Dioxide–Poly(vinylidene Fluoride) Interactions at High Pressure” Karen A. Kennedy, Karen A. Kennedy Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Search for more papers by this authorJoseph M. Desimone, Joseph M. Desimone Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905 Department of Chemistry, CB 3290, Venable and Kenan Laboratories, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290Search for more papers by this authorGeorge W. Roberts, Corresponding Author George W. Roberts groberts@eos.ncsu.edu Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Search for more papers by this author Karen A. Kennedy, Karen A. Kennedy Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Search for more papers by this authorJoseph M. Desimone, Joseph M. Desimone Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905 Department of Chemistry, CB 3290, Venable and Kenan Laboratories, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-3290Search for more papers by this authorGeorge W. Roberts, Corresponding Author George W. Roberts groberts@eos.ncsu.edu Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Department of Chemical Engineering, North Carolina State University, Raleigh, North Carolina 27695-7905Search for more papers by this author First published: 01 February 2002 https://doi.org/10.1002/polb.10103Citations: 1Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume40, Issue615 March 2002Pages 602-604 RelatedInformation DA - 2002/3/15/ PY - 2002/3/15/ DO - 10.1002/polb.10103 VL - 40 IS - 6 SP - 602-604 SN - 0887-6266 KW - poly(vinylidene fluoride) KW - carbon dioxide KW - sorption KW - phase equilibrium KW - Sanchez-Lacombe model ER - TY - JOUR TI - Temperature-dependent property development in hydrogels derived from hydroxypropylcellulose AU - Hirsch, SG AU - Spontak, RJ T2 - POLYMER AB - Hydrogels constitute an important class of responsive materials that are employed in numerous biomedical and personal-care applications, most notably of which are controlled drug delivery, separations and superabsorbency. Since aqueous hydroxypropylcellulose (HPC) solutions exhibit lower critical solution behavior, hydrogels produced from this cellulose ether are temperature-responsive, swelling at low temperatures and contracting at high temperatures. If HPC hydrogels are synthesized at temperatures in the single-phase regime, they remain nonporous, whereas those crosslinked in the biphasic regime become microporous. In this work, we employ the modified temperature-induced phase separation (TIPS) protocol to generate nonporous and microporous HPC hydrogels crosslinked at different temperatures. The dynamic mechanical properties and swelling capacities of these hydrogels are reported as functions of crosslinking temperature. DA - 2002/1// PY - 2002/1// DO - 10.1016/S0032-3861(01)00608-5 VL - 43 IS - 1 SP - 123-129 SN - 1873-2291 KW - hydrogels KW - hydroxypropylcellulose KW - temperature-induced phase separation ER - TY - JOUR TI - The effect of position along the chain on the dynamic properties of hard chain segments AU - McCormick, JA AU - Hall, CK AU - Khan, SA T2 - JOURNAL OF CHEMICAL PHYSICS AB - Discontinuous molecular dynamics simulations are performed on systems containing 32 hard chains of length 192 at three volume fractions, φ=0.40, 0.45, and 0.50, to investigate the effect of position on the segmental mean squared displacement. The mean squared displacements of various sized blocks of segments at different positions along the chain are calculated. First, the effect of block size on the dynamics of end and middle blocks is considered. It is found that small blocks provide a greater difference between the mean squared displacements of middle blocks, end blocks, and the whole chain than larger equal-sized blocks. Next, the portions of the chain exhibiting end and middle behavior are determined. It is found that a large portion of the chain displays middle behavior, while a small portion displays end behavior. Finally, the dynamics of segment relaxation along the chain are studied. The relaxation of small blocks of segments at different positions along the chain starts at the chain ends and progresses toward the chain middle with time, as the tube model predicts. The minor chain length, the portion of the chain that has relaxed, follows a power law with time, but the power is somewhat less than predicted. DA - 2002/7/8/ PY - 2002/7/8/ DO - 10.1063/1.1483295 VL - 117 IS - 2 SP - 944-957 SN - 1089-7690 ER - TY - JOUR TI - Low-temperature Ar/N-2 remote plasma nitridation of SiO2 thin films AU - Khandelwal, A AU - Niimi, H AU - Lucovsky, G AU - Lamb, HH T2 - JOURNAL OF VACUUM SCIENCE & TECHNOLOGY A-VACUUM SURFACES AND FILMS AB - Low-temperature nitridation of SiO2 thin films by Ar/N2 remote plasma processing was investigated using on-line Auger electron spectroscopy, angle-resolved x-ray photoelectron spectroscopy (ARXPS), and optical emission spectroscopy (OES). Nitridation experiments were performed at 300 °C using 30 W Ar/N2 remote plasmas at 0.1 and 0.3 Torr. Ar/N2 remote plasma exposure of 5 nm SiO2 films for 30 min results in nitrogen incorporation throughout the films, independent of process pressure and plasma reactor configuration (i.e., upstream versus downstream N2 injection). ARXPS indicates a N–Si3 local bonding configuration with second nearest neighbor oxygen atoms. Ar/N2 remote plasma exposure at 0.1 Torr results in higher nitrogen concentrations (8–10 at. %). Reactor configuration has a negligible effect at 0.1 Torr; conversely, downstream N2 injection results in higher nitrogen concentrations (5–6 at. %) than upstream injection (3–4 at. %) at 0.3 Torr. OES indicates that the Ar/N2 remote plasmas contain N2 triplet excited states and ground-state N atoms. The Ar emission intensities and the saturation N concentrations in the resultant films follow similar trends with processing pressure and reactor configuration; the N2 first positive emission intensities run counter to these trends. We infer that low-temperature SiO2 nitridation by Ar/N2 remote plasmas is a two-step process: O removal by Ar+ ion bombardment and N insertion by plasma-generated active N species. Moreover, the first step appears to be rate limiting under the conditions employed in this study. Annealing the oxynitride films in N2 at 900 °C decreases the N concentration and results in a more uniform nitrogen distribution. DA - 2002/// PY - 2002/// DO - 10.1116/1.1513635 VL - 20 IS - 6 SP - 1989-1996 SN - 0734-2101 ER - TY - JOUR TI - Interactions between dendrimer biocides and bacterial membranes AU - Chen, CZS AU - Cooper, SL T2 - BIOMATERIALS AB - Dendrimer biocides have been shown to be more potent than their small molecule counterparts. In this study, several techniques were utilized to investigate the interactions between quaternary ammonium functionalized poly(propylene imine) dendrimers and bacterial membranes. Both Gram-positive and Gram-negative bacteria were tested. The techniques employed include UV-Vis spectroscopy, differential scanning calorimetry, and bioluminescence. When treated with dendrimer biocides, release of 260nm adsorbing materials from Escherichia coli strains quickly increased and reached a plateau afterwards, while release of 260 nm absorbing materials from Staphylococcus aureus increased monotonically with the concentration due to the difference in cell structures. The different release behavior also correlates with the antimicrobial properties against these two types of bacteria. Bioluminescence experiments using bacteria containing stress-responsive bioluminescent reporter gene fusions provided information suggesting that damage to the cell membranes is the primary mechanism of the antimicrobial action for dendrimer biocides. High concentrations of calcium ions can limit the efficacy of the dendrimer biocides, although the tested concentration range is much higher than most practical applications. Differential scanning calorimetry studies showed at high concentrations that dendrimer biocides formed precipitates with phospholipid vesicles, suggesting a strong interaction with this model of bacterial membrane. These results provide insight about the antibacterial action of dendrimer biocides and establish the basis for their mode of action. DA - 2002/8// PY - 2002/8// DO - 10.1016/S0142-9612(02)00036-4 VL - 23 IS - 16 SP - 3359-3368 SN - 1878-5905 KW - dendrimer KW - biocide KW - bacterial membrane KW - phospholipid KW - antimicrobial KW - mechanism KW - interaction ER - TY - JOUR TI - Computer simulation of copolymer phase behavior AU - Schultz, AJ AU - Hall, CK AU - Genzer, J T2 - JOURNAL OF CHEMICAL PHYSICS AB - Discontinuous molecular dynamics simulation is used to study the phase behavior of diblock copolymers modeled as chains of tangent hard spheres with square shoulder repulsions between unlike species as a function of chain length, volume fraction and interaction strength (χ). The location of the order–disorder transition for a symmetric copolymer is close to the predictions of Fredrickson and Helfand. Our simulation results for packing fractions of 0.35, 0.40, and 0.45 and chain lengths 10 and 20 are summarized in phase diagrams which display disordered, lamellae, perforated lamellae (PL), cylindrical, and BCC spherical (S) phases in the χN versus f plane. These phase diagrams are consistent with phase diagrams from other simulation studies. Contrary to theoretical predictions we observe the PL phase near regions of predicted gyroid stability, and the S phase only in the systems with high packing fraction and long chain length. These discrepancies may be due to the short chain lengths considered, as they are less evident in the 20-bead chains than the 10-bead chains. We examine the structural spacing of the microphases and the variation of that spacing with χN. We also examine the internal energy and entropy and their variation with χN. Our results are consistent with self-consistent field theory results for the strong segregation limit. DA - 2002/12/8/ PY - 2002/12/8/ DO - 10.1063/1.1519839 VL - 117 IS - 22 SP - 10329-10338 SN - 1089-7690 ER - TY - JOUR TI - Water absorption and interface reactivity of yttrium oxide gate dielectrics on silicon AU - Niu, D AU - Ashcraft, RW AU - Parsons, GN T2 - APPLIED PHYSICS LETTERS AB - High dielectric constant insulators deposited at low temperatures rapidly absorb water during exposure to the atmosphere, and the resulting OH leads to detrimental interface reactions. We report the effect of atmospheric exposure on ultrathin yttrium oxide, and details of silicon substrate reactions during postdeposition anneals. Infrared absorption analysis indicates significant absorption of water vapor during atmospheric exposure, even for very short times (&lt;15 min). X-ray photoelectron spectroscopy demonstrates that after OH absorption, a thermally activated interface reaction proceeds with an activation energy of 0.33 eV, consistent with substrate reaction with OH present in the film. The OH absorption rate is reduced for annealed films or when capping layers are deposited in situ. Similar oxidation processes are expected to occur in other high-k materials of interest, where the rate of OH absorption will depend on the deposition process and material thermal history. DA - 2002/5/13/ PY - 2002/5/13/ DO - 10.1063/1.1477268 VL - 80 IS - 19 SP - 3575-3577 SN - 0003-6951 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000175464100037&KeyUID=WOS:000175464100037 ER - TY - JOUR TI - Using a localized fluorescent dye to probe the glass/resin interphase AU - Lenhart, JL AU - Zanten, JH AU - Dunkers, JP AU - Parnas, RS T2 - POLYMER COMPOSITES AB - Abstract A novel technique has been developed to study the buried polymer/substrate interfacial regions by localizing a fluorescent probe on the substrate surface. Epoxy functional multi‐layers of silane coupling agents were deposited on glass and doped with small amounts of a fluorescently labeled silane‐coupling agent (FLSCA). When the dye‐doped silane layers were immersed in an epoxy/amine cured resin, a blue shift in the emission maximum was measured after resin cure. Silane layers of varying thickness were tested. Thicker layers showed smaller fluorescence shifts during cure, suggesting incomplete resin penetration into these layers. The fluorescence sensitivity to the interfacial reaction was verified with external reflection Fourier Transform Infrared Spectroscopy (FTIR) of the silane layers immersed only in the amine hardener. DA - 2002/8// PY - 2002/8// DO - 10.1002/pc.10456 VL - 23 IS - 4 SP - 555-563 SN - 0272-8397 ER - TY - PCOMM TI - Thermodynamics of light alkane carboxylation AU - Wilcox, E. M. AU - Roberts, G. W. AU - Spivey, J. J. DA - 2002/// PY - 2002/// SP - 317-318 ER - TY - JOUR TI - Real time monitoring of lipoplex molar mass, size and density AU - Lai, E AU - Zanten, JH T2 - JOURNAL OF CONTROLLED RELEASE AB - Time-resolved multiangle laser light scattering (TR-MALLS) is used to monitor the temporal variation of DNA/cationic liposome lipoplex molar masses and geometric sizes throughout the complexation process. The measured molar masses and geometric sizes are in turn used to estimate lipoplex density. The DNA/cationic lipid charge ratio is found to be the primary factor governing lipoplex formation kinetics and the final lipoplex molar mass, geometric size and density. Charge ratios near unity lead to a growing kinetic regime in which initially formed primary lipoplexes undergo further aggregation eventually forming large molar mass lipoplexes of high density, while charge ratios very far from unity yield low molar mass lipoplexes of lower density. It is also noted that solvent composition can play a significant role in the lipoplex formation process with lipoplexes formed in ion-containing media being larger and denser than those formed in dextrose solution. DA - 2002/7/18/ PY - 2002/7/18/ DO - 10.1016/S0168-3659(02)00104-9 VL - 82 IS - 1 SP - 149-158 SN - 0168-3659 KW - cationic liposome KW - lipoplex KW - molar mass KW - nonviral gene delivery vector KW - light scattering ER - TY - JOUR TI - Reaction pathways in remote plasma nitridation of ultrathin SiO2 films AU - Niimi, H AU - Khandelwal, A AU - Lamb, HH AU - Lucovsky, G T2 - JOURNAL OF APPLIED PHYSICS AB - Low-temperature nitridation of 3 nm SiO2 films using He/N2 and N2 remote radio frequency (rf) plasmas was investigated. On-line Auger electron spectroscopy and angle-resolved x-ray photoelectron spectroscopy (ARXPS) were employed to determine the concentration, spatial distribution, and local chemical bonding of nitrogen in the resultant films. Experiments were performed using a substrate temperature of 300 °C and 30 W rf power. Nitridation using an upstream He/N2 remote plasma at 0.1 Torr incorporates nitrogen at the top surface of the SiO2 film. In contrast, a lower concentration of nitrogen distributed throughout the film is obtained when the process pressure is increased to 0.3 Torr. ARXPS indicates a N–Si3 local bonding configuration, irrespective of the spatial distribution of N atoms. Slightly more nitrogen is incorporated using a downstream He/N2 plasma at each process pressure. By comparison, nitridation of SiO2 films using a N2 remote plasma at 0.1 Torr is very slow. Optical emission spectroscopy indicates that He dilution enhances the generation of N2+(B 2Σu+) species by altering the plasma electron energy distribution and by providing an additional kinetic pathway (Penning ionization). Changing the He/N2 remote plasma configuration from upstream to downstream (at 0.1 and 0.3 Torr) also enhances N2+(B 2Σu+) generation. For upstream He/N2 remote plasmas, the intensity of N2 first positive emission from N2(B 3Πg) states increases with pressure, whereas the N2+ first negative emission from N2+(B 2Σu+) states decreases. We infer from these observations that N2+ species are primarily responsible for top surface nitridation at 0.1 Torr, and that neutral species [N2(A 3Σu+) metastables and N atoms] are associated with sub-surface nitrogen incorporation. DA - 2002/1/1/ PY - 2002/1/1/ DO - 10.1063/1.1419208 VL - 91 IS - 1 SP - 48-55 SN - 1089-7550 ER - TY - JOUR TI - Practical approaches to green solvents AU - DeSimone, JM T2 - SCIENCE AB - Solvents are widely used in commercial manufacturing and service industries. Despite abundant precaution, they inevitably contaminate our air, land, and water because they are difficult to contain and recycle. Researchers have therefore focused on reducing solvent use through the development of solvent-free processes and more efficient recycling protocols. However, these approaches have their limitations, necessitating a pollution prevention approach and the search for environmentally benign solvent alternatives. This report highlights opportunities for the practical implementation of such green solvents. DA - 2002/8/2/ PY - 2002/8/2/ DO - 10.1126/science.1069622 VL - 297 IS - 5582 SP - 799-803 SN - 0036-8075 ER - TY - JOUR TI - Polymer melt rheology with high-pressure CO2 using a novel magnetically levitated sphere rheometer AU - Royer, , JR AU - Gay, YJ AU - Adam, M AU - DeSimone, JM AU - Khan, SA T2 - POLYMER AB - A magnetically levitated sphere rheometer (MLSR) designed to measure viscosity of fluids exposed to high-pressure carbon dioxide has been developed. This device consists of a magnetic sphere submerged inside a test fluid within a high-pressure housing and levitated at a fixed point. The housing is constructed from an optically transparent sapphire tube. The cylindrical tube can be moved vertically to generate a shear flow around the levitated sphere. The difference in magnetic force required to levitate the sphere at rest and under fluid motion can be directly related to fluid viscosity. Rheological properties, specifically zero shear viscosities, of transparent high-pressure materials can be measured to a precision of about 5% and over a wide range of viscosities. In addition, operation at constant pressure, in concentration regimes from a pure polymer to an equilibrated polymer/supercritical fluid solution, and at shear rates over several orders of magnitude is possible, eliminating many of the disadvantages associated with other high-pressure rheometers. Experiments performed at different temperatures with a poly(dimethylsiloxane) melt at atmospheric pressure are compared with data from a commercial Couette rheometer to demonstrate device sensitivity and viability. Measurements of a PDMS melt plasticized by high-pressure CO2 are performed to illustrate the utility of the new rheometer under high-pressure conditions. Experimental data are obtained at 30 °C, for pressures up to 20.7 MPa and CO2 concentrations reaching 30 wt%. Viscosity reductions of nearly two orders of magnitude compared with the pure polymer viscosity at atmospheric pressure are observed. Additionally, the effects of pressure on a polymer/CO2 system are directly investigated taking advantage of the constant pressure operation mode of the MLSR. This allows us, for the first time in experiments of polymers with supercritical fluids, to decouple the effects of CO2 concentration and pressure in a single device. DA - 2002/4// PY - 2002/4// DO - 10.1016/S0032-3861(01)00804-7 VL - 43 IS - 8 SP - 2375-2383 SN - 0032-3861 KW - viscosity KW - CO2 KW - supercritical fluid ER - TY - JOUR TI - Nitrogen adsorption in carbon aerogels: A molecular simulation study AU - Gavalda, S AU - Gubbins, KE AU - Hanzawa, Y AU - Kaneko, K AU - Thomson, KT T2 - LANGMUIR AB - We present a molecular model for carbon aerogel in which the mesopore space is represented by carbon spheres in a connected network. This matrix was prepared by first generating a random close-packed structure of slightly overlapping spheres, followed by removal of spheres to match the targeted porosity, while maintaining connectivity. The spheres were then replaced by a model microporous carbon generated by applying the Reverse Monte Carlo method to fit the experimental carbon radial distribution function, g(r), obtained by X-ray diffraction. The resulting model aerogel had a surface area, porosity, and pore size distribution that closely matches that of the experimental material. We used a parallelized Grand Canonical Monte Carlo algorithm to study nitrogen adsorption in this model aerogel. The resulting adsorption isotherm shows satisfactory agreement with the experimental results. Adsorption occurred in the micropores at very low pressure, followed by adsorption in the mesopores, with capillary condensation occurring at the higher pressures. DA - 2002/3/19/ PY - 2002/3/19/ DO - 10.1021/la011132o VL - 18 IS - 6 SP - 2141-2151 SN - 0743-7463 ER - TY - JOUR TI - Issues in high-kappa gate stack interfaces AU - Misra, V AU - Lucovsky, G AU - Parsons, GN T2 - MRS BULLETIN DA - 2002/3// PY - 2002/3// DO - 10.1557/mrs2002.73 VL - 27 IS - 3 SP - 212-216 SN - 1938-1425 UR - http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000174442100022&KeyUID=WOS:000174442100022 KW - gate stacks KW - high-dielectric-constant materials KW - high-kappa dielectrics KW - interface reactions KW - metal gates ER - TY - JOUR TI - Interfacial stability between lithium and fumed silica-based composite electrolytes AU - Zhou, J AU - Fedkiw, PS AU - Khan, SA T2 - JOURNAL OF THE ELECTROCHEMICAL SOCIETY AB - Composite electrolytes consisting of methyl-capped poly(ethylene glycol) oligomer lithium bis(trifluoromethylsulfonyl)imide and fumed silica were investigated. In particular, the effects of fumed silica-surface chemistry and weight percentage in the composite on cycling behavior of Li/electrolyte/Li, Li(Ni)/electrolyte/Li, and Li/electrolyte/metal oxide cells were studied. Four types of fumed silicas with various surface groups were employed, A200 (native hydroxyl groups), R805 (octyl-modified), R974 (methyl-modified), and FS-EG3 (ethylene oxide-modified). The presence of fumed silica enhances lithium cyclability by reducing the interfacial resistance and cell-capacity fading, regardless of surface chemistry. However, the extent of the enhancing effect of fumed silica strongly depends on its surface chemistry, with the largest effect seen with A200 and the least effect seen with FS-EG3. Increasing fumed silica weight fraction intensifies the stabilizing effect. © 2002 The Electrochemical Society. All rights reserved. DA - 2002/9// PY - 2002/9// DO - 10.1149/1.1496483 VL - 149 IS - 9 SP - A1121-A1126 SN - 0013-4651 ER - TY - JOUR TI - Electrodeposition of tin needle-like structures AU - Rinne, CL AU - Hren, JJ AU - Fedkiw, PS T2 - JOURNAL OF THE ELECTROCHEMICAL SOCIETY AB - Electrodeposition is reported of arrays of needle-like Sn structures with tip radii ∼7 nm that can be used as electron emitters for field electron emission applications. It is well documented in the literature that in the absence of additive agents, a variety of morphological structures such as fractal, dendritic, and densely branched deposits may result from electrodeposition. It is also known that in the absence of additives, Sn dendrites can be formed. In the present research, it is shown that by controlling the electrode potential and concentration of two additive agents, a nonionic ethoxylated surfactant (Triton X-100) and a Pb(II) salt, an array of needle-like Sn structures is deposited from a Sn(II) salt in methane sulfonic acid. Although these structures may be used as electron emitters for field emission, the low melting point of Sn precludes its use in practical devices. Nevertheless, the unique preparation method that we describe may be used to investigate electrodeposited field emitter tips from higher melting metals (e.g., Ni, Pd, Ag, Au, and Cu). © 2002 The Electrochemical Society. All rights reserved. DA - 2002/3// PY - 2002/3// DO - 10.1149/1.1445172 VL - 149 IS - 3 SP - C150-C158 SN - 0013-4651 ER - TY - JOUR TI - Designing tests to maximize learning AU - Felder, R. M. T2 - Journal of Professional Issues in Engineering Education and Practice AB - This is a continuing series of quarterly articles on lessons learned and best practices in civil engineering education. The intent of the series is to reinforce good practices, describe new or developing practices, and provide a forum for what works well and what does not. It is hoped that this series will be an important quarterly read for all civil engineering educators and all those interested in what’s going on in civil engineering education today. Authors and topics will vary from issue to issue. Contact the associate editor, Mark Evans, if you wish to contribute to an upcoming issue. DA - 2002/// PY - 2002/// DO - 10.1061/(ASCE)1052-3928(2002)128:1(1) VL - 128 IS - 1 SP - 1-3 ER - TY - JOUR TI - Characterization and toxicity of Amanita cokeri extract AU - Drehmel, DC AU - Chilton, WS T2 - JOURNAL OF CHEMICAL ECOLOGY DA - 2002/2// PY - 2002/2// DO - 10.1023/A:1017986108720 VL - 28 IS - 2 SP - 333-341 SN - 0098-0331 KW - Basidiomyces KW - Amanita KW - Lepidella KW - 2-amino-3-cyclopropylbutanoic acid KW - 2-amino-5-chloro-4-pentenoic acid KW - Oncopeltus KW - Cercospora KW - Agrobacterium KW - Erwinia KW - Xanthomonas ER - TY - JOUR TI - Accurate CO2 Joule-Thomson inversion curve by molecular simulations AU - Colina, CM AU - Lisal, M AU - Siperstein, FR AU - Gubbins, KE T2 - FLUID PHASE EQUILIBRIA AB - We present simulation of the Joule–Thomson inversion curve (JTIC) for carbon dioxide using two different approaches based on Monte Carlo (MC) simulations in the isothermal–isobaric ensemble. We model carbon dioxide using a two-center Lennard–Jones (LJ) plus point quadrupole moment (2CLJQ) potential. We show that a precision of four significant figures in ensemble averages of thermodynamic quantities of interest is needed to obtain accurately the JTIC. The agreement between the experimental data, Wagner equation of state (EOS) and our simulations results indicates that the 2CLJQ potential represents an excellent balance between simplicity and accuracy in modeling of carbon dioxide. Additionally, we calculate the JTIC using the BACKONE EOS (that uses the same intermolecular potential as in our simulations) and show that the BACKONE EOS performs very well in predicting the JTIC for carbon dioxide. DA - 2002/11/15/ PY - 2002/11/15/ DO - 10.1016/S0378-3812(02)00126-7 VL - 202 IS - 2 SP - 253-262 SN - 0378-3812 KW - carbon dioxide KW - Joule-Thomson inversion curved KW - molecular simulation KW - Monte Carlo method ER - TY - JOUR TI - A unified model for signal transduction reactions in cellular membranes AU - Haugh, JM T2 - BIOPHYSICAL JOURNAL AB - An analytical solution is obtained for the steady-state reaction rate of an intracellular enzyme, recruited to the plasma membrane by active receptors, acting upon a membrane-associated substrate. Influenced by physical and chemical effects, such interactions are encountered in numerous signal-transduction pathways. The generalized modeling framework is the first to combine reaction and diffusion limitations in enzyme action, the finite mean lifetime of receptor–enzyme complexes, reactions in the bulk membrane, and constitutive and receptor-mediated substrate insertion. The theory is compared with other analytical and numerical approaches, and it is used to model two different signaling pathway types. For two-state mechanisms, such as activation of the Ras GTPase, the diffusion-limited activation rate constant increases with enhanced substrate inactivation, dissociation of receptor–enzyme complexes, or crowding of neighboring complexes. The latter effect is only significant when nearly all of the substrate is in the activated state. For regulated supply and turnover pathways, such as phospholipase C-mediated lipid hydrolysis, an additional influence is receptor-mediated substrate delivery. When substrate consumption is rapid, this process significantly enhances the effective enzymatic rate constant, regardless of whether enzyme action is diffusion limited. Under these conditions, however, enhanced substrate delivery can result in a decrease in the average substrate concentration. DA - 2002/2// PY - 2002/2// DO - 10.1016/S0006-3495(02)75424-6 VL - 82 IS - 2 SP - 591-604 SN - 0006-3495 ER - TY - JOUR TI - Hydrodynamics of trickling flow in packed beds: Relative permeability concept AU - Lakota, A AU - Levec, J AU - Carbonell, RG T2 - AICHE JOURNAL AB - Abstract Liquid holdups and pressure drops for gas and liquid concurrent flow in packed beds were measured experimentally. To calculate the Ergun type constants, pressure drops were also measured for single‐ (gas)‐phase flow through the same packings. These measurements reveal that the Ergun type inertial constant depends on the particle shape. The beds were packed with porous and nonporous spheres, cylinders, extrudates, and Raschig rings. The experimental data were analyzed using the concept of relative permeabilities. The liquid‐phase relative permeability correlated well with the reduced liquid saturation in a unique power‐law form for all particles independent of their shape. The gas‐phase relative permeability as a function of the gas‐phase saturation followed the same law, but the exponent depends on the particle shape and gas‐phase Reynolds number. Predicted and experimental values for liquid holdups for all particle shapes agreed well with mean relative deviations less than 10%. Predictions of pressure drops for spherical particles, cylinders, and extrudates are at least as accurate as other less rigorous correlations (mean relative errors between 25 and 40%). Pressure drop predictions for Raschig rings are poorer (mean relative deviations of 90%), reflecting in part the variations in pressure drops from experiment to experiment with these particles. DA - 2002/4// PY - 2002/4// DO - 10.1002/aic.690480408 VL - 48 IS - 4 SP - 731-738 SN - 1547-5905 ER - TY - JOUR TI - Equilibria between solid, liquid, and vapor phases in binary Lennard-Jones mixtures AU - Lamm, MH AU - Hall, CK T2 - FLUID PHASE EQUILIBRIA AB - We have used Monte Carlo simulation and the Gibbs–Duhem integration technique to calculate temperature–composition and pressure–temperature phase diagrams for binary Lennard–Jones mixtures. We systematically explore Lennard–Jones parameter space to demonstrate how the features of these phase diagrams change as a function of diameter ratio, well-depth ratio, binary interaction parameter, and pressure. We find a number of cases in which the vapor–liquid and liquid–liquid equilibria become metastable with respect to the solid–liquid and solid–vapor equilibria. DA - 2002/3/30/ PY - 2002/3/30/ DO - 10.1016/s0378-3812(01)00650-1 VL - 194 IS - 2002 Mar 30 SP - 197-206 SN - 0378-3812 KW - molecular simulation KW - phase equilibria KW - solid-fluid equilibria KW - Lennard-Jones potential ER -