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Molecular modeling study of adsorption of poly-L-lysine onto silica glass

Journal of Biomedical materials Research Part B: Applied Biomaterials 1998年第4期37卷

作者： Jon K. West Robert Latour Jr. Larry L. Hench Department of Materials Science and Engineering University of Florida Gainesville Florida 32611 Department of Bioengineering and Materials Science and Engineering Program Clemson University 501 Rhodes Engineering Research Center Clemson South Carolina 29634-0905 Imperial College of Science Technology and Medicine Department of Materials London UK

A research program was initiated with both experimental and computational chemistry based molecular modeling components to investigate specific amino acid-surface interactions. The experimental portion of this study, with details reported elsewhere, investigated the adsorption of selected molecular weights of poly( L -lysine) onto silica glass microspheres with the adsorption enthalpy per adsorbed mer determined to be −0.23 ± 0.13 kcal/mol (mean ± 95% confidence interval). Molecular modeling of this system was then conducted using two approaches: an AM1 semiempirical molecular orbital method to predict L -lysine/glass interaction energy and an MM2 molecular mechanics method to investigate the structural configuration for poly( L -lysine). The modeling predicted a minimum energy configuration of a rotational backbone structure for poly( L -lysine) with approximately one full rotation occurring about every 8 mers, and that the amine side chains of the L -lysine will hydrogen bond with the silica surface with an average adsorption energy of approximately −0.34 kcal/mol/mer. The molecular modeling results are in good agreement with the experimentally measured value and provide insights into possible molecular-level behavior which would be very difficult to determine by experimental analyses alone. This work demonstrates the use of molecular modeling in conjunction with experimental studies to investigate complex molecular interactions. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res , 37 , 585–591, 1997.

关键词： AM1 molecular orbital models silica amino acid lysine

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Electrical properties of block copolymers containing silver nanoclusters within oriented lamellar microdomains

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Journal of Applied polymer science 1998年第4期65卷

作者： B. H. Sohn R. E. Cohen Program in Polymer Science and Technology Massachusetts Institute of Technology Cambridge Massachusetts 02139 Department of Chemical Engineering Massachusetts Institute of Technology Cambridge Massachusetts 02139

Films containing silver nanoclusters within a lamellar morphology were obtained via postprocessing reduction of the silver‐containing regions of block copolymers synthesized by ring opening metathesis polymerization. Solution‐cast films (0.1 mm thickness) of the block copolymer exhibited an oriented lamellar morphology with lamellar normals perpendicular to the film plane. The slightly anisotropic dielectric properties, perpendicular and parallel to the film plane, were investigated by direct measurement and by model calculations. The conductivity was highly anisotropic, differing by at least four orders of magnitude in directions parallel and perpendicular to the film plane. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 723–729, 1997

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Studies on thermally stimulated shape memory effect of segmented polyurethanes

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Journal of Applied polymer science 1998年第8期64卷

作者： Fengkui Li Xian Zhang Jianan Hou Mao Xu Xiaolie Luo Dezhu Ma Byung Kyu Kim Polymer Physics Laboratory Institute of Chemistry Academia Sinica Beijing 100080 China Department of Materials Science Chinese University of Science and Technology Hefei 230026 China Department of Polymer Science and Engineering Pusan National University Pusan 609‐735 Korea

The shape memory behavior of a series of polycaprolactone/methane diisocyanate/butanediol (PCL/MDI/BDO) segmented polyurethanes of different composition was studied. The molecular weight of PCL diols was in the range of 1600–7000, and the hard segment content varied from 7.8 to 27% by weight. Film specimens for shape memory measurements were prepared by drawing at temperatures above the melting temperature of the soft segment crystals and subsequent quick cooling to room temperature under constrained conditions. The shape memory process was observed and recorded in a heating process. Parameters describing the recovery temperature, ability, and speed were used to study the influence of structure and processing conditions on the shape memory behavior of the sample. It was found that the high crystallinity of the soft segment regions at room temperature and the formation of stable hard segment domains acting as physical crosslinks in the temperature range above the melting temperature of the soft segment crystals are the two necessary conditions for a segmented copolymer with shape memory behavior. The response temperature of shape memory is dependent on the melting temperature of the soft segment crystals. The final recovery rate and the recovery speed are mainly related to the stability of the hard segment domains under stretching and are dependent on the hard segment content of the copolymers. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1511–1516, 1997

关键词： segmented polyurethanes shape memory effect

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Sedimentation‐resistant electrorheological fluids based on PVAL‐coated microballoons

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Journal of Applied polymer science 1998年第3期65卷

作者： Mancun Qi Montgomery T. Shaw Department of Chemical Engineering University of Connecticut Storrs Connecticut 06269‐3136 Polymer Science Program Institute of Materials Science University of Connecticut 97 North Eagleville Road U‐136 Storrs Connecticut 06269‐3136

Sedimentation is often a problem in electrorheological (ER) fluids featuring solid particles suspended in a low‐density hydrocarbon oil. This problem was addressed by synthesizing particles comprising silica microballoons coated with PVAL using a salt‐induced coacervation process. The ER performance of the fluids based on these particles was equivalent to prototypical commercial fluids, both with respect to current leakage and shear stress under steady simple shear flow. For comparing diverse fluids as to these practical characteristics, a dimensionless ER effectiveness number, Er, was proposed: Er = σγ˙/ EJ where σ is the shear stress, γ˙ is the electric field, and J is the current. The resulting uniform coatings were also found to impart a degree of resistance to breakage. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:539–547, 1997

关键词： ER fluids electrorheology PVAL‐coated microballoons ER effectiveness number sedimentation attrition

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Self-organization and polyolefin nucleation efficacy of 1,3:2,4-di-p-methylbenzylidene sorbitol

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Journal of polymer science 1998年第16期35卷

作者： Thomas A. Shepard Carl R. Delsorbo Richard M. Louth Jonathan L. Walborn David A. Norman Noel G. Harvey Richard J. Spontak Department of Materials Science & Engineering North Carolina State University Raleigh North Carolina 27695-7907 Polymer Science & Technology Department Becton Dickinson Research Center Research Triangle Park North Carolina 27709-2016

Recent studies have demonstrated that addition of a small quantity of dibenzylidene sorbitol (DBS) to a molten polymer may result in a physical gel if conditions permit the DBS molecules to self-organize into a three-dimensional network composed of highly connected nanofibrils. If the polymer crystallizes, DBS may also serve as a nucleating agent, promoting the formation of spherulites, especially in commercially important polyolefins such as polypropylene. We examine the thermal and mechanical properties, as well as the morphological characteristics, of an isotactic polypropylene copolymer with 3 wt % ethylene upon addition of less than 1 wt % of 1,3:2,4-di- p -methylbenzylidene sorbitol (MDBS). From dynamic rheological measurements, pronounced complex viscosity increases, attributed to MDBS nanofibril network formation, are observed at concentration-dependent temperatures above the melting point of the nucleated copolymer. Transmission electron micrographs of RuO 4 -stained sections confirm the existence of MDBS nanofibrils measuring on the order of 10 nm in diameter and, at higher concentrations, fibrillar bundles measuring up to about 200 nm across and several microns in length. The addition of MDBS at different concentrations is also found to promote increases in optical clarity, yield strength, tensile strength, and ultimate elongation of modified copolymer formulations. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 2617–2628, 1997

关键词： dibenzylidene sorbitol polymer crystal nucleation polypropylene clarifying agent

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A relationship between the glass transition temperature (Tg) and fractional conversion for thermosetting systems

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Journal of Applied polymer science 1998年第1期64卷

作者： R. A. Venditti J. K. Gillham Department of Wood and Paper Science North Carolina State University Box 8005 Raleigh North Carolina 27695‐8005 Polymer Materials Program Department of Chemical Engineering Princeton University Princeton New Jersey 08544

An equation, based on thermodynamic considerations to relate the glass transition temperature, T g , to compositional variation of a polymer system, is adapted in this article for modeling the T g vs. fractional conversion ( x ) relationship of reactive thermosetting systems. Agreement between the adapted equation and experimental T g vs. x data is found for several thermosetting crosslinking systems (i.e., epoxies and cyanate ester/polycyanurate) as well as for reactive thermosetting linear polymer systems (i.e., polyamic acid and esters to polyimides). The equation models the experimentally obtained T g vs. x behavior of thermosetting systems which include competing reactions. Agreement for widely varying molecular structures demonstrates the generality of the equation. The entire T g vs. x relationship can be predicted for a thermosetting material by using the T g vs. x equation and the values of the initial glass transition temperature, T g 0 , the fully reacted system glass transition temperature, T g∞ , and the ratio of the change in specific heat from the liquid or rubbery state to the glassy state (Δ c p ) at T g 0 and T g∞ , Δ c p∞ /Δ c p 0 . The values of T g 0 , T g ∞ , and Δ c p∞ /Δ c p 0 can be measured generally from two differential scanning calorimetric experiments. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 3–14, 1997

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Conductive blends of thermally dodecylbenzene sulfonic acid‐doped polyaniline with thermoplastic polymers

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Journal of Applied polymer science 1998年第2期66卷

作者： M. Zilberman G. I. Titelman A. Siegmann Y. Haba M. Narkis D. Alperstein Department of Materials Engineering Technion—Israel Institute of Technology Haifa 32000 Israel Department of Chemical Engineering Technion—Israel Institute of Technology Haifa 32000 Israel Computer Aided Polymer Science Center P.O. Box 228 Kfar Vradim Israel

In the present study, a conductive polyaniline‐dodecyl benzene sulfonic acid (PANI‐DBSA) complex, prepared by a thermal doping process, and its blends with thermoplastic polymers, prepared by melt processing, were investigated. PANI‐DBSA characterization included conductivity measurements, morphology, crystallography, and thermal behavior. The blends' investigation focused on the morphology and the interaction between the components and on the resulting electrical conductivity. The level of interaction between the PANI and the matrix polymer determines the blend morphology and, thus, its electrical conductivity. Similar solubility parameters of the two polymeric components are necessary for a high level of PANI dispersion within the matrix polymer and, thus, enable the formation of conducting paths at low PANI content. The morphology of these blends is described by a two‐structure hierarchy: (a) a primary structure, composed of small dispersed polyaniline particles, and (b) a short‐range fine fibrillar structure, interconnecting the dispersed particles. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 243–253, 1997

关键词： polyaniline thermoplastic polymers blend conductivity

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Dielectric relaxation spectroscopy of amorphous and liquid-crystalline side-chain polycarbonates

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MACROMOLECULAR RAPID COMMUNICATIONS 1997年第2期18卷 139-147页

作者： Wubbenhorst, M vanKoten, EM Jansen, JC Mijs, W vanTurnhout, J Delft University of Technology Faculty of Chemical Engineering and Materials Science Department of Polymer Science and Technology Julianalaan 136 2628 BL Delft. The Netherlands [*]Delft University of Technology Faculty of Chemical Engineering and Materials Science Department of Polymer Science and Technology Julianalaan 136 2628 BL Delft. The Netherlands

The molecular dynamics of amorphous and liquid-crystalline (LC) side-chain polycarbonates was studied by dielectric spectroscopy at frequencies from 10(-2) to 10(6) Hz and at temperatures from -160 to 180 degrees C. 'Model' compounds containing no mesogenic side-groups showed two relaxations, which originate from the carbonate group (alpha, beta(m)-relaxation). By contrast, in LC-polycarbonates bearing a mesogenic nitrostilbene side group around and above the glass transition temperature Tg UP to three relaxation modes were distinguished (alpha-, lambda(1)-, lambda(2)-process);below T-g four secondary relaxations (gamma-, beta(m)-, beta(s)-, beta(sc)- relaxation) were observed. The gamma-relaxation was found only in compounds possessing an aliphatic spacer linked to the backbone by an ether bond. Apart from beta(m)-, two additional beta-processes were identified as relaxations associated with the mesogenic unit in the glassy (beta(s)) or in the crystalline state (beta(sc)).

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THERMAL BEHAVIOR OF THERMOTROPIC HYDROXYETHYL CELLULOSE ACETATE/POLYETHYLENE BLENDS

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Chinese Journal of polymer science 1997年第1期15卷 57-64页

作者：王海琳陈进明黄勇沈家瑞 Laboratory of Cellulose and Lignocellulosics Chemistry Guangzhou Institute of Chemistry Chinese Academy of Sciences Guangzhou 510650 Department of Polymer Materials Science and Engineering South China University of Technology Guangzhou 510641

The thermal behavior of thermotropic hydroxyethyl cellulose acetate (HECA)/polyethylene (PE) blends has been studied by DSC. It is found that the blends of HECA and PE are immiscible but the crystallization of PE is affected by HECA chains in the blends with more than 50% HECA, which results in the subordinate crystallization of PE and the formation of imperfect structures in the PE crystals. The imperfection of PE crystals in the blends can be eliminated after annealing at 393K.

关键词： hydroxyethyl cellulose acetate polyethylene blends thermal behavior polyethylene blends

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Controlling the Surface Cleanliness of Nanostructured Alpha-iron and M50 Type Steel (Fe-Cr-Mo-V-C) Powders

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MRS Online Proceedings Library 1997年第1期501卷 179-183页

作者： S. F. Schady C. C. Law M. Gell K. E. Gonsalves J. E. Morral S. P. Rangarajan Pratt & Whitney Materials and Mechanics Engineering United Technologies Corporation East Hartford USA Department of Metallurgy and Materials Engineering Institute of Materials Science University of Connecticut Storrs USA Department of Chemistry University of Connecticut Polymer Science Program Institute of Materials Science and Storrs USA

The cleaning effectiveness of flowing hydrogen to remove oxygen (adsorbed and metal oxide) and carbon (elemental, carbides and carbon-hydrogen complex) from the surface of nanostructured alpha-iron and M50 type steel (Fe-Cr-Mo-V-C) alloy powders was investigated. The hydrogen treated powders and consolidated material were examined by bulk chemical analysis and metallographic examination. The trends in the cleaning effectiveness compared favorably with predictions from Richardson and Jeffies plots of metal-metal oxide equilibria.

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