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Molecular dynamics simulation of complex molecules at interfaces: dendritic surfactants in clay and amyloid peptides near lipid bilayersHan, Kunwoo 02 June 2009 (has links)
We apply a molecular dynamics (MD) simulation technique to complex molecules at
interfaces. Partitioning of dendritic surfactants into clay gallery and Ab protein behavior
near hydrated lipids are chosen for the purpose. Using a full atomistic model of dendritic
surfactants, the confinement force profiles featuring oscillatory fashion at moderate layer
separation of 10 to 25 Å were observed. Integration of the confinement forces led to free
energy profiles, which, in turn, were used to determine the final morphology of the
nanocomposite. From the free energy profiles, smaller and linear surfactants (G1 and
G2L) are expected to intercalate into the clay comfortably, while larger surfactants (G2
and G3) are expected to form frustrated intercalated structures due to the location and
depth of the free energy minima. This would agree with the previous observations.
As primary steps to understand the Ab protein behavior under biological conditions,
simulations of bulk water and hydrated lipids were performed and the results were
compared with the literature. Hydrated lipids were simulated using a full atomistic
model of lipids (dipalmitoylphosphatidylcholine) and water with a cvff force-field and it
was found that structural properties such as the molecular head group area and
membrane thickness were accurately produced with MD simulation. Systems of the
protein Ab(1-42) in bulk water were simulated and some secondary structural change,
with loss of part of the a-helical structure, occurred during the 1 ns of simulation time at
323K. The fragment Ab(31-42) with b-sheet conformation was also simulated in bulk
water, and the extended b-sheet structure became a bent structure. Simulations of Ab(1-
42) or Ab(31-42) near lipid bilayers have been performed to investigate the structural property changes under biological conditions. The different nature of structural change
was observed from the simulations of the protein or fragment in water and near lipid
bilayers due to the different solvent environment. The protein has close contacts with the
membrane surface. It was impossible to observe the conformational change to b-sheet
and protein entrance into the lipid bilayer within 1 ns simulations.
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Melt Processing Fabrication and Characterization of Functional Nanocomposites of Linear Low-Density Polyethylene/Halloysite NanotubeBaheri, Bahareh 23 May 2022 (has links)
No description available.
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Processing and Properties of Hybrid Silane-Epoxy Nanocomposite CoatingsBeemat, Jaspreet S. January 2012 (has links)
No description available.
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SYSTEMATIC STUDIES ON HIGH PERFORMANCE FLAME RETARDANT OF THIAZOLE SUBSTITUTED POLYBENZOXAZINE AND POLYBENZOXAZINE-LAPONITE NANOCOMPOSITE CONTAINING HIGH NANOFILLER CONTENTShan, Fei, Shan 04 June 2018 (has links)
No description available.
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Síntese de látices hibridos de poliestireno e argila montmorilonita pelos mecanismos de polimerização via radical livre em emulsão e miniemulsão / Synthesis of polystyrene and montmorillonitic clay hybrid latexes by free radical emulsion and miniemulsion polymerization.Souza, Fatima Cristina Torres de 17 September 2010 (has links)
Materiais nanocompósitos híbridos polímero-argila nos quais lamelas nanométricas de argila montmorilonita são encapsuladas e dispersas em matriz polimérica são em geral mais rígidas, tenazes e resistentes do que os materiais poliméricos convencionais e tem o potencial de aplicações em revestimentos e filmes com propriedades de barreira. Dentre as várias técnicas de preparação de nanocompósitos poliméricos, as técnicas de polimerização \"in-situ\" em emulsão e mini-emulsão vem sendo empregada na síntese de látices híbridos com lamelas de argilas encapsuladas pelo polímero. Neste trabalho foram preparados látices híbridos de poliestireno e argila montmorilonita esfoliada através de dois métodos: no primeiro, a polimerização em emulsão e miniemulsão convencional na presença de argila modificada com sal quaternário de amônio é realizada com surfatante catiônico; no segundo método, um surfatante aniônico reativo foi usado para modificar uma argila natural sódica e empregada na polimerização em emulsão. Os resultados obtidos tanto para a polimerização em emulsão como em miniemulsão empregando idênticos reagentes (argila organofílica modificada e surfatante catiônico) mostraram boa conversão, aumento na velocidade de polimerização com aumento da concentração de surfatante e de argila, aumento na temperatura de pico na máxima velocidade de decomposição (TG), aumento no módulo de armazenamento no patamar vítreo e no patamar borrachoso (DMTA) com aumento da concentração de argila, encontrando um valor mínimo em ambos a 5% de argila. Apesar dessas características positivas, não foi obtida a encapsulação das lamelas da argila que era o objetivo principal do trabalho. Por outro lado, o método de polimerização em emulsão não convencional com surfatante reativo mostrou baixa eficiência na conversão mas que se mostrou eficaz na encapsulação das lamelas da argila para os látices com baixa conversão e elevado diâmetro de partícula. / Polymer-clay nanocomposite materials, in which nanometer-thick layers of clay dispersed in polymers, are generally stiffer, stronger, and tougher than normal polymeric materials and can be potentially useful in a variety of applications. These polymer-clay nanocomposites can be prepared in several ways, namely by emulsion \"in-situ\" polymerisation where polymer chains are coagulated on silicate layers producing capped silicate layers are more or less uniformly dispersed in aqueous medium. The objective of this work is to prepare polymer-clay hybrid latexes with exfoliated clay platelets encapsulated inside latex particles in order to improve the exfoliation of the clay platelets in the final polymeric film. To achieve this objective two separate approaches have been investigated, first by conventional emulsion polymerization and miniemulsion polymerization in the presence of montmorillonite clay modified by cationic surfactant and in the other approach a reactive anionic surfactant was used to modify the natural montmorillonite clay layers by emulsion polymerization. The results for both the emulsion polymerization as in miniemulsion using identical reagents (organoclay modified and cationic surfactant) showed good conversion, polymerization rate increased with increasing concentration of surfactant and clay, increased peak temperature at maximum speed decomposition (TG), an increase in storage modulus in the glassy plateau and the rubbery plateau (DMTA) with increasing concentration of clay, finding a minimum value in both the 5% clay. Despite these positive characteristics, encapsulation was not obtained from lamellar clay that was the main objective. Moreover, the method of emulsion polymerization with non-conventional reactive surfactant showed low conversion efficiency but has proved effective in the encapsulation of the lamellae of the clay for the lattices with low conversion and high particle diameter.
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Síntese de látices hibridos de poliestireno e argila montmorilonita pelos mecanismos de polimerização via radical livre em emulsão e miniemulsão / Synthesis of polystyrene and montmorillonitic clay hybrid latexes by free radical emulsion and miniemulsion polymerization.Fatima Cristina Torres de Souza 17 September 2010 (has links)
Materiais nanocompósitos híbridos polímero-argila nos quais lamelas nanométricas de argila montmorilonita são encapsuladas e dispersas em matriz polimérica são em geral mais rígidas, tenazes e resistentes do que os materiais poliméricos convencionais e tem o potencial de aplicações em revestimentos e filmes com propriedades de barreira. Dentre as várias técnicas de preparação de nanocompósitos poliméricos, as técnicas de polimerização \"in-situ\" em emulsão e mini-emulsão vem sendo empregada na síntese de látices híbridos com lamelas de argilas encapsuladas pelo polímero. Neste trabalho foram preparados látices híbridos de poliestireno e argila montmorilonita esfoliada através de dois métodos: no primeiro, a polimerização em emulsão e miniemulsão convencional na presença de argila modificada com sal quaternário de amônio é realizada com surfatante catiônico; no segundo método, um surfatante aniônico reativo foi usado para modificar uma argila natural sódica e empregada na polimerização em emulsão. Os resultados obtidos tanto para a polimerização em emulsão como em miniemulsão empregando idênticos reagentes (argila organofílica modificada e surfatante catiônico) mostraram boa conversão, aumento na velocidade de polimerização com aumento da concentração de surfatante e de argila, aumento na temperatura de pico na máxima velocidade de decomposição (TG), aumento no módulo de armazenamento no patamar vítreo e no patamar borrachoso (DMTA) com aumento da concentração de argila, encontrando um valor mínimo em ambos a 5% de argila. Apesar dessas características positivas, não foi obtida a encapsulação das lamelas da argila que era o objetivo principal do trabalho. Por outro lado, o método de polimerização em emulsão não convencional com surfatante reativo mostrou baixa eficiência na conversão mas que se mostrou eficaz na encapsulação das lamelas da argila para os látices com baixa conversão e elevado diâmetro de partícula. / Polymer-clay nanocomposite materials, in which nanometer-thick layers of clay dispersed in polymers, are generally stiffer, stronger, and tougher than normal polymeric materials and can be potentially useful in a variety of applications. These polymer-clay nanocomposites can be prepared in several ways, namely by emulsion \"in-situ\" polymerisation where polymer chains are coagulated on silicate layers producing capped silicate layers are more or less uniformly dispersed in aqueous medium. The objective of this work is to prepare polymer-clay hybrid latexes with exfoliated clay platelets encapsulated inside latex particles in order to improve the exfoliation of the clay platelets in the final polymeric film. To achieve this objective two separate approaches have been investigated, first by conventional emulsion polymerization and miniemulsion polymerization in the presence of montmorillonite clay modified by cationic surfactant and in the other approach a reactive anionic surfactant was used to modify the natural montmorillonite clay layers by emulsion polymerization. The results for both the emulsion polymerization as in miniemulsion using identical reagents (organoclay modified and cationic surfactant) showed good conversion, polymerization rate increased with increasing concentration of surfactant and clay, increased peak temperature at maximum speed decomposition (TG), an increase in storage modulus in the glassy plateau and the rubbery plateau (DMTA) with increasing concentration of clay, finding a minimum value in both the 5% clay. Despite these positive characteristics, encapsulation was not obtained from lamellar clay that was the main objective. Moreover, the method of emulsion polymerization with non-conventional reactive surfactant showed low conversion efficiency but has proved effective in the encapsulation of the lamellae of the clay for the lattices with low conversion and high particle diameter.
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