京都大学 / 新制・課程博士 / 博士(理学) / 甲第23735号 / 理博第4825号 / 新制||理||1690(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)准教授 齊藤 尚平, 教授 依光 英樹, 教授 若宮 淳志 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

The objective of this research work was to understand the molecular mechanism of gas transport through amorphous glassy polymers. Especially, emphasis was placed on determining whether or not gas transport in amorphous glassy polymers is directly correlated with the free volume content. Free volume arguments are indeed commonly used to explain the gas transport process. The gas transport properties of bisphenol-A polycarbonate films were examined as a function of the cooling rate, physical aging, and orientation. Such conditions affect the free volume content and its size and shape distribution. Results obtained from permeation experiments were accompanied with dynamic mechanical and density measurements. The experimental results suggest that the diffusion coefficient of small gas molecules in glassy polycarbonate is influenced by the local dynamics or mobility of the polymer chains rather than by the overall free volume content. Indeed, the diffusion coefficient of nitrogen for instance was reduced in fast-cooled samples, despite of the fact that those samples possessed a greater overall free volume content. Fast cooling rates may generate highly restricted conformations which hinder local motions, and therefore tend to increase the activation energy of diffusion. As expected, the greater the free volume content, the greater was the solubility coefficient. The increase in the polymer relaxation times with aging time is believed to restrict the local chain motions, leading to enhanced activation energies of diffusion, and therefore to reduced diffusion coefficients. The change in the solubility coefficients with physical aging revealed that the aging process might not affect all the cavity sizes in polycarbonate equally. According to free volume arguments, one would anticipate that the physical aging of fast-cooled samples (which possess more free volume) should be enhanced compared to that of slowly-cooled samples. Quite interestingly, the decrease in the diffusion coefficient with aging was found to occur much slower in fast-cooled samples, despite of the higher initial free volume content. In contrast, properties directly related to the free volume content, such as density or isothermal DMTA measurements actually showed a greater aging rate in the sample containing the greatest amount of free volume. Slow-cooled samples that are in a low energy conformational state may loose their internal degrees of freedom more rapidly, due to the closer interchain packing and the possibly restricted segmental motions. Studies dealing with orientation and gas transport were complicated by several factors. For instance the fact that the permeation experiments were performed perpendicularly to the orientation of the chains and not along the orientation axis limited the sensitivity of the gas transport properties to orientation. This work points out that dynamic rather than static models should be developed to predict the gas transport phenomenon. / Ph. D.

The facile synthesis of engineering thermoplastics enabled the development of structure-morphology-property relationships for a wide range of applications. Utilizing step-growth polymerization techniques, a myriad of reaction conditions probed various polymer families including polysulfones, polyesters, polyimides and polyureas. Copolymers ranging from random to segmented sequences provided insight into the influence of segment length on physical properties. Melting temperatures, glass transition temperatures, and mechanical properties responded systematically to segment length and morphology. Leveraging several complementary analytical techniques identified critical segment lengths required for phase separation and crystallization within these copolymers. Introduction of hydrogen bonding further complicated the interrelationships between thermal and mechanical properties, and possible co-crystallization between dissimilar segments occurred. Finally, branching out from linear copolymers to other topologies determined the influence of branch length on rheological and mechanical properties. The commercially-viable synthesis of these various thermoplastics further highlights the immediate impact on state-of-the-art materials, and the fundamental development described herein provides a road map for future development in this field. / Ph. D.

The diffusion of small-molecule penetrants in polyethylene is hindered by impenetrable crystals and by the segmental constraints imposed by the crystals on the penetrable phase. Liquid and vapour n-hexane sorption/desorption measurements were performed on metallocene catalyzed homogenous poly(ethylene-co-octene)s. It was shown that the fractional free volume of the polymer penetrable component increased with increasing amount of penetrable polymer. It also increased with the relative proportion of liquid-like component in the penetrable polymer fraction. The detour effect was found to increase with decreasing crystallinity. The experimental study of the morphology of the polymers showed that the geometrical impedance factor followed the same trend with increasing crystallinity as the data obtained from n-hexane desorption. The changes in phase composition and character upon n-hexane sorption were monitored with Raman spectroscopy, WAXS and NMR spectroscopy. Partial dissolution of the orthorhombic and the interfacial component was observed upon nhexane sorption. Changes in the character of the components were furthermore analyzed: an increase of the density in the crystalline component and a decrease of the density in the amorphous component were observed in the n-hexane-sorbed-samples. Molecular dynamics simulations were used for studying diffusion of n-hexane in fully amorphous poly(ethylene-co-octene)s. The branches in poly(ethylene-co-octene) decreased the density by affecting the packing of the chains in the rubbery state in accordance with experimental data. Diffusion of n-hexane at low penetrant concentration showed unexpectedly that the penetrant diffusivity decreased with increasing degree of branching. Spherulitic growth was mimicked with an algorithm able to generate structures comparable to those observed in polyethylene. The diffusion in the simulated structure was assessed with Monte Carlo simulations of random walks and the geometrical impedance factor of the spherulitic structures was calculated and compared with analytical values according to Fricke’s theory. The linear relationship between geometrical impedance factor and crystallinity in Fricke’s theory was confirmed. Fricke’s theory, however, underestimated the crystal blocking effect. By modelling systems having a distribution of crystal width-to-thickness ratio it was proven that wide crystals had a more pronounced effect on the geometrical impedance factor than is indicated by their number fraction weight. / QC 20100909

In this study, the time-dependent deformation behavior of several model bulk metallic glasses (BMGs) was studied. The BMGs were obtained in different structural states by thermal relaxation below their glass transition temperature, cryogenic thermal cycling, and chemical rejuvenation by micro-alloying. The creep behavior of Zr52.5Ti5Cu17.9Ni14.6Al10 BMG in different structural states was investigated as a function of peak load and temperature. The creep strain rate sensitivity (SRS) indicated a transition from shear transformation zone (STZ) mediated deformation at room temperature to diffusion dominated mechanisms at high temperatures. The relaxation enthalpy of Zr47Cu46Al7 BMG was found to increase significantly with the addition of 1 at% Ti, namely for Zr47Cu45Al7Ti1. Comparison of their respective free volumes indicated that chemical rejuvenation had a more pronounced effect compared to cryogenic thermal rejuvenation. Micro-pillar compression tests supported the improved plasticity with increase in free volume from the rejuvenation effect. Effect of chemistry change on mechanical response and time-dependent deformation was investigated for topologically equivalent Pt-Pd BMGs, where the Pt atoms were systematically replaced with Pd atoms (Pt42.5-xPdx)Cu27Ni9.5P21: x=0, 7.5, 20, 22.5, 35, 42.5). The hardness and reduced modulus increased while the degree of plasticity decreased with increase in Pd-content, which was attributed to the increase in stiffer 3-atom cluster connections. STZ volume was calculated for all the BMGs using cooperative shear model (CSM) for fundamental understanding of the underlying deformation mechanisms.

The non-reactive Dreiding and the reactive ReaxFF atomic potentials were applied within a family of atom molecular dynamics (MD) simulations to investigate and understand interfacial adhesion in graphene/vinyl ester composites. First, a liquid vinyl ester (VE) resin was equilibrated in the presence of graphene surfaces and then cured, resulting in a gradient in the monomer distribution as a function of distance from the surfaces. Then the chemically realistic relative reactivity volume (RRV) curing algorithm was applied that mimics the known radical addition regiochemistry and monomer reactivity ratios of the VE monomers during three-dimensional chain-growth polymerization. Surface adhesion between the cured VE resin and the graphene reinforcement surfaces was obtained at a series of VE resin “crosslink densities.” Both pristine and oxidized graphite sheets were employed separately in these simulations using a Dreiding potential. The pristine sheets serve as a surrogate for pure carbon fibers while oxidizing the outer graphene sheets serve as a model for oxidized carbon fibers. Hence, the effects of local monomer distribution and temperature on the interphase region formation and surface adhesion can be investigated. Surface adhesion was studied at various curing conversions and as a function of temperature. Uniaxial loading simulations were performed at different curing conversions for both models to predict the composites’ modulus of elasticity, Poisson’s ratio, and yield strength. The same analysis was performed for the neat cured matrix. The glass transition temperature (Tg) for the homogenized composite and neat VE matrix was determined at different degrees of curing. Subsequent MD simulations were performed to predict structural damage evolution and fracture in the neat VE matrix. The ReaxFF potential was used to quantify irreversible damage due to bond breakage in the neat VE matrix for different degrees of cure, stress states, temperatures, and strain rates. The predicted damage mechanisms in the bulk VE thermosetting polymer were directly compared to those for an amorphous polyethylene (PE) thermoplastic polymer.

No description available.

<p>High-performance fibers used for ballistic protection are characterized by having outstanding mechanical properties such high modulus and strength. These mechanical properties are granted by the fiber’s chemical and physical structure as well as their high degree of orientation. Twaron fibers are one of the most commonly used fibers on soft body armors such as bulletproof vests. They are made from poly (p-phenylene terephthalamide) (PPTA), a rigid-rod and highly crystalline polymer. Although these fibers are crystalline and have great mechanical properties, their performance can decrease when they are exposed to different degradation factors. Free volume is the unoccupied space between the polymer molecules. It is responsible for characteristics such as diffusion and viscosity. Hence, the free volume changes as the polymer degrades. This thesis focuses on the effects of sonication, pH changes, and sweat on the free volume of PPTA fibers. </p><p><br></p> <p>A non-destructive technique known as positron annihilation lifetime spectroscopy (PALS) was used to measure the free volume in PPTA. Changes in the free volume of fibers degraded under different conditions were compared to their mechanical performance. Degradation in DI water, pH 4 and pH 10 aqueous solutions was conducted for 10 weeks at 80^oC. Sweat degradation of PPTA fibers was also conducted for 10 weeks at 25^oC, 50^oC, and 100^oC. Fibers degraded in pH4 and sweat solutions had greater loss of mechanical performance and changes in the free volume. PALS was able to detect changes in the nanostructure of PPTA fibers at early stages of degradation. This data was supported by mechanical tests and is complementary to other characterization techniques such as small angle X-ray scattering (SAXS). Results of this research are a steppingstone for future studies on lifetime predictions of bulletproof vests and the development of the next generation of soft body armors. </p>

Orientador: Sergio Persio Ravagnani / Tese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia Quimica / Made available in DSpace on 2018-08-07T03:49:14Z (GMT). No. of bitstreams: 1 Trochmann_JoseLuizLino_D.pdf: 1070584 bytes, checksum: 3407aee7ad6d88d9de0a1326aaf3d29d (MD5) Previous issue date: 2006 / Resumo: Neste trabalho de tese foi realizado um estudo do potencial de predição de propriedades de transporte em matrizes poliméricas de poli - imidas, utilizando a simulação dinâmica molecular de gases simples como Oxigênio, Nitrogênio e Dióxido de Carbono. A propriedade de transporte de interesse prático, a permeabilidade de uma membrana polimérica a um dado penetrante, envolve a determinação de propriedades de ordem cinética e termodinâmica, respectivamente a determinação do coeficiente de difusão e da solubilidade deste penetrante na matriz polimérica. Atenção especial foi conferida à propriedade cinética, pela predição do coeficiente de autodifusão dos penetrantes. Num procedimento experimental clássico é de vital importância para significância das conclusões derivadas dos experimentos, o uso de amostras de membranas poliméricas adequadamente preparadas quanto à composição química, estrutura física e morfologia. Analogamente, quando se utiliza a simulação molecular para a predição de propriedades, tais como o coeficiente de autodifusão, também é de fundamental relevância para os resultados obtidos, a qualidade dos modelos moleculares das matrizes poliméricas, que serão usados como base. Assim para a preparação de modelos moleculares com o adequado empacotamento, um procedimento para a obtenção de modelos bem equilibrados foi desenvolvido neste trabalho. Os modelos moleculares desenvolvidos foram usados para a obtenção dos valores de massa específica em função da temperatura, e comparados aos valores experimentais disponíveis e quando necessário a, valores preditos por meio da expressão de massa específica em função da temperatura, acima e abaixo da temperatura de transição. A capacidade do modelo molecular desenvolvido em predizer a massa especifica e temperatura de transição vítrea foi usada como critério para a validação da adequação do empacotamento proposto para o referido modelo molecular da matriz polimérica. Os modelos validados de empacotamento, células amorfas, foram utilizados para o cálculo do coeficiente de autodifusão dos gases acima mencionados, através do da simulação dinâmica molecular. A comparação dos coeficientes de autodifusão obtidos das poli-imidas aromáticas e éster imidas, BAAF, 6FDA-ODA, PMDA-ODA e BA-20DA, para os gases O2, N2 e CO2, com os dados experimentais, permitiu concluir a adequação das células amorfas e do esquema de simulação dinâmica molecular para a predição do coeficiente de autodifusão.. A versão preditiva de Vrentas e Duda, baseada na teoria do volume livre, foi utilizada para a predição dos coeficientes de autodifusão da água e do etanol para as poli-imidas acima. , Estes valores, quando comparados com os valores obtidos através da simulação dinâmica molecular mostram a validade de ambas as teorias para a predição da cinética de difusão de penetrantes em matrizes poliméricas complexas / Abstract: In this thesis a study of the predictive potential of the molecular dynamic simulation was performed for transport properties of light gases in polyimide matrix. From de practical point of view permeability is the property of most interest, and involves kinetics as well as thermodynamics properties, diffusion coefficient and solubility of the penetrants molecule in the bulk polymeric matrix, this work will be focus in the former. As important as is in as experimental work, a well prepared polymeric membrane is essential for the significance of the draw conclusions. Therefore a special attention was take in the preparation of the bulk molecular polymeric model, the so called amorphous cell, in order to obtain well-equilibrated molecular packing models for the polyimide matrixes. The amorphous cells were prepared throughout thermodynamic transforms, using one or more of the statistical ensembles and cell specific volume obtained as a function of temperature, this data was compared against the experimental data available, and when necessary to data obtained via predictive methods. The molecular packing model ability to predict the glass transition temperature was used as criteria to validate de amorphous cell, to be used in the molecular dynamic' simulations allow the matrix to be locally flexible and coupled to the classic molecular dynamics simulation. The resulting self diffusion coefficients for the polyimide, BAAF, 6FDA-ODA, PMDA­ODA and BA-20DA for the gases O2, N2 e CO2 were compared to the experimental data. The lack of quality experimental diffusion data available for polyimide membranes for larger penetrants as water and ethanol, showed up as a good opportunity to assess the predictive capability of the molecular dynamic simulation for self diffusion coefficients, considering the relevant technological relevance of polyimide membranes for pervaporation process. The data of self diffusion coefficient produced by the predictive version of free-volume theory after Vrentas and Duda, was compared with the data produced via coupled molecular dynamic simulation for the water and ethanol penetrants, showing the relevance of both theories for the prediction of penetrants kinetic in complex polymeric matrixes / Doutorado / Ciencia e Tecnologia de Materiais / Doutor em Engenharia Química

Étude des mécanismes de la plasticité dans les verres métalliques massifs. Ce travail a porté sur une approche des mécanismes de la plasticité à la transition vitreuse dans les verres métalliques massifs base zirconium. Une étude bibliographique des verres métalliques, ses caractéristiques essentielles a été tout d'abord introduite, particulièrement orientée vers leurs propriétés de stabilité structurale, ainsi que vers leurs propriétés mécaniques à haute température. Le modèle de volume libre (selon l'approche de Spaepen) a été utilisé dans une modélisation par éléments finis de la plasticité du verre. Le verre métallique de composition Zr_{52,5}Cu_{22}Al_{10}Ni_{13}Ti_{2,5}, étudié dans cette thèse, est élaboré par différentes méthodes d'hypertrempe sous forme de barreaux et de rubans. Les caractérisations physico-chimiques ont été menées par DSC, DRX et MEB. Les résultats de DSC ont montré que les verres élaborés possèdent un large intervalle de transition vitreuse et une bonne stabilité thermique. L'étude couplant DSC et DRX à haute température a permis d'établir la nature des phases et leur ordre d'apparition en cours de cristallisation. La transition vitreuse et la cristallisation ont été étudiées en détail par DSC modulée (MDSC) par la suite. La cinétique de cristallisation du verre a été généralement analysée par DSC isotherme.La caractérisation de la relaxation du verre métallique à partir de traitements thermiques successifs, par DSC et DRX à température proche de la température de transition vitreuse T_g pendant des temps différents, est rapportée dans le quatrième chapitre. Ce phénomène de relaxation peut être observé directement par les études structurales en utilisant la DSC et la diffraction des rayons X. Ensuite, l'évolution de la relaxation du verre est étudiée par mesure de dureté et de densité. La variation de la dureté H_v par rapport à la profondeur de pénétrateur h, après les traitements thermiques, a été menée par micro-dureté. La mesure de volumique du verre Zr_{52,5}Cu_{22}Al_{10}Ni_{13}Ti_{2,5} a été menée après les différents temps de relaxation thermique, nous donnent une densité d'environ de 6,769g/cm^3. Les traitements thermiques isothermes sur ce verre ont montré une augmentation de sa densité au cours du temps. Afin d'observer l'apparition puis l'évolution des mécanismes de déformation dans le verre métallique à l'échelle locale, une nouvelle technique - lithographie électronique - avec un dispositif d'essai mécanique in situ, permettant de déposer des microgrilles à la surface d'une éprouvette et de réaliser un essai de compression dans un MEB, est présentée dans le cinquième chapitre. Puis, les résultats sont analysés par corrélation d'images. La démarche expérimentale des essais MEB in situ est détaillée dans ce chapitre.Des essais à vitesse de déformation constante sont présentées dans le chapitre suivant. Ils ont été conduits dans l'intervalle de transition vitreuse (entre 673K et 713K). Enfin, les études de champs de déformation par corrélation d'image ont montré une limite de détection de la localisation supérieure à 2 micromètre sur les cartes de déformation. S'il y a des bandes de cisaillement, soit leurs déformation en inférieure à celles due à l'oxydation, soit elles sont plus fines que 2 micromètre (échelle de mesure). Le dernier chapitre présente une modélisation pour décrire le comportement élastique et plastique des verres métalliques. Dans le cadre de cette thèse, une approche de la modélisation des essais mécanique en se basant sur le modèle du volume libre a été conduite à l'aide du logiciel ZéBulon. Des travaux préliminaires pour étudier la localisation dans le cadre du volume libre ont été conduits et vont nécessiter une étude plus poussée.Mots clef : verre métallique, transition vitreuse, relaxation structurale, volume libre, caractérisation, micro-dureté, lithographie, compression, MEB in situ, modélisation / Study of the mechanisms of the plasticity in the massive metallic glasses. This work concerned an approach of the mechanisms of the plasticity in the glassy transition in the massive metallic glasses base zirconium. A bibliographical study of the metallic glasses, its essential characteristics was introduced first of all, particularly directed to their properties of structural stability, as well as to their high-temperature mechanical properties. The model of free volume (according to the approach of Spaepen) was used in a modelling by elements finished by the plasticity of the glass. The metallic glass of composition Zr _ (52,5) Cu _ (22) Al _ {10} Nor _ (13) Ti _ {2,5}, studied in this thesis(theory), is developed by various methods of hypertempering in the form of bars and of ribbons.