Polymer electrolyte membrane fuel cells (PEMFCs) have the potential to play a major role as energy generators for transportation and portable applications. One of the current barriers to their commercialization is the cost of the components and manufacturing, specifically the bipolar plates. One approach to preparing PEMFCs for commercialization is to develop new bipolar plate materials, related to mass production of fuel cells. Thermoplastic/carbon filler composites with low filler loading have a major advantage in that they can be produced by a conventional low-cost injection molding technique. In addition, the materials used are inexpensive, easy to shape, and lightweight. An optimal bipolar plate must possess high surface and bulk electronic conductivity, sufficient mechanical integrity, low permeability, and corrosion resistance. However, it is difficult to achieve high electrical conductivity from a low-cost thermoplastic composite with low conductive filler loading. Concerns over electrical conductivity improvement and the injection processability of composites have brought forth the idea of producing a polypropylene/three-carbon-filler composite for bipolar plate application. The thesis addresses the development of synergistic effects of filler combinations, investigating composite conductive materials and using composite bipolar plate testing in PEMFCs. One significant effect of conductive network formation is the synergetic effects of different carbon filler sizes, shapes, and multiple filler ratios on the electrical conductivity of bipolar plate materials. A polypropylene resin combined with low-cost conductive fillers (graphite, conductive carbon black, and carbon fibers with 55 wt% of filler loading) compose the main composite for all investigations in this research. Numerous composite formulations, based on single-, two-, and three-filler systems, have been created to investigate the characteristics and synergistic effects of multiple fillers on composite conductivity. Electrical conductivity measurements corresponding to PEMFC performance and processing characteristics were investigated. Experimental work also involved other ex-situ testing for the physical requirements of commercial bipolar plates. All combinations of fillers were found to have a significant synergistic effect that increased the composite electrical conductivity. Carbon black was found to have the highest influence on the increase of electrical conductivity compared to the other fillers. The use of conjugated conducting polymers such as polypyrrole (PPy) to help the composite blends gain desirable conductivities was also studied. Electrical conductivity was significantly improved conductivity by enriching the conducting paths on the interfaces between fillers and the PP matrix with PPy. The conductive network was found to have a linkage of carbon fibers following the respective size distributions of fibers. The combination of Fortafil and Asbury carbon fiber mixture ameliorated the structure of conductive paths, especially in the through-plane direction. However, using small fibers such as carbon nanofibers did not significantly improve in electrical conductivity. The useful characteristics of an individual filler and filler supportive functions were combined to create a novel formula that significantly improved electrical conductivity. Other properties, such as mechanical and rheological ones, demonstrate the potential to use the composites in bipolar plate applications. This research contributes a direction for further improvement of marketable thermoplastic bipolar plate composite materials.

No description available.

With excellent electrical, thermal and mechanical properties as well as large specific surface area, graphene has been applied in next-generation nano-electronics, gas sensors, transparent electrical conductors, thermally conductive materials, and superior energy capacitors etc. Convenient and productive preparation of graphene is thereby especially important and strongly desired for its manifold applications. Chemically developed functionalized graphene from graphene oxide (GO) has significantly high productivity and low cost, however, toxic chemical reduction agents (e.g. hydrazine hydrate) and raised temperature (400-1100°C) are usually necessary in GO reduction yet not preferred in current technologies. Here, microwaves (MW) are applied to reduce the amount of graphene oxide (GO) at a relatively low temperature (~165°C). Experimental results indicate that resurgence of interconnected graphene-like domains contributes to a low sheet resistance with a high optical transparency after MW reduction, indicating the very high efficiency of MW in GO's reduction. Moreover, graphene is usually recumbent on solid substrates, while vertically aligned graphene architecture on solid substrate is rarely available and less studied. For TIMs, electrodes of ultracapacitors, etc, efficient heat dissipation and electrical conductance in normal direction of solid surfaces is strongly desired. In addition, large-volume heat dissipation requires a joint contribution of a large number of graphene sheets. Graphene sheets must be aligned in a large scale array in order to meet the requirements for TIM application. Here, thermally conductive fuctionalized multilayer graphene sheets (fMGs) are efficiently aligned in a large scale by vacuum filtration method at room temperature, as evidenced by SEM images and polarized Raman spectroscopy. A remarkably strong anisotropy in properties of aligned fMGs is observed. Moreover, VA-fMG TIMs are prepared by constructing a three-dimensional vertically aligned functionalized multilayer graphene architecture between contact Silicon/Silicon surfaces with pure Indium as a metallic medium. Compared with their counterpart from recumbent A-fMGs, VA-fMG TIMs have significantly higher equivalent thermal conductivity and lower contact thermal resistance. Electrical and thermal conductivities of polymer composite are also greatly interested here. Previous researches indicated that filler loading, morphology of fillers, and chemical bonding across filler/polymer interfaces have significant influence on electrical/thermal conductivity of polymer composite. Therefore, the research also pays substantial attention to these issues. First, electrical resistivity of CPCs is highly sensitive on volume or weight ratio (filler loading) of conductive fillers in polymer matrix, especially when filler loading is close to percolation threshold (pc). Thermal oxidation aging usually can cause a significant weight loss of polymer matrix in a CPC system, resulting in a filler loading change which can be exhibited by a prompt alteration in electrical resistivity of CPCs. Here, the phenomena are applied as approach for in-situ monitoring thermal oxidation status of polymeric materials is developed based on an electrical sensors based on conductive polymeric composites (CPCs). The study developed a model for electrical resistivity of sensors from the CPCs as a function of aging time at constant aging temperature, which is in a good agreement with a Boltzmann-Sigmoidal equation. Based on the finding, the sensors show their capability of in-situ in-situ monitor and estimate aging status of polymeric components by a fast and convenient electrical resistance measurement. Second, interfacial issues related to these thermal conductive fillers are systemically studied. On the one hand, the study focuses on relationship between morphology of h-BN particles and thermal conductivity of their epoxy composites. It is found that spherical-agglomeration of h-BN particles can significantly enhance thermal conductivity of epoxy resin, compared with dispersed h-BN plates, by substantially reducing specific interfacial area between h-BN and epoxy resin. On the other hand, surface of high thermal conductive fillers such as SiC particles and MWNTs are successfully functionalized, which makes their surface reactive with bisphenol A diglycidyl ether and able to form chemical bonding between fillers and epoxy resin. By this means, thermal conductivity of polymer composites is found to be significantly enhanced compared with control samples, indicating the interfacial chemical bonding across interface between thermal conductive fillers and polymer matrix can promote heat dissipation in polymeric composites. The finding can benefit a development of high thermal conductive polymer composites by interfacial chemical bonding enhancement to meet the demanding requirements in current fine pitch and Cu/low k technology.

Uma maneira de quantificar a resistência da interface de materiais compósitos é medindo a tensão necessária para separar o filme do substrato. Esta tensão é frequentemente usada como um parâmetro de projeto para desenvolver estes materiais. Entretanto, muitos métodos de medição da adesão não são capazes de eliminar as falhas de coesão das falhas de adesão filme/substrato. Neste trabalho um novo método de medição de adesão é proposto com o objetivo de eliminar a interferência da falha de coesão por cisalhamento, inerente ao filme delaminado, da medida da tensão normal de adesão feita por método padrão. O novo método provou ser eficiente e seus resultados mostraram serem mais precisos que os do método normalizado. Foram testados os seguintes compostos obtidos por evaporação de cobre usando canhão de elétrons através do processo de deposição física de vapor (PVD), formando um filme metálico sobre quatro substratos poliméricos: polipropileno (PP), poliamida 6 (PA 6), poliestireno de alto impacto (HIPS) e poli(tereftalato) de etileno (PET). A análise de espectroscopia de retroespalhamento Rutherford foi utilizada para caracterizar os filmes e o ângulo de contato para caracterizar a interface. As superfícies dos polímeros foram modificadas através de flambagem e lixamento para validar os resultados do novo método. Finalmente os polímeros delaminados através dos métodos padrão e proposto foram observados por microscopia óptica e eletrônica de varredura (MEV), comprovando assim, que somente no método novo ocorre a separação da interface metal-polímero livre da influência da falha coesiva do filme de cobre. / One of the methods to quantify the interface strength of composites is to measure the tensile stress necessary to separate a film from the substrate surface. Such value is often used as a project parameter to develop the composite. However, most of methods cannot avoid the interference of the cohesion bulk failures from the film/substrate adhesion measures. In this work a new method is proposed in order to eliminate the influence of the cohesion shear failure inherent to the delaminated film of the normal adhesion stress measured by the standard method. The new method has proved to work and their results have become more accurate than the standard pull-off method. The experiment consisted in delaminate a copper film deposited by physical vapor evaporation (PVD) through electron gun on four polymers: polypropylene (PP), polyamide 6 (PA 6), high impact polystyrene (HIPS) and polyethylene terephthalate (PET). The Rutherford backscattering spectrometry was used to characterize the films and the contact angle analysis to characterize the interfaces. The polymer surfaces have also been modified to verify the adhesion strengths of the copper film through sanding and flaming processes to validate the new method. Finally the substrates delaminated were analyzed for both methods, standard and proposed, through optical and scanning electron microscopies, proving that only the new method is effective in pulling-off the metal/polymer interface without the cohesive failure influence of the copper film.

Uma maneira de quantificar a resistência da interface de materiais compósitos é medindo a tensão necessária para separar o filme do substrato. Esta tensão é frequentemente usada como um parâmetro de projeto para desenvolver estes materiais. Entretanto, muitos métodos de medição da adesão não são capazes de eliminar as falhas de coesão das falhas de adesão filme/substrato. Neste trabalho um novo método de medição de adesão é proposto com o objetivo de eliminar a interferência da falha de coesão por cisalhamento, inerente ao filme delaminado, da medida da tensão normal de adesão feita por método padrão. O novo método provou ser eficiente e seus resultados mostraram serem mais precisos que os do método normalizado. Foram testados os seguintes compostos obtidos por evaporação de cobre usando canhão de elétrons através do processo de deposição física de vapor (PVD), formando um filme metálico sobre quatro substratos poliméricos: polipropileno (PP), poliamida 6 (PA 6), poliestireno de alto impacto (HIPS) e poli(tereftalato) de etileno (PET). A análise de espectroscopia de retroespalhamento Rutherford foi utilizada para caracterizar os filmes e o ângulo de contato para caracterizar a interface. As superfícies dos polímeros foram modificadas através de flambagem e lixamento para validar os resultados do novo método. Finalmente os polímeros delaminados através dos métodos padrão e proposto foram observados por microscopia óptica e eletrônica de varredura (MEV), comprovando assim, que somente no método novo ocorre a separação da interface metal-polímero livre da influência da falha coesiva do filme de cobre. / One of the methods to quantify the interface strength of composites is to measure the tensile stress necessary to separate a film from the substrate surface. Such value is often used as a project parameter to develop the composite. However, most of methods cannot avoid the interference of the cohesion bulk failures from the film/substrate adhesion measures. In this work a new method is proposed in order to eliminate the influence of the cohesion shear failure inherent to the delaminated film of the normal adhesion stress measured by the standard method. The new method has proved to work and their results have become more accurate than the standard pull-off method. The experiment consisted in delaminate a copper film deposited by physical vapor evaporation (PVD) through electron gun on four polymers: polypropylene (PP), polyamide 6 (PA 6), high impact polystyrene (HIPS) and polyethylene terephthalate (PET). The Rutherford backscattering spectrometry was used to characterize the films and the contact angle analysis to characterize the interfaces. The polymer surfaces have also been modified to verify the adhesion strengths of the copper film through sanding and flaming processes to validate the new method. Finally the substrates delaminated were analyzed for both methods, standard and proposed, through optical and scanning electron microscopies, proving that only the new method is effective in pulling-off the metal/polymer interface without the cohesive failure influence of the copper film.

Les effets du vieillissement accéléré, comme la décoloration et la perte de propriétés mécaniques, limitent les utilisationsdes composites bois-polymère (WPC) dans les applications en extérieur. Dans la présente étude, il a été tenté d'étudier l'influence de l'utilisation de fibres délignifiées de bagasse (canne a sucre) en renfort sur les propriétés des WPC et de suivre leur effet sur le contrôle de la photo- et de la bio-dégradation (vis-à-vis des champignons et des termites). A côté des échantillons délignifiés, les effets d'une finition finition transparente ont également été étudiés sur la qualité de surface et la réduction des défauts causés par la photo- et la bio-dégradation d'échantillons pigmentés et non pigmentés. Afin de faciliter l'analyse des données et avoir des résultats plus fiables, des analyses statistiques ont été effectuées sur des données provenant de différentes techniques de mesure. Toujours dans cette étude, les effets positifs et négatifs de l'utilisation de pigments granulaires ont été étudiés. Les résultats ont montré que l'utilisation de fibres délignifiées, selon le type de solvant et le niveau de délignification, provoque des changements sur la qualité de surface et les propriétés mécaniques. En outre, les échantillons délignifiés ont montré une perte de rigidité comparés aux échantillons non-délignifiées. Après vieillissement, les échantillons délignifiés ne montraient pas de réduction du changement de couleur total causé par le vieillissement. Toutefois, les fibres délignifiées accompagnées de pigments entrainent, dans une certaine mesure, une stabilisation de la rigidité des échantillons exposés au vieillissement par rapport aux échantillons non-exposés.De plus, les échantillons avec la finition transparente ont montré des résultats très prometteurs. La finition réduit le changement de couleur total du au vieillissement, et un prétraitement de surface favorise le maintien de l'efficacité de la finition, dans toutes les étapes de la photo et la bio-dégradation. Par ailleurs, les échantillons délignifiés à 70% et les échantillons ayant subi un vieillissement montrent une plus forte biodégradation et une plus grande perte de masse par rapport aux témoins. L'étude métrologique montre que le test non-destructif par vibration est une méthode fiable pour étudier les propriétés mécaniques des WPC et les effets du vieillissement. Néanmoins, il n'a pas été montré d'effet important de la délignification sur le contrôle du vieillissement. Les études sur la corrélation entre les variables ont montré que les changements avant et après le vieillissement peuvent être prédits à partir des résultats de tests non-destructifs. / The effects of weathering, such as color fading and loss in mechanical properties, limit the performance of wood-polymer composites (WPC) in outdoor applications. In the current study, it has been tried to investigate the influence of using delignified sugar cane bagasse fibers as a reinforcement on properties of WPC and follow the effects that it cause on controlling photo and bio-degradation (fungi and termite attacks). Beside delignified samples, the effects of clear coating also have been studied on surface quality and reduction of defects caused by photo and bio-degradations of pigmented and non-pigmented samples. To facilitate the data analysis and having more reliable results, some statistical analyses have been carried out on data from different variables. Also in this study the positive and negative effects of using granule pigments in master batch of components have been investigated. Results have shown that using delignified fibers, depending on type of solvent and level of delignification, cause changes on surface qualities and mechanical properties. As well, delignified samples have shown loss in MOE compare to non-delignified samples. After weathering, none of the delignified samples had reduced the total color change caused by weathering. However delignified fibers with pigments, to some extent, stabilized the MOE in weathered samples compared to un-weathered samples. In addition, clear coated samples have shown very promising results. Total color change was reduced in coated samples and by means of pre-treatments of surface, coating remained efficient in all steps of the photo and bio-degradations. This is while the 70% delignified samples and weathered samples showed higher degradation and weight loss compared to controls and un-weathered ones. Methodology investigation did show that vibration none-destructive test is the reliable method to study the mechanical properties of WPC and weathering effects. Nevertheless, it did not show the significant effects of delignification on controlling weathering. Studies on correlation between variables have shown changes before and after weathering which can be used in further studies on modeling.

Laminados compósitos com matrizes poliméricas, respectivamente termorrígida e termoplástica, reforçadas com fibras contínuas de carbono foram submetidos a impacto único transversal com diferentes níveis de energia. Os danos imprimidos aos materiais estruturais foram avaliados por termografia ativa infravermelha na modalidade transmissão. Em geral, os termogramas do laminado termoplástico apresentaram indicações mais claras e bem definidas dos danos causados por impacto, se comparados aos do compósito termorrígido. O aquecimento convectivo das amostras por fluxo controlado de ar se mostrou mais eficaz que o realizado por irradiação, empregando-se lâmpadas incadecentes. Observou-se também que tempos mais longos de aquecimento favoreceram a visualização dos danos. O posicionamento da face impactada do espécime, relativamente à câmera infravermelha e à fonte de calor, não afetou a qualidade dos termogramas no caso do laminado termorrígido, enquanto que influenciou significativamente os termogramas do compósito termoplástico. Os resultados permitiram concluir que a termografia infravermelha é um método de ensaio não-destrutivo simples, robusto e confiável para a detecção de danos por impacto inferior à 5 Joules em laminados compósitos poliméricos reforçados com fibras de carbono. / Continuous carbon fiber-reinforced thermosetting and thermoplastic composite laminates were exposed to single transversal impact with different energy levels. The damages marked to the structural materials were evaluated by active infrared thermography in transmission mode. In general, the thermoplastic laminate thermograms showed more clear and delineated damage indications when compared to the ones from thermosetting composite. The convective heating of the samples by controlled hot air flow was more efficient than via irradiation using lamp. It was also observed that longer heating times improved the damage visualization. The positioning of the specimen´s impacted face regarding the infrared camera and the heating source did not affect the thermo-imaging of thermosetting specimens, whereas it substantially influenced the thermograms of thermoplastic laminates. The results allow concluding that infrared thermography is a simple, robust and trustworthy methodology for detecting impact damages as light as 5 Joules in carbon fiber composite laminates.

京都大学 / 0048 / 新制・課程博士 / 博士(農学) / 甲第22081号 / 農博第2373号 / 新制||農||1073(附属図書館) / 学位論文||R1||N5235(農学部図書室) / 京都大学大学院農学研究科森林科学専攻 / (主査)教授 矢野 浩之, 教授 和田 昌久, 教授 辻井 敬亘 / 学位規則第4条第1項該当 / Doctor of Agricultural Science / Kyoto University / DFAM

The diploma thesis deals with the study of Inter-Laminar Shear Strength (ILSS) of polymer composites, based on unsaturated polyester resin with unidirectionally oriented basalt or glass fibers. The basis of the experimental part is the preparation of composite samples with different types of surface treatment of a fibers (a reinforcement) as well as the surface treatment itself. The untreated, the commercially treated fibers and the plasmatreated fibers used as reinforcement in the polymer composites were analysed by a short beam shear test and their ILSS was determined. The effect of various deposition conditions during Plasma-Enhanced Chemical Vapour Deposition (PECVD) on the value of ILSS of the composite with originally unsized glass or basalt fibers was studied. The impact of aging on the interlaminar shear strength of the composites was investigated for commercially treated glass fibers. The Scanning Electron Microscopy (SEM) is also used in the thesis together with the Energy Dispersive Spectroscopy (EDS). Based on all the results a proposal was made to correct and improve the deposition conditions and thus improve the interphase to achieve the required shear properties of polymer composites.

The evaluation of concentration of ions and molecules with the help of biosensors have been regarded as an emerging technology. Bio and chemical sensors have a variety of applications in the field of medicine, military, environmental and food industries alike. With an estimated investment growth of over 4.31% in the development of pH sensors in the next five year, the objective of a developing a robust measurement system is all the more required. The scope of this research is to evaluate the ability of conducting polymer-based gel electrolytes for pH sensitivity, as a function of the transistor characteristics using an Extended Gate Field Effect Transistor or a conducting film in an electrochemical cell. Polymer gels were prepared by dissolving a suitable conducting polymer in an acidic media. The interaction of the gel with a buffer solution of known pH was collected as electric signals using a glassy carbon as an electrode. The electrochemical cell was further connected to the gate of a Metal-Oxide-Semiconductor Field Effect transistor (MOS-FET). The drain current was measured under two conditions; a) voltage across the gate (VGS) was kept constant, with varying voltage across the drain (VDS) and b) voltage across drain was fixed, while gate voltage changed. The drain current versus voltage of the transistor was plotted as a function of the ion interaction between the gel and the buffer. Different plots were recorded for different values of pH solutions. Final results were plotted to calculate the change in threshold voltage, for every change in pH of the observed solution. pH sensitivity of the gels was further tested through the Electrochemical Impedance Spectroscopy method, using a potentiostat and a three-electrode electrochemical cell. With a small excitation, the AC current flowing through the circuit at different frequencies were recorded and the plots discussed, to evaluate sensitivity to pH.