京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21795号 / 工博第4612号 / 新制||工||1718(附属図書館) / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 辻井 敬亘, 教授 山子 茂, 教授 渡辺 宏 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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The primary goal of this research is to investigate the mechanical reinforcing efficiencies of carbon nanofibers in a thermoset polymer material (vinyl ester), considering the presence of the three-dimensional interphase region between nanofiber and matrix, as well as the waviness of the nanofibers. The elasticity-driven response (buckling) and energy absorption efficiency (crush performance) of the structures made of those composites are investigated. The structural/material optimization problem is solved for both buckling and energy absorption. Due to the nondeterministic nature of the influential parameters (fiber, matrix, and interphase geometric and material properties) on the overall properties of the composite, this study considers the probabilistically distributed random variables associated with the material constituents. The uncertainties associated with the material constituents are propagated to the overall properties of the composite material as well as the performance of composite structures made of such nanocomposites. Finally, the design optimization of a composite structure under uncertainty of material constituents is performed for both buckling and energy absorption as structural performance.

Corrosion is an unstoppable process that occurs spontaneously in many areas of industry, specially, oil and gas industries. Therefore, the need of developing protective coating to lower the cost of corrosion is very consistent. Among different methods, electrodeposition has been a popular method since it offer many advantages such as low cost, ability to control the surface and thickness of the coating, ability to perform at low temperature and pressure, and very convenience. Ceramic nanoparticles have been widely incorporated into metal coating and used as a protective layer to improve both corrosion and hardness properties. Diazonium synthesis was used to modify cerium oxide nanoparticles by grafting with ferrocene for use in nickel nanocomposite coating. Citric acid and citrate salt were used as stabilizing ligands for yttrium oxide and praseodymium oxide nanoparticles in nickel plating solution to prevent the formation of hydroxide, thus, higher amount of nanoparticles was able to incorporate into nanocomposite coatings. These fabricated coatings were evaluate for the corrosion and mechanical properties using many different instruments and electrochemical techniques. As modified cerium oxide, stabilized yttrium oxide or praseodymium oxide added into nickel coatings. The results showed an increase in hardness and corrosion resistance leading to the overall improvement compare to pure nickel coating.

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Conductive nanocomposites are finding many uses as multi-functional materials. One recent development involves the creation of high displacement strain gauges, which have potential applications in a variety of engineering roles. The piezoresistive nature of the gauges makes possible their strain sensing capability. The intent of this research is to show that specific High Displacement Strain Gauges can successfully be used in one human-machine interface application that will demonstrate their potential for a range of other human-machine interface applications. This will be shown in the development of these sensors to accomplish hand pose determination. The flexible and inexpensive gauges are attached to several locations on a glove. It is then shown that by linking this glove with software, the position of the hand can be interpreted into the letters of the American Sign Language alphabet. This use of this nanocomposite sensor establishes the potential for future applications. Issues such as accuracy of response, cyclability, recalibration and reliability are discussed. A design of experiments is accomplished in order to evaluate the effects of modification of the gauges in order to overcome these issues. This work develops the potential of these sensors for use in human-machine interface applications such as computer games, remote controls, robotics, prosthetics and virtual reality applications.

Multifunctional "self-sensing" materials at the frontiers of current research are generally designed to gather only a single type of information (such as quasi-static strain data). This project introduces a new sensor that is both multifunctional and dual-response, indicating its ability to not only perform in mechanical and sensing functions but also in its ability to sense multiple types of response. The proposed new class of sensing materials, comprised of nanocomposite polymer foams, exhibits measurable piezoresistive and quasi-piezoelectric phenomena in the form of change in resistance and voltage generation in response to deformation, respectively. An initial sampling of the envelope of dual-response nanocomposite foam sensors is mapped. The sensing materials can also be tailored to provide desired mechanical compliance and damping. Nanocomposite foam sensors decrease in resistance with increased strain in both static and cyclic compression environments. The quasi-piezoelectric voltage response of nanocomposite foam sensors increases linearly with compression frequency. A circuit and signal demodulation system was developed enabling simultaneous capture of a dual-response foam sensor's change in resistance and voltage generation. Measuring the two responses provides both long-term and immediate performance and health status of mechanical systems, enabling improved monitoring and decreased risk of failure.

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New electrochemical methods were developed to fabricate superparamagnetic organic-inorganic nanocomposites. The methods were based on the electrosynthesis of (gamma)Fe2O3, Mn3O4 and NiFe2O4 in situ in a polymer matrix. Various composite materials were developed using new electrochemical strategies, which were based on the use of strong and weak polyelectrolytes and polymer-metal ion complexes. The deposited films were studied by XRD, TG, DTA, SEM and AFM. The results show that cathodic deposits with thickness of several microns can be obtained on various conductive substrates. The results reveal that the weight percentage of inorganic phase in the deposits reduced with the increase of the polymer concentration in the electrochemical bath solution. The particle size distribution was measured by HRTEM and evaluated by theoretical models interpreting the magnetic measurement data. The two methods are in good agreement with each other. The results show that the average particle sizes of Mn3O4 and (gamma)-Fe2O3 can be adjusted by the selection of polymers with different functional properties, the polymer concentration in the solutions and annealing temperatures. The particle size distribution in the developed composites followed the lognormal distribution. A double-lognormal distribution was required to interpret the magnetization data of the system containing strong interparticle interactions, and to interpret the double-peak phenomenon observed in the imaginary part of the susceptibility in some nanocomposites. DC magnetization and AC susceptibility measurements were used to study the relationship between the magnetic properties .and the average particle size by studying the superparamagnetic behavior and ferrimagnetic phase transitions of (gamma)-Fe2O3 and Mn3O4 nanoparticles in the temperature range of 2 K - 300 K. The results show that the blocking temperature TB is mainly controlled by the average particle size of the nanoparticles, and increasing the average particle size results in an upward shift of the TB. One observes no frequency dependence of TB, which indicates strong interparticle interaction in the nanoparticle assembly, in agreement with the structural results. The results revealed superparamagnetic behavior in Mn3O4 nanoparticles below the ferrimagnetic Néel temperature TN, and that TB was identified by a peak in the temperature lower than the ferrimagnetic transition peak marked by TN in the AC measurement. It is found that both TB and TN of Mn3O4 depend on the average particle size, and reducing the average particle size of Mn3O4 from 3.5 nm to 2.8 run results in a shift of TB from 14 K to 7 K, and TN from 36 K to 31 K (bulk Mn3O4 TN= 42 K) / Thesis / Doctor of Philosophy (PhD)

The use of supercritical carbon dioxide (scCO₂) as a processing aid to help exfoliate nano-clays and improve their dispersion during melt blending in polymer matrices has been reported in the literature. One of the best processes in terms of improving the degree of nano-clay dispersion and composite mechanical properties was developed in our laboratory. This process allows the clay to be in direct contact with scCO₂ and expanding the clay-CO₂ mixture via rapid depressurization into a two-stage screw extruder to mix with the polymer pellets. However, composites with clay loading higher than 6.6 wt % were not reported. In addition, the scCO₂ aided processing method has not been applied to carbon nanotube (CNT) based composites. This dissertation initially focused on applying the scCO₂ aided processing technique to the field of CNT expansion and CNT/polymer composite preparation. The relationship with the expanded CNT morphology and the experimental conditions of the expansion procedure (including pressures, temperatures, exposure time, and depressurization rates) was studied. Microscopy results showed improved CNT dispersion in the polymer matrix and more uniform networks formed with the use of scCO₂, which indicated that CO₂ expanded CNTs are easier to disperse into the polymer matrix during the blending procedure. The CNT/ poly(phenylsulfone) (PPSF) composites prepared with scCO₂ aided method provided continuous improvements in Young's modulus up to the addition of 7 wt % CNTs. However, the Young's modulus of the composite prepared by means of conventional direct melt blending failed to increase beyond the addition of 1 wt % CNT. The second part of this work is concerned with the development of a semi-continuous process using scCO₂ to process polymer-clay composites with clay loading higher than 6.6 wt % (i.e. 10 wt %). Two major modifications are involved in the new procedure: exfoliating the nano-clay directly into the hopper filled with pellets followed by processing the composite immediately and sequentially mixing the clay into the melt. Transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD) results show that this modified procedure help to reduce the clay collapse when processing the composites with high clay loadings. Surface modified montmorillonite (MMT) nano-clay/polypropylene (PP) composite at 10 wt % nano-clay with improved clay dispersion was obtained with increased modulus and tensile strength of 63 % and 16%, respectively, compared to the pure PP matrix. Additional mechanical property improvements for nano-clay based composites are then obtained with the use of high crystallinity polypropylene (HCPP) and polypropylene grafted with maleic anhydride (PP-g-MA). HCPP has higher crystallinity and stiffness than conventional PP and, therefore, composites made from HCPP have better mechanical properties to start with. PP-g-MA has polar groups grafted on the PP chains that promote the intercalation of PP with clay. By using the newly developed procedure, the HCPP nanocomposite at 10 wt % of nano-clay has a Young's modulus as high as 3.236 GPa, and the modulus of the 10% MMT/PP-g-MA sample is found to be 2.595 GPa, both higher than that of the composite prepared by the direct blending method and that of a composite based on a conventional PP matrix. / Ph. D.