The influence of silane treated amorphous fumed silica fillers on properties of the cured epoxy was examined in the first part of the study. Silica particles were treated with 3- aminopropyldiethoxymethylsilane (APDS) and 3-aminopropyltriethoxysilane (APTS) coupling agents. The filler and coupling agents decreased the mobility of the polymer chains in the vicinity of the filler leading to an increase in the activation energy for the glass transition and an increase in cooperativity. Fumed silica did not significantly affect moisture diffusion properties. Next, a linear dilatometer was used to investigate the effects of cure conditions, mold types, and the presence of filler in the model epoxy. These studies revealed that there was substantial shrinkage in the cured epoxy on heating it through its glass transition region. The shrinkage was determined to be the result of stress in the epoxy generated during cure and could be minimized by curing at lower temperatures, followed by a postcuring heat treatment. Additional free volume in the sample increased the magnitude of the shrinkage by allowing increased stress release through increased network mobility. Decreasing the polymer mobility by adding fillers decreased the observed shrinkage. The influence of the model epoxy crosslink density was examined by varying the content of 1,4-butanediol in the model system. Addition of 1,4-butanediol led to a decrease in the modulus and glass transition temperature, which resulted in a reduction in residual stress and subsequent shrinkage. Moisture uptake increased with the addition of 1,4-butanediol due to an increase in the free volume of the epoxy. However, even with greater moisture uptake, the addition of 1,4-butanediol to the epoxy increased its adhesion to quartz by promoting lower residual stress and increased energy dissipation. These results indicate that bulk diffusion of water is not the controlling factor in adhesive degradation in this system. / Ph. D.

Glass fiber reinforced poly(ethylene terephthalate), GF/PET has excellent potential for future structural applications of composite materials. PET as a semi-crystalline thermoplastic polyester has high wear resistance, low coefficient of friction, high flexural modulus and superior dimensional stability make it a versatile material for designing mechanical and electromechanical parts. Glass fibers are currently used as strength giving material in structural composites because of their high strength and high performance capabilities. In order to obtain high interfacial adhesion between glass fiber and polymer, glass fibers are treated with silane coupling agents. The objective of this study is to produce GF/PET composites with varying glass fiber concentration at constant process parameters in a twin screw extruder. Also, by keeping GF content constant, it is aimed to observe the effects of process parameters such as screw speed and feed rate on structural properties of the composites. Another objective of the study is to investigate the influence of different coupling agents on the morphological, thermal and mechanical properties and on fiber length distributions of the composites. Tensile strength and tensile moduli of the GF/PET composites increased with increasing GF loading. There was not a direct relation between strain at break values and GF content. The interfacial adhesion between glass fiber received from the manufacturer and PET was good as observed in the SEM photograps. Degree of crystallinity values increased with the addition of GF. Increasing the screw speed did not affect the tensile strength of the material significantly. While increasing the feed rate the tensile strength decreased. The coupling agent, 3-APME which has less effective functional groups than the others showed poor adhesion between glass fiber and PET. Therefore, lower tensile properties were obtained for the composite with 3-APME than those of other silane coupling agents treated composites. Number average fiber length values were reduced to approximately 300&amp / #61549 / m for almost all composites prepared in this study.

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The adhesion and durability of model epoxy/silane/SiO2/Si bonded systems were investigated under various conditions, including the type of surface preparation, pH of the environmental media, temperature, cyclic thermal stress, and external applied stress. The fundamental debond mechanism was studied for bonded systems exposed to selected environments. The bond failure mode was characterized by examining the failed bond surfaces using X-ray photoelectron spectroscopy. The effectiveness of combining the oxygen plasma treatment and silane coupling agent (SCA) derivatization in adhesion promotion for an epoxy bonded to a silicon surface was evaluated in this research. SCAs with different amine functionalities were studied. The oxygen plasma treatment time was varied systematically to achieve a different extent of oxidation on the Si wafer. The surface chemistry/composition of various silane derivatized Si surfaces was investigated. The studies revealed that SCA interaction with the Si surface was enhanced by the oxygen plasma pre-treatment of the Si substrates. XPS surface analysis results showed that the SCA/SiO2 ratio did not correlate strongly with the increase in oxygen plasma pretreatment time. However, for Si surfaces treated for longer oxygen plasma pretreatment times, more silanol groups may be available to interact with the hydrolyzed silanol groups on silane, resulting in a stronger SCA-Si attachment. Three different tests were employed to determine adhesion and durability of the model epoxy/SCA/SiO2/Si bonded specimens. The immersion test qualitatively evaluates the bond durability for various systems exposed to different chemical and thermal conditions. Second, a novel probe test was used to quantitatively determine adhesion under critical debonding conditions for bonded specimens with different SCA preparations. A general trend of bond durability varied in the manner SCA-2 > SCA-3 > SCA-1 > no silane. Bond durability also increased for samples: model epoxy/SCA modified/O2 plasma treated/Si as the oxygen plasma pre-treatment time increased. Third, bond durability was studied using the wedge DCB (double cantilever beam) test under subcritical debonding conditions with environment-assisted crack growth as a function of applied strain energy release rate. Higher crack velocity and the absence of a Gthreshold value were noted in tests at 70 oC. The Gthreshold value increased as the strength of the interface increased and as the chemical aggressiveness of the environment decreased. For tests involving 25 oC -70 oC thermal cycling, only limited crack growth was found. / Ph. D.

Adding layered double hydroxides (LDHs) to polymer compounds has been shown to make them more resistant to corrosion and improve their physical and chemical properties. However, the main challenge lies in the compatibility between inorganic LDH fillers and organic polymer matrices. The incompatibility between these two is due to differences in polarity and surface properties, which makes dispersion of LDHs within the polymer very difficult, negatively affecting the final material's performance and characteristics. In this work, Zn-Al-NO3 LDH particles were synthesized through co-precipitation method and then modified by decavanadate via the anion exchange process. Then, a silane coupling agent was used to functionalize intercalated LDH particles to make them more hydrophobic; this helped the particles to disperse well inside epoxy coating, which ultimately resulted in better corrosion inhibition performance for the coating. The concentration effect of silane coupling agent on LDHs' surface grafting was also studied using various concentrations of 3-aminopropyltriethoxy silane (APTES). Compositional and structural characterization study on revealed more insight into how the surface treatments worked. Finally, to modify LDHs, sodium dodecyl sulfate was inserted in LDH structure, then APTES molecules were grafted on the dodecyl sulfate intercalated LDHs' surface. These organic intercalation and grafting steps made LDHs more suitable with acrylic resin to form uniform composite mixture through solvent solution mixing. The thermal stability of acrylic coating improved by adding modified hybrid LDH fillers and elevation in decomposition temperature was confirmed using thermogravimetric analysis.

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