Since the carbon nanotubes were first discovered by Iijima in 1991, CNTs have been the focus of intense research by many groups. Nearly 7000 papers and 700 theses on carbon nanotubes can be found from the eminent journals such as Nature and Science in the last decade. Since carbon nanotubes show impressive mechanical, physical and electronic properties such as high stiffness, high strength, low density, and excellent thermal conductivity, suggesting its role in light-weight high strength material application. A great quantity of important research has evidently been done in this field. The purpose of this thesis research is to investigate the feasibility of MWCNTs for the application of polymer organic photovoltaics, and to study the formed MWCNTs-P3HT polymer nanocomposites properties, which are optical absorption, fluorescence emission, and morphology, as well as the formed photovoltaic device performance. This fundamental research would significantly contribute to the advanced technology development for how to improve the efficiency of the polymer organic photovoltaics.

Polyaniline/Gold Nanocomposites J. Anthony Smith 141 Pages Directed by Dr. Ji and #345;?anata The expectation that it is possible to create a range of new materials from two basic components, polyaniline fibers and gold particles is explored. Three synthetic methods were employed each of which created different materials and required different investigation techniques. The methods are: chemical, one step aniline oxidation / AuCl4- reduction; electrochemical/chemical, a two-step composite growth achieved by electrochemical polyaniline thin film growth followed by film immersion in AuCl4- solution and spontaneous reduction to gold particles; electrochemical, resulting in freestanding polyaniline thin film/Au nanoparticles carried out by electrochemical stripping of a polyaniline thin film grown over a sacrificial gold layer in the presence halide solutions. The incorporation of particles was shown to affect film morphology and electrical properties in all synthetic methods. The changes are in large part attributed to the development of a contact potential between the polyaniline and the gold particles. Applications for the composites include use as chemically sensitive layers, corrosion inhibition materials, and use as probes to evaluate nanoparticle substrate interactions.

Segmented polyurethaneureas (SPUU) are thermoplastic elastomers with excellent elastic properties, high abrasion resistance and tear strength, making them very useful in numerous industrial applications ranging from microelectronics (slurry pad) to biomedical (artificial heart vessels) applications. The elastic and mechanical properties of these materials are strongly influenced by their two phase morphology. The factors that influence phase separation include difference in polarity between the hard and soft phases, composition and temperature. In general good phase separation results in materials with superior mechanical and elastic properties. Due to the immense potential applications of SPUU elastomers, there is a need for materials with higher strength. However, higher strength is not desired at the detriment of elasticity. If fact, stronger materials with enhanced elasticity are desired. In this thesis, high-strength SPUU elastomers were synthesized by incorporating reactive Laponite particles with surface-active free amine. The synthesis of pure SPUU is very complex, and addition of a reactive silicate further increases the complexity. To remedy this challenge, combinatorial methods and high-throughput screening techniques were used to optimize the diamine concentration and cure temperature. It was determined that pure SPUU elastomers prepared at a diamine stoichiometry of 85 100 mole %, and cured at 90 95 oC produced materials with higher strength and elongation at break. SPUU nanocomposites were prepared by maintaining the overall diamine stoichiometry at 95 mole %, and cured at 90 oC. Uniaxial tensile strength was optimized at a particle weight fraction of 1 wt. %, with a nearly 200 % increase in tensile strength and a 40 % increase in elongation at break, compared to pristine SPUU.

Underfill material is a special colloidal dispersion system with silicon dioxide particles in the organic liquid. It is used to improve the reliability of integrated circuits (IC) packaging in the microelectronics. In order to successfully synthesize the nanocomposite underfill meeting the requirements of the chip package, it is necessary to have a fundamental understanding about the particle stability in the non-aqueous liquid and the relationship between materials properties and interphase structure in the composite. The results of this thesis contribute to the knowledge of colloidal dispersion of nanoparticles in organic liquid by systematically investigating the effects of particle size, particle surface chemistry and surface tension, and liquid medium polarity upon the rheological and thermal mechanical properties of underfill materials. The relaxation and dielectric properties studies indicate that the polymer molecular chain motion and polarization in the interphase region can strongly influence the material properties of nanocomposite, and so a good interaction between particle and polymer matrix is key. With this study, a potential nanocomposite underfill can be synthesized with low viscosity, low thermal expansion, and high glass transition temperature. The excellent transmittance of nanoparticles leads to further investigation of their ability as reinforcing filler in the photo-curable polymer.

This thesis is devoted to the fabrication of carbon nanotube structures for microelectronics packaging applications with an emphasis on fundamental studies of nanotube growth and assembly, wetting of nanotube structures, and nanotube-based composites. A CVD process is developed that allows controlled growth of a variety of CNT structures, such as CNT films, bundles, and stacks. Use of an Al2O3 support enhances the Fe catalyst activity by increasing the CNT growth rate by nearly two orders of magnitude under the same growth conditions. By introducing a trace amount of weak oxidants into the CVD chamber during CNT growth, aligned CNT ends can be opened and/or functionalized, depending on the selection of oxidants. By varying the growth temperature, CNT growth can be performed in a gas diffusion- or kinetics-controlled regime. To overcome the challenges that impede implementation of CNTs in circuitry, a CNT transfer process was proposed to assemble aligned CNT structures (films, stacks &bundles) at low temperature which ensures compatibility with current microelectronics fabrication sequences and technology. Field emission and electrical testing of the as-assembled CNT devices indicate good electrical contact between CNTs and solder and a very low contact resistance across CNT/solder interfaces. For attachment of CNTs and other applications (e.g. composites), wetting of nanotube structures was studied. Two model surfaces with two-tier scale roughness were fabricated by controlled growth of CNT arrays followed by coating with fluorocarbon layers formed by plasma polymerization to study roughness geometric effects on superhydrophobicity. Due to the hydrophobicity of nanotube structures, electrowetting was investigated to reduce the hydrophobicity of aligned CNTs by controllably reducing the interfacial tension between carbon nanotubes (CNTs) and liquids. Electrowetting can greatly reduce the contact angle of liquids on the surfaces of aligned CNT films. However, contact angle saturation still occurs. Variable frequency microwave (VFM) radiation can greatly improve the CNT/epoxy interfacial bonding strength. Compared to composites cured by thermal heating, VFM-cured composites demonstrate higher CNT/matrix interfacial bonding strength, which is reflected in composite negative thermal expansion. The improved CNT/epoxy interface enhances the thermal conductivity of the composites by 26-30%.

The overall goal of the present research is to provide a computationally based methodology to realize the projected extraordinary properties of Carbon Nanotube (CNT)- reinforced composites and polymeric nanofibers for engineering applications. The discovery of carbon nanotubes (CNT) and its derivatives has led to considerable study both experimentally and computationally as carbon based materials are ideally suited for molecular level building blocks for nanoscale systems. Research in nanomechanics is currently focused on the utilization of CNTs as reinforcements in polymer matrices as CNTs have a very high modulus and are extremely light weight. The nanometer dimension of a CNT and its interaction with a polymer chain requires a study involving the coupling of the length scales. This length scale coupling requires analysis in the molecular and higher order levels. The atomistic interactions of the nanotube are studied using molecular dynamic simulations. The elastic properties of neat nanotube as well as doped nanotube are estimated first. The stability of the nanotube under various conditions is also dealt with in this dissertation. The changes in the elastic stiffness of a nanotube when it is embedded in a composite system are also considered. This type of a study is very unique as it gives information on the effect of surrounding materials on the core nanotube. Various configurations of nanotubes and nanocomposites are analyzed in this dissertation. Polymeric nanofibers are an important component in tissue engineering; however, these nanofibers are found to have a complex internal structure. A computational strategy is developed for the first time in this work, where a combined multiscale approach for the estimation of the elastic properties of nanofibers was carried out. This was achieved by using information from the molecular simulations, micromechanical analysis, and subsequently the continuum chain model, which was developed for rope systems. The continuum chain model is modified using properties of the constituent materials in the mesoscale. The results are found to show excellent correlation with experimental measurements. Finally, the entire atomistic to mesoscale analysis was coupled into the macroscale by mathematical homogenization techniques. Two-scale mathematical homogenization, called asymptotic expansion homogenization (AEH), was used for the estimation of the overall effective properties of the systems being analyzed. This work is unique for the formulation of spectral/hp based higher-order finite element methods with AEH. Various nanocomposite and nanofibrous structures are analyzed using this formulation. In summary, in this dissertation the mechanical characteristics of nanotube based composite systems and polymeric nanofibrous systems are analyzed by a seamless integration of processes at different scales.

The research presented in this dissertation pertains to the evaluation of stiffness of carbon nanotubes (CNTs) in a multiscale framework and modeling of the interfacial mechanical behavior in CNT-polymer nanocomposites. The goal is to study the mechanical behavior of CNTs and CNT-polymer interfaces at the atomic level, and utilize this information to develop predictive capabilities of material behavior at the macroscale. Stiffness of CNTs is analyzed through quantum mechanical (QM) calculations while the CNT-polymer interface is examined using molecular dynamics (MD) simulations. CNT-polymer-matrix composites exhibit promising properties as structural materials and constitutive models are sought to predict their macroscale behavior. The reliability of determining the homogenized response of such materials depends upon the ability to accurately capture the interfacial behavior between the nanotubes and the polymer matrix. In the proposed work, atomistic methods are be used to investigate the behavior of the interface by utilizing appropriately chosen atomistic representative volume elements (RVEs). Atomistic simulations are conducted on the RVEs to study mechanical separation with and without covalent functionalization between the polymeric matrix and two filler materials, namely graphite and a (12,0) Single Wall zig zag CNT. The information obtained from atomistic studies of separation is applicable for higher level length scale models as cohesive zone properties. The results of the present research have been correlated with available experimental data from characterization efforts.

Magnesium alloys have attracted considerable attention owing to its low density of ~1.7 g/cm3. On the other hand, the carbon fiber (CF) reinforced polyether ether ketone (PEEK) polymer composites possess extraordinary specific strength and stiffness along the longitudinal (or fiber) direction. It follows that the combination of Mg/CF/PEEK would offer an alternative in forming a high specific strength and stiffness composite. In the first part of this study, the low density and high performance Mg-based laminated composites were fabricated by means of sandwiching the AZ31 Mg foils with the carbon-fiber/PEEK prepreg through hot pressing. Proper surface treatments of AZ31 sheet using CrO3 base etchants are necessary in order to achieve good interface bonding characteristics. The resulting Mg base laminated composite, with a low density of 1.7 g/cm3, exhibits high modulus of 75 GPa and tensile strength of 932 MPa along the longitudinal direction. The experimentally measured tensile modulus and strength data along both the longitudinal and transverse direction are within 90-100% of the theoretical predictions by rule of mixtures, suggesting that the bonding between layers and the load transfer efficiency are satisfactory. The flexural stress and modulus along the longitudinal direction are 960 MPa and 54.6 GPa, respectively, suggesting a sufficiently high resistance against bending deflection. The peel strengths are about 2.75 and 4.85 N/mm along the longitudinal and transverse directions, respectively, superior to that of the epoxy-resin-adhered and carbon-fiber-reinforced aluminum laminated composites. Polymer nanocomposites have attracted considerable attention during the past decade due to their versatile and extra-ordinary performances. The polymer nanocomposites can be prepared by the well-known sol-gel method. It is well known that PEEK is a good solvent resistant polymer. Hence, it is impossible to fabricate the PEEK nanocomposite by means of sol-gel method. In the second part of this study, the PEEK nanocomposites filled with nano-sized silica or alumina measuring 15-30 nm to 2.5-10 weight percent were fabricated by vacuum hot press molding at 400oC. The resulting nanocomposites with 5-7.5 wt% SiO2 or Al2O3 nanoparticles exhibit the optimum improvement of hardness, elastic modulus, and tensile strength by 20-50%, with the sacrifice of tensile ductility. With no surface modification for the inorganic nanoparticles, the spatial distribution of the nanopartilces appears to be reasonably uniform. There seems no apparent chemical reaction or new phase formation between the nanoparticle and matrix interface. The crystallinity degree and thermal stability of the PEEK resin with the addition of nanopartilces were examined by X-ray diffraction, differential scanning calorimetry, and thermogravity analyzer, and it is found that a slight decrease in crystallinity fraction and a higher degradation temperature would result in as compared with the prestine PEEK.

Polypropylene, PP, based nanocomposites were produced via melt blending method by using twin-screw extrusion in this study. The effects of organoclay type, compatibilizer type, and mixing order of components on the morphology, thermal, mechanical and flow properties of ternary nanocomposites were investigated. Terpolymer of ethylene/butyl acrylate/maleic anhydride, ethylene/methyl acrylate/glycidyl methacrylate, and copolymer of ethylene/glycidyl methacrylate elastomers were used as compatibilizer, whereas Cloisite&reg / 30B, Cloisite&reg / 15A, and Cloisite&reg / 25A were used as organoclay. iv In order to determine the optimum amount of compatibilizer, PP/compatibilizer blends were produced with different compositions. The content of compatibilizer was determined as 5 wt % based on the mechanical tests. Then, ternary nanocomposites were prepared with 5 wt % compatibilizer and 2 wt % organoclay contents. In addition, neat PP and PP/organoclay composites were prepared in order to make comparison. After that, the samples were characterized. According to the XRD analysis, the highest increase in the interlayer spacings of organoclays were observed in the PP/E-MA-GMA/Cloisite&reg / 15A (23%) and PP/E-MA-GMA/ Cloisite&reg / 25A (88.3%) ternary systems. SEM micrograms revealed that compatibilizer E-MA-GMA is the most compatible elastomer with PP. Thus, it was decided to investigate the effect of mixing order on the properties of these nanocomposites with E-MA-GMA. DSC analysis showed that the melting behavior of the nanocomposites does not change significantly with the presence of organoclay and compatibilizer. In addition, compatibilizers and organoclays have no significant nucleation activity in PP. The systems PP/E-MA-GMA/Cloisite&reg / 15A and PP/E-MA-GMA/Cloisite&reg / 25A have the highest improvements according to the results of mechanical tests. The results of mechanical tests showed that the mixing sequence (PEC), in which PP, organoclay and compatibilizer were compounded simultaneously in the first extrusion run, is the best sequence.

ABSTRACT CHARACTERIZATION OF SERPENTINE FILLED POLYPROPYLENE Can, Semra Ph.D., Department of Polymer Science and Technology Supervisor: Prof. Dr. Teoman Tin&ccedil / er March 2008, 158 pages In this study, the aim is to prepare polypropylene (PP)/serpentine composites and study their mechanical, thermal and morphological properties. Another objective is to explore whether it is possible to have PP/serpentine nanocomposites with melt intercalation method by using the advantage of the layer silicate structure of serpentine. The most widely used fillers in PP are talc and mica which belong to the phyllosilicates group of silicate minerals. So far, there has been almost no study employing serpentine as filler in either any polymers or PP, although it also belongs to the same group of minerals as talc and mica. Accordingly, it was planned to divide the work into the study of two groups. In group 1, for the compositions with 2, 5, 10 and 20 wt% serpentine, the particulate filler effects of serpentine both alone and in the presence of surface treatments with hydrochloric acid (HCl) and silane coupling agent (SCA) were investigated. The most impressive results in terms of static and dynamic mechanical properties were achieved with SCA rather than HCl. When the effect of serpentine without any treatment is considered, reinforcing effect of it can easily be observed without deteriorating the composite properties even at high filler loadings. In group 2, the nanofiller effects of serpentine in 2 and 5 wt% filled compositions by modification of both the filler and the matrix were aimed to be examined with melt intercalation method. In addition to HCl and SCA treatments, maleic anhydride grafted polypropylene (PP-g-MA) and quaternary ammonium salt (QAS) of cetyl-trimethyl-ammonium bromide were used as compatibilizer and intercalating agent, respectively. While the amount of QAS was kept constant, different percentages of compatibilizer were employed. The presence of QAS and PP-g-MA further improved the properties with respect to group 1 members. Interestingly, the percentage strain at break values did not decrease as much as group 1 compositions with the same filler content. It can be concluded that partial intercalation of group 2 compositions was achieved, according to the X-ray and TEM results. Keywords: Serpentine, PP/serpentine composites, SCA, PP-g-MA, serpentine nanocomposites