This dissertation presents a procedure to fully characterize the thermal and elastic constants for orthotropic as well as transversely isotropic polymeric films and coatings. Linear elasticity theory was used to describe the response of the studied materials. All of the Young's moduli, shear moduli, Poisson's ratios, and the thermal expansion coefficients (TEC) of the materials were determined. The structure and properties of films or coatings being processed under different conditions were studied, and the relationship of process-structure-property was investigated to instruct the manufacturing of films and coatings with high quality. Sequentially biaxially stretched PET films that were heat set at different temperatures were characterized in the first project. The compliance matrices of the two studied films were determined by special techniques such as vibrational holographic interferometry, pressure-volume-temperature (PVT) apparatus, high-pressure gas dilatometry, and torsion pendulum. The effects of heat treatments, including heat setting and annealing, on the calorimetric properties, the iso-strain force temperature test (IFTT) results, the thermal expansion and shrinkage behavior, and the structure and orientation of the molecules were also studied. In the second project, a new epoxy based negative photoresist, SU8, was investigated. The influence of three important processing parameters: the baking time, baking temperature, and UV exposure dose, on the thermal and mechanical properties of the resultant coatings were studied in detail, SU8 coatings that were processed or post treated under ten different conditions by Hewlett-Packard Company were characterized. The residual stresses generated during processing and post treatments were measured by holography technique, and the moisture absorption of the coatings was also studied. In the last project, the volume-pressure behavior of porous silica gels with different properties was studied using the PVT apparatus. Mercury as well as water was used as the confining liquid for the PVT measurements. The intrusion pressure, extrusion pressure, and the hysteresis between the pressurizing and depressurizing process were all obtained. Some porous polymeric materials, such as porous PS and SAN, were also studied.

Chapter One describes the use of supercritical carbon dioxide (scCO 2) as an agent for the conduction of silane chemistry at the buried interfaces between silicon wafers and spin-cast polymer thin films. Above the critical point of CO2, organosilanes react with surface silanols at the SiO2/polystyrene interface to form a monolayer quantitatively. The ability to do chemistry selectively at weak interfaces offers the potential to rehabilitate coatings and composites. Chapter Two describes the chemical surface modification of nylon 6/6. Several methods were developed for introducing reactive functional groups to nylon 6/6 surfaces using amide-selective reagents at the solid polymer - solution interface. Hydrolysis of nylon 6/6 yields a surface mixture of amine and carboxylic acid groups. Different alkylating agents, including 2-bromoethylamine, allyl bromide, 1,4-dibromobutane and 4-(trifluoromethyl)benzyl bromide were studied. Reaction of the activated amides with 3-glycidoxypropyltriethoxysilane offers a pathway for generating surfaces with silica-like reactivity. The enrichment of nylon 6/6 with amine functional groups greatly enhances the electroless deposition of gold. Equally important is the ability to generate surface structures at the nanometer scale in a controlled fashion. Chapter Three and Chapter Four describe the generation of silicon dioxide (SiO2) nanostructures on silicon wafers using both an organosilane monolayer and a block copolymer thin film as templates, respectively. The resulting surfaces exhibit controlled variation of roughness at the nanometer scale. Contact angle analysis indicates that the effect of nanoscale roughness on wettability is important. Nanoporous films generated from asymmetric block copolymers of styrene and methyl methacrylate (P(S-b-MMA)) were used as scaffolds to define an ordered array of nanoscopic reaction vessels. Nanoscopic posts of silicon oxide on silicon wafers were produced within the pores defined by the crosslinked matrix. Reactive ion etching selectively removed the organic matrix, leaving free-standing silicon dioxide posts on silicon wafers. Chapter Five describes the examination of the adsorption behavior of different proteins (albumin, lysozyme and collagen) toward surfaces that exhibit nanoscale features. (Abstract shortened by UMI.)

In order to better understand structure-property relationships, semi-crystalline polymers were synthesized, and the influence of hydrogen-bonds, heteroatoms, and uniformed lamellar thickness were examined. Literature procedures were modified, optimized, and then used to synthesize long-chain α,ω-diols containing up to 46 consecutive methylene groups. Melt polyadditions of these diols with short, aliphatic α,ω-diisocyanates produced a series of polyethylene-like polyurethanes whose hydrogen-bonding densities were systematically decreased. The hydrogen-bonds (or perturbations) were located at regular and controlled distances. These model, polyethylene-like polymers were characterized in order to determine the influence of the perturbations to the aliphatic backbone on the physical, thermal, and morphological properties of these polymers. The increasingly long-chain polyurethanes displayed physical and thermal characteristics (including melting point, lamellar stacking periodicity, and solubility) typical of polyethylene despite the presence of hydrogen-bonding. Crystallization studies showed that, although diluted, hydrogen-bonding still controlled the crystallization process of these polyethylene-like polymers. This resulted in analogous crystal structures and morphologies as polyamides and polyurethanes containing higher hydrogen-bonding densities. The effect of further perturbations, caused by heteroatoms on the aliphatic backbone, where also investigated with an emphasis on the resulting thermal properties of the polymers. The heteroatoms (oxygen and sulfur) caused a decrease in the melting temperature of the polymers without affecting the decomposition temperature or crystal structure. Ongoing research focuses on chemically controlling the lamellar thickness in order to engineer polyethylene-like crystals with hydrogen-bonding sites on the surface.

A novel process for discontinuous deformation in perfectly elastic materials is established in the first part of this two-part thesis. A discontinuous deformation for an elastic material will involve a “jump” in stretch from one state to another. In such a process, it is established that the work per unit volume of the elastomer required to perform the stretch will be greater than the corresponding area under the stress-strain curve for loading and will depend only upon the end states of deformation. The important implication of this analysis is that a cyclic process of discontinuous deformation will involve heat build-up and dissipation due to a difference between the work required to stretch and the work recovered on contraction. Experimental demonstrations indicate a large amount of heat build-up in a rubber belt that is subjected to cyclic deformation involving discontinuities. Elastomers have tremendous strain energy potential. However, in order to utilize this potential, losses associated with discontinuities should be minimized. This research sheds light on how that can be achieved by performing the stretch and the contraction process in as many small steps as possible. The second part of this thesis describes efforts to understand the phenomenon of environmental stress cracking (ESC) in polycarbonate. Environmental stress crazing or cracking is the failure of inherently ductile polymers under the combined effects of stresses and solvent environments. Polycarbonate is studied under a variety of environmental conditions in this research. Thermodynamics of the system, effects of residual latent energy and orientation in the polymer, tendency of the environmental agent to swell the polymer and the nature of morphological damage are some of the effects characterized. Interestingly, the formation of micro-cracks rather than crazes is observed in the systems studied. Under commensurate exposure conditions over different stress states, it appears that the component of stress normal to the direction of cracks determines the crack patterns. Constant hydrostatic stress, as predicted by the modified Flory-Huggins equation, is not observed to have an influence. Experimental findings indicate that ESC is a stochastic process, influenced by a surface flaw induced mechanism.

Seminconducting nanoparticles, also known as quantum dots or quantum rods depending on the shape, have unique optical and electronic properties. Polymers, on the other hand, have excellent processing properties. Therefore, it is desirable, in many cases, to integrate nanoparticles in polymers. The surface chemistry of nanoparticles is the key for them to be integrated into a polymer matrix in a controlled way. Nanoparticles are generally covered with alkyl ligands directly from typical synthetic procedures and surface modification is required to provide them with desired surface chemistry. First, water-soluble cadmium selenide (CdSe) nanoparticles and nanorods were made by modifying nanoparticle surfaces with charged ligands or poly(ethylene oxide) ligands and these water-soluble nanoparticles were selectively assembled into the holes and channels of nanotemplates fabricated from diblock copolymers. Second, nanoparticle surfaces were functionalized with ligands (e.g., poly(ethylene oxide)) that were compatible with a polymer matrix (e.g., poly(methyl methacylate)) such that the nanoparticles were well-dispersed into the polymer matrix and a self-healing bilayer material was developed using these well-dispersed nanoparticle-filled polymer matrix. Third, CdSe nanorods were oriented normal to a substrate in regioregular poly(3-hexylthiophene) matrix. However, the oriented CdSe nanorods were found to phase separate from poly(3-hexylthiophene) matrix. Then, chemistry was developed to synthesize vinyl-terminated poly(3-hexylthiophene) and Heck coupling was used to attach vinyl-terminated poly(3-hexylthiophene) (hole transporting material) onto aryl bromide-covered CdSe nanorods (electron transporting material) for photovoltaic applications. The poly(3-hexylthiophene) functionalized CdSe nanorods showed the expected charge transfer between these two semiconductors, a prerequisite for an efficient photovoltaic material. Stimulated by the design of poly(3-hexylthiophene)-functionalized CdSe nanorods, donor-acceptor poly(3-hexylthiophene)-b-poly(perylene diimide acrylate) block copolymer was synthesized. This block copolymer also showed photoluminescence quenching in solid states.

Ionic complexes of polyelectrolytes with molecules of opposite polarity are ubiquitous and important in both nature and synthetic arenas. DNA condensation by multivalent counterions enables long stiff DNA chains to be condensed for storage in small volumes such as nuclei and virus capsids. Applications of synthetic polyelectrolytes as complexation (or encapsulation) agents for proteins and nucleic acids have proliferated in recent decades in quest for more effective drug and gene delivery. This dissertation investigated several aspects of the structure and thermodynamics of polyelectrolyte complexes, using both computer simulation and experimental characterization. We applied a Langevin dynamic simulation to the complexation of a semiflexible polyelectrolyte with multivalent counterions. The central issue is the interplay of polyelectrolyte intrinsic stiffness and counterion valency in shaping ordered structures such as toroid and folded-chain bundles as seen in DNA condensation studies. Also in accordance with experiments, our simulation has uncovered multiple kinetic pathways leading from disordered to ordered states. The simulation is extended to the complexation by polyelectrolytes of opposite polarities. The major issue is to differentiate enthalpic and entropic contributions to complexation in both weak and strong electrostatic coupling systems. Two regimes of complexation are delineated: (1) enthalpy-driven in weak polyelectrolytes where mutual Coulombic attraction between polycations and polyanions drives complexation; (2) entropy-driven in strong polyelectrolytes where although polycations and polyanions still attract each other strongly, a large entropy gain from releasing condensed counterions during complexation becomes dominant. We have also studied conformational properties of comb polyelectrolytes and their complexes. Static and dynamic light scattering studies reveal that polycyclooctene-g-pentalysine adopts an extended rodlike conformation due to strong electrostatic repulsion of the oligolysine side chains. It is demonstrated that rigid polycyclooctene-g-pentalysine could self-assemble with dsDNA to generate stable nanosized particles whose dimension can be finely adjusted by pH and polyelectrolyte/DNA mixing ratio. In conjunction with experiments, we also set forth to simulate electrostatic-mediated rigidity of comb polyelectrolytes. Interestingly, comb polyelectrolytes of greatest rigidity are those grafted with modestly charged side chains (like oligolysines) which could maximize inter-side chain repulsion without significant disruption from the counterions.

The phase behavior and properties of strongly segregated crystalline-amorphous diblock copolymers with rubbery amorphous block were investigated. For low crystallinity PE-containing diblock copolymers, well-ordered microphase separated morphology was observed in the melt-state. Upon crystallization, in most cases, two-dimensional crystallization confined within the microphase-separated microdomains was observed with retention of the microphase-separated morphology formed in the melt-state. However, the crystallization temperature was found to have significant effect on morphology. Both the extent of microdomain confinement on crystallization and the crystalline chain orientation inside the microdomain were observed to be crystallization temperature dependent. Utilizing the unique properties of crystalline polymers, a novel method for preparing photonic band gap crystals was developed based on self-assembly behavior of crystalline block copolymers. It opened up avenues to fabricate novel polymeric optical devices. For high crystallinity PEO containing diblock copolymers, TEM coupled with electron diffraction revealed a microphase separated, alternating lamellar morphology with PEO crystalline chains oriented perpendicular to the microdomain interface regardless of the crystallization temperature. As suggested from optical microscopy and TEM experiments, the melt microphase separated morphology acted as template for crystallization. In contrast to the extended chain crystals always preferred by homopolymers, folded chain crystals were formed for crystalline/amorphous block copolymers at equilibrium state. The results were interpreted based on thermodynamic consideration of the system. The morphology of block copolymers where both block were crystalline was also investigated in this study. The effect of soft and rigid confinement on crystallization in P(E-b-EO), a crystalline/crystalline block copolymer, was evaluated. The morphological evolution of crystalline block copolymers in thin films was studied. Multiple parallel layers of crystalline PEO were found to be in perfect orientational registry even though they were separated by approximately 10 nm thick layers of amorphous polymer.

Described here are two methods for functionalizing the surfaces of multiple materials. It is often useful to modify only the surface of a material. Surface modifications described here concentrate on the application of ceramics such as diamond-like carbon (DLC) and silicon carbide as well as surface initiated polymerization from either anionic or catalytic mechanisms. The syntheses of soluble preceramic polymers to DLC are shown. The synthesis of poly(hydridocarbyne) is simple and gives high yields. The polymer is soluble in tetrahydrofuran and other common organic solvents, which enables films and moldings to be formed from it. Ceramic resulting from the pyrolysis of poly(hydridocarbyne) is the purest DLC formed from any polymeric precursor found in the literature. The DLC ceramic films produced from the poly(hydridocarbyne) precursor are extremely smooth, continuous and impurity free. This polymeric precursor offers a potential alternative to the CVD process for making DLC films. In the current work a synthesis for high molecular weight precursor for SiC has been demonstrated. The synthesis of poly(methylsilyne) (PMSi) is a simple synthesis and gives high yields. The polymer is non-pyrophoric, which is unique among high yield stoichiometric SiC preceramic polymers. The polymer is also soluble in tetrahydrofuran and other common organic solvents. The ceramic resulting from the pyrolysis of PMSi is the closest to stoichiometric SiC that has been obtained from any polymeric precursor. The SiC ceramic film produced from PMSi is more continuous, defect-free and smoother than any reported silicon carbide film. A novel method of functionalizing metal surfaces with surface-initiated grafted polymer films is reported. This method uses 3-bromopropyltrichlorosilane to form a silane layer on the native oxide of a variety of metals, which is attached to the oxide by a degree of surface attachment. The bromopropyl group is converted to a surface-bound lithium alkyl by reaction with lithium di-t-butylbiphenyl (LiDBB), generating a surface-bound site for anionic initiation of polymerization. Polymer films of poly(methylmethacrylate) have been generated on copper, nickel, tungsten, brass, steel, titanium, and aluminum metal surfaces. These films range from 1-2 microns thickness and are robust and adhere well to the substrate surface. A degree of surface attachment of the polymer layer is seen through its robust adhesion to the substrate. Alternatively, polymer films of polyethylene and poly(methylmethacrylate) were generated on silicon and copper wafers using an organometallic initiator.

This thesis is divided in two independent parts. The work described in the first part involves the development of a new system for the synthesis of organic-inorganic hybrids utilizing ozone and silicon chemistry. Polydimethylsiloxane proved to be resistant to ozone over 24 hr. This indicates that the Si-CH$\sb3$ group is resistant to ozone attack. Investigation of the ozonization of phenyl-containing siloxane copolymers (PSX-80) suggested that ozone attack takes place in two steps. In the first step ozone attacks and breaks the aromatic ring attached to silicon and subsequently the weakened Si-C moiety is cleaved to form the siloxane group. Mixtures of phenylsilane with several hydrosiloxanes having variable amount of hydride content were oxidized in order to effect hybridization. Ozonization of phenylsilane (PhSiH$\sb3)$ generates the inorganic component of the hybrid material, while the organic constituent is due to the siloxane polymers. The ability to vary the hydride concentration on the polymer backbone enables the control of the inorganic content of the hybrid. The hybrid materials exhibit low surface polarity and high thermal stability which depends on the inorganic content of the material. Application of ozonized hydrosiloxanes as coatings for cellulose paper was investigated. Contact angle and tensile testing data suggested that even the smallest amount of silicone coating dramatically affects the surface behavior and the wet strength of the cellulose paper. In the second part of this document the mechanical properties of oriented elastomers at low temperatures are investigated. A dramatic increase, to the levels of high performance plastics, was observed in the modulus and strength of the oriented elastomers ($\sim$32 GPa, 1.2 GPa). A polyetherimide-b-polystyrene ABA type block copolymer was synthesized and its properties were examined. The weak and brittle behavior of the copolymer indicated that a higher molecular weight soft segment (polystyrene) is necessary in order to perform tensile testing in the elongated state.

In this research, we develop models to describe the impact of nanostructures on the elastic deformation and failure of polymer thin films. First, we use polystyrene-b-poly(2-vinyl-pyridine) as a model material to investigate the effect of nanodomains and surface terracing on the crazing process. Here, we find that well-aligned lamellar domains can alter the extension ratio of craze fibrils and delay craze growth rate. Additionally, nanoscaled surface terraces impede the craze initiation and significantly decrease the failure strain of polymer thin films. To investigate the impact of inorganic nanodomains on the crazing process, we use a model and well-dispersed nanocomposite of polystyrene blended with surface modified cadmium selenide nanoparticles (diameter ∼3.5 nm). With this material design, enthalpic interaction is minimized and entropic interaction dominates the mechanical properties. Due to high surface-to-volume ratio of nanoparticles and nanoparticle-polymer entropic interaction, the elastic modulus of our nanocomposites decreases as a function of volume fraction of nanoparticles (V). During craze formation and growth, nanoparticles undergo three stages of rearrangement: (1) alignment along the precraze, (2) expulsion from craze fibrils, and (3) assembly into clusters entrapped among craze fibrils. This entropically-driven rearrangement leads to the altered craze morphology and an increase in failure strain by 60% at an optimal V. This optimal volume fraction is related to the balance of two mechanisms: (1) the decrease in the volume fraction of cross-tie fibrils, and (2) the decrease in extensibility of the craze. In the last part of this research project, larger nanoparticles (diameter is ∼6.0 nm) are used to increase nanoparticle-polymer entropic interaction. Here, we find that nanoparticles segregate to the film surface during the film casting process on the substrate. This entropically-driven segregated layer of nanoparticles leads to a significant drop in the elastic modulus at very low V (0.2%) and an increase in failure strain by 100% in an optimal V.