In order to understand the fundamental cause of preferential lattice orientations when certain metals are vapor deposited onto oriented semicrystalline polymers, Sn deposited onto various polyolefins was investigated as a function of polymer crystallinity, crystallography, morphology and Sn deposition conditions. Crystallinity is necessary, however, the invariance of the orientations to changes in the polymer crystallography indicates that the orientation of the metal is not due to lattice matching, but the result of artificial epitaxy on anisotropic surface features related to the direction of the chain axis (possibly atomic scale surface steps parallel to the chain axis) and the shape anisotropy of the polymer crystals. Features common to many semicrystalline polymers can thus induce orientations in metal overgrowths. The influence of a spherical external surface constraint on the microphase separation of block copolymers (poly(styrene-co-butadiene) and poly(styrene-co-isoprene)) and block copolymer-polystyrene homopolymer blends was investigated by producing very small droplets of the polymers via an aerosol technique. In microdroplets, compositions which exhibit bulk lamellar, OBDD, cylindrical and spherical morphologies result in concentric packing of lamellae, concentric disordered 'honeycomb-like' layers, layers of curved cylinders and irregularly packed spheres respectively. This constraint changes the magnitude of various contributions to the free energy, the respective roles of which can be better understood by observing which structures are produced. External surface energy is the strongest influence, resulting in the spherical microdroplets with uniform surface coatings of the lower surface free energy diene component. Maintaining preferred separations between adjacent intermaterial dividing surfaces (IMDS), which were approximately equivalent to those in the corresponding bulk structures, was also a dominant factor. Except for spherical microdomains, the observed IMDS exhibit radially dependent shapes and curvatures. Locally this results in additional interfacial area relative to the bulk, but likely provides a minimum in interfacial area given the microdroplet spherical geometry and required separations of adjacent IMDS. The most accommodating factor is the IMDS curvature. Rather than create interfacial area by truncation of the continuous microdomain morphology at the surface of the droplet, the structures curve to fit within the spherical external constraint by adopting radially periodic, concentrically ordered morphologies.

Molecular simulation technique together with spectroscopic methods were utilized to study the phase separation behavior of thermoplastic elastomers. Several kinds of systems were investigated, which included diacetylene-containing polyurethane elastomers, polyurethane elastomers with monodisperse hard segments, and a bio-degradable polyester elastomer. For the semi-rigid segmented polyurethane elastomers, we found that the chain rigidity of hard segment is the dominating factor responsible for their phase separation behavior. Chemical immiscibility, crystallization, and presence of hydrogen bonding are not necessary to drive phase separation even though they can promote it. The phase diagrams for semi-rigid polyurethane elastomers associated with different lengths in hard/soft segments were explicitly calculated using molecular simulation technique based on rod-coil model. It was found that longer hard segment or shorter soft segments have higher degree of phase separation than their counterparts. This result was verified by vibrational spectroscopy. It was also shown that DSC is not appropriate to evaluate the phase composition of polyurethane elastomers. The phase separation kinetics and the ultimate degree of phase separation for ultra-thin films of polyurethane elastomers are different from their bulk forms. Hard segments will also show preferential orientation onto the substrate surface. These are the direct consequence of hard segment chain rigidity effect. All the experimental results were successfully reproduced by Monte Carlo simulation based on rod-coil model. Finally, the phase transformation process and mechanical deformation process of a bio-degradable thermoplastic elastomer, PHO, was investigated by FT-Raman spectroscopy and normal coordinate analysis. The long side-chains of PHO will form more extended conformations when PHO undergoes crystallization. It was also found that the strain-induced crystallization and crystalline break-up are not significant for deformed sample. We proposed that the high permanent tensile set associated with PHO comes from the amorphous part rather than from the crystalline part of the system.

A diglycidylether of bisphenol A, DGEBA, base epoxy resin has been modified with several different types of poly(ether imide)s with the goal of increasing the toughness of this high Tg epoxy system. Initially, Ultem$\sp\circler $ 1000-1000 from GE was blended into Epon 828/DDS. Phase separated systems resulted with a 2.5-fold increase in the fracture energy over the neat epoxy resin (676 J/m$\sp2$ vs. 265 J/m$\sp2).$ As seen under the SEM, the included phase pulled out of the continuous phase, indicating poor adhesion between the two phases. Next an amine terminated poly(ether imide), ATPEI, of Mn equal to 8600 was reacted into the same epoxy resin system. There was no increase in the fracture energy with the addition of the ATPEI except at the 40 weight percent loading level. At this level, the fracture energy was comparable to that of the 40% Ultem$\sp\circler$/E828/DDS (700 J/m$\sp2).$ Phase separation was not observed in the TEM above 10 weight percent of the ATPEI in the E828/DDS. A mix of the Ultem$\sp\circler$ and the ATPEI were added to the epoxy resin with favorable results. Phase separation was present. Good adhesion between the phases was evident. And at 20 weight percent, the mixed PEI modified E828/DDS had a higher fracture energy than either of the other two systems investigated previously in this study (409 J/m$\sp2$ for the mix vs. 176 J/m$\sp2$ for the ATPEI and 353 J/m$\sp2$ for the Ultem$\sp\circler).$ Finally, an amine terminated poly(ether imide) with Mn equal to 25,500 was reacted into the same epoxy resin. The fracture energy at 20 weight percent was higher than any of the systems studied previously (451 J/m$\sp2$ vs. 409 J/m$\sp2$ for the mixed PEI modified system). Phase separated morphologies occurred at lower loading levels than anticipated-co-continuous at 20% and phase inverted at 30%. In all cases the Tg's remained above 200$\sp\circ$C.

The three projects, chemical modification (Chapter 1), layer-by-layer deposition (Chapter 2), and surface reconstruction (Chapter 3), that constitute this Ph.D. thesis are closely related in their overall objectives: using polymer surface modification to manipulate microscopic surface structures and control macroscopic properties. Alcohol functionality can be introduced to the surface of poly(ethylene terephthalate) (PET) using either reduction or glycolysis; both of which cleave the PET chain. Both of these modified surfaces (PET-OH$\rm\sp{R}$ and PET-OH$\rm\sp{G})$ and hydrolyzed PET (PET-OH/COOH) can be prepared using conditions that optimize surface functional group concentration, but minimize sample degradation. The surface alcohol density is higher on PET-OH$\rm\sp{G}$ than on PET-OH$\rm\sp{R}$ by a factor of $\sim$2. The concentration of alcohols on reduced surfaces is increased by solvent annealing of the PET film prior to reduction. Reactivities of PET-OH$\rm\sp{R}$ and PET-OH$\rm\sp{G}$ samples were assessed and compared. Layer-by-layer deposition of polyelectrolytes (poly(allylamine hydrochloride)) and poly(sodium styrenesulfonate)) has been used to build up multilayer films on three organic polymer substrates: PET, PET-CO$\sb2\sp-$ and PET-NH$\sb3\sp+.$ XPS and contact angle data indicate that the layers are stratified and the wettability of the multilayer assemblies is largely controlled by the identity of the outermost polyelectrolyte layer. The layer thickness and the stoichiometry of the deposition process (ammonium ion:sulfonate ion ratio) are affected by the substrate surface chemistry and can be controlled by adjusting the ionic strength of the polyelectrolyte solutions. Peel tests indicate that the multilayer assemblies show good mechanical integrity. A perfluorohexylated-C$\sb{60}$ (fullerene) was prepared and its surface activity and mobility were studied as a function of bulk concentration, annealing temperature, and annealing time in a polymer matrix (polystyrene). Perfluorohexylated-C$\sb{60}$ is extremely surface-active in the polystyrene matrix and occupies 95%-85% of the outermost 10 A-40 A (XPS results), and renders a surface that is similar to a monolayer containing -CF$\sb3$ groups (hexadecane contact angle data). Surface reconstruction studies were carried out via either spin-casting or transferring a free standing polystyrene film over the composite materials (the surface-active agent and polystyrene). Both approaches show similar behavior of migration of perfluorohexylated-C$\sb{60}$ from the bulk to the surface.

The addition of low levels of polyaspartate to a supersaturated calcium carbonate (CaCO$\sb3$) solution leads to unusual morphologies in the inorganic phase. Spherulitic vaterite aggregates with helical protrusions, and distorted calcite crystals that contain spiral pits, have been produced. The helical particles are coated with an inorganic membrane that appears to be responsible for the helical twist. The polymer also causes deposition of thin CaCO$\sb3$ tablets and films on the glass substrate. Two distinct types of films are deposited; the first is a mosaic of calcite crystals, and the second is spherulitic vaterite. In situ observations of the crystallization reaction have determined that the thin-film morphology is a result of the phase separation of a hydrated CaCO$\sb3$/polymer liquid-precursor, whereby accumulation of isotropic droplets creates a coating on the substrate, and subsequent dehydration and crystallization yields birefringent CaCO$\sb3$ films. During the amorphous to crystalline transition, incremental growth steps lead to "transition bars" and sectored calcite tablets. This in vitro system was originally modeled after certain aspects of CaCO$\sb3$ biomineralization, in which the soluble proteins extracted from biominerals tend to have high levels of aspartic acid residues. Based on the similarities between features exhibited by the products of this system and those in biominerals, an argument has been presented to suggest that this polymer-induced liquid-precursor (PILP) process is involved in the morphogenesis of CaCO$\sb3$ biominerals. These features include the following: thin CaCO$\sb3$ tablets that grow laterally; tablets that express unstable crystallographic faces; non-faceted single crystals with curved surfaces; spatially-delineated single crystals; sectored calcite tablets; hollow-shell spheres; calcium carbonate cements; and magnesium-bearing calcites. This work has demonstrated that a means of morphological control can be accomplished through non-specific organic/inorganic interactions, whereby the polyelectrolyte transforms the solution crystallization to a solidification process. Not only are such findings of significance to the field of biomineralization, but a better understanding of the interactions between polymers and inorganic materials may be expected to lead to new strategies for crystal and particle engineering.

This dissertation investigates the elastic constants of the polypropylene (PP) film, the radial and circumferential stress states of the layers in the wound roll and the influence of compressive stress on the dielectric breakdown of the metalized polypropylene film. The metalized polypropylene film was mechanically and thermally characterized to determine 7 of its 9 elastic constants and 3 linear coefficients of thermal expansion. The results show that the in-plane tensile moduli (E$\sb{11}$ = 2.7 GPa, E$\sb{22}$ = 5.7 GPa) of the film are quite different and smaller than the out-of-plane modulus (E$\sb{33}$ = 13.0 GPa) of the film. Similarly, the out-of-plane thermal expansion coefficient (CTE) of the film is much larger than the in-plane CTE ($\alpha\sb3 \approx$ 10 $\alpha\sb2$). This large anisotropy in the moduli and the expansion coefficients will influence the winding and thermal stresses generated in the wound rolls. The radial and circumferential stresses in the layers of the wound roll were evaluated using the elastic constants of the film obtained in chapter 2. Expressions were derived to determine the influence of elastic constants of the film and the core on the radial and circumferential stresses in the roll. Stresses generated due to the thermal expansion of the assembly during operating temperature changes were also evaluated. The analysis showed that because of the applied winding stress, the layers near the core have compressive radial stresses. The circumferential stresses in the layers also decrease, becoming compressive in some cases for the layers near the core. The influence of the interfacial pressure (compressive stress) on the dielectric behavior of the film was the subject of chapter 4. Applying interfacial pressure, parallel to the electric field, changes the apparent dielectric breakdown strength of the film. At pressures of 0-4 MPa, the PP film has a catastrophic failure at 40% lower potential than its intrinsic breakdown potential. However, for slightly higher pressures ($\approx$5 MPa) the dielectric recovers the loss and can sustain potentials much higher than its intrinsic breakdown potential. The metalized PP films have a surface roughness imposed upon them to increase the interlayer frictive forces. This minimizes the axial slippage of layers in the roll. The surface roughness leads to entrapment of air (voids) within the layers of the roll. The air pockets are harmful for the film since they lead to premature failure of the dielectric. The capacitors are prepared by encapsulating the wound PP roll in a PP case surrounded by a dielectric fluid. At temperatures above 80$\sp\circ$C, the dielectric fluid diffuses through the PP containers. (Abstract shortened by UMI.)

The addition of a low concentration of dissolved high molecular weight polymer can greatly modify the rheological properties of a simple. Many of the modification can be attributed to flow-induced departures of the average chain conformation from its isotropic value at quiescence. The statistical deformation and orientation of polymer chains in flow has been predicted by various molecular models, but these predictions have not been adequately tested. This research provides an important molecular-level understanding of chain conformation in dilute solutions undergoing elongational flow; the work applies light scattering and birefringence techniques to probe chain conformation in situ. We have investigated the influences of chain stiffness and solvent quality on the chain conformations produced in and around the stagnation point of opposed jet flow. By light scattering, the average radius of gyration of the examined polymers has been probed both parallel and perpendicular to the stretching axis for flows of various strength. Flexible polymers are not deformed affinely under any circumstances, with statistical coil deformation falling much below this limit. Although solvent quality has little impact, slightly more coil deformation is observed in a theta solvent than in a good one. For a relatively stiff polymer of approximately 15 persistence lengths, the behavior of chain deformation/orientation in opposed jet flow is different; Because less strain is required to orient a stiff polymer than to deform an analogous flexible polymer, conformation changes are less localized, extending outside the region between the jets. Nevertheless, the overall conformational changes remain less than that predicted by a rod model.

A complete characterization of the mechanical, thermal and physical properties of acrylic-based latex blends films and a thermodynamic analysis of their deformation is presented in this study. These blends are composed of a glassy poly(methyl methacrylate-co-ethyl acrylate) $\rm(T\sb{g}=45\sp\circ$C), and a rubbery poly(methyl methacrylate-co-butyl acrylate) $\rm(T\sb{g}={-}5\sp\circ$C). Blend films are prepared, in different proportions of the two copolymers, by drying at temperatures high enough to ensure complete coalescence of the latex particles. Thermo-mechanical characterization provides evidence for the phase separation of the blend components by the existence of two distinct glass transitions. Effective blend moduli and Poisson's ratios exhibit sigmodial shaped profiles with composition, indicating the transformation of a continuous rubbery phase, with dispersions of the glassy phase, to a continuous glassy phase, with dispersions of a rubbery phase. Although not precisely measured, a range of 30-40% hard phase in the blend is identified as the interval of this transformation, bridged by a co-continuous morphology. A large amount of water is absorbed by these blends, which turns them white and opaque from their transparent dry state. The impact on mechanical properties is relatively minor as absorbed water is located in separate domains. Redrying at ${-}70\sp\circ$C preserves this whiteness, while redrying at elevated temperatures returns the blends to their original transparency. A qualitative model associates the absorbed water molecules with phase separated domains of residual surfactant within the dry films. Deformation calorimetry of these blends measures the work, heat and change in internal energy of isothermal deformation. An optimal combination of stiffness and extensibility maximizes the blend toughness by a synergistic distribution of energy between the two phases in their respective energy absorbing and energy dissipating mechanisms. The work of deformation increases at higher strain rates but the change in internal energy over fixed extensions remains constant. The additional work, consequently, is dissipated as heat by rate-dependent viscous effects. In summary, these blends provide an excellent model system to study the energy balance of deformation of two phase systems. The results highlight the need of a shift in focus when designing blends for optimum toughness and stiffness, by providing for a simultaneous maximization of energy dissipation and absorption.

This thesis describes investigations into the mechanical and thermal characteristics of amorphous polymeric materials by structural changes on the molecular and the microscopic scale. On the molecular scale, the structure of a cross-linked polymeric material is controlled by changes in the molecular weight between cross-links, cross-link functionality, and chain stiffness. With control of the network structure, an expansive range of mechanical and thermal characteristics is possible. These properties range from intrinsic properties, such as the glass transition temperature, to performance properties, such as impact behavior. Relationships between the network structure and measured properties are established by the use of a variety of theories from rubber elasticity to free volume. Relationships are also established between the various measured properties through solid and fracture mechanics. The introduction of soft rubbery particles on the microscopic scale into a glassy polymeric matrix is commonly employed to create a tougher material. Despite the prevalent use, the mechanisms and sequence of mechanisms of toughening are poorly understood. The mechanisms and sequence of mechanisms are elucidated in this investigation through the use of unique mechanical tests and materials with favorable properties. The unique mechanical tests in this investigation include tensile dilatometry and a multi-axial stress state test. The multi-axial stress state test, which allows independent control of the dilational and deviatoric stresses of a material between uniaxial compression and equal biaxial tension, consists of a uniaxially loaded and pressurized thin walled hollow cylinder. The materials include liquid rubber modified epoxies, voided epoxies, and core-shell rubber modified polyvinylchloride. The voided epoxy material separates the matrix contributions from those of the rubbery phase, while the core-shell rubber modified polyvinylchloride provides optical verification of rubber particle cavitation. By combined use of these materials and the unique mechanical tests, the mechanics of rubber toughening are evaluated.

This dissertation describes the use of supercritical carbon dioxide (SC CO2) as an aid in fabricating polymer/polymer composites. Monomers and initiators were infused into solid polymer substrates using SC CO 2. The monomers were subsequently polymerized within the substrates to form composites. CO2 swells the polymer substrate and increases the diffusively of reactants within the substrate. The solvent strength of SC CO2 is tunable allowing control over the degree of swelling and over the partitioning behavior of the reactants. CO2 can be easily removed from the final products. First, polystyrene/polyethylene bulk composites were investigated. Styrene and a radical initiator were infused into and reacted throughout the bulk of polyethylene substrates. The composite composition was controlled by controlling infusion time, reaction time and partitioning conditions. Characterization of the composites showed that the crystalline domains of the polyethylene were unaffected. Styrene infused into and polymerized within only the amorphous domains of polyethylene. Polyethylene and polystyrene are immiscible; the semicrystalline nature of polyethylene frustrated gross phase separation of the polystyrene. The resulting “kinetically trapped” phase morphology gave the composites interesting mechanical properties. The phase morphology was characterized, and the polystyrene was found to reside within the interlamellar regions and the centers of the polyethylene spherulites. The polystyrene formed a continuous “scaffold” that reinforced the polyethylene. The reinforcement provided efficient and dramatic improvement in the composite modulus and strength. However, the composites fracture toughness decreased with increasing polystyrene content. The fracture behavior was correlated to the microstructural damage mechanisms in the composites. Second, surface composites were investigated. Using a two-stage process, ethyl 2-cyanoacrylate (ECA) monomer was anionically polymerized in the surface regions of poly(tetrafluoroethylene-co-hexafluoropropylene) substrates. An investigation of the anionic polymerization of ECA in CO 2 established the viability of that system. The composite fabrication process involved first infusing a basic initiator into the substrate using SC CO2. In the second step, monomer was introduced (using SC CO 2) to the substrate. As the monomer absorbed into the initiator-containing substrate, it would polymerize. The composite surfaces were characterized using surface-sensitive techniques. The mechanical performance of the composites were determined by measuring the adhesive fracture toughness.