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Surface modification of polystyrene thin films was achieved using a plasma process with reactive gases to form functional groups. Advancing contact angles were measured after modification. Polystyrene surfaces were observed to reach a minimum average wetting contact angle of 7 degrees. The time required to achieve this contact angle decreased significantly by increasing the power of the discharge or by lowering the discharge source closer to the polymer substrate. Characterization studies of power, height, and corona exposure time versus contact angle led to the formation of surface energy gradients across the substrate. Photoluminescent tagging agents were used to quantify the degree of carboxyl modification achieved with water plasma and amine modification achieved with ammonia plasma. AMCA (7-amine-4-methyl coumarin hydrazide) was used to show that surface modification reaches a maximum functionalization before degradation of the polymer substrate occurs with water vapor. A parallel study with OPA (O-phthaldialdehyde) yielded similar results when ammonia was ionized over the surface. Additionally, stable surfaces were created by chemical reaction of zinc acetate with the freshly modified polymer. Zinc sulfide particles were formed within the polymer surface by reaction with hydrogen sulfide gas. Flourescence spectroscopy was used to verify the formation of zinc sulfide. / Master of Science

The effects of fundamental solution parameters including polymer molecular weight, concentration and solvent on electrospinning of polystyrene were investigated. Each parameter was found to play a vital role in determining the morphology of beads and fibers. For dilute to semi-dilute solutions, a wide range of bead structures including wrinkled beads, cups, dishes, and toroids were observed when a volatile solvent, tetrahydrofuran, was used. Various rheological regimes where these structures may be obtained were identified. The morphological transition from bead to fiber was characterized by two critical concentrations, Ci and Cf, at which incipient and complete fibers may be observed respectively. These values were determined as a function of molecular weight. A comparison with the models proposed in the literature indicated that solvent evaporation may play an important role in jet stabilization. The fiber diameter and distribution was found to decrease significantly with molecular weight at the critical concentration, Cf. The use of N,N-dimethylformamide, a solvent with relatively high dielectric constant, also resulted in an appreciable reduction in fiber diameter and improved uniformity. The observation of solution jet evolution during the process with high speed camera (2000 frames/s) indicated that solvents have a significant influence on the jet breakdown behavior. Two types of behavior were identified based on the extent of extensional flow, bending instability, and the number of secondary jets. Solvents with high dielectric constant were found to induce extensive bending instability, which resulted in extremely fine microstructures of electrospun polymer.

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Polystyrene samples prepared in emulsion at 55 C were carefully fractionated. The resulting fractions were in turn fractio­nated, combined in groups having similar intrinsic viscosities, and re-­fractionated. As the intrinsic viscosity of these fractions increased, the value of Huggins' k' in methyl ethyl ketone was found to increase a slightly ( from 0.39 to 0.41). Polystyrene samples prepared in exactly the same way except for the addition of small amounts of divinylbensene, a cross-linking agent, were similarly fractionated. The value of k' in methyl ethyl ketone for these fractions increased considerably (from 0.41 to 0.68) as the intrinsic viscosity increased, even though the amount of divinylbensene added was very small (from 0.003to 0.05%). Relations were then established for these cross-linked fractions between k' and the proportion of divinylbensene present, and between k' and the intrinsic viscosity of the fractions. It was concluded that polystyrene prepared in emulsion at 55 C. is essentially linear in structure, and that the value of Huggins' k* seems to provide a convenient and sensitive test for the presence of any appreciable branching that might occur in polystyrene. / Thesis / Master of Science (MS)

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