Studies of Polymer Structure at Solid-Liquid Interfaces Using IR-Visible Sum-Frequency Generation Spectroscopy

Hasnain Rangwalla, University of Akron

This talk will focus on the structure of polymer molecules at the interface between the bulk phases of a solid and a liquid that are immiscible. In particular, two such interfaces will be discussed: 1) a polymer.water interface for an alkyl-side-chain comb polymer [poly(vinyl n-octadecyl carbamate-co-vinyl acetate) (PVNODC)], and 2) adsorption of poly(methyl methacrylate) (PMMA) on sapphire substrates from a dilute solution of PMMA in carbon tetrachloride. The main experimental technique used to probe these interfaces is the nonlinear vibrational spectroscopy of IR-visible sum-frequency generation (SFS). For 1), SFS spectra indicate that in contact with water, the PVNODC surface is heterogeneous (having areas of differing surface energies). This evidence of surface heterogeneity supports the hysteresis observed in the advancing and receding contact angles of the polymer surface with water. Additionally, observing the structural changes of the PVNODC-water interface at elevated temperatures provides molecular-level insights in the reduction of wettability of the PVNODC surface. For 2), the adsorbed chains appear to be in a flat conformation, which is not affected by changes in the solvent quality brought about by crossing the theta temperature.

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