Diffusion of Binary Non-Solvent Mixtures in Polymers: Aqueous Ethanol Solutions in Poly(Vinyl Acetate)

Abstract

The diffusion of binary non-solvent mixtures of ethanol and deuterium oxide (D₂O) into poly(vinyl acetate) (PVAc) was studied by FT-IR imaging. Initial diffusion rates were calculated for all mixtures from the concentration profiles, and a positive deviation from ideal behavior was observed; higher initial diffusion rates and greater degrees of swelling were observed for the solvent mixtures than for the pure liquids. PVAc swells to various extents in pure deuterium oxide, 20, 30, and 40 weight percent (wt %) ethanol, and pure ethanol. Dissolution of PVAc occurs for 50, 60, 70, 80, 90, and 95 wt % ethanol–water mixtures. The lowest initial diffusion rate occurred for pure deuterium oxide and the highest initial rate for 80 wt % ethanol. The spectral data suggest that ethanol and water form a complex that solvates PVAc more effectively than either pure liquid. Furthermore, the data indicate that sufficient quantities of this complex for effective dissolution are formed above 40 wt % ethanol, while optimum quantities occur between 70 and 90 wt % (50 to 80 mole %) ethanol.