Solute Probe Diffusion in Aqueous Solutions of Poly(vinyl alcohol) As Studied by Pulsed-Gradient Spin-Echo NMR Spectroscopy

Abstract

A pulsed-gradient spin-echo NMR technique was used to measure the self-diffusion coefficients (D) of water and several different solute probe molecules in ternary poly(vinyl alcohol) (PVA)−water−solute systems, as a function of PVA concentration (up to 0.35 g/mL). The self-diffusion coefficient of water decreased with increasing PVA concentration, in a manner consistent with the Mackie−Meares obstruction effect model, and was independent of the polymer molecular weight, degree of hydrolysis, or the presence of the solute probes. The self-diffusion coefficients of the solute probes (methanol, tert-butanol, formamide, acetic acid, trimethylamine, tetramethylammonium cation, and poly(ethylene glycol) of molecular weight 400 and 4000) decreased with increasing PVA concentration and increasing probe size. The free volume theory could be used to describe the self-diffusion of solute probes only. The dependence of all the probe self-diffusion coefficients on polymer concentration could also be described using a ...