Solute diffusion in hydrated polymer networks. Part 2.—Polyacrylamide, hydroxyethylcellulose and cellulose gels

Abstract

Diffusion measurements on oligomeric solutes (n-alcohols, polyhydric alcohols, oligosaccharides) and polyethylene oxide polymers in sparsely crosslinked, water-swollen, polymer networks are described. Diffusion coefficients in the gel phase are much lower than those in the bulk liquid, which may be expressed as being mainly due to a change in the local viscosity. Diffusion coefficients ranged from 4.8 × 10^–6(methanol) to 1.4 × 10^–7 cm² s^–1(polyethylene oxide 4000) in the hydroxyethylcellulose gel. The corresponding ratios to the free diffusion values are 0.31 and 0.10₆. The reduction of D for small solutes is shown to depend on the concentration and polar character of the matrix polymer but not on the degree of crosslinking of the network. Much of the stability of the postulated water structuring is attributed to the inertia of the polymeric component, with a minor contribution from the strength of the polymer–solvent interaction. Estimates of polymer–solvent interaction energies in the gels are obtained from diffusion data at different temperatures.