Chemical and Morphological Effects on Solute Diffusion Through Block Copolymer Membranes

Abstract

The rate of aqueous diffusion of a solute through Cuprophane and other cellulosic membranes is controlled primarily on the basis of its molecular size, with the chemical structure of the solute having little influence on the diffusion rate. Stretching or chemical etching of cellulosic membranes can increase their permeabilities to solutes (1–3), but only at the expense of decreasing the limited selectivity of the transport of the smaller solutes (3). A study of block copolymer membranes was undertaken as a possible route to develop membranes which might show selectivity for both the molecular size and chemical structure of the diffusing solute. These block copolymer systems would be composed of suitable hydrophilic blocks to influence the aqueous permeability properties, and hydrophobic blocks to give the necessary mechanical strength to the membranes. Since solute diffusion would be through an aqueous solution of the hydrophilic block rather than just through water, one would expect that the interactions between the solute, water, and hydrophilic block would influence the rate of diffusion.