Comparison of the transport properties of normal and expanded forms of a cation-exchange membrane by use of an irreversible thermodynamic approach. Part I. Membranes in the sodium form in 0·1M-sodium chloride

Abstract

The transport properties of normal and expanded forms of a cation exchange membrane in 0·1M-sodium chloride are presented. Electrical, self-diffusion properties, and flows under salt gradient have been used to give a complete analysis of membrane phase interactions, using an irreversible thermodynamic approach. Equations are derived for this purpose. In particular, when salt uptake is small, it is shown that salt diffusional flow is accurately predicted from a knowledge of electrical conductivity, transport, and transference numbers. Onsager mobility and frictional coefficients are calculated by use of a direct method and two others, based upon limiting assumptions. All three are shown to be in good agreement.

Mobility coefficients in the membranes have been converted to a solvent-fixed frame of reference and compared with those of an aqueous sodium chloride model. When due account is taken of the tortuosity of the membrane phases both sets of coefficients are in close agreement. It is concluded that membrane transport properties of ions and water are largely unaffected by the organic matrix and that major changes observed in expansion are primarily due to reduction in path tortuosity.