Selective behaviour of hyperfiltration cellulose acetate membranes: Part II. Streaming potential

Abstract

Streaming potentials have been measured by the fast pulse method for cellulose acetate membranes cured at 85 and 95°C. Bounding, solutions of Li +, Na +, K +, Cs +, Mg 2+, Sr 2+, Ba 2+ and La 3+ chlorides were used in the concentration of 10 −4-10 −1 M. The streaming potenial was shown to depend on the nature of the cation and to increase with decreasing solution concentration. Rather good consistency was obtained in dilute solutions between the electroosmotic cross coefficients calculated from the streaming potentials and from the electroosmosis measurements for Part I (M.G.A. Khedr, S.M. Abd el Haleem and A. Baraka, J. Electronal. Chem. 182 (1985) 157), according to the Onsager reciprocal relations. The deviation observed at higher concentrations, independent of the cation nature, is attributed to concentration polarization and/or excessive water transport encountered in electroosmosis measurements. Determination of additional phenomenological coefficients of the same system, the hydraulic permeability and the electric resistance enabled the estimation of the effective exchange capacity of modified cellulose acetate membranes. The resulting value of 2.1×10 −3 mol of unit charge/1 of pore liquid is compared to the corresponding values previously reported on a different basis.