MEMBRANE POTENTIAL AND PERMEABILITY OF CHARGED CELLULOSIC MEMBRANE IN AQUEOUS ALKALI METAL SALTS SYSTEMS

Abstract

The membrane potential and permeability of charged cellulosic membrane in alkaline metal salts solution were determined at 25°C. The membranes used were carboxyethyl cellulose (CEC), sulphoethyl cellulose (SEC) and phosphorylated cellulose (PC) with the same degree of substitutions. The membrane potential and permeability as a function of the salt concentration were analysed by means of TMS theory.
In a series of alkali metal chlorides the diffusion coefficients of cations in membranes decrease with increasing Stokes radius of the cations. On the other hand the diffusion coefficients of chloride anion which is the common counterion species increase with increasing Stokes radius of the cations. In the case of sodium salts carrying different counter anion, i.e., NaCI, NaNO₃, and C₆H₅SO₃Na, the larger the ionic sizes the diffusion coefficients of anion decrease. While the diffusion coefficients of sodium ions in these salts are approximately the same value.
The effective fixed charge density and the diffusion coefficient of ions in the membranes increase in a sequence of CEC<SEC≤PC membranes. These results are explained by considering the counterion binding by the negatively charged groups in the membranes.