MEMBRANE-POTENTIAL OF SEPARATION MEMBRANES AS AFFECTED BY ION ADSORPTION

Recently it has been reported that membrane charge density depends on the bulk concentration. In this paper, we investigate the effect of ion adsorption on membrane charge and on membrane potential by using the selective ion adsorption model, which considers that a membrane which has no fixed charge can adsorb anions selectively. We find that the membrane potential depends on the bulk concentration as if the membrane itself had a fixed charge. However, the magnitude of the membrane potential in the region of low bulk concentration is determined by the adsorption coefficient and the saturated ion concentration of adsorbed ions. These parameters can be determined by analysis of the membrane potential using our model. After obtaining values of parameters which characterize the membrane, the variation of the membrane charge density and the interfacial potential difference caused by ion adsorption can be predicted theoretically.