THEORETICAL-STUDY OF THE EFFECT OF ION ADSORPTION ON MEMBRANE-POTENTIAL AND ITS APPLICATION TO COLLODION MEMBRANES

Charged membranes have been characterized by many investigators. Their attention has mostly focussed on the fixed charge of uniform membranes, but in recent years it has been pointed out that real membranes are not perfectly homogeneous. In this paper, the effect of selective ion adsorption on the membrane potential has been investigated theoretically in order to find a suitable model for a real membrane. The membrane considered here is, for simplicity, one which has a positive fixed charge and adsorbs anions selectively. As a result, it is found that the membrane potential shows a minimum with the decrease of bulk concentration. This phenomenon, which results from changes in the effective membrane charge density, is due to the variation of the amount of ions adsorbed by the membrane. The theory is applied to the analysis of the membrane potential of a collodion membrane, and it is shown that the theory is in good agreement with experimental data. Our model is adequate for obtaining information on the fixed membrane charge density, the saturated amount of adsorbed ion and the adsorption coefficient by the analysis of the membrane potential. The positive deviation of the products of the partition coefficients of co-ion and counter-ion for the membrane charge is well explained by the model. © 1990.