Abstract
Ion transport phenomena across a membrane such as membrane potential and ion permeability have been explained using Nernst-Planck ion flux and Donnan equilibrium theories. They are predicted as a function of membrane charge density, ion mobility and solution concentration. Membrane charge density is one of the important parameters to characterize a charged membrane and defined as concentration of fixed charge groups in it, that is, those numbers per unit volume of water (If it is defined as an amount of charge per unit weight of dry membrane, it is called as ion exchange capacity.) . It is based on the solution of Nernst-plank's ion flux equation, where it implies that tubular pores with water exist in the membrane for ion penetration. It has been pointed out that the fixed charge groups are distributed in the membrane heterogeneously. On the contrary it is assumed that the fixed charge groups are distributed homogeneously if Donnan equilibrium theory is applied to the charged membrane. These are the contradiction on the analysis of the membrane transport phenomena, and have been used without any deep consideration. In this paper the effect of fixed charge density on the membrane potential and the permeability coefficient was explained from the fundamental point of view in order to understand the problems cited above. Therefore it is helpful for developing further advanced ion exchange membranes.
