ACTIVITY-COEFFICIENTS AND COLON EXCLUSION IN CHARGED POLYMERIC MEMBRANES WITH MACROSCOPIC INHOMOGENEITIES

We consider a simple model to evaluate mean activity coefficients in c harged polymeric membranes with an inhomogeneous distribution of the f ixed charge concentration on the macroscopic spatial scale, and apply the results obtained to the colon exclusion characteristic of the Donn an equilibrium. Model calculations with two fixed charge distributions of experimental interest (the asymmetric and the skin-core distributi ons) show that the inhomogeneity effects can be important when the ext ernal salt solution concentration is lower than the membrane-fixed cha rge concentration, especially if spatial regions of low charge concent ration exist within the membrane. The results obtained appear to be in qualitative agreement with previous experiments.