THE PERMSELECTIVITY OF MEMBRANE SYSTEMS WITH AN INHOMOGENEOUS DISTRIBUTION OF FIXED CHARGE GROUPS

The influence of the inhomogeneities in the fixed charge distribution on the transport properties (permselectivity and current-voltage chara cteristics) of ion-exchange membranes is theoretically studied. A simp le, approximate method for the analytical solution of the Nernst-Planc k equations with the assumption of local electroneutrality is presente d. Special attention is paid to the effect of the diffusion boundary l ayers on the permselectivity of the membrane system. Two fixed charge distributions (linear and exponential) are considered in detail. It is predicted that these distributions could show higher permselectivitie s than a homogeneous distribution with the same average concentration. Still, the membrane permselectivity is mainly determined by the avera ge fixed charge concentration and the thickness of the boundary layers . (C) 1994 Academic Press, Inc.