A PERTURBED ELECTRIC DOUBLE-LAYER NEAR A SOFT POLAR INTERFACE

A perturbation analysis is applied to a nonequilibrium double electric layer (NDEL) near a membrane with extended soft permeable interfaces (polar zones) under steady-state ion flux conditions. The membrane has been modeled as composed of three layers: an inner hydrophobic layer and two polar zones with fixed charges and dipoles. Ion flux is descri bed according to Nernst-Planck and Poisson equations, A first order ap proximation of the nonequilibrium electric potential has been obtained , using the electric current as the small parameter. The influence of the ionic flux, the surface dipole density, and the thickness of the p olar zone on the NDEL near the membrane has been analyzed. The electri c potential and hence the ion concentration profiles in the NDEL chang e considerably with surface dipole density. A maximum in the electric potential, which is determined by ion flux and polar zone parameters, is predicted in certain cases. The effects shown can help in the inter pretation of permselectivity measurements. (C) 1997 Academic Press