Approximation method for electrolyte diffusion through a fixed charge medium

Abstract

The diffusion of a binary salt through media containing uniformly dispersed immobile ions is formally equivalent to the diffusion of a nonelectrolyte with a concentration-dependent diffusion coefficient. This permits the application of a quasi-steady-state approximation, developed in a previous paper (Bull. Math. Biophysics,21, 19–32, 1959), to problems of transient diffusion. Free diffusion across an interface involving a discontinuity in immobile ion concentration is considered and expressions for the salt concentration and electrical potential at any point are developed. The dependence of electrical potential on the fixed charge density, ionic mobilities, as well as on the boundary concentrations is illustrated by a numerical example. This particular example is suggested by experiments on connective tissue.