NUMERICAL-SIMULATION OF THE NONEQUILIBRIUM DIFFUSE DOUBLE-LAYER IN ION-EXCHANGE MEMBRANES

We have analyzed theoretically the complex phenomena taking place when an electric current passes through the nonequilibrium diffuse double layer at the ion-exchange membrane/solution interface. Interesting results arise due to the nonlinear character of the system of equations consisting of the Nernst-Planck and Poisson equations, and the inhomogeneous nature of the membrane system (membrane plus bathing solutions). Some of these results confirm the conclusions concerning the space-charge distribution obtained previously by other authors using different methods. Others provide new physical insights into problems such as the question of the validity of the Donnan equilibrium relations at the membrane/solution interfaces, and the selectivity of ion-exchange membranes.