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 res ults arise due to the nonlinear character of the system of equations c onsisting of the Nernst-Planck and Poisson equations, and the inhomoge neous nature of the membrane system (membrane plus bathing solutions). Some of these results confirm the conclusions concerning the space-ch arge distribution obtained previously by other authors using different methods. Others provide new physical insights into problems such as t he question of the validity of the Donnan equilibrium relations at the membrane/solution interfaces, and the selectivity of ion-exchange mem branes.