ROLE OF CONDUCTIVE INHOMOGENEITY OF CATION EXCHANGE MEMBRANE SURFACE IN CONCENTRATION POLARIZATION IN ELECTRODIALYSIS.

In the work reported concentration polarization measurements were carried out in a thin cell, with a well defined thickness of the diffusion layer, at gravitationally stable conditions. I - V curves were determined and the excess noise was recorded and analysed. The limiting current observed for several homogeneous cation-exchange membranes are 1. 5 to 4 times lower than expected for a homogeneous permselective interface, with an unstirred layer of a given thickness. A composite-heterogeneous membrane, comprising a highly permselective homogeneous layer facing the cathode with a relatively loose heterogeneous weakly permselective layer facing the anode was studied. A remarkably high limiting current was found in this system. It is shown that spacial inhomogenuities of the electric field, formed in the course of concentration polarization at an inhomogeneous cation exchange membrane, give rise to a laterally inhomogeneous space charge. Furthermore it is shown that the interaction of the above inhomogeneous space charges with the electric field gives rise to a spacially inhomogeneous bulk force which is bound to set in motion the fluid in the depletion diffusion layer.