ELECTRICAL TRANSPORT PHENOMENA IN A CATION-EXCHANGE MEMBRANE .2. CONDUCTANCE AND ELECTROOSMOSIS

The specific conductance and electroosmotic permeability of a homogeneous cation-exchange membrane are reported as functions of composition and concentration of the ambient solutions of NaBr, CsBr, and SrBr2 and their mixtures at 25°C. The equivalent conductances of the ions in the membrane were evaluated by using transport numbers determined earlier (see Part I). The conductances of the counterions were found to be greater and of the coions smaller than calculated from their tracer diffusion coefficients in the membrane. This was attributed mainly to interactions between the ionic currents and the electroosmotic stream. When the membrane contained only one kind of counterion about 60% of the mean electroosmotic stream velocity had to be added to the diffusional mobility to obtain the electrical mobility of the counterions. At low concentrations the coions were scarcely retarded by the electroosmotic stream. At high concentrations the retardation was greater than the electroosmotic stream velocity and this was attributed to an additional retardation of the coions caused by the counterions moving in the opposite direction. When the membrane contained a mixture of counterions the thermodynamically preferred species derived less assistance in conduction from the electroosmotic stream than did the nonpreferred species. This was attributed to the preferred ions occupying on average the denser regions in the membrane where the electroosmosis is less strong. © 1969.