Modification of the transport properties of ion exchange membranes. XII. Ionic composition in cation exchange membranes with and without a cationic polyelectrolyte layer at equilibrium and during electrodialysis

It is considered that the mechanism of specific permselectivity of a cation exchange membrane with a cationic polyelectrolyte layer is due to the different electrostatic repulsion forces of ions relative to the cationic charge on the membrane surface. In order to prove this experimentally, the ionic composition of a cation exchange membrane with a polyethylenimine layer that had been formed by acid-amide bonding and that of a cation exchange membrane without such a layer were determined by using a 1:1 solution of calcium chloride and sodium chloride of various concentrations. p]Donnan adsorbed salt (Δm), ratio of calcium ions and sodium ions in the Δm (DNaCa), ratio of ion-exchanged calcium ions to ion-exchanged sodium ions (KNaCa) and selectivity coefficients were measured when both membranes had been equilibrated with the solutions and also used in electrodialysis. In the case of equilibrium, the ionic composition of both membranes was almost the same except in the low concentration range. However, in the case of electrodialysis, the ionic composition of the membrane with the layer was completely different from that of the membrane without the layer. The content of calcium ions in the membrane with the layer decreased markedly in comparison with that of the membrane without the layer. The effect of current density on the ionic composition in the membrane also showed the same behavior.