Modification of properties of ion exchange membranes V. Structure of cationic polyelectrolyte on the surface of cation exchange membranes

Summary Electrodialytic transport properties of cation exchange membrane are changed by adhesion of polyethylene imine on the membrane surface. The effect of conformation of polyethylene imine molecules on the transport properties of the membrane, thickness of adherent layer and mechanism of adhesion were discussed. Observed were relative transport numbers of calcium ions to sodium ions,P_Na^Ca, current efficiency, electric resistance of the membrane during electrodialysis and pH-shift of anolyte after electrodialysis.P_Na^Ca decreased remarkably, when the conformation of polyethylene imine was compact by adding salt to the solution, adjusting pH of the solution to a high value where polyethylene imine was scarcely protonated and adding water-soluble neutral polymers and multivalent anions. It was confirmed that the conformation of polyethylene imine on the membrane surface controlled the degree of the change of the transport properties of the membrane. The adherent amount of polyethylene imine on the cation exchange membrane was calculated assuming that a monolayer of polyethylene imine molecules with hydrodynamic radii was formed. This differed markedly from the amount observed. The reason for the difference was discussed. There was no observation of salting out by sodium chloride and calcium chloride. It was concluded that the polyethylene imine molecules on the cation exchange membrane are mainly bound by ion-exchange.

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Zusammenfassung Die elektrodialytischen Transporteigenschaften von Kationenaustauschmembranen werden mit Polyäthylenimin (PEI) als kationischer Polyelektrolyt verändert. Sie werden durch die Konformation des PEI in der Lösung beeinflußt.Als Transporteigenschaften werden die relativen Transportzahlen der Ca-Ionen im Vergleich zu Na-Ionen, der elektrische Widerstand der Membran während der Elektrodialyse and die pH-Änderung nach der Elektrodialyse im Anodenraum untersucht.

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With 13 figures and 3 tables