Abstract
Measurements of bi-ionic potential across anion-exchange membranes were carried out for KCl/mem-brane/KIO3 systems. Anion-exchange membranes used were prepared by copolymerization of 4-vinyl-pyridine and styrene with 2, 2'-azobisisobutyronitrile as initiator, and then quaternized with methyl iodide or 1,6-dibromo-n-hexane. The absolute values of bi-ionic potential increased with an increase in the external electrolyte molality even though the transport number of counterions in the membrane was nearly unity. The magnitude of bi-ionic potential was discussed in connection with the properties of membranes. The value of bi-ionic potential was larger if the membrane has the lower water content and the higher weight fraction of hydrophobic membrane matrix. The dependence of bi-ionic potential on the molality of the external solution was assigned to the decrease in free water in the membrane with varying the swelling pressure by the change in the external molality.
