Shrinking Behavior and Dehydration of Ionic Hydrogel in an Electric Field

Abstract

The mechanism of shrinkage and dehydration of ionic hydrogels packed in an electric cell were investigated on the basis of the distribution of pH around the gel, the Na⁺ ion concentration within the gels packed in the cell and the dehydration rate.
It was found that shrinkage and dehydration of the ionic gels take place through the following processes : (1) generation of H⁺ and OH^- ions by electrolysis ; (2) ion-exchange between H⁺ ions generated on the anode and Na⁺ ions dissociated originally within the gels ; (3) accumulation of Na⁺ ions near the cathode by electrophoresis ; and (4) increasein ionic strength near the cathode caused by process (3). Therefore, the shrinkage and dehydration of ionic gels depend on the generation of H⁺ ions by electrolysis and electrophoresis of Na⁺ ions.