MECHANISM OF POLYACRYLATE GEL SHRINKAGE IN AN ELECTRIC-FIELD

Shrinkage of sodium polyacrylate gel in an electric field was studied from the viewpoint of the ion exchange between sodium ions dissociated from -COONa groups in the original gel and hydrogen ions generated by the electrolysis of water. This mechanism was confirmed qualitatively by the following facts, obtained in a study of spherical gel particles in vinyl alcohol/sodium acrylate copolymer. 1) Remarkable shrinkage is observed at voltages above the electrolysis voltage of water. 2) The shrinkage proceeds near the anode, where hydrogen ions are generated. 3) The amount of sodium ions released from the gel particles by exchange with hydrogen ions increases with increasing amount of electricity. 4) The degree of shrinkage of gel particles amount of electricity. 5) The rate of shrinkage increases with increasing electric current as well.