TIME-DEPENDENT RESPONSE OF IONIC POLYMER NETWORKS TO PH AND IONIC-STRENGTH CHANGES

Changes of ionic strength of pH of a swelling medium may lead to expansion or contraction of ionic polymer networks or charged hydrogels which have been immersed in this swelling medium. This phenomenon is analyzed by using a Boltzmann superposition equation which relates the strain to the applied ionic strength or pH. A material property, the ionic mechanochemical compliance, L(t - tau), is introduced which describes the viscoelastic response of a gel to the swelling environment. Experiment results of swelling of anionically charged hydrogels are presented and analyzed.