Development of a Model for Analyzing the Swelling Rate of Ionic Gels on the Basis of the Diffusion of Mobile Ions: Application to the pH-Sensitive Swelling of a Polyelectrolyte Complex Gel Prepared from Xanthan and Chitosan

Abstract

A model for analyzing the swelling rate of ionic gels was developed on the basis of the diffusion of a species of mobile ion. This model was applied to the analysis of pH-sensitive swelling of a xanthan/chitosan complex gel in NaOH solutions of pH 9–12, using the sodium ion as the reference mobile ion. The time–course for swelling of gel beads with a pH change from 11 to 10 was successfully described by the developed model. The values for the diffusion coefficient obtained by fitting the model to the data were of the same order as those for the diffusion coefficient of the sodium ion measured for a membrane of the complex gel. Thus, it was confirmed that the swelling rate of the gel due to pH change was mainly controlled by the diffusion of mobile ions. However, the time-course for swelling of the gel at pH values below 10 was not satisfactorily explained by the model developed, suggesting that the change in the degree of ionization during swelling also affected the swelling rate of the xanthan/chitosan complex gel.