Method for Analyzing pH-Sensitive Swelling of Amphoteric Hydrogels : Application to a Polyelectrolyte Complex Gel Prepared from Xanthan and Chitosan

Abstract

The pH-sensitive swelling of a natural-polyelectrolyte complex gel, prepared from xanthan and chitosan, was investigated using a model based on the Donnan equilibrium theory with special attention to the dissociation behavior of the polyelectrolytes. First, the pH dependence of the degree of ionization for the xanthan-chitosan complex was evaluated by the potentiometric titration method, and the value of the dissociation constant for analyzing the swelling behavior was obtained. Second, the validity of the Donnan equilibrium was confirmed by measuring the concentration of sodium ion in the gels. By analyzing the swelling behavior of the gel using the model, it was suggested that the network properties of the gel altered with changes in the ambient pH. These results indicate that analysis using the parameters evaluated by potentiometric titration is useful for investigating the swelling behavior of ionic gels.