Abstract
Understanding of swelling behaviors of polymer gels is essential for the development of superior gel materials for foods and other applications. This article describes equilibria and kinetics of their swelling, especially of polyelectrolyte complex gels, which can show pH-responsive swelling behaviors. Polyelectrolyte complex gels can be prepared from natural polymers. Examples of their pH-responsive swelling behaviors were described. The swelling equilibria were successfully explained by pH-dependent change in the degree of dissociation (deprotonation) of the chargeable functional groups fixed on the polymer chains. Theoretical analysis of swelling equilibria for dextran sulfate/chitosan complex gels showed that the complex formation lowered the acid dissociation constant of amino group. Thus the analysis of swelling equilibrium should include not only Donnan effect of fixed charge but also lowering of the dissociation constant due to complex formation. Cooperative diffusion of polymer chain has been known to control swelling rate of non-ionic gels, whereas diffusion of such mobile ions as Na+ was found to be the rate limiting factor for swelling of ionic gels.
