Swelling behavior of covalently cross-linked gellan gels

The equilibrium swelling behaviors of covalently cross-linked gellan gels were investigated as a function of electrolyte concentration, pH at various ionic strengths. A marked decrease in the degree of swelling is observed when the gels are exposed to an aqueous salt solution, and to low and high pH. A hysteresis that observed for the gel in aqueous SrCl2 solution may be attributed to strong interactions with glucuronate, introducing additional cross links which affect the elasticity and ionic swelling power of the gel. The numerical analysis of the Flory theory applied to the swelling of gels shows that the ionic contribution to swelling is the main factor determining the degree of swelling of the gels. Volume change in aqueous solution may be explained mainly by the ionic contribution to swelling. Continuous volume change in the gel is attributed to the high stiffness of polymer chains and the Donnan equilibrium.