SWELLING OF COVALENTLY CROSS-LINKED ALGINATE GELS - INFLUENCE OF IONIC SOLUTES AND NONPOLAR-SOLVENTS

The equilibrium swelling volume of covalently crosslinked sodium algin ate (a highly ionized stiff polymer network) gels has been studied as a function of electrolyte concentration, pH, and concentration of salt s in ethanol-water mixtures. It is shown by numerical analysis of the Flory theory for swelling of gels that the ionic contribution to swell ing seems to be the main determining factor for the swelling of these gels. Volume changes in aqueous solutions may be explained mainly by t he ionic contribution to swelling. Reduced swelling and marked hystere sis are observed when the gels are exposed to low pH or cations that i nduce gelling in soluble Na-alginate. In contrast to predictions found in the literature, no discrete volume changes have been observed as a result of altering solvent composition. This discrepancy is attribute d to the effect of the Donnan equilibrium and the high stiffness of th e alginate chains. The gel volume changes in ethanol-water mixtures re semble the solubility of uncrosslinked alginates.