SWELLING PROPERTIES OF ACRYLAMIDE-BASED AMPHOLYTIC HYDROGELS - COMPARISON OF EXPERIMENT WITH THEORY

Ampholytic hydrogels were synthesized by copolymerizing acrylamide with specialty monomers. Two monomers, [(methacrylamido)propyl]trimethylammonium chloride (MAPTAC) and sodium styrene sulfonate (SSS), were copolymerized with acrylamide to form one ampholytic hydrogel. Also, the zwitterionic monomers N-(3-sulfopropyl)-N-methacrylamidopropyl-N,N-dimethylammonium betaine (SB1) and N-(3-sulfopropyl)-N-methacroyloxyethyl-N,N-dimethylammonium betaine betaine (SB2) were both, in turn, copolymerized with acrylamide to form ampholytic hydrogels. Swelling equilibria were measured in water and in aqueous sodium chloride solutions ranging in concentration from 10(-5) to 5 M. Antipolyelectrolyte behaviour was observed for the ampholytic hydrogels prepared, hydrogel swelling increases as the sodium chloride concentration rises. To demonstrate theoretically antipolyelectrolyte behaviour for ampholytic hydrogels, we incorporate the Debye-Huckel theory of electrolyte solutions into a Flory-type swelling model to account for Coulombic interactions between fixed and mobile ions. Calculated swelling equilibria are in qualitative agreement with experiment.