SWELLING EQUILIBRIA FOR ACRYLAMIDE-BASED POLYAMPHOLYTE HYDROGELS

Polyampholyte hydrogels were synthesized by copolymerizing acrylamide with the cationic monomer methacrylamidopropyl trimethylammonium chloride and the anionic monomer sodium styrene sulfonate. The total nominal charge density of the hydrogels was held constant at 4.7 +/- 0.1 mol % (dry basis), while the molar ratio of anionic to cationic moieties within the hydrogels was varied. Swelling equilibria were measured in water and in aqueous sodium chloride solutions ranging in ionic strength from 10(-5) to 1.0 M. The hydrogels showed increasing insensitivity to ionic strength as the molar ratio of anionic to cationic moieties in the hydrogel approached unity. Donnan membrane equilibria qualitatively explain the experimental results.