Swelling equilibria for acrylamide-based polyampholyte hydrogels
Polyampholyte hydrogels show promise for use in applications that require the material to maintain appreciable swelling capacity in highionic-strength aqueous media.Polyampholyte hydrogels were synthesized by copolymerizing acrylamide (AAm) with the cationic monomer methacrylamidopropyl trimethylammonium chloride (MAPTAC) and the anionic monomer sodium styrene sulfonate (SSS).The total nominal charge density of the hydrogels was held constant at 4.70.1 mole percent (dry basis), while the molar ratio of anionic to cationic moieties within the hydrogels was varied.Swelling equilibria were measured in water and in 0 .aqueous sodium chloride solutions ranging in ionic strength from 10-5 to 1.0 M. The hydrogels show increasing insensitivity to ionic strength as the molar ratio of anionic to cationic moieties in the hydrogel approached unity.At ionic strengths of 0.1 M and above, all hydrogels prepared show an increase in water content with rising NaCl concentration.