Swelling-contraction of sodium polyacrylate hydrogels in media with various pH values

Abstract

The swelling kinetics of sodium polyacrylate gels has been studied in media with different pH values. The pH dependence of the degree of equilibrium swelling shows a maximum at pH 6. The degree of swelling decreases with an increase in the crosslink density, and this dependence follows an S-shaped pattern for all examined gels. When a gel swollen in media with pH 3–13 is dried in air, its contraction is reversible, while in the case of the gel swollen in acidic media at pH < 3, the process is irreversible owing to the replacement of sodium ions with protons.