Swelling behavior of a polyacrylamide gel in water/acetonitrile mixtures across the solvent phase separation temperatures

Abstract

Swelling behavior of polyacrylamide gels in water/acetonitrile system is examined. The linear swelling ratio of the gels decreases with increasing temperature when the water content of the mixtures is low but increases with increasing temperature for the gel in pure water. At high temperatures, the swelling ratio increases with increasing water content of the mixtures. On the other hand, swelling ratio at low temperatures shows interesting behavior: The temperature dependence curves of the linear swelling ratio became convergent for the gels in the mixed solvents, and the data points obtained in the phase-separated circumstances are well superimposed to form a single curve, which can be explained by the Gibbs phase rule. A drastic change occurs in solvent composition inside the gel as well as in the gel volume by cooling, which corresponds to a crossover from collapsed to swollen state of the polymer gels.