Swelling-deswelling kinetics of ionic poly(acrylamide) hydrogels and cryogels

A series of ionic poly(acrylamide) (PAAm) gels was prepared by free-radical crosslinking copolymerization of acrylamide and N,N'-methylenebisacrylamide in aqueous solutions. The gels were prepared both below and above the bulk freezing temperature of the polymerization solvent water, which are called as the cryogels and the hydrogels, respectively. The deswelling behavior of swollen gels in acetone as well as the reswelling behavior of the collapsed gels in water were investigated. It was shown that the cryogels respond against the external stimuli much faster than the hydrogels. The interior morphology of the cryogel networks exhibits a discontinuity and a two-phase structure, compared to the continuous morphology of the hydrogel networks. Introduction of the ionic units in the network chains further increased the response rate of the cryogels. In contrast to these advantages of cryogels, they exhibit lower swelling capacities than the conventional hydrogels. (c) 2005 Wiley Periodicals, Inc.