Multiple phases of polymer gels

SYNTHETIC polymer gels are known to exist in two phases, swollen and collapsed^1,2. Volume transitions may occur between the phases either continuously or discontinuously. We report here that more than two phases can be found in gels consisting of copolymers of randomly distributed positively and negatively charged groups. In these gels, polymer segments interact with each other through attractive or repulsive electrostatic interactions and through hydrogen bonding. It is the combination of these forces that seems to result in the existence of several phases. Each phase is characterized by a distinct degree of swelling, with abrupt jumps between them. The number of phases depends on the proportions of positively and negatively charged monomers, and decreases from a maximum of seven to just one for pure cationic or anionic gel compositions. The existence of these phases presumably reflects the ability of macromolecular systems to adopt different stable conformations in response to changes in environmental conditions.