Swelling and phase transitions in deforming polymeric gels

Abstract

Deformation of physically cross-linked gels is shown to increase their swelling capacity significantly and induce new volume phase transitions in the gels. Both of these phenomena are novel and are demonstrated here for the first time. The physical origin of the increased swelling lies in the breakage of some of the physical cross-links in the gel due to deformation. A phenomenological kinetic model is developed to describe the rate of breakage of physical cross-links in the gel due to shearing deformation. Coupling this model with the thermodynamics of swelling of polymeric networks gives quantitative predictions for the time evolution of the increase in the swelling capacity of such a gel. The enhanced swelling capacity of the gels due to deformation is also shown to be retained in the "memory" of the gel during further swelling-collapse cycles, a somewhat surprising result, which needs further elucidation.