PATTERNS IN SHRINKING GELS

POLYMER gels can undergo a volume phase transition (either continuous or discontinuous) when an external condition, such as temperature or solvent composition, is altered1-3. During this transition, the volume may change by a factor of several thousand, and various patterns develop in the gel. The patterns arising from swelling and shrinking differ in both their appearance and their physical mechanisms. The mechanism for the formation and evolution of patterns on swelling gels has been established as being due to a single kind of mechanical instability4-7; in contrast, the shrinking patterns seem to be sensitive to both the initial and final states of the transition. Here we classify the various shrinking patterns in the form of a phase diagram, and explain the polymorphism in terms of macroscopic phase separation.