Kinetics of discontinuous volume–phase transition of gels

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Abstract
Kinetics of the first order volume–phase transition of submillimeter gels is investigated for various initial and final states of the transition. Characteristic times for swelling and shrinking critically depend on the final state, but are much less influenced by the intial state. The transition becomes infinitely slow when the final temperature is near the transition threshold. The study of the dependence of the transition time on the gel size reveals that the overall volume change is described approximately as a collective diffusion process, but not precisely. The exponent for time–radius relation is smaller than 2. The transitions having large volume change are accompanied by formation and evolution of transient patterns which appear on the surface of a gel. The patterns for swelling and shrinking are quite different, but both play an important role in the kinetic processes.