Kinetics of one-dimensional swelling and shrinking of polymer gels under mechanical constraint

The swelling and shrinking kinetics of thin-plate poly(N-isopropylacrylamide) gels with rectangular surfaces under mechanical constraint was investigated. The top and bottom surfaces were chemically clamped on the glass plates, and the gel could swell and shrink only along the thickness direction between two swollen states by the temperature jumps. The time evolution of the thickness was well described by a single exponential except immediately after the temperature change. The characteristic time was found to depend on the lengths of the constrained surfaces and not on the thickness at the time of sample preparation. The swelling and shrinking kinetics of the one-dimensional thickness direction is essentially governed by the relaxation of the polymer network in the two-dimensional direction along the surface. (C) 2001 American Institute of Physics.