Spinodal decomposition in N-isopropylacrylamide gel

Spinodal decomposition in a chemically crosslinked N-isopropylacrylamide (NIPA) polymer gel was investigated using turbidity and ultrasonic techniques. The turbidity of the quenched NIPA gel was measured over five orders of magnitude of timescales. With an increase of time, the gel transfers from a transparent and swollen gel to a cloudy and inhomogeneous gel, and eventually to a transparent and collapsed gel. The first transformation is a rapid process that only involves local arrangement of the polymer network and solvent into dilute and dense domains. The second transformation is a very slow process that involves global arrangement of the polymer network and solvent. The characteristic time for disappearance of the turbidity is proportional to the linear size squared at a constant temperature above T-c and increases exponentially as a function of the quenching depth of T - T-c. By probing the movement of domains, a possible time-dependent gel structure in the spinodal decomposition region is presented. (C) 2001 John Wiley & Sons, Inc.