The temperature dependence of the intensity and of the correlation time of laser light scattered by the network density fluctuations in polyacrylamide gels is reported. The density fluctuations show critical behavior at - 17°C. This behavior is quantitatively explained as a phase transition of a binary mixture of the covalently cross-linked polymer network and the fluid medium.

• Received 7 December 1976

DOI:https://doi.org/10.1103/PhysRevLett.38.771