Transition features in the dehydration of polymer gels

The property changes of some wet gels (the heat-treated egg white gel and poly-acrylamide gel) during the dehydration process, and those of the dehydrated gels during the temperature increasing process has been investigated with several methods. In the dehydration process, anomalies in the evolution of weight, volume, elasticity and Raman scattering spectrum were observed when the free water in the gel has been almost dissipated. This feature indicated the occurrence of a kind of transition analogous to the glass transition. The dehydrated gels looked like plastics and showed anomalies in elastic and thermal properties around 60 °C with increasing temperature. Though these behaviors resembled those in the glass transition of non-crystalline polymers, we have also observed some differences between the dehydrated gels and usual polymer glasses from the observation of the temperature dependence of the low frequency Raman scattering spectrum (∼ 300 cm^-1).