Thermal analysis of water in p(HEMA) hydrogels.

Hydrogels composed of poly(hydroxyethyl methacrylate) (pHEMA) and water were investigated using differential thermal analysis (DTA) and adiabatic calorimetry (AC). The results show that the crystallization of water in the gels is a very gradual process, leading to the development of a metastable, non-equilibrium state. They are not in agreement with models that assume the actual presence of thermodynamically different classes of water in the gels, based on the abnormal melting behaviour of this water. The results indicate that the internal structure of these gels can be described as that of an elastic solution, in which the water molecules are distributed continuously over all possible orientations to and interactions with the polymer.