The glass transition of water, based on hyperquenching experiments

The glass transition temperature (T-g) in water is still uncertain, with conflicting values reported in the literature. As with other hyperquenched glasses, water exhibits a large relaxation exotherm on reheating at the normal rate of 10 kelvin (K) per minute. This release of heat indicates the transformation of a high enthalpy state to a tower one found in slow-cooled glasses. When the exotherm temperature is scaled by T-g, the good glass-formers show a common pattern. However, for hyperquenched water, when this analysis is performed using the commonly accepted T-g = 136 K, its behavior appears completely different, but this should not be the case because enthalpy relaxation is fundamental to the calorimetric glass transition. With T-g = 165 5 K, normal behavior is restored in comparison with other hyperquenched glasses and with the binary solution behavior of network-former systems (H2O, ZnCl2, or BeF2 plus a second component). This revised value has relevance to the understanding of water-biomolecule interactions.