The glass transition of water, insight from phase change materials

The calorimetric features that have been broadly used to assign a glass transition temperature Tg of 136 K to amorphous water are qualitatively reproduced with a phase change material. Annealing treatments and ultrafast calorimetry measurements indicate that this feature is only a shadow-Tg and that the real Tg lies at higher temperature above the glass transition. A Kissinger analysis of the crystallization kinetics confirms that crystallization occurs below Tg from the glassy state at conventional heating rates. These results strongly suggest that the amorphous water endotherm at 136 K is indeed a shadow-Tg and that the real Tg lies at higher temperature as predicted from structural relaxation considerations.