Multiple glass transitions and two step crystallization for the binary system of water and glycerol

Abstract

Glass formation/crystallization phenomena were studied in water and glycerol mixtures using adiabatic calorimetry. The sample was cooled rapidly from room temperature and its thermal response was followed on heating from 80 to 300 K. The binary mixtures with the glycerol contents more than 55% (w/w) (19 mol%) yielded the homogeneous glassy states, consisting of randomly mixed water and glycerol molecules. Their glass transition temperatures showed the composition dependence of the Gordon–Taylor equation, and extrapolated exactly to that of pure water (135 K). The mixtures in the 0–55% (w/w) glycerol range crystallized partly on cooling and exhibited three anomalies in the temperature drift rate on heating. The first of these three is associated with the onset of reorientational motions of water molecules in the hexagonal ice which increases from 107 to 120 K on increasing the glycerol composition. The second is the composition independent temperature of 164 K that corresponds to the mixture with 76% (w/w) glycerol (38 mol%, known as the maximally freeze-concentrated solution), which is the mixture with the maximum composition of water that can be cooled without crystallization. The third is associated with the ice crystallization followed by ice dissolution in the range 185–202 K. In addition, the sample with 60% (w/w) glycerol composition (23 mol%) exhibited two distinguishable exothermic peaks on heating. The initial one is large and is attributed to crystallization into a novel two-dimensionally ordered structure of ice, and the second is due to the transformation of the layered structures into the hexagonal ice.