A DEFECT THEORY FOR THE GLASS-TRANSITION AND RESIDUAL ENTROPY OF HYPERQUENCHED WATER

The ground state structure of thermodynamically equilibrated metastable amorphous water at 0 K is considered as a continuous random network of H-bonded water molecules. At higher temperatures, this structure contains a fixed number of broken H bonds, or frozen-in fluctuations of local density, termed defects, where molecules have a considerable degree of configurational freedom to allow viscous flow. Their concentration has been calculated from the known change in the heat capacity at its T(g) of 136 K, and statistical thermodynamics. The configurational enthalpy and entropy of a thermodynamically equilibrated glassy water, according to this theory, become zero at 0 K, and not at 20%-30% below its T(g), and lead to a residual entropy of 0.20 J/K/mol for the 0.23% defects containing structure. This is in addition to the entropy of R ln(3/2) due to the orientational disorder, as in ice. Any attempt to include an extra configurational enthalpy leads to a further lower value for residual entropy. The metastable equilibrium at different temperatures and the relaxation towards this equilibrium structure have been expressed in terms of free energy-defect concentration diagrams for glassy water.