Dielectric relaxation time of bulk water at 136-140 K, background loss and crystallization effects

Dielectric relaxation time, tau, of ultraviscous bulk water has been determined by analyzing its loss tangent, tan delta, data, which had been measured on heating the vapor-deposited amorphous solid water and hyperquenched glassy water in our earlier studies. [Johari, Hallbrucker, and Mayer, J. Chem. Phys. 95, 2955 (1991); 97, 5851 (1992)]. As for glasses and liquids generally, the measured tan delta of water is the sum of a frequency-independent background loss and a frequency-dependent relaxational loss. A two-frequency method is provided for determining the background loss and used for obtaining the relaxational part of tan delta. After considering the structural relaxation and crystal-nuclei growth effects, tau for water has been determined. At 136+/-1 K, it is 2.5+/-0.6 s when a single relaxation time is (untenably) assumed, and 42+/-14 s when a distribution of relaxation times, a characteristic of viscous liquids, is assumed, with Davidson-Cole distribution parameter of 0.75. Structural relaxation time of approximately 70 s for water at 136 K, which was originally estimated from the DSC endotherm [Johari, Hallbrucker, and Mayer, Nature (London) 330, 552 (1987)], has been revised to approximately 33 s. Temperature dependence of tau could not be determined because ultraviscous water crystallizes too rapidly to cubic ice containing stacking faults and intergranular water. The study demonstrates that water is a liquid over the 136-155 K range, thus removing the basis for a recent contention on its state.