Isotope effect on the glass transition and crystallization of hyperquenched glassy water

Abstract

The thermal behavior of hyperquenched glassy D2O was investigated by differential scanning calorimetry from 103 to 250 K, in order to investigate the isotope effect on the glass→liquid transition and on the liquid to cubic, and cubic to hexagonal ice. For a heating rate of 30 K min−1 the temperatures of the thermal effects are: 137 K for the onset of the reversible glass→liquid transition (Tg), 154 and 173 K for the beginning and the peak minimum of the crystallization exotherm, and ≊229 K for the peak minimum of the transformation cubic→hexagonal ice. Increase in heat capacity at Tg and the width of the glass transition are similar to those reported for glassy H2O. Tg of D2O is higher than that of H2O by an amount that is expected for isorelaxational and/or isoviscous states assuming that the functional form of the molecular reorientation rates with temperature is unaffected by the isotopic substitution. The increase in the temperature of crystallization of ‘‘fluid’’ D2O is ≊three times greater than the increase in the glass→liquid transition which causes Tg and devitrification to become more separated in D2O than in H2O. Implications of these results for both the inferred λ-type anomally at ≊228 K in H2O and at ≊233 K in D2O, and the presumed formation of a gel-like structure at these temperatures are discussed.