Abstract
Liquid water exhibits anomalous behavior in the supercooled region. A popular hypothesis to explain supercooled water’s anomalies is the existence of a metastable liquidliquid transition terminating at a critical point. The hypothesized phase transition is not directly accessible in a bulk experiment because it is expected to occur in “no-man’s” below the kinetic stability limit of the liquid phase at about 233 K, the temperature of homogeneous ice formation. Therefore, verifications of this hypothesis are usually based on extrapolations from the experimentally accessible region. In this work, we present the results of highresolution adiabatic calorimetry measurements of cold and supercooled liquid water in the range from 294 to 244 K, the lowest temperature of water’s supercooling achieved so far in a bulk adiabatic-calorimetry experiment. The resolution of the measurements is also record-high, with the average statistical (random) error of about 0.1%. The data are consistent with adiabatic-calorimetry measurements of supercooled water earlier reported by Tombari et al (1999 Chem. Phys. Lett. 300 749) but significantly deviate from differential-scanning calorimetry measurements in emulsified water reported by Angell et al (1982 J. Phys. Chem. 86 998) and by Archer and Carter (2000 J. Phys. Chem. 104 8563) Consequences of the new heat-capacity data in interpretation of the nature of water’s anomalies are discussed.
Highlights
Liquid water exhibits anomalous behavior in the supercooled region, as manifested by the growth of the isothermal compressibility and isobaric heat capacity [1]
The hypothesized phase transition is not directly accessible in a bulk experiment because it is presumably located a few degrees below the kinetic stability limit of the liquid phase at about 235 K, the temperature of homogeneous ice formation [6, 7]
All the data demonstrate that the isobaric heat capacity of supercooled water exhibits a striking anomaly with an apparent tendency to a “divergence” or to a sharp maximum at a temperature beyond the kinetic stability limit of liquid water
Summary
Liquid water exhibits anomalous behavior in the supercooled region, as manifested by the growth of the isothermal compressibility and isobaric heat capacity [1]. The hypothesized phase transition is not directly accessible in a bulk experiment because it is presumably located a few degrees below the kinetic stability limit of the liquid phase at about 235 K, the temperature of homogeneous ice formation [6, 7] Verifications of this hypothesis are usually based on extrapolations of the anomalies observed in the experimentally accessible region [8,9,10,11]. The results of the both adiabatic calorimetry measurements significantly deviate from differential-scanning calorimetry measurements in water (emulsified in heptane) reported by Angell et al [21] and, even more significantly, from the data reported by Archer and Carter [23]. Consequences of the new heat-capacity data in interpretation of the nature of water’s anomalies are discussed
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