Using Microwave Spectroscopy to Study the State of Supercooled Water
One of the anomalies of water is its second critical point of the liquid-liquid transition at a temperature of -53 °C and a pressure of about 100 MPa. It is known that on the pressure-temperature diagram the so-called Widom line flows from this point into a single-phase region. This line is characteristic of increased entropy fluctuations and water density. At a pressure of 0.1 MPa, the temperature on the Widom line is -45 °C. This temperature is reached in Earth’s polar regions and atmosphere. It is, therefore, important to investigate the physical and chemical processes determined by the second critical point of water. However, the study of deeply supercooled water is difficult due to the lack of a technology for its production. For this reason, the temperature range from -37 to -120 °C is called “no man’s land”. This complexity can be overcome by cooling water in the pores of solid bodies. It is also possible to produce supercooled water by creating an amorphous phase in ice. Methods and methodology. This paper presents methods for the study of supercooled water in the pores of silicate materials and in the case of ice amorphization. Amorphization was achieved with plastic deformation caused by a temperature gradient. The techniques are based on the measurements of water microwave characteristics in samples since silicates and polycrystalline ice are sufficiently transparent for microwave radiation and do not have a significant effect on it. The distinctive features of the techniques are associated with the expansion of the range of used frequencies from 5 to 200 GHz and the measurement of the intensity and the phase of the transmitted and the reflected radiation. In case of amorphization, the peculiarities are associated with the creation of special heating and cooling modes for ice samples. Results. As an example, the study presents the results of determining the temperature range on the Widom line, for which increased entropy fluctuations and density of supercooled water were observed. This range was about 1 °C. During the plastic deformation of ice caused by the heating of the sample, a decrease in microwave losses was found in the proximity of -45 °С. Strong fluctuations in the phase of radiation reflected from a block of fresh polycrystalline ice with an extremum in proximity of 13 GHz were also detected. Conclusions. This effect is supposed to be associated with the emergence of macrolocalized plasticity waves. Thus, the proposed methods of microwave spectroscopy of supercooled water can complement the known methods used to study its state.