Physicists have used the method of rapid vacuum evaporation
For cooling we used a method of rapid vacuum evaporation, and the temperature was determined according to the Raman scattering light based on the size of the droplets, scientists have reported in Physical Review Letters.
While water cooling in nonequilibrium conditions, it may remain liquid even at temperatures significantly below the melting point (i.e. zero degrees Celsius). Such water is called supercooled, and you will need the absence of crystallization centers. To SuperCool water more than a few degrees, it is difficult, therefore, all the experimental records for the receipt of the coldest liquid known for very clean microdroplets, which are not in contact with solid surfaces.
To date, the lowest temperature at which microdroplets of water was able to remain in the liquid state and which was able to measure reliably was approximately -41 °C (it should be noted that the water droplets supercooled to minus 39 °C can be found naturally in the clouds in the upper atmosphere). As the results of theoretical analysis and computer simulation it is known that the minimum temperature at which the water can still exist in a metastable liquid state, is about -45 °C, below which the supercooled state is unstable.
A team of physicists from Germany, France, Spain and Italy under the leadership of Robert Grisenti from Frankfurt University Goethe suggested the use of hypothermia for the microdroplets of water method of fast evaporation in a vacuum. The main drawback of this approach is that this cooling is quite difficult to accurately determine the temperature. To solve this problem, the authors proposed to use the method of Raman scattering. By measuring the shift of Raman peak frequency, with a very good precision measurement of the droplet distribution in the jet size on the basis of which then calculate the mass loss due to evaporation and after that the temperature drops. The accuracy of this method, according to scientists, is about 0.5 °C.
Using the proposed approach, the scientists were able to cool the drops, the size of which was approximately about 6.3 microns, to a temperature -42,55 °C, even given the relatively large error of more than about one degree below the previous record, a particular reliable method of measurement. The authors note that in one of the papers wrote about hypothermia drops even larger up to the same temperatures as in the present work, however, apparently, the authors of previous studies did not take into account a possible heating of the droplets by irradiation. The reliability of the method of temperature measurement proposed in this work has yet to be tested.
Scientists report that the proposed method allows cooling and larger drops to a sufficiently low temperature. In addition, the method of Raman scattering simultaneously with the droplet size gives you the ability to monitor the status of the connection between oxygen and hydrogen within the molecules and the hydrogen bonds between molecules. Based on the data, in the future, scientists hope to obtain information on the structural change of hydrogen bonds in the water when hypothermia to critically low temperatures. According to the authors of the study, the results of the work, in particular, will help to examine in more detail the processes occurring during the crystallization of ice in the atmosphere, and to build a more reliable climate models.
Because the rate of crystallization of ice from supercooled water is very large, an experimental study of this process is also quite difficult. To observe the crystallization front, scientists in particular, using irradiation by short laser pulses of light of water. With the help of this method, physicists have described the crystallization of ice from water, supercooled to temperatures from -90 to -10 °C and showed that the rate of crystal growth depending on temperature can vary by 11 orders of magnitude.