Nucleation curves of ice in quasi-free water droplets

Ice nucleation is important in global climate change and could also have implications to nucleation of more complex systems like clathrate hydrates. A new setup for experimental investigations of nucleation of ice that uses linear cooling ramps is described. The nucleation rates of ice in (1) microliter-sized quasi- free water droplets suspended at an interface between an inert fluorocarbon oil, perfluoromethyldecalin, and an inert hydrocarbon oil, squalane, and (2) microliter-sized quasi-free water droplets supported by stable wetting films of squalane, were determined from the procedure that was previously developed for clathrate hydrates. The impact of the number of the data points and the experimental cooling rate was investigated in detail. The nucleation curve of a given system was found to remain largely unchanged with the addition of data after about the first 100 data points. Additional 300 to 400 data points confirmed such convergence. The results also showed that the nucleation rate increased with the system supercooling, as expected, and the whole nucleation curve shifted somewhat downward with the use of a slower cooling rate. The nucleation rates of ice in the water droplets supported by stable wetting films of squalane were broadly similar to but slightly greater than those suspended between two immiscible liquids. We then compared our data to the nucleation rate of ice reported in the literature, which showed broad agreements when the differences in the scales were accounted for. The experimental method described was found to be reliable and the setup provides a basis for future studies on ice nucleation that may involve nucleation promoters, inhibitors or more complex entities. (c) 2021 Elsevier Ltd. All rights reserved.

Automated summary

The experimental setup allows for accurate determination of ice nucleation rates, demonstrating that nucleation rates increase with system supercooling. The entire nucleation curve shifts somewhat downward with the use of a slower cooling rate, indicating the importance of cooling rate in ice nucleation studies.