Statistical characteristics of heterogeneous ice nucleation temperature for sessile saltwater droplets on supercooled solid surfaces

The formation of ice nuclei in seawater droplets on supercooled solid surfaces is a prevalent phenomenon in nature and industrial applications. However, the statistical characteristics and mechanism of types of salt affecting their nucleation temperature remain poorly understood. This study experimentally investigates the nucleation process of saltwater droplets on solid surfaces, focusing on the effects of salinity, droplet volume, and the types of salt on nucleation temperature. The results reveal that the nucleation temperatures of saltwater droplets with varying salinities, volumes, and types of salt exhibit stochastic behavior and conform to a normal distribution. As salinity increases or droplet volume decreases, the nucleation temperature distribution broadens, shifts toward lower temperatures, and shows a decline in the average nucleation temperature. Furthermore, nucleation rates decrease with reduced droplet volume, increased salinity, or higher temperature. For droplets containing different types of salt, MgCl2 and CaCl2 droplets exhibit lower average nucleation temperatures and nucleation rates compared to LiCl, NaCl, and KCl droplets, with MgCl2 showing the lowest values. In contrast, LiCl, NaCl, and KCl droplets exhibit no notable differences. This trend is inversely correlated with the energy required during nucleation (the sum of dehydration energy and the energy barrier) for droplets containing different cations. These results offer valuable insight into the nucleation behavior and mechanisms of seawater droplets on supercooled solid surfaces, advancing the understanding and optimization of desalination technologies for seawater droplet freezing.