Nucleation of Aqueous Salt Solutions on Solid Surfaces

AK Metya and JK Singh, JOURNAL OF PHYSICAL CHEMISTRY C, 122, 8277-8287 (2018).

DOI: 10.1021/acs.jpcc.7b12495

The freezing of water in the presence of salts is very common and widely investigated phenomena. However, the role of the substrate during crystallization, and in particular the molecular-level resolution of nucleation mechanism, is still not well-understood. In this work, we investigated the freezing behavior of supercooled water and aqueous lithium chloride solutions on smooth graphitic surfaces. We illustrate the role of solid surfaces in the freezing process of aqueous solutions as a function of mole fraction of a salt exhibiting lowering of freezing temperature, irrespective of a water-binding affinity to the surface. Our molecular dynamics simulations show that the hydrophobic surface is a better nucleating surface when the mole fraction of the salt is over 5%. Our findings reveal that nucleation of ice occurs heterogeneously at the liquid-solid interface. Consequently, propagation of the ice front yields phase-segregated brine near the liquid-vapor interface. Furthermore, we have investigated the effect of salt-surface interaction on the freezing process. We observe lowering of the freezing point with an increase in the water-surface interaction. The simulations demonstrate that nucleation of ice occurs heterogeneously at the liquid- solid interface for low values of interaction, whereas homogeneous nucleation of ice takes place away from the substrate at higher interaction strengths.

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