The ice accretion on the cold surface of a substrate spans a variety of length scales. Multiscale computer simulations are needed to (i) understand the underlying atomic-level events that dictate the water droplet crystallization process; and (ii) determine the parameter among several, such as substrate surface microstructure, the cooling rate, or the chemical impurities, that controls the grain structure (columnar or equiaxed) and the product phases (cubic or hexagonal) of the ice resulting from water freezing.  To meet this need, here we perform a series of coarse-grained atomistic simulation of the ice formation through freezing a water slab confined by two substrates. Several major findings are: (a) the ice formation is significantly promoted when the substrate grain size, d, is at the same level as the lattice constant of ice. In details, when d is ~6 nm and blow, the ice nucleation is largely promoted by forming special topological defects which consequently catalyze the ice crystal growth; (b) the cooling rate dictates the ice nucleation rate and the critical freezing temperature; (c) the chemical impurities deliquesce the ice crystal nucleation due to an increased energetic cost of creating an ice‚Äìfluid interface; and (d) the grain structure in the ice is columnar nearby the ice-substrate interface, but is equiaxed away from the interface. After the water slab is fully frozen into polycrystalline ice, a tensile and shear loading is then applied on the substrates to mimic a de-icing process. The adhesive-to-cohesive fracture behavior and its dependence on the ice microstructure, substrate surface topography as well as the chemical impurities are investigated. Results show that the columnar-to-equiaxed microstructure crossover intrinsically gives rise to the experimentally observed adhesive-to-cohesive fracture transition. This knowledge may be used to minimize the ice-substrate adhesion, and to optimize the existing de-icing strategy for a minimum power requirement.

Coarse-grained Atomistic Simulation of the Formation of Polycrystalline Ice from Water Freezing under a Confinement and Its Fracture Behavior during De-icing

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