Quasi-water layer sandwiched between hexagonal ice and wall and its influences on the ice tensile stress.

The presence of a quasi-water/premelting layer at the interface between wall and ice when the temperature ( T ) is below the melting point was extensively observed in experiments. In this work, molecular dynamics simulations are performed to analyze the underlying physics of the quasi-water layer and the effects of the layer on the ice tensile stress. The results indicate that each molecule and its four nearest neighbours in the quasi-water layer representing an equilibrium structure gradually form a tetrahedral ice-like arrangement from an unstructured liquid-like structure along the direction away from the wall. The average density of the quasi-water layer is equal to or higher than the bulk density of water at T ≥ 240 K or T ≤ 240 K respectively, and reaches 1.155 g cm -3 at T = 210 K, suggesting a structural correlation with the high-density liquid phase of water. Depending on the temperature and wall wettability, the thickness of the quasi-water layer ( H q ) ranges from ∼2 Å to ∼25 Å. For prescribed hydrophilic walls, H q increases monotonically with temperature, and is almost proportional to( T m - T ) -1/3 , where T m is the melting temperature of ice. H q keeps an almost constant value (2 Å) as the temperature increases and rises sharply after passing a threshold temperature of T ≈ 250 K. In the joint effects of the wall wettability and quasi-water layer's thickness, the ice tensile stress decreasing monotonically at a larger temperature shows an upward trend and then reduces to almost a constant value as the wall changes from a hydrophobic to a hydrophilic one. The results reveal the potential development of anti-icing/de-icing techniques by heating the wall or modifying its surface to increase H q .