Edge premelting of two-dimensional ices

The surface of a three-dimensional ice crystal naturally has a quasi-liquid layer (QLL) at temperatures below its bulk melting point, due to a phenomenon called surface premelting. Here, we show that the edges of a two-dimensional (2D) bilayer hexagonal ice adsorbed on solid surfaces undergo premelting as well, resulting in the formation of quasi-liquid bands (QLBs) at the edges. Our extensive molecular dynamics simulations show that the QLB exhibits structure and dynamics indistinguishable from the bilayer liquid phase, acting as a lower-dimensional analog of the QLL on the bulk ice. We further find that at low temperatures, the width of the QLBs at armchair-type edges of the 2D ice is almost identical to that at zigzag-type edges but becomes far greater than the latter at temperatures near the melting point. The chirality-dependent edge premelting of 2D ices should add an important new ingredient to the heterogeneity of premelting.