Phase Transitions Induced by Nanoconfinement in Liquid Water

We present results from molecular dynamics simulations of water confined by two parallel atomically detailed hydrophobic walls. Simulations are performed at $T=300\text{ }\text{ }\mathrm{K}$ and wall-wall separation $d=0.6--1.6\text{ }\text{ }\mathrm{nm}$. At $0.7\ensuremath{\le}d\ensuremath{\le}0.9\text{ }\text{ }\mathrm{nm}$, a first order transition occurs between a bilayer liquid (BL) and a trilayer heterogeneous fluid (THF) as water density increases. The THF is characterized by a liquid (central) layer and two crystal-like layers next to the walls. The BL-THF transition involves freezing of the two surface layers in contact with the walls. At $d=0.6\text{ }\text{ }\mathrm{nm}$, the THF transforms into a bilayer ice (BI) upon decompression. Both the BL-THF and BI-THF transitions are induced by the surface regular atomic-scale structure.