Liquid-liquid-like phase transitions between high, mid, and low density phases in confined water

TL;DR

This study uses simulations to reveal stable liquid-liquid phase transitions in confined supercooled water, driven by hydrogen bond network ordering, and identifies critical points in water's phase diagram.

Contribution

It demonstrates real stable first-order phase transitions between high and low density liquids in supercooled water, driven by hydrogen bond orientation and network ordering.

Findings

Identification of stable HDL and LDL phase transitions in confined water.

Discovery of a mid-density, stable intermediate mixed-phase.

Demonstration of water's second and third critical points.

Abstract

Liquid-liquid phase transition (LLPT) in supercooled water has been a long-standing controversial issue. We show simulation results of real stable first-order phase transitions between high and low density liquid (HDL and LDL)-like structures in confined supercooled water in both positive and negative pressures. These topological phase transitions originate from H-bond network ordering in molecular rotational mode after molecular exchanges are frozen. It is explained by the order parameter-dependent free energy change upon mixing liquid-like and ice-like moieties of H-bond orientations which is governed by their two- to many-body interactions. This unexplored purely H-bond orientation-driven topological phase gives mid-density and stable intermediate mixed-phase with high and low density structures. The phase diagram of supercooled water demonstrate the second and third critical points of water.