Some Aspects of the Liquid Water Thermodynamic Behavior: From The Stable to the Deep Supercooled Regime.

Francesco Mallamace,Domenico Mallamace,Giuseppe Mensitieri,Sow-Hsin Chen,Martina Salzano De Luna

doi:10.3390/ijms21197269

Abstract

Liquid water is considered to be a peculiar example of glass forming materials because of the possibility of giving rise to amorphous phases with different densities and of the thermodynamic anomalies that characterize its supercooled liquid phase. In the present work, literature data on the density of bulk liquid water are analyzed in a wide temperature-pressure range, also including the glass phases. A careful data analysis, which was performed on different density isobars, made in terms of thermodynamic response functions, like the thermal expansion and the specific heat differences , proves, exclusively from the experimental data, the thermodynamic consistence of the liquid-liquid transition hypothesis. The study confirms that supercooled bulk water is a mixture of two liquid “phases”, namely the high density (HDL) and the low density (LDL) liquids that characterize different regions of the water phase diagram. Furthermore, the isobars behaviors clearly support the existence of both a liquid–liquid transition and of a liquid–liquid critical point.

Highlights

Water is the most important substance in nature, but, at the same time, it is one of the least understood
The numerous MD simulations studies on water with different model potentials [37] and the experiments performed on confined water have given many important suggestions on what happens in the temperature region between Tx and Th
The aim is to show that the thermodynamic functions that correspond to the bulk density data alone are sufficient to clarify the most significant water anomalies in the supercooled region including the liquid–liquid (or second) critical point (LLCP)

Summary

Introduction

Water is the most important substance in nature, but, at the same time, it is one of the least understood. An idea proposed to interpret different experimental observations on the system thermodynamical functions that are characterized by diverging behaviors [11,12] The verification of such a hypothesis was with continuity, over the past twenty-eight years, the body of work of many studies. Of these researches, the vast majority come from the MD simulation [13,14], often with controversial results, but rich in profound and significant suggestions Despite these efforts, to date no unambiguous experimental proof on the existence of this second critical point has yet been found

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