Collaboration internationale en Chimie : origines des anomalies thermodynamiques et dynamiques de l'eau liquide métastable – ANOMWATER

Water is among the most important and most studied substances on earth, yet, the origins of its anomalous thermodynamic, dynamic, and structural properties have eluded complete understanding. Theoretical, computational, and experimental work suggests that clues to these origins lie in the metastable states of water at negative pressures (stretched superheated regime) and at supercooled temperatures. This collaborative proposal brings a broad, new set of techniques to bear on the challenge of providing a complete, experimental analysis of these states. The outcomes of this project will build the foundation of improved understanding of water and will provide a rich training ground for students in experimental physical chemistry. Outstanding questions: Q1) Phase diagram and structure in the stretched superheated and supercooled regimes. The equation of state has never been mapped deep into these regimes, leaving open fundamental questions about features that could explain the anomalous properties of water. Computational studies indicate a tight correlation between the evolution of molecular structure and macroscopic anomalies. The minimal experimental data on structure in the streched superheated regime leave open important questions regarding the accuracy of these predictions and the energetics (enthalpy vs. entropy) that may dictate these phenomena. Q2) Mechanisms of failure of metastable states. In all but one experiment, the observed stability limit in the stretched superheated regime has been several fold lower than predicted theoretically. Recent experiments by Caupin suggest that there may exist a fundamental mechanism of nucleation that is not accounted for in conventional predictions; the elucidation of this mechanism would have profound scientific and technological implications. Q3) Viscosity in the supercooled regime. Only one reliable experiment is available at 1 bar in the supercooled regime; none exist in the streched superheated regime. These measurements, combined with existing diffusivity data, will allow to check the Stokes-Einstein and Stokes-Einstein-Debye relations, thought to be violated in water at higher temperatures than usual glass forming liquids and to provide a signature of the liquid-liquid critical point predicted by simulations in the supercooled region.