Anomalies in bulk supercooled water at negative pressure

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 111; no. 22; pp. 7936 - 7941
• Main Authors: Pallares, Gaël, El Mekki Azouzi, Mouna, González, Miguel A., Aragones, Juan L., Abascal, José L. F., Valeriani, Chantal, Caupin, Frédéric
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 03.06.2014; National Acad Sciences
• Subjects: Chemical Sciences; Cold Temperature; Compressibility; Cooling; Critical points; Crystallization; Density; Engineering Sciences; Experiments; Ice; Isochores; Liquids; Metastability; Minerals - chemistry; Models, Chemical; Particle velocity; Phase diagrams; Phase Transition; Physical Sciences; Physics; Plants - chemistry; Pressure; Scattering, Radiation; Simulation; Steam; Stress, Mechanical; Thermodynamics; Velocity; Water; Water - chemistry; Water pressure; scenarios for water; Berthelot tube; Widom line
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.1323366111

Water anomalies still defy explanation. In the supercooled liquid, many quantities, for example heat capacity and isothermal compressibility [Formula], show a large increase. The question arises if these quantities diverge, or if they go through a maximum. The answer is key to our understanding of water anomalies. However, it has remained elusive in experiments because crystallization always occurred before any extremum is reached. Here we report measurements of the sound velocity of water in a scarcely explored region of the phase diagram, where water is both supercooled and at negative pressure. We find several anomalies: maxima in the adiabatic compressibility and nonmonotonic density dependence of the sound velocity, in contrast with a standard extrapolation of the equation of state. This is reminiscent of the behavior of supercritical fluids. To support this interpretation, we have performed simulations with the 2005 revision of the transferable interaction potential with four points. Simulations and experiments are in near-quantitative agreement, suggesting the existence of a line of maxima in [Formula] ([Formula]). This [Formula] could either be the thermodynamic consequence of the line of density maxima of water [Sastry S, Debenedetti PG, Sciortino F, Stanley HE (1996) Phys Rev E 53:6144–6154], or emanate from a critical point terminating a liquid–liquid transition [Sciortino F, Poole PH, Essmann U, Stanley HE (1997) Phys Rev E 55:727–737]. At positive pressure, the [Formula] has escaped observation because it lies in the “no man’s land” beyond the homogeneous crystallization line. We propose that the [Formula] emerges from the no man’s land at negative pressure.