Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number.

Water keeps puzzling scientists because of its numerous properties which behave oppositely to usual liquids: for instance, water expands upon cooling, and liquid water is denser than ice. To explain this anomalous behaviour, several theories have been proposed, with different predictions for the properties of supercooled water (liquid at conditions where ice is more stable). However, discriminating between those theories with experiments has remained elusive because of spontaneous ice nucleation. Here we measure the sound velocity in liquid water stretched to negative pressure, and derive an experimental equation of state, which reveals compressibility anomalies. We show by rigorous thermodynamic relations how these anomalies are intricately linked with the density anomaly. Some features we observe are necessary conditions for the validity of two theories of water.Liquid water exhibits numerous anomalies and different scenarios have been proposed to explain them (1). In particular, the existence of a line of density maxima along isobars has been related to putative maxima in compressibility (2) and heat capacity (3). These maxima may arise from an intriguing phase separation of water in two distinct liquids (1,4), although they can also be explained without resorting to such a phase separation (2). However, the compressibility and heat capacity maxima, whose existence is predicted by molecular dynamics simulations (3,5), have hitherto not been observed in experiments. Alternative theoretical scenarios, namely 1 arXiv:1708.00063v1 [physics.chem-ph] 31 Jul 2017 the stability limit conjecture (6) and the critical-point-free scenario (7, 8), do not require the existence of compressibility and heat capacity maxima, but rather predict a divergence of these quantities at low temperature.Another type of anomaly, namely a minimum in sound velocity along one isochore, was recently discovered at negative pressure (9,10). At negative pressure, the liquid is mechanically stretched, in a state metastable with respect to vapor. To date, the only method able to reach significantly negative pressures (beyond −100 MPa) uses 3 − 10 µm fluid inclusions (FIs) of water in a quartz crystal, and stretching is obtained by cooling liquid water at nearly constant volume (11,12). In our previous work (9, 10), we could only study two FIs along different isochores, and only one clearly showed a minimum in sound velocity. In the present work, we have measured more FIs showing a sound velocity minimum, and reached more negative pressures. We have thus established a more accurate experimental equation of state (EoS) down to −137 MPa. The new EoS strongly supports the existence of the compressibility maxima predicted by some theories of water. Furthermore, we establish new thermodynamic relations between the line of density maxima and the sound velocity anomalies. In contrast to previous works, this provides a relation between quantities that are directly observable in experiments. The corresponding lines of extrema obtained from our experimenta...

No abstract

We present new experimental data of the low-temperature metastable region of liquid water derived from high-density synthetic fluid inclusions (996-916 kg m) in quartz. Microthermometric measurements include: (i) prograde (upon heating) and retrograde (upon cooling) liquid-vapour homogenisation. We used single ultrashort laser pulses to stimulate vapour bubble nucleation in initially monophase liquid inclusions. Water densities were calculated based on prograde homogenisation temperatures using the IAPWS-95 formulation. We found retrograde liquid-vapour homogenisation temperatures in excellent agreement with IAPWS-95. (ii) Retrograde ice nucleation. Raman spectroscopy was used to determine the nucleation of ice in the absence of the vapour bubble. Our ice nucleation data in the doubly metastable region are inconsistent with the low-temperature trend of the spinodal predicted by IAPWS-95, as liquid water with a density of 921 kg m remains in a homogeneous state during cooling down to a temperature of -30.5 °C, where it is transformed into ice whose density corresponds to zero pressure. (iii) Ice melting. Ice melting temperatures of up to 6.8 °C were measured in the absence of the vapour bubble, i.e. in the negative pressure region. (iv) Spontaneous retrograde and, for the first time, prograde vapour bubble nucleation. Prograde bubble nucleation occurred upon heating at temperatures above ice melting. The occurrence of prograde and retrograde vapour bubble nucleation in the same inclusions indicates a maximum of the bubble nucleation curve in the ϱ-T plane at around 40 °C. The new experimental data represent valuable benchmarks to evaluate and further improve theoretical models describing the p-V-T properties of metastable water in the low-temperature region.

No abstract