Final Report Summary - WASSR (Water anomalies in the stretched and supercooled regions)
Water is the most abundant liquid on Earth’s surface. It is essential for life. Surprisingly, despite extensive studies, many of its properties remain to be explained. The aim of this project is to contribute to the understanding of water, by studying its anomalies in the metastable liquid state.
A liquid should transform into vapour at its boiling point, or into a solid at its freezing point. However, it can be observed beyond these limits. It is then in a metastable state, separated from the stable phase by an energy barrier due to surface tension. The short lifetime of the liquid under such extreme conditions renders measurements particularly challenging. Nevertheless, we undertook this challenge, with the aim of bringing valuable information on the properties and structure of water.
We followed two major directions:
− we stretched water into the negative pressure region, where the liquid is metastable with respect to the vapour, using several methods. With an acoustic method, we studied water and other liquids. Whereas for ethanol and heptane we can reach negative pressures close to the theoretical limit, we cannot do so with water: vapour bubbles nucleate under much less tension than expected. This limited our first measurement of the equation of state of stretched water to -26 MPa. Then we demonstrated that one method, using micron-sized water droplets trapped in quartz, was by far more efficient. Using Brillouin spectroscopy, we were able to measure the sound velocity in water at pressures in excess of -100 MPa, and for the first time in the doubly metastable region where the liquid is metastable with respect to the vapour and to the solid. We found new anomalies of water in this region. We also obtained an experimental equation of state of water down to -120 MPa. Our work found an unexpected application: Brillouin spectroscopy can be used on fluid inclusions in natural samples to gain insight on the conditions of their formation, with possible application to reconstruction of past temperatures.
− in the supercooled region, where the liquid is metastable with respect to the solid, we used special viscometers to measure the viscosity of supercooled liquid water. At ambient pressure, we used Brownian motion to measure viscosity down to -34°C. We obtain more reliable values than were available. We used them to show the violation of the relations between viscosity and translational and rotational diffusion coefficients (Stokes-Einstein and Stokes-Einstein-Debye, respectively). The fractional versions of these relations show a crossover in the link between viscosity and translational diffusion, whereas viscosity remains coupled to rotation down to the lowest temperatures. This is reminiscent of what happens near the glass transition of a liquid, whereas water is very far from this transition at -34°C. This suggests that dynamic heterogeneities (transient clusters of fast or slow molecules) may appear in supercooled water. We also measured for the first time the viscosity of supercooled water up to 300 MPa.
A liquid should transform into vapour at its boiling point, or into a solid at its freezing point. However, it can be observed beyond these limits. It is then in a metastable state, separated from the stable phase by an energy barrier due to surface tension. The short lifetime of the liquid under such extreme conditions renders measurements particularly challenging. Nevertheless, we undertook this challenge, with the aim of bringing valuable information on the properties and structure of water.
We followed two major directions:
− we stretched water into the negative pressure region, where the liquid is metastable with respect to the vapour, using several methods. With an acoustic method, we studied water and other liquids. Whereas for ethanol and heptane we can reach negative pressures close to the theoretical limit, we cannot do so with water: vapour bubbles nucleate under much less tension than expected. This limited our first measurement of the equation of state of stretched water to -26 MPa. Then we demonstrated that one method, using micron-sized water droplets trapped in quartz, was by far more efficient. Using Brillouin spectroscopy, we were able to measure the sound velocity in water at pressures in excess of -100 MPa, and for the first time in the doubly metastable region where the liquid is metastable with respect to the vapour and to the solid. We found new anomalies of water in this region. We also obtained an experimental equation of state of water down to -120 MPa. Our work found an unexpected application: Brillouin spectroscopy can be used on fluid inclusions in natural samples to gain insight on the conditions of their formation, with possible application to reconstruction of past temperatures.
− in the supercooled region, where the liquid is metastable with respect to the solid, we used special viscometers to measure the viscosity of supercooled liquid water. At ambient pressure, we used Brownian motion to measure viscosity down to -34°C. We obtain more reliable values than were available. We used them to show the violation of the relations between viscosity and translational and rotational diffusion coefficients (Stokes-Einstein and Stokes-Einstein-Debye, respectively). The fractional versions of these relations show a crossover in the link between viscosity and translational diffusion, whereas viscosity remains coupled to rotation down to the lowest temperatures. This is reminiscent of what happens near the glass transition of a liquid, whereas water is very far from this transition at -34°C. This suggests that dynamic heterogeneities (transient clusters of fast or slow molecules) may appear in supercooled water. We also measured for the first time the viscosity of supercooled water up to 300 MPa.