Water at the cavitation limit: Density of the metastable liquid and size of the critical bubble

Abstract

The ability of a liquid to sustain mechanical tension is a spectacular manifestation of the cohesion of matter. Water is a paradigmatic example, because of its high cohesion due to hydrogen bonds. The knowledge of its limit of rupture by cavitation can bring valuable information about its structure. Up to now, this limit has been obscured by the diversity of experimental results based on different physical measures of the degree of metastability of the liquid. We have built a fiber optic probe hydrophone to provide the missing data on the density of the liquid at the acoustic cavitation limit. Our measurements between 0 and 50 • C allow a clear-cut comparison with another successful method where tension is produced in micron-sized inclusions of water in quartz. We also extend previous acoustic measurements of the limiting pressure to 190 • C, and we consider a simple modification of classical nucleation theory to describe our data. Applying the nucleation theorem gives the first experimental value for the size of the critical bubble, which lies in the nanometer range. The results suggest the existence of either a stabilizing impurity in the inclusion experiments, or an ubiquitous impurity essential to the physics of water.

A coherent picture of water at extreme negative pressure

“…3) is amplified by taking the derivative, but the agreement remains satisfactory. For comparison, in the acoustic cavitation experiment 11 at the same temperature, the cavitation pressure was around five times less negative but − V c was only slightly higher, around 10 nm 3 : this suggests that acoustic cavitation occurs heterogeneously on a ubiquitous impurity 11 , which helps to keep a small critical nucleus with a free-energy barrier that can be overcome by thermal fluctuations. The nature of this ubiquitous impurity remains an outstanding question and calls for more experiments and simulations.…”

Communication: Superstabilization of fluids in nanocontainers

“…Proper understanding and accurate description of these fluids remains one of the main challenges in thermodynamics and is crucial in many phenomena of scientific and industrial relevance. 1 One example is cavitation of water at large negative pressures, [2][3][4][5][6] which causes damage to tissues, pumps, and propellers. Despite major efforts, it is still a phenomenon which is not completely understood, as evidenced by the deviations with respect to predictions by Classical Nucleation Theory (CNT) 1,2,7,8 and even between different experimental techniques.…”

“…Despite major efforts, it is still a phenomenon which is not completely understood, as evidenced by the deviations with respect to predictions by Classical Nucleation Theory (CNT) 1,2,7,8 and even between different experimental techniques. 3,6 In industry, much attention has been given to explosive boiling and rapid phase transitions, where metastable liquids such as liquefied nitrogen or natural gas vaporize violently. 9 In a broader context, proper predictions of nucleation rates rely on a precise knowledge of the properties of the metastable phase.…”

“…5,6 The motivation is to understand the anomalies of water, specially locating the line of maximum density (LMD) at negative pressures and a possible re-entrant behavior of the spinodal. In these experiments, water was confined in sealed inclusions in quartz of typical sizes ∼ V = 500 μm 3 , and the onset of cavitation was monitored by first heating the system until all vapor condensed filling the inclusion (the saturation line was exceeded), and subsequently cooling it along an isochor to generate large negative pressures. Cavitation of water at very large negative pressures, down to −140 MPa, which is close to the limit of spontaneous cavitation predicted by CNT, were reported.…”

Effect of compressibility in bubble formation in closed systems

“…Part of the problem lies on the fact that bubbles in open systems are intrinsically unstable, so it is not easy to determine accurately their thermodynamic properties and their kinetic evolution. Moreover, the critical bubble sizes of interest for cavitation and nucleation phenomena are typically very small, [8][9][10] and that adds an extra complication to their description. However, it is in principle possible to stabilize bubbles in a closed system, where the volume and total number of molecules (or mass) are fixed.…”