Compressibility anomalies in stretched water and their interplay with density anomalies

TL;DR

This study investigates the unusual compressibility and density anomalies of stretched water by measuring sound velocity at negative pressures, providing experimental evidence that supports certain theories of water's anomalous behaviour.

Contribution

It presents the first experimental measurement of sound velocity in stretched water and links compressibility anomalies with density anomalies through thermodynamic relations.

Findings

Revealed compressibility anomalies in stretched water.

Linked anomalies with density behaviour of water.

Supported specific theoretical models of water.

Abstract

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.