There is yet another round of evidence that suggests supercooled water has two separate phases of liquidity.
|Evidence mounts for liquid-liquid transition in supercooled water|
More evidence that supercooled water exists in two distinct liquid phases has surfaced in experiments done by Austen Angell and colleagues at Arizona State University (ASU) and the University of Amsterdam. The idea of two liquid phases was proposed 25 years ago to explain the thermodynamic properties of supercooled water, but physicists had been unable to cool water to low enough temperatures to observe a transition between the phases.
The physics of water is a rich and active field of research because the substance has many poorly-understood physical properties that do not fit the mould of a normal liquid. “Water is a rather unique liquid,” says Angell. For instance, liquid water exhibits negative thermal expansion below 4 °C, meaning that its volume expands as it cools instead of contracting like most liquids.
One hotly-debated issue for scientists studying water is the “second critical point hypothesis”. This suggests that at low temperatures liquid water makes a transition from its familiar liquid phase to a lower density phase that is also more viscous.