Liquid-liquid Phase Transition Observed for the First Time

Liquid-liquid Phase Transition Observed for the First Time

Esther Pilla reports on the state of water research

On Earth, water can exist as solid, liquid and
 gas. These phase transitions are important because they occur within a range of temperatures compatible with human life (or, in the case of boiling water, temperatures that allow cooking).

This March, a team from Arizona State University and the University of Amsterdam demonstrated for the first time that water can transition from one liquid state to a different liquid state. This proves that super-cooled aqueous liquids can change to a liquid form with lower density and higher viscosity.

This transition could not previously be observed because when reaching super-cooling conditions (about -90°C), water tends to crystallise to ice before the critical temperature point for a liquid-liquid transition is reached. This technical limitation, defined as the ‘crystallisation curtain’, can now be lifted because newly discovered solutes permit the super-cooling of water, acting as anti- freeze. The anti-freeze solutes described in the article allow water to behave in its normal way, without disrupting the liquid-liquid phase transition that is prevented by freezing. Professor C Austen Angell and colleagues speculate that liquid-liquid phase transition of water may occur also in neat water. Further experiments are needed to determine the effects of other factors, such as pressure and ionic concentration, on this phenomenon, and especially to understand whether this transition can be exploited without the need for super-cooling.