What is anomalous in liquids and is there liquid-liquid phase transition?

Tomaž Urbič
Faculty of Chemistry and Chemical Technology, Chair of Physical Chemistry, University of Ljubljana, Slovenia, EU


The most known anomaly of water is that density of ice is lower than density of liquid. This is why ice in beverage is floating on liquid and beverage is ice cold on top. There are many other water anomalies; number depends on reference state we are choosing. Question remains why should water be treated as anomalous liquid being the most abundant liquid on earth. Why shouldn’t we say water is normal and other liquids anormal?

The existence of a liquid-liquid first order phase transition in supercooled water has been one of the most heavily debated questions. The liquid-liquid critical point (LLCP) hypothesis was put forward in 1992 after simulations of the ST2 water model showed a putative phase transition in the supercooled range.7 Much of the subsequent research was focused on proving or disproving the existence of LLCP and results to this day remain mixed. There is limited experimental evidence to back these claims up because the supposed LLCP is well below the homogenous nucleation temperature of water.