New Form of Liquid Identified

When water is "supercooled" to 207 Kelvins, or 87 degrees below zero on the Fahrenheit scale, it transforms into a new form of liquid, according to a new study.

This so-called "liquid-liquid" phase transition in supercooled water had been used in the past to explain many of water's anomalous behaviors, though direct experimental verification of such a phase transition had not been accomplished and theoretical studies from different simulations contradicted each other.

Led by chemist Feng Wang, however, researchers at the University of Arkansas report they successfully confirmed via simulation this phase transition at these temperatures.

In order to do this, they investigated the liquid-liquid phase transition using a simulation model called "Water potential from Adaptive Force Matching for Ice and Liquid." In doing so, they found that, while normal water is a high-density liquid, low-density liquid emerged at lower temperatures.

"On a miscrosecond time scale, the water did not actually form ice but it transformed into a new form of liquid," Wang said in a press release.

The properties of supercooled water are important for understanding basic processes during cryoprotection, or the preservation of tissue cells by liquid nitrogen so they can be thawed without damage, explained Wang.

"The study provides strong supporting evidence of the liquid-liquid phase transition and predicted a temperature of minimum density if water can be cooled well below its normal freezing temperature," he added, stating that their analysis "shows water will expand at a very low temperature even without forming ice." 

The research was supported by a National Science Foundation Faculty Early Career Development Award and by a startup grant from the school itself. The University of Arkansas High Performance Computing Center provided the main computational resource for the study.

The findings were published online July 8 in the journal Proceedings of the National Academy of Sciences.