How supercooled water is prevented from turning into ice (Vol. 46 No. 4)

Calculating the energy barrier that keeps liquid water below zero from immediately turning into ice provides the key to understanding its ability to be compressed as temperature drops.

Water behaves in mysterious ways. Especially below zero, where it is dubbed supercooled water, before it turns into ice. Physicists have recently observed the spontaneous first steps of the ice formation process, as tiny crystal clusters as small as 15 molecules start to exhibit the recognisable structural pattern of crystalline ice. This is part of a new study, which shows that liquid water does not become completely unstable as it becomes supercooled, prior to turning into ice crystals. The team reached this conclusion by proving that an energy barrier for crystal formation exists throughout the region in which supercooled water’s compressibility continues to rise. Previous work argued that this barrier vanished as the liquid gets colder.

C. R. C. Buhariwalla, R. K. Bowles, I. Saika-Voivod, F. Sciortino and P. H. Poole, Free energy of formation of small ice nuclei near the Widom line in simulations of supercooled water, Eur. Phys. J. E, 38, 39 (2015)
[Abstract]