Water is unique, as it can exist in two liquid states that have different ways of bonding the water molecules together. The water fluctuates between these states as if it can’t make up its mind and these fluctuations reach a maximum at -44°C. It is this ability to shift from one liquid state into another that gives water its unusual properties and since the fluctuations increase upon cooling also the strangeness increases.
“What was special was that we were able to X-ray unimaginably fast before the ice froze and could observe how it fluctuated between the two states,” says Anders Nilsson, Professor of Chemical Physics at Stockholm University. “For decades there has been speculations and different theories to explain these remarkable properties and why they got stronger when water becomes colder. Now we have found such a maximum, which means that there should also be a critical point at higher pressures.”
Another remarkable finding of the study is that the unusual properties are different between normal and heavy water and more enhanced for the lighter one. “The differences between the two isotopes, H2O and D2O, given here shows the importance of nuclear quantum effects,” says Kyung Hwan Kim, postdoc in Chemical Physics at Stockholm University. “The possibility to make new discoveries in a much studied topic such as water is totally fascinating and a great inspiration for my further studies,” says Alexander Späh, PhD student in Chemical Physics at Stockholm University.Paper. (paywall) – Kyung Hwan Kim, Alexander Späh, Harshad Pathak, Fivos Perakis, Daniel Mariedahl, Katrin Amann-Winkel, Jonas A. Sellberg, Jae Hyuk Lee, Sangsoo Kim, Jaehyun Park, Ki Hyun Nam, Tetsuo Katayama, Anders Nilsson. Maxima in the thermodynamic response and correlation functions of deeply supercooled water. Science, 2017; 358 (6370): 1589 DOI: 10.1126/science.aap8269 More.
Water is unique in lots of ways but don’t tell anyone.
See also: What becomes of science when the evidence does not matter?