Mysterious tetrahedrons: they can explain the uniqueness of water

Tetrahedrons explain the uniqueness of water

The special qualities of water that are necessary for any form of life, mainly come from the property of two states. This fact was proved by the specialists from the Institute of Industrial Sciences at the University of Tokyo. They analyzed the experimental data and found out the possibility of supercooled water to perform a phase transition between disordered and tetrahedral structured forms.

The scientists proved the existence of a critical point arising from the cooperation of tetrahedrons and showed its importance in water anomalies. Water, in its liquid form, does not match the behavior of other liquids.

Anomalies are considered to be the maximum density of water at a temperature of 4 degrees and its high heat capacity. They have important consequences for all living organisms. The origin of these features is the subject of important scientific debate. But the researchers' new model postulates the dynamic coexistence of two types of molecular structures in liquid water. It is the disordered structure of a normal liquid and the most preferred tetrahedral structure. In virtually all other phase transitions, there is a so-called tipping point, at which time the correlation between tetrahedra takes on a power-law form that means that there will no longer be any typical length scale.

Computer modeling of water and analysis of thermodynamic and dynamic data, including measurements of the process of the X-ray scattering, density, viscosity, allowed the scientists to narrow the search area where the critical point may be.

The lead author of the study, Rui Shi, believes that under the conditions created in the model, the formation of tetrahedral structures in liquid water occurs everywhere, that indicates phase transitions with a critical point. The process takes place at a temperature of 90 degrees and at a pressure of 1700 atmospheres.

It is difficult to conduct the experiments in such a physical range. That is because the water temperature is low, where ice crystals can form quickly. But the water samples can remain in a supercooled state for a long time at very high pressures.

The scientists were able to observe evidence of the actual behavior of the tipping point. But it turned out that its influence is almost insignificant in the experimentally accessible region of liquid water. It means that the water anomalies are due to a two-state property, and not due to criticality.