Scientists at the University of Bristol in the UK and the University of Tokyo in Japan have explained the anomalous properties of water that it exhibits when it cools and freezes. For this, the researchers, using computer modeling, made changes to the structure of the H2O molecule, endowing it with new features. This is reported by Science Alert.
Usually, liquids become denser as their temperature decreases, but water reaches its maximum density at four degrees Celsius. Below this point, the density decreases again, as a result of which ice floats on the surface of water bodies. In addition, water has a high surface tension, yielding to the liquid form of mercury, a high boiling point and is a good solvent.
Such physical features are explained by the presence of hydrogen bonds that form between water molecules. The latter are connected to each other and form a tetrahedron (triangular pyramid).
Scientists have used a supercomputer to create various models of the molecular structure of water. To do this, they varied the parameter λ, called the Stillinger-Weber potential, which is used to describe the physical properties of substances with a tetrahedral arrangement of molecules. The researchers tracked how changes in potential affected the density of matter and the number of chemical bonds between atoms (a two-state model). This made it possible to calculate at what values of λ the anomalous properties of water manifest themselves.
It turned out that with an increase in the Stillinger-Weber potential, the anomalous properties of water associated with density become weaker. As a result, the maximum density shifts towards the liquid-ice phase transition, and the solid form of water loses its buoyancy. As λ decreases, the properties predicted by the two-state model are also weakened.