The Physics of Water's Split Personality Explained by New Computer Model

Water may have a bit of a split personality. By using a computer model, researchers have uncovered the reasons behind water's odd behaviors, such as why its solid state floats. It turns out that at very cold temperatures and above a certain pressure, water may spontaneous split into two liquid forms.

At cold temperatures, the molecules in most liquids slow and eventually settle into a sense and orderly solid that sinks if placed in a liquid. Water, by contrast, forms into ice that floats due to the unusual behavior of its molecules. As the molecules become colder, they actually push away from each other and form regions of lower density.

In order to further investigate this phenomenon, the researchers used a computer model to simulate the behavior of water molecules as temperature dipped below the freezing point. The scientists found that under certain conditions, the virtual water molecules separated into two liquids that differed in density. In fact, the pattern of molecules in each liquid was also different.

"The existence of these two forms could provide a unifying theory for how water behaves at temperatures ranging from those we experience in everyday life all the way to the supercooled regime," said Jeremy Palmer, one of the researchers, in a news release.

The two liquids split into low-density and high-density liquids. The low-density one had a tetrahedral order. The high-density liquid, in contrast, had a fifth neighbor molecule that was trying to squeeze into the pattern.

"The research is a tour de force of computation physics and provides a splendid academic look at a very difficult problem and a scholarly controversy," said C. Austen Angell, professor of chemistry and biochemistry at Arizona State University, who was not involved with the study, in a news release. "Using a particular computer model, the Debenedetti group has provided strong support for one of the theories that can explain the outstanding properties of real water in the supercooled region."

The findings reveal a bit more about the properties of water. This, in turn, could help inform future research and could explain why water acts the way it does.

The findings are published in the journal Nature.