Another unusual property of water discovered

Researchers at the University of California, San Diego have discovered that under extreme conditions – high pressure and low temperature – liquid water can exist in two phases with different densities. This discovery confirms a theory proposed back in 1992, but until now not tested in practice.

The results of the work are published in the journal Nature Physics.

Water is a unique substance capable of existing in three states of matter: solid, liquid, and gaseous. However, new research shows that at a temperature of -75°C and a pressure of 1,250 atmospheres, it loses homogeneity and separates into two distinct liquid phases – one with high density, the other with low density.

Previously, it was not possible to experimentally reproduce this effect. However, a group led by Professor Francesco Paesani was able to do this using complex computer modeling based on machine learning and quantum mechanics methods.

In their work, the scientists used the MB-pol model, which allows for detailed analysis of water molecule interactions. Similar to how human behavior changes depending on the environment, water molecules also behave differently depending on neighboring particles.

The calculations were performed on powerful supercomputers, such as Expanse in San Diego, and took almost two years.

Although recreating this effect in laboratory conditions is still difficult, scientists hope that experimental methods to confirm it will emerge over time. One possible solution could be the use of nanodroplets, in which surface tension creates the necessary pressure.

Understanding this phenomenon could open the way to creating new materials with adjustable density, capable, for example, of absorbing pollutants or being used in water desalination technologies.

"Now it's up to the experimenters," notes Paesani. "If our theoretical calculations are confirmed, this could change our understanding of water."