Analysis of two liquid states of water by X-ray laser.

Written by AZoMNovember 20, 2020

Stockholm University scientists used X-ray lasers and successfully studied the transformation between two different liquid states of water (H.₂O), both being composed of H.₂Or molecules.

At a temperature of about −63 ° C, both liquids occur at distinct pressure regimes with a density variation of 20%. The team quickly changed the pressure before the sample froze and could see one liquid transform into another in real time. The results of their studies were reported in Science magazine.

Unlike other substances, water, common and essential to the existence of life on Earth, it is acting very strangely. The way the properties of H.₂Or, like density, viscosity, specific heat and compressibility, the change in response to changes in temperature and pressure is totally different from that of other common liquids. Therefore, H.₂Or it is often referred to as “anomalous”.

If water had acted as a “normal liquid”, man would not be able to exist, as marine life could not have formed. But what triggers these anomalies is still unsolved.

There have been several explanations for the odd properties of H.₂Or, where one of them suggests that H.₂O has the ability to present themselves as distinct two liquids at different pressures and low temperatures. If both liquids could be placed in a glass, they would separate with a distinct interface in between, as with oil and water.

Normal water under ambient conditions is just a liquid and no interfaces can be observed in a glass, but on a molecular scale it fluctuates and forms small local areas of similar density to the two liquids, resulting in strange water behavior.

The difficulty faced by the researchers is that no experiment has been feasible at temperatures where the two liquids would occur at the same time as ice would form practically immediately. So far, it has been possible to examine water under these conditions using various types of computer simulations, which has led to many contradictory results based on the model used.

The special thing was that we were able to take unimaginably fast x-rays, before the water froze, and we could observe how one liquid turns into another. For decades, there has been speculation and different theories to explain these anomalous properties and why they get stronger when the water gets colder. Now we have discovered that the two liquid states are real and can explain the strangeness of water.

Anders Nilsson, professor of chemical physics, Stockholm University

“I have long studied different forms of disordered ice with the aim of determining if they can be considered a glassy state representing a frozen liquid“Says Katrin Amann-Winkel, senior researcher in chemical physics at Stockholm University.”It’s a dream come true to see that actually represent real liquids and see the transformation between them. “

We have worked so hard for several years to conduct water measurements in such low temperature conditions without freezing and it is so rewarding to see the result. Many attempts around the world have been made to look for the two liquids by putting water in tiny compartments or mixing it with other compounds but here we could follow it as plain pure water.

Harshad Pathak, researcher in chemical physics, Stockholm University

“I wonder if the two liquid states as fluctuations could be an important ingredient for biological processes in living cells“States Fivos Perakis, assistant professor of physical chemistry at the University of Stockholm.”The new result may open up many new directions for water research in the life sciences as well. “

Perhaps one of the liquid forms is more prominent for the water in small pores inside the membrane used to desalinate water. I think that access to clean water will be one of the main challenges of climate change.

Marjorie Ladd Parada, Postdoc, Stockholm University

“There has been an intense debate on the origin of the strange properties of water for over a century since Wolfgang Röntgen’s early works. Researchers studying the physics of water can now settle on the model that water can exist as two liquids in the super-cooled regime“, Explains Anders Nilsson.

“The next step is to find out if there is a critical point where the two liquids cross to become a single liquid, as pressure and temperature vary. A great challenge for the next few years“, Concluded Nilsson.

Journal reference:

Kim, KH, et al. (2020) Experimental observation of liquid-liquid transition in bulk supercooled water under pressure. Science. doi.org/10.1126/science.abb9385.

Source: http://www.su.se/english