Using X-ray lasers, researchers at Stockholm University have been able to track the transformation between two different different liquid water states, both made from the H2O molecule. At about -63 celsius the two liquids exist in different pressure regimes with a density difference of 20%. By rapidly changing the pressure before the sample freezes, it was possible to observe that one fluid changed into another in real time. Their findings are published in the journal science.
Water, ordinary and necessary for life on Earth, behaves very strangely compared to other substances. The way water properties like density, specific heat, viscosity and compression react to changes in pressure and temperature is completely opposite to other liquids we know. Consequently, water is often called “abnormal”. If water had been brought in as a “normal fluid” we would not have existed, as marine life could not have developed. However, it is still an open question: what causes these anomalies?
There have been a number of explanations for the strange properties of water and one of them proposes that water have the ability to exist as two different liquids at different pressures and at low temperatures. If we were to be able to keep both liquids in a glass, they would separate with a clear interface in between, as for water and oil (see figure). Ordinary water in our ambient conditions is just a liquid and no interface can be seen in a glass – but at a molecular level, it fluctuates to create small local regions of similar density as the two liquids, causing strange behavior. of water. The challenge has been that no experiment has been possible at temperatures where the two liquids will coexist as ice would form almost immediately. So far it has only been possible to investigate water under these conditions using different types of computer simulations, which has led to many contradictory results depending on the model used.
“The special thing was that we were able to do X-rays unimaginably fast, before the water froze and we could observe how one liquid transformed into another,” says Anders Nilsson, Professor of Chemical Physics at Stockholm University. . “For decades, there have been various speculations and theories to explain these abnormal properties and why they intensify when the water gets colder. We have now discovered that the two liquid states are real and may explain the strangeness of water. “
“I have been studying several forms of disordered ice for a long time with the aim of determining whether they can be considered a glass state representing a frozen liquid,” says Katrin Amann-Winkel, Senior Researcher in Chemical Physics at the University of Stockholm. “It’s a real dream to see that they really represent real liquids and we see the transformation between them.”
“We have worked so hard for several years to perform water measurements at such low temperature conditions without freezing and it is so rewarding to see the result,” says Harshad Pathak, Researcher in Chemical Physics at Stockholm University. “Many attempts have been made all over the world to search for two liquids by placing water in small compartments or by mixing it with other ingredients, but here we can follow it as plain pure water.”
“I wonder if two liquid states like fluctuations can be an important component in biological processes in living cells,” says Fivos Perakis, Assistant Professor of Chemical Physics at Stockholm University. “The new result could open up many new research directions even in relation to water in the biological sciences.”
“Perhaps one of the liquid forms is most prominent for water in the small pores inside the membranes used to desalinate water,” says Marjorie Ladd Parada, Postdoc at Stockholm University. “I think access to clean water will be one of the main challenges with climate change.”
“There has been an intense debate about the origin of the strange properties of water for more than a century since the early work of Wolfgang Röntgen,” Anders Nilsson further explains. “Researchers studying the physics of water can now come to the conclusion that water can exist as two liquids in the super-cooled regime. The next stage is to find out if there is a critical point when both liquids pass to become just one liquid, as pressure and temperature change. A big challenge for the coming years. “
For more on this discovery, read Researchers Prove that Water Has Multiple Liquid Conditions With Different Characteristics.
Reference: “Experimental observation of the liquid-liquid transition in super cold water wholesale under pressure” by Kyung Hwan Kim, Katrin Amann-Winkel, Nicolas Giovambattista, Alexander Späh, Fivos Perakis, Harshad Pathak, Marjorie Ladd Parada, Cheolhee Yang Mariedahl, Tobias Eklund, Thomas. J. Lane, Seonju You, Sangmin Jeong, Matthew Weston, Jae Hyuk Lee, Intae Eom, Minseok Kim, Jaeku Park, Sae Hwan Chun, Peter H. Poole and Anders Nilsson, November 20, 2020, science.
DOI: 10.1126 / science.abb9385
The study was conducted in collaboration with POSTECH University in Korea, PAL-XFEL in Korea, the SLAC National Accelerator Laboratory in California, Brooklyn College of New York City University in the USA, and St. Louis University. Francis Xavier in Canada. Other contributors to the study include former members of the Chemical Physics group at Stockholm University – Kyung Hwan Kim, Alexander Späh, Daniel Mariedahl, Tobias Eklund and Matthew Weston.