Using x-ray lasers, researchers at the Stockholm University are ready to follow the transformation between 2 distinct different liquid states of water, both being made from H2O or water molecules. At around -63 Centigrade the 2 liquids exist at different pressure regimes with a density difference of 20% By rapidly varying the pressure before the sample could freeze, it had been possible to observe one liquid becoming the other in real-time. Their findings are published in the journal Science.
Water is both common & necessary for life on Earth, behaves very strangely as compared with other substances. How water properties like density, specific heat, viscosity & compressibility respond to change in pressure & temperature is totally opposite to other liquids that we know. Consequently, water is usually called “anomalous”. If water would have behaved as a “normal liquid” we might not exist, since marine life couldn’t have developed. However, it’s still an open question: what causes these anomalies?
There have existed variety of explanations to the strange properties of water and one among them propose that water has the power to exist as 2 different liquids at different pressures & at low temperatures. If we might be able to keep the 2 liquids in a glass, they might separate with a clear interface in between, as for water & oil. Ordinary water at our ambient conditions is merely one liquid & no interface would be seen in a glass. But on a molecular level, it fluctuates creating small local regions of comparable density as the 2 liquids, causing water’s strange behavior. The challenge has been that no experiment has been possible at the temperatures where the 2 liquids co-exist since ice would form almost instantaneously. Up to now, it’s only been possible to investigate water at these conditions using differing types of computer simulations, which has led to tons of contradicting results counting on the model used.
“What was special was that we were ready to X-ray unimaginably fast, before the water froze & will observe how one liquid transformed to the other form,” says Anders Nilsson, Professor of Chemical Physics at the Stockholm University. “For decades, there has been speculations & different theories to elucidate these anomalous properties, and why they get stronger when water becomes colder. Now we’ve found that the 2 liquid states are real & may explain the water strangeness.”
“I have studied several sorts of disordered ices for an extended time with the goal to determine whether or not they can be considered a glassy state representing a frozen liquid,” says Katrin Amann-Winkel, Senior Researcher in Chemical Physics at the Stockholm University. “It’s a dream come true to see that indeed, they represent real liquids & we see the transformation between them.”
“We worked so hard for several years to conduct measurements of water under such a low-temperature conditions without freezing and it’s so rewarding to see the outcome,” says Harshad Pathak, researcher in Chemical Physics at the Stockholm University. “Many attempts over the world are made to look for the 2 liquids by putting water in tiny compartments or mixing it with other compounds, but here we could follow it as simple pure water.”
“I wonder if the 2 liquid states as fluctuations might be a crucial ingredient to the biological processes in living cells,” says Fivos Perakis, professor in Chemical Physics at the Stockholm University. “The new result can open-up many new research directions also about water in biological sciences.”
“Maybe one among the liquid forms is more prominent for water in small pores inside membranes used to desalinate water,” says Marjorie Ladd Parada, Postdoc at the Stockholm University. “I think the access to clean water are going to be one among the main challenges with climate change.”
“There has been an intense debate about the origin of the strange properties of water for over a century, since the early work of Wolfgang Röntgen,” further explains Anders Nilsson. “Researchers studying the physics of water can now choose the model that water can exist as two liquids in the supercooled regime. The next stage is to find out if there’s a critical point when the 2 liquids cross over to become just one liquid as the pressure & temperature changes. A big challenge for the subsequent few years.”