Researchers Claim That Water Has Two Different Liquid Phases

Artist's impression of the two forms of ultra-viscous liquid water with different density. Credit: Mattias Karlén

We may take water for granted, but it’s an incredibly special substance. It is crucial to life on Earth and has many unique properties, including one that scientists have just discovered.

The researchers looked at two special phases of water called high-density and low-density amorphous ice, and discovered that as water goes from one type of amorphous ice to the other, it transforms into two different types of liquid water.

The research, published in Proceedings of the National Academy of Sciences, was able to track the movement of the molecules as the water changed from high-density to low-density amorphous ice.

"I have studied amorphous ices for a long time with the goal to determine whether they can be considered a glassy state representing a frozen liquid," co-author Katrin Amann-Winkel, researcher in chemical physics at Stockholm University, said in a statement. "It is a dream come true to follow in such detail how a glassy state of water transforms into a viscous liquid which almost immediately transforms to a different, even more viscous, liquid of much lower density."

The amorphous ice phase is achieved when water molecules are frozen way below 0°C (32°F). Due to factors like how quickly the freezing happens or if the pressure is particularly high, the ice might not become crystalline. While the ice we make in a freezer is crystalline, the amorphous ice on Earth is mostly formed in labs.

But amorphous ice is found in the top layers of the atmosphere and, most importantly, in interstellar clouds, which makes it the most common structure for water molecules in the universe. This, combined with its unusual properties, makes amorphous ice a particularly intriguing object of research.

For the study, the researchers used two sophisticated X-ray lasers – the Argonne National Laboratory near Chicago and the large X-ray laboratory DESY in Hamburg, Germany. The first allowed them to show that the two substances were different and the second allowed them to prove that the substances are indeed liquid.

"The new results give very strong support to a picture where water at room temperature can't decide in which of the two forms it should be, high or low density, which results in local fluctuations between the two," added Lars G.M. Pettersson, professor in theoretical chemical physics at Stockholm University. "In a nutshell: Water is not a complicated liquid, but two simple liquids with a complicated relationship."

With water being so prevalent in every aspect of our lives, this research has huge potential. It will be interesting to see what follow-up studies can do to further unravel the mystery that is water.

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