Water exists as two different liquids

June 26, 2017, Stockholm University
Artist's impression of the two forms of ultra-viscous liquid water with different density. On the background is depicted the x-ray speckle pattern taken from actual data of high-density amorphous ice, which is produced by pressurizing water at very low temperatures. Credit: Mattias Karlén

We normally consider liquid water as disordered with the molecules rearranging on a short time scale around some average structure. Now, however, scientists at Stockholm University have discovered two phases of the liquid with large differences in structure and density. The results are based on experimental studies using X-rays, which are now published in Proceedings of the National Academy of Science (US).

Most of us know that is essential for our existence on planet Earth. It is less well-known that water has many strange or anomalous properties and behaves very differently from all other liquids. Some examples are the melting point, the density, the heat capacity, and all-in-all there are more than 70 properties of water that differ from most liquids. These anomalous properties of water are a prerequisite for life as we know it.

"The new remarkable property is that we find that water can exist as two different liquids at low temperatures where ice crystallization is slow", says Anders Nilsson, professor in Chemical Physics at Stockholm University. The breakthrough in the understanding of water has been possible through a combination of studies using X-rays at Argonne National Laboratory near Chicago, where the two different structures were evidenced and at the large X-ray laboratory DESY in Hamburg where the dynamics could be investigated and demonstrated that the two phases indeed both were liquid phases. Water can thus exist as two different liquids.

"It is very exciting to be able to use X-rays to determine the relative positions between the molecules at different times", says Fivos Perakis, postdoc at Stockholm University with a background in ultrafast optical spectroscopy. "We have in particular been able to follow the transformation of the sample at between the two phases and demonstrated that there is diffusion as is typical for liquids".

When we think of ice it is most often as an ordered, crystalline phase that you get out of the ice box, but the most common form of ice in our planetary system is amorphous, that is disordered, and there are two forms of amorphous ice with low and high density. The two forms can interconvert and there have been speculations that they can be related to low- and high-density forms of . To experimentally investigate this hypothesis has been a great challenge that the Stockholm group has now overcome.

"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", says Katrin Amann-Winkel, researcher in Chemical Physics at Stockholm University. "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 possibility to make new discoveries in water is totally fascinating and a great inspiration for my further studies", says Daniel Mariedahl, PhD student in Chemical Physics at Stockholm University. "It is particularly exciting that the new information has been provided by X-rays since the pioneer of X-ray radiation, Wilhelm Conrad Röntgen, himself speculated that water can exist in two different forms and that the interplay between them could give rise to its strange properties".

"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", says Lars G.M. Pettersson, professor in Theoretical Chemical Physics at Stockholm University. "In a nutshell: Water is not a complicated , but two simple liquids with a complicated relationship."

These new results not only create an overall understanding of water at different temperatures and pressures, but also how water is affected by salts and biomolecules important for life. In addition, the increased understanding of water can lead to new insights on how to purify and desalinate water in the future. This will be one of the main challenges to humanity in view of the global climate change.

Explore further: Researchers attempt to uncover the origins of water's unusual properties

More information: Fivos Perakis el al., "Diffusive dynamics during the high-to-low density transition in amorphous ice," PNAS (2017). www.pnas.org/cgi/doi/10.1073/pnas.1705303114

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7 comments

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Nik_2213
3.8 / 5 (5) Jun 26, 2017
I was taught that water is weird, but learning it is an alloy {Of sorts !!} is still a shock.
Well done, team !!
HannesAlfven
2 / 5 (8) Jun 27, 2017
Those of us who have listened to Dr. Gerald Pollack's talks over the past 5+ years are yawning at these by-now frequent announcements that water has a structured state.

Yes, we know -- and realize that there are many important medical and scientific advances on the other side of this controversy, which the mainstream will in short order now "discover".

You can learn about all of these upcoming discoveries by reading Dr. Pollack's published books.
Nik_2213
4 / 5 (4) Jun 27, 2017
Well, HA, I took the trouble to check out your comment...
Kindest way I can put it is 'Wrong End Of The Stick'.
Water HAS AT LEAST 18 PHASES, and there may be others lurking in yet more extreme conditions. Dr. Pollack's methodology seems dogged by experimental problems. Surface effects, bubbles etc etc. And he seems to lack access to the very-short-exposure-time instrumentation required to study the structures he claims. As it stands, his claims are the basis for grant applications, which have yet to be funded. Sadly, his work's potential for pseudo-scientific misinterpretation are truly remarkable. If he could claim a tithe from each bottle of 'snake oil', he'd have funding...
Chris_Reeve
Jun 27, 2017
This comment has been removed by a moderator.
Dingbone
Jun 27, 2017
This comment has been removed by a moderator.
Joker23
1.5 / 5 (2) Jun 28, 2017
I heard about something like this years ago. The Founder of Lear Jet was working on a ''different'' form of water. Long time ago, I don't remember the date or the whole story......memory is going.
Kweden
1 / 5 (1) Jun 29, 2017
Hard to believe this was not discovered much sooner, due to the discovery of heavy and light water, and the importance of water (in just about everything). Even harder to believe that he can't find funding.

Maybe if he told them he was working on a water bomb, instead of desalinization or just discovery, then it would become important to the G and everyone funding them (for defense). Supercooled water is explosive when the pressure is released: think bombs, triggers, switches, killer bb for secret agents (sounds like he needs an agent).

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