New phases of water have been detected

New phases of water have been detected

Credit: Pixabay/CC0 Public Domain

Scientists at the University of Cambridge have discovered that water in a single-molecule layer behaves neither as a liquid nor as a solid, and that it becomes highly conductive at high pressures.

Much is known about how “bulk water” behaves: it expands when it freezes and has a high boiling point. But when water is compressed to the nanometer scale, its properties change dramatically.

By developing a new way to predict this unusual behavior with unprecedented accuracy, researchers have detected several new phases of water at the molecular level.

Water trapped between membranes or in tiny nanoscale cavities is common—it can be found in everything from membranes in our bodies to geological formations. But this nanoconfined water behaves very differently from the water we drink.

Until now, the challenges of experimentally characterizing water phases at the nanoscale have prevented a complete understanding of its behavior. But in a paper published in the journal The naturethe Cambridge-led team describes how they used advances in computational approaches to predict the phase diagram of a thick single-molecule water layer with unprecedented accuracy.

They used a combination of computational approaches to enable first-principles investigation of a single layer of water.

The researchers found that water that is confined in a one-molecule-thick layer passes through several phases, including a “hexatic” phase and a “superionic” phase. In the hexatic phase, water acts neither as a solid nor as a liquid, but something in between. In the superionic phase, which occurs at higher pressures, the water becomes highly conductive, rapidly propelling protons through the ice in a manner similar to the flow of electrons in a conductor.

First-principles simulations of the hexatic phase, corresponding to the state point of 1.00 GPa and 340 K, in the presence of carbon atoms explained at the revPBE0-D3 level of theory. Credit: The nature (2022). DOI: 10.1038/s41586-022-05036-x

Understanding the behavior of water at the nanoscale is central to many new technologies. The success of medical treatments can depend on how the water trapped in the small cavities in our body will react. The development of highly conductive electrolytes for batteries, water desalination, and frictionless fluid transport relies on predicting how confined water will behave.

First-principles simulation of the superionic phase, corresponding to the state point of 4.00 GPa and 600 K, in the presence of carbon atoms explained at the revPBE0-D3 level of theory. While we observe dissociation on a time scale of 10 ps, ​​we do not see any reactivity of the proton with the carbon atoms. Credit: The nature (2022). DOI: 10.1038/s41586-022-05036-x

“For all these fields, understanding the behavior of water is the fundamental question,” said Dr Venkat Kapil of the Yusuf Hamied Department of Chemistry at Cambridge, first author of the paper. “Our approach enables the study of a single layer of water in a graphene-like channel with unprecedented predictive accuracy.”

The researchers found that the thick single-molecule water layer in the nanochannel showed rich and diverse phase behavior. Their approach predicts multiple phases that include the hexatic phase—an intermediate between a solid and a liquid—and also a superionic phase, where water has high electrical conductivity.

“The hexatic phase is neither solid nor liquid, but an intermediate, which agrees with previous theories about two-dimensional materials,” Kapil said. “Our approach also suggests that this phase can be seen experimentally by confining water in a graphene channel.

“The existence of the superionic phase in easily accessible conditions is special because this phase is generally found in extreme conditions, such as the cores of Uranus and Neptune. One way to visualize this phase is that the oxygen atoms form a solid lattice and the protons flow. like liquid through bars, like children running through a maze.”

The researchers say that this superionic phase could be important for the future of electrolytes and battery materials because it shows electrical conductivity 100 to 1,000 times higher than current battery materials.

The results will not only help understand how water works at the nanoscale, but also suggest that “nanoconfinement” could be a new way to find the superionic behavior of other materials.

It predicts a new phase of superionic ice

More information:
Angelos Michaelides, First-Principles Phase Diagram of Monolayer Nanoconfined Water, The nature (2022). DOI: 10.1038/s41586-022-05036-x.

Provided by the University of Cambridge

Citation: New phases of water detected (2022, September 14) Retrieved September 21, 2022, from

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