Scientists from the University of Cambridge have found that water in a single molecule layer acts neither as a liquid nor as a solid and becomes highly conductive at high pressures.
Much is known about the behavior of “bulk water”: it expands when it freezes and has a high boiling point. But when water is compressed at the nanoscale, its properties change drastically.
By developing a new way to predict this unusual behavior with unprecedented accuracy, the researchers 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 our body’s membranes to geological formations. But this nanoconfined water behaves very differently from the water we drink.
Until now, the challenges of experimentally characterizing the phases of water at the nanoscale have prevented a full understanding of its behavior. But in an article published in the journal NatureThe Cambridge-led team describe how they used advances in computational approaches to predict the phase diagram of a molecule-thick layer of water with unprecedented accuracy.
They used a combination of computational approaches to enable first-principles-level study of a single layer of water.
The researchers found that water that is confined in a one-molecular thick layer goes 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 resembling the flow of electrons in a conductor.
Understanding the behavior of water at the nanoscale is essential for many new technologies. The success of medical treatments may depend on the reaction of the water trapped in the small cavities of our body. The development of highly conductive electrolytes for batteries, water desalination, and frictionless fluid transport all depend on predicting the behavior of confined water.
“For all of these areas, understanding the behavior of water is the fundamental question,” said Dr Venkat Kapil of the Department of Chemistry Yusuf Hamied 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 water layer of a molecule in the nanochannel exhibited rich and diverse phase behavior. Their approach predicts several phases including the hexatic phase – an intermediate between a solid and a liquid – and also a superionic phase, in which water has a high electrical conductivity.
“The hexatic phase is neither a solid nor a liquid, but an intermediate, which is in agreement with previous theories about two-dimensional materials,” Kapil said. “Our approach also suggests that this phase can be observed experimentally by confining water in a graphene channel.
“The existence of the superionic phase in easily accessible conditions is special, because this phase is usually found in extreme conditions like the core of Uranus and Neptune. One way to visualize this phase is that oxygen atoms form a solid lattice and that the protons circulate like a liquid through the lattice, like children running through a maze.”
The researchers say this superionic phase could be important for future electrolyte and battery materials, as it has 100 to 1,000 times greater electrical conductivity than current battery materials.
The results will not only help to 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.
Predicting a new phase of superionic ice
Angelos Michaelides, The First Principles Phase Diagram of Monolayer Nanoconfined Water, Nature (2022). DOI: 10.1038/s41586-022-05036-x. www.nature.com/articles/s41586-022-05036-x
Provided by the University of Cambridge
Quote: New Water Phases Detected (September 14, 2022) Retrieved September 14, 2022 from https://phys.org/news/2022-09-phases.html
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