(ORDO NEWS) — Water can be liquid, gaseous or frozen, right? Think again. Scientists from the University of Cambridge have discovered that water in a layer consisting of one molecule is neither a liquid nor a solid, but becomes highly conductive at high pressure.
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 to nanoscale, its properties change dramatically.
By developing a new way to predict this unusual behavior with unprecedented accuracy, the researchers discovered several new phases of water at the molecular level.
Water trapped between membranes or in tiny nano-sized cavities is commonplace – it can be found in everything from the membranes in our bodies to geological formations. But this nanoconfigured water behaves very differently from the water we drink.
Until now, the difficulties associated with the experimental determination of the phases of water at the nanoscale have not made it possible to fully understand its behavior.
But in a paper published in the journal Nature, a Cambridge team describes how they used advances in computational approaches to predict the phase diagram of a one-molecule-thick layer of water with unprecedented accuracy.
They used a combination of computational approaches to first-principle study of a single layer of water.
The researchers found that water, enclosed in a layer one molecule thick, goes through several phases, including a “hexatic” phase and a “superionic” phase. In the hexatic phase, water is neither a solid nor a liquid, but somewhere in between.
In the superionic phase, which occurs at higher pressures, the water becomes highly conductive, rapidly pushing protons through ice, similar to the movement of electrons in a conductor.
Understanding the behavior of water at the nanoscale is critical to many new technologies. The success of medical procedures may depend on how the water reacts when trapped in the small cavities of our body.
The development of highly conductive battery electrolytes, water desalination and frictionless transport of liquids all depend on predicting the behavior of water in a confined space.
“For all of these areas, understanding the behavior of water is a fundamental issue,” says Dr. Venkat Kapil of the Cambridge Yousuf Hamid School of Chemistry, the paper’s first author. “Our approach allows us to study a single layer of water in a graphene-like channel with unprecedented predictive accuracy.”
The researchers found that a one-molecule-thick layer of water in a nanochannel exhibits rich and varied phase behavior. Their approach predicts several phases, including a hexatic phase, intermediate between a solid and a liquid, and a superionic phase, in which water has a high electrical conductivity.
“The hexatic phase is neither a solid nor a liquid, but an intermediate state, which is consistent with previous theories about two-dimensional materials,” Kapil said. “Our approach also suggests that this phase can be observed experimentally by enclosing water in a graphene channel.”
“The existence of a superionic phase in easily accessible environments is unusual because this phase is usually found in extreme environments such as the cores of Uranus and Neptune.
You can think of this phase like this: oxygen atoms form a solid lattice, and protons flow through the lattice like a liquid, like children, running through the maze.”
The researchers say this superionic phase could be important for future electrolytes and battery materials because its electrical conductivity is 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 “nanoconfiguration” may be a new way to search for the superionic behavior of other materials.
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