“Square Ice” Could Be Ideal Material For Filtering Applications: Study

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Scientific researchers have created a new form of ice by pressing water between two sheets of graphene. Just a few molecules thick, the “square ice” atoms are formed in a square grid pattern.

This new study proving the existence of square ice brings another property of graphene, which consists of flat, atom-thick sheets of carbon, front and center. We already knew that graphene sheets were very stiff, strong and conductive, but they also put intense pressure on molecules trapped between them. The researchers point out that the formation of square ice explains why water (and nothing else) seeps through stacks of graphene rapidly, a characteristic that makes the material a likely candidate for desalination membranes to purify water as well as other filtering applications.

More on the discovery of square ice

In 2012, a team of physicists led by Andre Geim at the University of Manchester discovered that water vapor could pass through laminated sheets of graphene oxide, tiny helium gas molecules could do. A couple of years later, the team showed that liquid water also percolated through stacks of graphene oxide, even though no other molecules passed through.

The researchers noted that computer models showed the that water was forming very thin layers of square ice between the graphene sheets. In essence, adding water at one end pushed the ice and shunted all the molecules forward together, like interlocked train cars, out the other end. “But you never trust molecular-dynamics simulations,” said Geim. So the team decided to conduct a real-world experiment.

The proof of square ice

The experiment involved placing one microliter of water onto a sheet of graphene, and putting a second graphene sheet on top. As the water slowly evaporated, the graphene sheets were pulled together until they were under a nanometer apart, trapping the water in the graphene sandwich.

Transmission electron microscope images showed that square ice had formed in the graphene sandwich. “It’s not totally unexpected,” notes Alan Soper, a physicist at the Rutherford Appleton Laboratory in the UK, who authored an article accompanying the report of the discovery, which is published in Nature this week. It was already known that when water forms into small clusters of just eight molecules, it creates a cubic structure. “But it’s never been observed in such an extended layer,” he continued.

Soper says he believes that square ice is a new crystalline phase of ice, and will be added to the 17 other phases that are already known.

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