A super-thin layer of water that freezes at room temperature has the ability to create never before-seen square snowflakes when encased in graphene nano-capillaries.
The finding could provide insight into the behavior of water on a molecular level and lead to the development of efficient new technologies such as filtration, desalination, and distillation, the University of Manchester reported. Monolayers of water exist on essentially every surface on Earth, but little is known about its molecular structure and behavior, especially when it exists inside material and tiny capillaries.
"Scientists tried to understand the structure of water confined within narrow channels for decades but until now it was only possible by computer simulations, and the results often did not agree with each other," said Irina Grigorieva, of the University of Manchester. "Microscopic cracks, pores, channels are everywhere, and not only on this planet. Knowing that water on a nanoscale behaves so differently from the common bulk water is important for better understanding of materials."
To learn more about the abundant material, researchers created a transparent nanoscale capillary to see how water behaved inside of it. They then used high magnification electron microscopy to look at individual water molecules; the nano-capillary was made from one-atom-thick graphene so it did not obscure the electron microscopy imaging.
The scientists were shocked to discover small, square crystals of ice at room temperature within the graphene capillaries. The square lattices were composed of only three atomic layers of water and were spaced into even rows perpendicular to each other. This is extremely unusual for water molecules because they have always been known to form pyramidal structures.
"This study was stimulated by our previous observations of ultrafast flow of water through graphene nanocapillaries. We even speculated that this could be due to two-dimensional square ice ... but seeing is believing," said co-author Sir Andre Geim. "Water is probably the most studied substance ever but no one thought that ice could be square. This story shows how much new knowledge remains to be uncovered when one goes down to the nanoscale."
The findings were published in a recent edition of the journal Nature.
