If you zoom in on a snowflake, you'll see its six-sided symmetry mirrored at the molecular level. As water freezes, its molecules typically arrange themselves in a repeating pattern of hexagons, the geometry that forms the snowflake's star-shaped structure. Now, scientists have created a new type of ice they call "square ice," which forms a cube-shaped pattern instead, with water molecules arranged in neatly aligned rows. Scientists formed these crystals—which occur at room temperature—by squeezing tiny amounts of water between two sheets of graphene, planes of carbon a single atom thick. Van der Waals forces cause the carbon atoms in the two sheets to attract, squeezing nanometer-thick puddles of water inside a high-pressure graphene sandwich. The scientists imaged the crystals with high-resolution electron microscopy and found that the unique environment made the ice crystallize in a new, cubic configuration, they report online today in Nature. The crystals rearranged themselves as scientists imaged them, but remained in an ordered structure, as shown in the video above, in which dark spots indicate the position of water molecules. The crystals split and merge over a period of 4 minutes, which is sped up in the video. The result could be useful for understanding the movement of water when squeezed inside tiny channels, for instance, in carbon nanotubes or cell membranes. And if these crystals formed on a larger scale, they would make square snowflakes, instead of six-sided ones.
(Video credit: Courtesy of the University of Ulm [Germany])