The surface of ice is a slippery subject.
Ice’s melty coating appears even at temperatures well below freezing, a phenomenon known as “premelting.” That layer acts as a lubricant, explaining why ice is slippery even under frigid conditions. But ever since the idea of a liquidlike coating was first pondered by British scientist Michael Faraday in the 1850s, ice’s unusual surface has remained poorly understood.
In the new study, scientists used atomic force microscopy to measure the locations of atoms on the surface of ice. At temperatures around –150° Celsius, ice’s surface is made of not just one kind of ice, but two, physicist Ying Jiang of Peking University and colleagues report May 22 in Nature. What’s more, Jiang says, “ice is not so perfect.” The team found defects in the surface’s structure that seem to kick off the premelting.
Ice comes in a variety of types, depending on the arrangement of its molecules (SN: 2/2/23). Under normal conditions, the water molecules are arranged in layers of hexagons stacked on top of one another. This hexagonal ice, called ice Ih, is the variety Jiang and colleagues studied. But the team found that the surface of the ice wasn’t entirely hexagonal. The atomic force microscope images revealed that the surface consisted of some regions of ice Ih and other regions of ice Ic, in which the hexagons in each layer are shifted to create a structure similar to the arrangement of carbon atoms in diamond.
2024-05-22 10:00:00
Link from www.sciencenews.org