Before you blame Nebraska ice the next time your car windshield freezes over, first curse Nebraska Ice.
The difference is even more minuscule than a capital letter. Nebraska Ice is the colloquial name for bilayer hexagonal ice, or 2-D bilayer ice, and the name has a bit of a double meaning. Since “Nebraska” means “flat water” in the Otoe language, it’s a fitting title for the ultra-thin form of ice, which happened to be discovered about two decades ago by a team of scientists that included University of Nebraska-Lincoln chemistry professor Xiao Cheng Zeng.
“It’s so thin,” Zeng said. ”It’s a nanometer. It’s one-billionths of your hair.”
It is the microscopic base layer of an icy surface, and it grows in different ways depending on the surface upon which it forms, according to the most-recent follow-up study about Nebraska Ice that Zeng co-authored. The discovery, published last fall, could potentially provide relief for commuters who spend frigid winter mornings scraping away at icy windshields.
Zeng joined several Beijing-based scientists in comparing, on microscopic and computer-simulated levels, how ice grows on water-absorbent and water-repellent surfaces.
According to the study, published last fall in Proceedings of the National Academies of Science, the angle upon which water makes contact with a surface is key to which way ice will form upon it. If the contact angle is 40 degrees or greater, Zeng said, ice clings a bit to the surfaces but forms upward and three-dimensionally, like a snowflake. If it’s nearer 0 degrees, water spreads out, flatly, across the surface.
“After the temperature drops below freezing, that Nebraska Ice will start to creep,” Zeng said.
A typical car windshield, he said, has about a 10-degree contact angle, which many Lincolnites might have figured out while developing wintry versions of tennis elbow from scraping away at ice earlier this month.
With this discovery comes the potential for a solution, Zeng said. In studying the phenomenon, researchers at Beijing’s Chinese Academy of Sciences treated pieces of aluminum with a water-repellent coating. Water droplets sprayed on that treated surface beaded, rather than spread, and ice crystals grew up and out in clover-like forms. The researchers recorded not only the formation of this 3-D ice thanks to a high-powered microscope, but also the ease with which it could be removed from the surface compared to a water-absorbent surface. A stiff breeze blew much of the ice away.
“They suggest that this could be exploited to make surfaces such as car windscreens more resistant to icing by embedding nanoparticles inside them,” the science journal Nature reported when the study was released in October.
Zeng said the discovery is promising, but he hasn’t received an early sample of a revolutionary ice-proof windshield.
“I still have to scrape,” Zeng said. “I’m more worried about falling down. The ground is harder.”