Ice is a hazardous fact of winter life, playing havoc with roads, utility lines, buildings, and air travel. Conventional methods of getting rid of the ice, such as direct heating, applying salt, or using chemicals to trigger melting, all have liabilities: they can corrode the materials they’re applied to, and damage the environment, and they are only modestly or temporarily effective. But Harvard scientists say they have created materials that can prevent ice from forming on surfaces in the first place.
The researchers say their breakthrough, reported in the latest issue of ACS Nano, could apply not only to aviation but to road paving, construction, power transmission, and virtually any other industry for which chemical and physical deicing is a concern. “What we want to do is to have ice not form at all,” says Joanna Aizenberg, a materials scientist and leader of the project.
When an incipient ice droplet hits a conventional surface, it spreads out and grips, becoming a base for the aggregation of more droplets and ultimately a sheet of ice. But Aizenberg’s surfaces are “super-hydrophobic,” which literally means “very afraid of water.” They contain micron-sized geometric patterns, including posts, bricks, and other structures, that cause droplets to bounce away before they can adhere. “The key feature is that we design these structures to be nearly friction-free,” Aizenberg explains. “The droplets are effectively deflected before ice formation can occur.”
In tests, Aizenberg and her colleagues have found that their materials resist ice accumulation until the temperature drops to about -30° C. That’s far colder than nearly any industrial setting, she notes. Even at ultra-low temperatures, when the ice-repellency starts to break down, all’s not lost. The ice that does form has a weak grip, requiring a small fraction—less than 10 percent—of the normal force needed to remove it from traditional surfaces. “It’s very easy to strip off because it’s only contacting the surface at the tips of these nanostructured features,” says Aizenberg. “It can be removed just by the flow of air.”
via Technology Review.