'Ice-free' surfaces repel freezing water

CAMBRIDGE, Mass., Nov. 12 (UPI) -- Engineers at Harvard University say they've developed ice-free nanostructured materials that repel water droplets before they have a chance to freeze.

The finding could lead to a new way to keep airplane wings, buildings, power lines and even entire highways free of ice during the worst winter weather, a university release said Friday.

The technology provides a solution that is more efficient and sustainable than conventional solutions like chemical sprays, salt and heating, the researchers say.

Scientists at the Harvard School of Engineering and Applied Sciences focused on preventing rather than fighting ice buildup.

"Freezing starts with droplets colliding with a surface," says Joanna Aizenberg, a Harvard professor of materials science. "But very little is known about what happens when droplets hit surfaces at low temperatures."

Watching high-speed videos of supercooled droplets hitting surfaces that were modeled after those found in nature, they saw that when a cold droplet hits the nanostructured surface, it first spreads out, but then the process runs in reverse as the droplet retracts to a spherical shape and bounces back off the surface before ever having a chance to freeze.

By contrast, on a smooth surface without the structured properties, a droplet remains spread out and eventually freezes.

"We see this approach as a radical and much needed shift in anti-ice technologies," says Aizenberg.

In comparison with traditional ice prevention or removal methods like salting or heating, the nanostructured materials approach is efficient, non-toxic and environmentally friendly, she said.