'Bed of Nails' Surface Prevents Ice Formation

‘Tis the season for scraping frozen windshields, de-icing planes and salting roads and sidewalks. Wouldn’t it be great if the ice never accumulated in the first place?

A research team from Harvard University is working on just that. They’ve taken inspiration from nature — the surface of mosquitos’ eyes and water striders’ legs of all places — and developed a way to prevent ice from forming.

“Our approach to tackling ice buildup is inspired by the technology used by many organisms to manipulate water droplets on their surfaces,” said Joanna Aizenberg, a materials scientist at Harvard and leader of the project.

The results could reduce the use of salt or other de-icing chemicals that can corrode metals and are simply just not good for the environment.

In nature, animals don’t worry about ice buildup at all, because they have mechanisms for preventing water droplets from sticking to surfaces. For example, mosquito eyes automatically defog and the legs of water striders prohibit water droplets from sticking. In both cases, the water-repelling nature of the tissue is due to a microstructured pattern that prevents water droplets from accumulating.

Aizenberg likens these surfaces to a “bed of nails.” The air gaps between the nails provide a nearly friction-free condition, where water droplets cannot get a grip.

Based on this, the scientists fabricated a variety of water-repelling -- or hydrophobic -- surfaces with different patterns, including bristles, blades, honeycombs and bricks, and then investigated how water droplets behaved on top of these surfaces.

When a drop of water was placed on top, it would spread out, unable to properly adhere, and then would retract and bounce off before any freezing could occur.

Freezing was impossible on the patterned surfaces even at temperatures as cold as -22 degrees Fahrenheit. Even below that, water droplets only partially adhered to the surfaces and once they froze, were easily removed with just a small amount of force.

Surfaces fabricated with such a pattern could save us all from the time-consuming ice-scraping and de-icing that comes along with winter freezes. Aizenberg said that not only are the current methods of removing ice ineffective, they pollute the environment.

“Currently we have no sustainable technology for dealing with ice; the methods we have are resource-intensive, toxic and not reliably up to the task. Continuous heat guzzles energy, salts lower the freezing point but corrodes surface and disrupts the osmotic balance in the environment,” she said.

Although the scientific community has embraced Aizenberg and her team’s work as revolutionary, there are a few lingering concerns. In particular, she said, there have been questions about how feasible it is to scale up the surfaces for use on buildings, on vehicles, power lines and pipelines, and how robust the surfaces would be over time.

But folks from the airline industry would welcome such a technology sooner rather than later. Cary Myers, a flight attendant in Minneapolis, said the possibility for this technology to be used on planes is almost too good to be true.

“Passengers get grumpy when their flights are delayed because of ice,” she said. “If we could eliminate the problem faster and…better…it would make everything go much smoother.”

Aizenberg and her team have already begun testing the surfaces in wind tunnels to study how they might perform in real-world settings.