Spray-on coating may ice-proof airplanes, windshields

Scientists, including one of Indian-origin, have created a thin, clear ice-repellent spray-on coating that could make ice slide off the surface of airplanes and car windshields with only the force of gravity or a gentle breeze.
The finding could have major implications in industries like energy, shipping and transportation, where ice is a constant problem in cold climates.
The new coating could also lead to big energy savings in freezers, which today rely on complex and energy-hungry defrosting systems to stay frost-free.
An ice-repelling coating could do the same job with zero energy consumption, making household and industrial freezers up to 20 per cent more efficient.

Made of a blend of common synthetic rubbers, the formula marks a departure from earlier approaches that relied on making surfaces either very water-repellent or very slippery.
"Researchers had been trying for years to dial down ice adhesion strength with chemistry, making more and more water-repellent surfaces," said Kevin Golovin, a doctoral student at University of Michigan in US.

Led by associate professor Anish Tuteja, researchers initially experimented with water-repelling surfaces as well, but found that they were not effective at shedding ice.
But during their experiments, they noticed that rubbery coatings worked best for repelling ice, even when they were not water-repellent.

Eventually, they discovered that the ability to shed water was not important at all. The rubbery coatings repelled ice because of a different phenomenon, called "interfacial cavitation."
Golovin said that two rigid surfaces - say, ice and a car windshield - can stick tightly together, requiring a great deal of force to break the bond between them.
But because of interfacial cavitation, a solid material stuck to a rubbery surface behaves differently. Even a small amount of force can deform the rubbery surface, breaking the solid free.
"Nobody had explored the idea that rubberiness can reduce ice adhesion. Ice is frozen water, so people assumed that ice-repelling surfaces had to also repel water. That was very limiting," Tuteja said.

The new approach makes it possible to dramatically improve durability compared to previous icephobic coatings, which relied on fragile materials that lost their ice-shedding abilities after just a few freeze-thaw cycles.
The new coatings stood up to a variety of lab tests including peel tests, salt spray corrosion, high temperatures, mechanical abrasion and hundreds of freeze-thaw cycles.
The team has also found that by slightly altering the smoothness and rubberiness of the coating, they can fine-tune its degree of ice repellency and durability.
The research was published in the journal Science Advances.