University of Michigan researcher have come up with a durable and inexpensive ice-repellent coating. Thin, clear and slightly rubbery to the touch, the spray-on formula, they say, could make ice slide off equipment, aircraft or car windshields. This could offer significant opportunities in industries such as energy, shipping and transportation, where ice can be a problem in cold seasons. Made of a blend of common synthetic rubbers, their formula departs 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 in materials science and engineering. “We’ve discovered a new knob to turn, using physics to change the mechanics of how ice breaks free from a surface.” Led by Anish Tuteja, associate professor of materials science and engineering, the team initially experimented with water-repelling surfaces as well, but found these were not effective at shedding ice. But during their experiments, they noticed that rubbery coatings worked best for repelling ice, even if they were not water-repellent. Eventually, they found the ability to shed water was unimportant, since the coatings repelled ice through a different phenomenon called ‘interfacial cavitation.’ Golovin explained that two rigid surfaces – for example, ice and a car’s windshield ­– can stick tightly together, and need considerable 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,” Tuteja added. “Ice is frozen water, so people assumed that ice-repelling surfaces had to also repel water. That was very limiting.” The new approach makes it possible to improve durability significantly compared to previous icephobic coatings, which relied on fragile materials that lost their ice-shedding abilities after 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 research team also found that by slightly altering the smoothness and rubberiness of the coating, they could fine-tune its ice repellency and durability. Softer surfaces tend to be more ice-repellent but less durable, while the opposite is true for harder coatings. Golovin believes this flexibility will allow them to create coatings for a huge variety of applications. “An airplane coating, for example, would need to be extremely durable, but it could be less ice-repellent because of high winds and vibration that would help push ice off,” Golovin said. “A freezer coating, on the other hand, could be less durable, but would need to shed ice with just the force of gravity and slight vibrations. The great thing about our approach is that it’s easy to fine-tune it for any given application.” “I think the first commercial application will be in linings for commercial frozen food packaging, where sticking is often a problem. We’ll probably see that within the next year,” Tuteja said. “Using this technology in places like cars and airplanes will be very complex because of the stringent durability and safety requirements, but we’re working on it.”