Generally-speaking, hard objects and soft objects don’t bond well together. It comes down to a principle known as ‘interfacial cavitation,’ in which one surface (the soft one) deforms under pressure, while the other (the hard one) does not -– as a result, they pop apart. Now, scientists at the University of Michigan have used that principle to develop one of the most ice-repellent coatings ever made. Its applications could range from airplane wings to car windshields to freezers. (Those are the logical applications; I imagine all kinds of unique applications will follow, as people use their imagination…)
Previously, most anti-ice coatings have been rigid and slippery, with the idea being that what repels liquid water should also repel ice. According to the U Michigan team, however, that line of thought was flawed.
“Nobody had explored the idea that rubberiness can reduce ice adhesion,” says associate professor of Materials Science and Engineering Anish Tuteja. “Ice is frozen water, so people assumed that ice-repelling surfaces had to also repel water. That was very limiting.”
Instead of creating an ice-repelling solution, the team, led by Tuteja, created a rubbery coating, made from a blend of commonly available synthetic rubbers, such as polyurethane. The resulting clear spray-on coating, while somewhat tacky to the touch, might at first seem like it would “hold onto” the ice, but the fact is that the hard ice easily releases when the soft rubber deforms -– and the hardened ice slips off the surface. All that is required is the force of gravity, or a slight breeze.
By tweaking the composition of the coating, it is possible to select for factors such as durability versus ice repellency. This means that a coating designed for airplane wings could be very durable, as high winds would already blow much of the ice away, while a coating for industrial freezers would be more repellent, allowing ice to be shed with little effort.
The coating would also find instant users in the frozen North, where keeping windshields ice free is a constant battle. Despite not being able to repel water, the rubbery coating was able to stop ice from setting on the surfaces because of the previously mentioned interfacial cavitation. As the rubbery surface changes forms when exposed to even small amounts of force, it effectively prevents ice from becoming tightly bonded to it.