The anti-ice coating for large structures is based on a "beautiful demonstration of mechanics"

A new class of coatings that effortlessly removes ice from even the largest surfaces has brought researchers closer to their goal for decades: protecting cargo ships, planes, power lines and other large structures from the ice.

Aerosol coatings, developed at the University of Michigan, cause the ice of structures – whatever their size – to fall under the effect of a light breeze or often the weight of the ice itself. An article on research is published in Science.

When tested on a fictitious power line, the coating immediately melted the ice.

The researchers overcame a major limitation of previous anti-ice coatings – although they worked well on small surfaces, they discovered in field tests that they did not dissipate ice on very large surfaces as efficiently as they had hoped. This is a problem because ice tends to cause the most significant problems on larger surfaces: reduced efficiency, compromised effectiveness, compromised safety and costly removal.

They have overcome this obstacle with a "beautiful demonstration of mechanics". Anish Tuteja, Associate Professor of Materials Science and Materials Engineering, described how he and his colleagues have turned to a little-known property in icing research.

"For decades, research on coatings has focused on reducing the strength of adhesion – the force per unit area required to tear an ice layer from a surface", said Tuteja. "The problem with this strategy is that the wider the ice layer, the more force you need.We have found that we meet the limits of low grip strength and that our coatings have become ineffective when the surface has become big enough. "

The new coatings solve the problem by introducing a second strategy: low interfacial tenacity, abbreviated LIT. Surfaces with low interfacial tenacity promote the formation of cracks between the ice and the surface. And unlike breaking the adhesion of the surface of an ice sheet, which requires tearing the entire sheet, a crack breaks only the free surface along its edge. attack. Once this crack starts, it can quickly spread all over the icy surface, regardless of its size.

"Imagine pulling a carpet on a floor," said Michael Thouless, professor of mechanical engineering at Janine Johnson Weins. "The wider the mat, the harder it is to move – the resistance of the entire interface between the mat and the floor resists you." The frictional force is similar to the interfacial resistance.

"But now, imagine that there is a wrinkle in this carpet, it's easy to keep pushing this wrinkle on the carpet, whatever its size." The resistance to the spread of the wrinkle is similar to the toughness interfacial that prevents the spread of a crack. "

Thouless stated that the concept of interfacial toughness is well known in the field of fracture mechanics, where it is at the base of products such as laminated surfaces and adhesive-based aircraft seals. . But until now, it has not been applied to mitigate the effects of ice. The breakthrough occurred when Thouless became aware of Tuteja's previous work and saw an opportunity.

"Traditionally, fracture mechanics researchers are only interested in interfacial resistance, and ice mitigation researchers are often interested only in interfacial resistance," he says. said Thouless. "But both parameters are important for understanding membership.

"I pointed out to Anish that if he tested longer and longer lengths of ice, he would find that the breaking load would increase while interfacial resistance was important, but then, once toughness became important, the plateau was changing.Anish and his students have tried a very nice demonstration of mechanics, and a new concept for the adhesion of ice. "

To test this idea, the Tuteja team used a technique that he perfected during his previous research on coatings. By mapping the properties of an extensive library of substances and adding interfacial tenacity as well as a strength of adhesion to the equation, they were able to mathematically predict the properties of the substances. a coating without the need to physically test them. This allowed them to concoct a wide variety of combinations, each with a specially adapted balance between interfacial toughness and adhesion strength.

They tested a variety of coatings on large surfaces – a rigid aluminum sheet of about 3 square feet and a flexible aluminum piece about 1 inch wide and 3 feet thick. long to imitate a power line. On each surface, the ice fell immediately due to its own weight. However, it quickly adhered to control surfaces, whose size was the same, one uncoated and the other covered with a previous anti-phobe coating.

The next step of the team is to improve the durability of LIT coatings.