The anti-ice coating for large structures is based on a 'beautiful mechanical demonstration'

ANN ARBOR – 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 – while working well on small surfaces – they found in field tests that they did not produce ice on very large surfaces as effectively as they did in the field. they had hoped. This is a problem because ice tends to pose the biggest problems on larger surfaces: reduced efficiency, compromised safety and the need for costly disposal.

Anish Tuteja, Associate Professor of Materials Science and Materials Engineering, described how he and his colleagues have turned to a property that is not well known in icing research.

"For decades, the research on coatings has focused on reducing the strength of adhesion – the force per unit area required to tear a layer of ice from a surface," he said. said Tuteja. "The problem with this strategy is that the wider the ice layer, the more force you need. We found that we encountered the limitations of low adhesion strength and our coatings became ineffective when the surface became large 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 leading edge. 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 carpet, the harder it is to move. The strength of the entire interface between the carpet and the floor prevents you from resisting. The friction force is similar to the interfacial force.

"But now, imagine that there is a wrinkle in this carpet. It's easy to keep pushing this ride on the mat, no matter how big it is. The resistance to the propagation of the wrinkle is similar to the interfacial tenacity that resists the propagation 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 so far, it had not been applied to mitigate the effects of ice. The breakthrough came when Thouless learned about 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 the interfacial resistance was high, but it would stabilize as soon as the toughness became. Anish and his students tried the experiments and came up with a great demonstration of mechanics and a new concept of ice grip. "

To test the idea, the Tuteja team used a technique that they perfected during their 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.

The document entitled "Low interfacial hardness materials for efficient large-scale defrosting". Besides Tuteja and Thouless, the team also included U-M graduate researcher in Macromolecular Sciences and Engineering, Abhishek Dhyani, and the former doctor of Materials Science and Engineering U-M. student Kevin Golovin. The research was funded by the Office of Naval Research, the Air Force Scientific Research Bureau, the National Science Foundation, and the Nanofabrication Program (Grant No. 1351412).

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