A team of University of Michigan (UM) (Ann Arbor, Michigan, USA) researchers have developed a new class of coatings that deice the surfaces of large structures, including airplanes, cargo ships, and power lines.
Decades in the making, this ice-proofing spray-on coating sheds ice from surfaces with a force as minimal as a light breeze or even under the weight of the ice itself. This innovation was made possible through “a beautiful demonstration in mechanics,” according to Michael Thouless, UM’s Janine Johnson Weins Professor of Engineering.
Whereas previous ice-repellent coatings failed to effectively shed ice on large surfaces, UM researchers embarked on a new strategy that’s unusual to the field of icing research. “For decades, coating research has focused on lowering adhesion strength—the force per unit area required to tear a sheet of ice from a surface,” explains Anish Tuteja, an associate professor of materials science and engineering at UM. “The problem with this strategy is that the larger the sheet of ice, the more force is required. We found that we were bumping up against the limits of low adhesion strength, and our coatings became ineffective once the surface area got large enough.”
To solve this problem, Tuteja and his fellow researchers relied on a strategy of low interfacial toughness (LIT). As opposed to low adhesion strength coatings, LIT coatings cause cracks to form between the ice and the surface, resulting in a chain reaction that spreads across the entire iced surface. Thouless uses the analogy of a large rug that becomes easier to move once a wrinkle forms in that rug. “It’s easy to keep pushing that wrinkle across the rug, regardless of how big the rug is. The resistance to propagating the wrinkle is analogous to the interfacial toughness that resists the propagation of a crack,” says Thouless.
Interfacial toughness is a key concept in fracture mechanics and has informed the creation of such products as laminated surfaces and adhesive-based aircraft joints. But Thouless saw its potential applications in ice mitigation and suggested to Tuteja that “the failure load would rise while interfacial strength was important.” This insight led to the “beautiful demonstration in mechanics” that Tuteja and his graduate student researchers to test the LIT theory of ice proofing. They mapped the properties of a vast library of substances, including those that relied on interfacial toughness, and mathematically predicted their individual success rates.
After devising various combinations, Tuteja’s team developed a coating that balanced interfacial toughness and adhesion strength, and then they tested it on different large surfaces. They found that ice fell off the surfaces with the coating, while ice stuck to the control samples that were either uncoated or had another ice-proof coating. The team plans on improving the durability of the LIT spray-on coatings.
The results from the research project of Tuteja and Thouless, along with UM graduate students Abhishek Dhyani and Kevin Golovin, can be found in a paper entitled “Low interfacial toughness materials for effective large-scale de-icing” in Science Magazine. A video made by the Michigan Engineering department on the ice-shedding coating can be seen here.
Source: Michigan News, www.news.umich.edu.