University Demonstrates Ice-Proof Coatings
Developed at the University of Michigan (Ann Arbor, Michigan), a new class of coatings is moving researchers one step closer to being able to ice-proof airplanes, marine vessels, powerlines and other large structures.
The decades-long goal is finally shining light on the possibility through a “beautiful demonstration of mechanics,” revealing ice shedding effortlessly from large testing surfaces with the help of a light breeze, or in other cases, the weight of the ice itself.
Ice-Proof Coating Development
Anish Tuteja, an associate professor of materials science and engineering at U-M, along with his colleagues, decided to test a new method, not common in 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,” Tuteja said.
“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.”
By introducing a low interfacial toughness strategy instead, surfaces with LIT encourage cracks to form between the ice and surface it's shaped upon. Once a crack begins to form, it can quickly spread across the entire iced surface and break from it. In previous methods involving breaking an ice sheet’s surface adhesion, cracks would only break the surface free along its leading edge.
Michael Thouless, the Janine Johnson Weins Professor of Engineering in mechanical engineering, compares the LIT strategy like “pulling a rug across a floor.”
(In trying to pull a large rug, one would be more resistant compared to a small rug because of the strength of the interface between the rug and the floor. This friction force should be equivalent to the interfacial strength.)
“But now imagine there’s a wrinkle in that rug,” continues Thouless.
“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.”
The concept is most popular in the field of fracture mechanics, where it reinforces products such as adhesive-based aircraft joints and laminated surfaces. However, regarding the study, the concept can now begin exploring its use in ice mitigation.
In the mitigation studies, it is important that both the LIT and interfacial strength have an equal focus.
“I pointed out to Anish that if he were to test increasing lengths of ice, he would find the failure load would rise while interfacial strength was important, but then plateau once toughness became important,” said Thouless.
“Anish and his students tried the experiments and ended up with a really beautiful demonstration of the mechanics, and a new concept for ice adhesion.”
In the testing stage, Tuteja’s team mapped out the properties of a vast library of substances, adding LIT and interfacial strength data into the equation. By doing this, the team was able to mathematically predict the properties of a coating system without having to test all of them.
The mathematical process also enabled them to develop a variety of combinations, each specifically tailored to Thouless’ concept of equal interfacial focuses. In physical testing of the coatings on large surfaces—a rigid aluminum sheet and a flexible aluminum sliver (to mimic a power line)—ice fell off immediately due to its own weight.
What’s Happening Now
In continuing research, the team plans to continue to improve its durability of the LIT spray-on coatings.
Since their discoveries, a paper titled, “Low Interfacial Toughness Materials for Effective large-Scale De-Icing,” has been published in the journal Science.
In addition to Tuteja and Thouless, the team also included U-M macromolecular science and engineering graduate researcher Abhishek Dhyani and former U-M materials science and engineering Ph.D. student Kevin Golovin.
The research was funded by the Office of Naval Research, the Air Force Office of Scientific Research, and the National Science Foundation and the Nanomanufacturing program.
Ice-Fighting Coatings of the Past
In March 2016, U-M released research on spray-on coatings that could be used to repel ice on airplanes, oil rigs, powerlines and other industrial machinery or structures. The alternative coating system involved the use of synthetic rubber materials.
Other studies by Virginia Tech (Blacksburg, Virginia) released earlier that year were inspired by the Namib Desert Beetle in the development of anti-frost coating systems. The technology used chemical micropatterns which helped to control the growth of frost caused by condensation.
In more ice-related coating studies, researchers at Rice University (Houston, Texas) began testing the use of epoxy coatings infused with graphene nanoribbons to prove its ability to melt ice under certain conditions.
And in November 2016, Colorado State University (Fort Collins, Colorado) announced a breakthrough in anti-icing coatings research through its development of a new ice-repellent coating system. The gel-based system involved a soft coating made from polydimethylsiloxane.