Polymer coating relies on interfacial toughness to shed ice
A coating that shrugs off ice with no effort could help make large objects like airplanes, wind turbines, and ships ice-free. The ice-phobic coating reported in a study published in the journal Science is made from well-known materials that are easily available in large quantities and should be easy to coat on various surfaces, say its developers.
Researchers have usually taken one of two approaches to make coatings that can prevent ice buildup on structures. One is to delay ice formation. “But the best you can do is delay ice for a few hours in the real world,” says Anish Tuteja, a professor of materials science and engineering at the University of Michigan. “Eventually ice will still form.” So Tuteja and others are trying to make coatings that shed ice as easily as possible once it has formed.
Typically, scientists have tried to do this by reducing the strength with which ice sticks to a surface. This adhesion strength is the force it takes to detach ice from a specific area. De-icing airplanes and ship hulls, which have surfaces of thousands of square meters, requires a lot of force.
So Tuteja along with University of Michigan mechanical engineering professor Michael Thouless, and their colleagues chose to make a coating that instead minimizes interfacial toughness between the coating and ice. “In simple terms, that’s how much energy [is] required to propagate a crack at the interface between ice and the underlying surface,” Tuteja says.
Surfaces with low interfacial toughness easily form cracks between the ice and the surface, so that the ice can slip off the surface easily. The researchers made the coating with commonly used polymers like polydimethylsiloxane (PDMS) and polyvinyl chloride (PVC), which are known to have low interfacial toughness. Adding plasticizers to the polymers made them more flexible and reduced the interfacial toughness further, the research team found. They used medium-chain triglyceride and silicone oil as plasticizers for the PVC and PDMS respectively. Making the coatings thinner also helped since it is easier for a crack to spread and dislodge the ice. So by optimizing the thickness and plasticizer content, the researchers were able to make 1–2 µm-thick PVC and polystyrene coatings with very low interfacial toughness, with PDMS boasting the lowest value.
As a demonstration, they applied the PDMS coating to a rigid 1 m × 1 m aluminum panel and a flexible aluminum piece 1.2-m-long, 1-inch wide to mimic a power line. Once the ice reached 1 cm thickness, its weight was enough for it to fall off the aluminum on its own. But the ice stuck fast to aluminum surfaces that were uncoated or coated with an earlier ice-phobic coating also based on PDMS.
“This work provides valuable insight into the factors that affect a surface’s ability to shed ice, especially at the much larger length scales that are required for real-world applications,” says Atsushi Hozumi, a materials engineer and group leader at the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan. Importantly, he adds, “the coating is made with commonly used polymers and a simple procedure, making it suitable for industry.”
Indeed, says Tuteja, “the formulations are based on well-known materials that are available in millions-of-gallons quantities.” And the coatings should be easy to make on different surfaces by spraying or dip coating. The researchers plan to test the coatings on wind turbines in Europe this winter through Hygratek, a startup that Tuteja has co-founded.
Read the abstract in Science.