New discovery could stop ice freezing on aircraft wings

A new method that controls whether freezing droplets stick to a surface or bounce off it could have applications in manufacturing, 3D printing and the design of aircraft wings.

Hydrophobic coatings that deflect or repel water are becoming commonplace in industry and consumer goods. Researchers at Massachusetts Institute of Technology have now discovered that changing the thermal properties of surfaces can also influence how readily things stick to them.

“We found something very interesting,” said MIT associate professor of mechanical engineering Kripa Varanasi, whose team was studying how drops of molten metal froze onto a surface. “We had two substrates that had similar wetting properties [the tendency to either spread out or bead up on a surface] but different thermal properties.”

Conventional wisdom dictated that the differing thermal properties shouldn’t have made a difference, but that was not the case. Varanasi said this finding opened up a “whole new approach” for determining how liquids interact with surfaces and that “we can control the adhesion of a droplet freezing on a surface by controlling the thermal properties” of that surface. “It provides new tools for us to control the outcome of such liquid-solid solutions.”

The experiments in the study, which was published in the journal Nature Physics, used molten metal – an important part of industrial processes such as the use of thermal spray coatings that are applied to turbine blades and other machine parts.

“The way droplets impact and form splats dictates the integrity of the coating itself,” said Varanasi. “If it’s not perfect it can have a tremendous impact on the performance of the part, such as a turbine blade. Our findings will provide a whole new understanding of when things stick and when they don’t.”

That could have useful engineering applications in areas such as 3D printing, to make sure the layers stick together thoroughly, or when it’s important to prevent droplets from sticking – such as ice on aeroplane wings.

 "We can imagine scenarios where thermal properties can be adjusted in real time through electric or magnetic fields, allowing the stickiness of the surface to impacting droplets to be adjustable,” said Dan Soto, a postdoctoral researcher at MIT.