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Department of Chemical and Petroleum EngineeringGao Research Group

Research Highlight

Anti-Icing Superhydrophobic Coatings

(Collaborator: Prof. Jianzhong Wu at Univ. of California, Riverside)

Above figure is a demonstration of our superhydrophobic anti-icing coating in naturally occurred freezing rain. (a) Uncoated side of an aluminum plate is completely covered by ice. (b) Coated side of the aluminum plate has little ice. (c) Uncoated side of a dish antenna is completely covered by ice, while the coated side is ice-free. (d) A close-up view of the red box in (c), showing the boundary between the coated and the uncoated surfaces.

Brief Introduction to Our Work

Ice may form through two routes: (i) freezing of liquid water as the temperature drops across the freezing point, and (ii) striking of supercooled water droplets onto a solid surface, which is the cause of “freezing rain” and “impact ice”. While icing through the first route may be prevented by adding anti-freezing agents, there has not been an effective method to prevent icing through the second route. Therefore, although “freezing rain” and “impact ice” are notorious for glazing roadways, breaking tree limbs and power lines, and stalling airfoil of aircrafts, prevention of such icing has been proven challenging by many generations of scientists and engineers.

Using composites of polymers and nanoparticles, our group has developed a series of anti-icing coatings that can be conveniently applied to a variety of substrates, including metal, ceramics, plastics, concrete, and glass. The nanoparticles provide the coating with roughness that repels water in the same manner as lotus leaves, and render the coating superhydrophobic (see figure below).

While superhydrophobic surfaces have been fabricated and extensively studied by many researchers, the anti-icing function of such surfaces has been under debate for over a decade, due to the lack of direct experimental evidence. A key issue we have found that explains the previous debate and failure in making superhydrophobic anti-icing coatings is that the anti-icing property of the coatings depends not only on their superhydrophobicity but also on the critical dimension of the surface roughness. For example, in our experiments when the superhydrophobic coating is made of polymer-nanoparticle composites, the critical particle sizes that determine the superhydrophobicity and the anti-icing property, respectively, are in two different length scales. This result implies that the anti-icing property of a surface may not be directly correlated to its superhydrophobicity, and thus it is uncertain whether a superhydrophobic surface is anti-icing without detailed knowledge of the surface morphology. The result also opens up possibilities for rational design of anti-icing superhydrophobic surfaces by tuning surface textures in multiple length scales.

Highlights by Media and Press

Our work on the anti-icing superhydrophobic coatings has attracted much attention from media and press. The following are examples.