Nanoparticle Coating Prevents Freezing Rain Ice Buildup

Ice storms can be disastrous when freezing rain builds up on power lines, trees, roads, and aircraft surfaces. Entire cities can be left without power, heat, water supplies, and cut off from food supplies. Fatal aircraft accidents are still happening, due to ice build-up on control surfaces, even though engineers have been working on the problem for decades. Now researchers at the University of Pittsburgh-have developed an easily applied nanoparticle-based coating that prevents the buildup of ice on solid surfaces.

Developed in the lab of Di Gao, a chemical and petroleum engineering professor in Pitt's Swanson School of Engineering, the coating presents the first evidence of anti-icing properties for a new class of water repellants known as superhydrophobic coatings. The thin films mimic the rutted surface of lotus leaves by creating microscopic ridges that reduce the surface area to which water can adhere. However, an ability to repel water is not so easily applied to ice inhibition, since ice behaves differently than water. The team found that superhydrophobic coatings must be specifically formulated to ward off ice buildup.

Gao and his team created different batches made of a silicone resin solution combined with nanoparticles of silica ranging in size from 20 nanometers to 20 micrometers, at the largest. They applied each variant to aluminum plates then exposed the plates to supercooled water (-20 degrees Celsius) to simulate freezing rain. The results are presented in a paper, by lead author and Pitt doctoral student Liangliang Cao. Cao concludes that while each compound containing silica bits of 10 or fewer micrometers deflected water, only those with silica pieces less than 50 nanometers in size completely prevented icing.

The minute surface area of the smaller fragments means they make minimal contact with the water. Instead, the water mostly touches the air pockets between the particles and falls away without freezing. Though not all superhydrophobic coatings follow the Pitt recipe, the researchers conclude that every type will have a different particle-scale for repelling ice than for repelling water.

To watch a video that illustrates the experiments: pitt.edu/news2009/ice.html