Like most things, ice can be a blessing or a burden depending on the circumstances. It’s perfect crushed in a drink on a hot summer’s day, but can wreak havoc when it collects on roads, power lines and aircraft in freezing temperatures. A University of Pittsburgh-led team has found a way to reduce these dangers by developing a nanoparticle-based coating that can be easily applied to impede the buildup of ice on solid surfaces.
The superhydrophobic coating developed by the researchers mimics the rutted surface of lotus leaves by creating microscopic ridges that reduce the surface area to which water can adhere. Although the surface of the lotus leaf has already served as the inspiration for self-cleaning plastics, more efficient solar cell surfaces, and a special coating for spaceflight equipment, because ice behaves differently than water, relying on the same method used to repulse water used in these examples couldn’t be readily applied to ice.
To ward off ice buildup the team found that superhydrophobic coatings must be specifically formulated. Di Gao, a chemical and petroleum engineering professor in Pittsburgh University's Swanson School of Engineering, 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. They applied each variant to aluminum plates then exposed the plates to supercooled water (-20 degrees Celsius) to simulate freezing rain.
They found that, although 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 test its real world potential Gao tested the coating with 50-nanometer particles outdoors in freezing rain. He painted one side of an aluminum plate and left the other side untreated. As can be seen in the video below the treated side had very little ice, while the untreated side was completely covered. He produced similar results on a commercial satellite dish where the glossed half of the dish had no ice and the other half was encrusted.
The research team’s findings are detailed in the paper, Anti-Icing Superhydrophobic Coatings, which appears in Langmuir.
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