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Beetle Shell Inspires Anti-Frost Coating

Wednesday, January 27, 2016

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Researchers from Virginia Tech are looking to inhabitants of one of the hottest areas on the planet for inspiration in developing a coating that would inhibit ice formation on critical surfaces.

By successfully creating chemical micropatterns to control the growth of frost caused by condensation, the team foresees end-use applications that would work to prevent frost on airplane wings, wind turbines, condenser coils and windshields, the school announced Monday (Jan. 25).

Their research was published Friday (Jan. 22) as “Controlling condensation and frost growth with chemical micropatterns” in Scientific Reports, an online journal from the publishers of Nature.

Inspiration from a Hot Environment

The Virginia Tech team noted that the Namib Desert Beetle—the inspiration for this study—lives in one of the hottest places in the world but still has a natural way of collecting airborne water.

By Schnobby / CC BY-SA 3.0 via Wikimedia Commons
By Schnobby / CC BY-SA 3.0 via Wikimedia Commons

The Namib Desert Beetle—the inspiration for this study—helped the Virginia Tech research team understand how to control where dewdrops grow in order to control frost formation.

The beetle’s shell features a water-repellent surface covered with tiny bumps that attract moisture and form it into drops. The collected water then flows to the insect’s mouth by way of smooth-sided water-repellant channels between the bumps.

“I appreciate the irony of how an insect that lives in a hot, dry desert inspired us to make a discovery about frost,” said Jonathan Boreyko, lead author on the paper and assistant professor of Biomedical Engineering and Mechanics in the Virginia Tech College of Engineering.

“The main takeaway from the desert beetle is we can control where dewdrops grow,” he added.

Preventing Ice Bridges

According to the researchers, the journey of frost across a surface begins with a single, frozen dewdrop.

“The twist is how ice bridges grow,” Boreyko said. He explained that ice takes water from dewdrops, causing ice bridges to propagate frost across the droplets on the surface.

“Only a single droplet has to freeze to get this chain reaction started,” he added.

However, by controlling the spacing of the condensation, the researchers were able to control the speed at which the frost grew across surfaces, or even completely prevent it from forming.

Explaining that fluids go from high pressure to low pressure, Boreyko said that ice “serves as a humidity sink,” because the vapor pressure of ice is lower than the vapor pressure of water.

“The pressure difference causes ice to grow,” he said, “but designed properly with this beetle-inspired pattern, this same effect creates a dry zone rather than frost.”

Boreyko used this knowledge to successfully make a single dry zone around a piece of ice.

He explained that, while dewdrops preferentially grow on the array of hydrophilic dots, when the dots are spaced far enough apart, ice formation is inhibited.

The video shows frost spreads more quickly when drops are closer, and the chain reaction is not as quick when the drops are farther apart.

With controlled spacing, if one of the drops freezes into ice, the ice is unable to spread frost to the neighboring drops because they are too far away, he said, adding, “Instead, the drops actually evaporate completely, creating a dry zone around the ice.”

Expanding the Technology

While the team created its beetle-inspired, frost-controlling chemical pattern on a surface only about the size of a centimeter, the scientists believe they will be able to scale it up to larger surface areas with hydrophilic patterns overtop of a hydrophobic surface.

The team anticipates this technology effectively creating frost-free zones on larger surfaces, and points to the current use of harsh chemicals to deice wind turbines or airplane wings or the water that forms and freezes on heat pump coils.

“Keeping things dry requires huge energy expenditures,” said C. Patrick Collier, a research scientist at the Nanofabrication Research Laboratory Center for Nanophase Materials Sciences at Oak Ridge National Laboratory and a co-author of the study.

“That’s why we are paying more attention to ways to control water condensation and freezing,” he added. “It could result in huge cost savings.”

The team performed its work at the Oak Ridge National Laboratory, as well as the Center for Nanophase Materials Sciences, a Department of Engineering Office of Science user facility. The Department of Biomedical Engineering and Mechanics at Virginia Tech provided startup support.

   

Tagged categories: Asia Pacific; Coating Materials; Coatings; Coatings Technology; Colleges and Universities; EMEA (Europe, Middle East and Africa); Latin America; North America; Oak Ridge National Laboratory; Research and development; Specialty Coatings; Water repellents

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