The world's first passive anti-freeze surface fights ice with ice

Nothing announces the arrival of winter as the frost on the windshields.

Although the inconvenience caused by scraping or de-icing car windows can set cold mornings for many drivers, the toll freeze that affects the entire economy is more than just a simple nuisance. Delayed flights to power outages, ice accumulation can cost billions of dollars each year to consumers and businesses in loss of efficiency and mechanical breakdown.

New search for Virginia Tech, published this week in Applied materials and ACS interfaces, hope to change that. With the world's first demonstration of a passive anti-frost surface, the study provides a proof of concept to keep surfaces at 90% dry and frost-free indefinitely, all without any chemicals or additives. 39; energy.

"Icing is a major problem, and researchers have been working for years to solve this problem," said Farzad Ahmadi, a Ph.D. student in the Department of Biomedical Engineering and Mechanics at Virginia Tech at the College of Engineering and senior author of the 39; study.

Ahmadi explained that traditional methods of freezing were based on the application of anti-freeze chemicals or energy, such as heat. Even the age-old method of throwing salt on the roads is essentially a chemical treatment. Other recent advances include special coatings for surfaces that prevent frost formation, but these coatings are not durable and tend to wear easily.

"For this project, we do not use any kind of special coating, chemicals or energy to overcome the frost," Ahmadi said. "Instead, we use the unique chemistry of the ice itself to prevent frost formation."

Using a simple approach to design, the researchers created their anti-icing surface on untreated aluminum by drawing strips of ice on a microscopic network of raised grooves. The microscopic grooves act as sacrificial zones, where bands of intentional ice form and create areas of low pressure. These low pressure areas attract the surrounding air humidity to the nearest ice band, keeping the overlapping intermediate zones free of frost, even in wet sub-freezing conditions.

These sacrificial ice bands represent only 10% of the surface of the material, leaving the remaining 90% completely dry.

"The real power of this concept is that the ice bands themselves are chemistry, which means that the material we use is unimportant," said Jonathan Boreyko, an assistant professor in the Department of Biomedical Engineering and Mechanics. "As long as you have this proper pattern of sacrificial ice, the material you use can be just about anything, so there are many possibilities."

Researchers see immediate applications for HVAC technology, where the external components of heat exchangers (such as heat pumps and ventilation systems) already use a micro-fin model on their surfaces. Manufacturers would just need to apply the proper pattern of grooves on these fins to prevent frost from accumulating in the systems.

Other applications include aerospace materials, such as airplane wings. And yes, with a little more development, car windshields are also an option for the anti-freeze technology, which has already obtained a full patent.

In addition to its unprecedented anti-freeze properties, this technology could provide additional benefits: it could help offset traditional ice-fighting methods that have serious environmental consequences. For example, it takes thousands of gallons of antifreeze chemicals to defrost the wings of an airplane in a single flight. These chemicals flow into groundwater, disperse into the air as tiny droplets, and can have lasting effects on vegetation and wildlife – even people.

"The good thing with the ice cream is that it's environmentally friendly," Ahmadi said. "It's not like other chemicals or even salt, which not only stay, but are also diluted or diluted over time."

Boreyko said that one of the most important contributions of the study was the development of a rational model of the amount of chemical (in this case, the chemical is ice ) to apply to keep a dry surface.

"We have known the trick for centuries," he said. "You put a chemical at low pressure, like salt, and everything else is dry, but now we have this effect last and we make it rationally sound."

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This research was funded in part by the National Science Foundation and the 3M Company.

Other co-authors of the study include Grady Iliff, a graduate in engineering sciences and mechanics in the Virginia Tech undergraduate program in 2017; Saurabh Nath, graduated in 2017 from the Virginia Tech Master's Program in Mechanical Engineering; Pengtao Yue, Associate Professor, Virginia Tech Department of Mathematics; and Bernadeta Srijanto and C. Collier, both of Oak Ridge National Laboratory.

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