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Ice Repellent

Nanotechnology: Small structures keep water off supercooled surfaces

by Bethany Halford
November 22, 2010 | A version of this story appeared in Volume 88, Issue 47

Ice phobia
Credit: ACS Nano
Surfaces studded with honeycombs (35 μm), bricks (15 x 39 μm), and pillars (4 μm across) repel water before it can freeze.
Credit: ACS Nano
Surfaces studded with honeycombs (35 μm), bricks (15 x 39 μm), and pillars (4 μm across) repel water before it can freeze.

With the official first day of winter less than a month away, it’s almost time to break out the heaters, scrapers, and deicers. But according to a new study, the future of ice fighting may not involve thermal, mechanical, or chemical ice removal. Rather, it may belong to tiny structures that can repel water from surfaces before it even has a chance to freeze (ACS Nano, DOI: 10.1021/nn102557p).

Inspired by the nanostructured surfaces that help water striders keep their legs dry and that render mosquitoes’ eyes fog-free, a team led by Harvard University materials science professor Joanna Aizenberg created surfaces covered in various micro- and nanostructures, such as honeycombs, bricks, and pillars. They then used high-speed video to study how water droplets behave when they strike these surfaces at low temperatures.

“Freezing starts with droplets colliding with a surface, and very little is known about what happens when droplets hit surfaces at low temperatures,” Aizenberg explains. Her team found that on smooth surfaces, water droplets spread and freeze. But on micro- and nanostructured surfaces at temperatures as low as –30 °C, the droplets spread but then retract and bounce off before freezing can occur. At lower temperatures the droplets will freeze, but, Aizenberg says, “any ice that forms does not adhere well and is much easier to remove than the stubborn sheets on flat surfaces.”

Di Gao, an engineering professor at the University of Pittsburgh who studies ice-phobic materials, calls the work “a promising experimental result.” He notes that the retraction behavior of supercooled water droplets noted by Aizenberg’s team provides additional insights on ice-phobic materials and could aid the design of anti-icing surfaces.

Aizenberg thinks micro- and nanostructured surfaces could help prevent ice buildup on airplanes, buildings, power lines, and pipelines. Her team is now testing the technology in real-world settings, such as wind tunnels. “We are certain that this new form of coatings integrated directly into a variety of materials could soon be developed and commercialized,” she says.



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