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Posted: January 9, 2008
How nanocones could help you stay dry
(Nanowerk News) Were you soaked in last summer's heavy rainstorms? John Simpson, a senior research scientist at the Department of Energy's Oak Ridge National Laboratory in Tennessee, has developed a new super-water-repellent coating that might make a dismal British summer more bearable. Although helping stay dry in bad weather is one application, Simpson believes that there are many other possibilities.
"My goal was to make the best possible water-repellent surface," says Simpson. "What I developed is a glass powder coating material with remarkable properties that cause water-based solutions to bounce off virtually any coated surface."
His project began from a demonstration of a novel fabrication method to make uniform microarrays of spiked cones - he calls them nanocones - which would have the best water-repellent properties theoretically possible. Following that research, he's now developed a superhydrophobic coating from inexpensive base materials - a phase-separated borosiliciate glass like that used to make test tubes.
Although superhydrophobic coatings aren't new, existing materials are difficult and expensive to produce, which generally restricts them to laboratory use. Simpson's breakthrough has been to make a cheaper borosilicate glass powder coating using heating and acid etching to produce nanoscale sharpened features with superhydrophobic properties.
The arrays of sharp-pointed nanocones trap and maintain a microscopic layer of air on surfaces, even when submerged in water. What happens next is something that Simpson describes as the "Moses effect": water will completely avoid a treated area, leaving a totally dry patch surrounded by a high rim of liquid held in place by surface tension. Any water on the treated surface remains as droplets until it rolls off, just like the waxy leaf of the water lily, which has similar properties.
The result of Simpson's pioneering work is something that betters nature by amplifying the effect of water's surface tension. What's more, only a small amount of the very fine-grained glass powder is needed to coat a relatively large surface area.
Simpson hopes the patent-pending process will lead to a new generation of water-repellent products including windscreens, eyewear, clothing, building materials, road surfaces, ship hulls and self-cleaning coatings. The glass-based material also offers good insulation and anti-corrosion properties because of trapped air between the water and the coated substrate. This could reduce hull friction to save energy or extend the life of bridges and buildings.
"We now have a number of different superhydrophobic materials. The powder version shows great promise as a coating, but further research is needed to address bonding and durability issues," says Simpson. Many companies are now said to be interested in the new technology.