Researchers say they've bombarded ordinary metals with lasers to create new self-cleaning surfaces that are super-hydrophobic -- water-repelling -- without the need of temporary coatings.
The new surfaces, which can also absorb light, could be used for durable, low maintenance solar collectors and other applications, scientists at the University of Rochester in New York say.
While most present hydrophobic materials rely on the use of chemical coatings, the Rochester researchers used laser pulses to create intricate patterns of micro- and nanoscale structures to endow the metals with the new properties.
"This is the first time that a multifunctional metal surface is created by lasers that is super-hydrophobic (water repelling), self-cleaning, and highly absorptive," says physicist Chunlei Guo.
The improved light absorption will be useful in technologies that require light collection, such as sensors and solar power devices, while the water-repellant capability will make a surface rust-resistant, anti-icing and anti-biofouling, Guo and fellow researcher Anatoliy Vorobov report in the Journal of Applied Physics.
Devices built with such materials would be more robust and easier to maintain, Guo says, and because "the structures created by our laser on the metals are intrinsically part of the material surface" they won't rub off like coatings can.
As water runs off the metals' newly super-hydrophobic surfaces it collects dust and takes it along, giving the materials their self-cleaning quality.
That suggests a potential application in developing countries, Guo says, which has led to the Bill and Melinda Gates Foundation supporting his and Vorobov's work.
"In these regions, collecting rain water is vital and using super-hydrophobic materials could increase the efficiency without the need to use large funnels with high-pitched angles to prevent water from sticking to the surface," says Guo. "A second application could be creating latrines that are cleaner and healthier to use."
The researchers created the surfaces by zapping platinum, titanium and brass samples with extremely short laser pulses lasting just a millionth of a billionth of a second.
The pulses created microgrooves, on top of which bumpy nanostructures were formed that altered the optical and wetting properties of the surfaces of the three metals.
The water-repellent abilities surpass even those of a famous non-stick coating, Guo points out.
"Many people think of Teflon as a hydrophobic surface, but if you want to get rid of water from a Teflon surface, you will have to tilt the surface to nearly 70 degrees before the water can slide off," Guo explains. "Our surface has a much stronger hydrophobicity and requires only a couple of degrees of tilt for water to slide off."
Commercial use of the technique will require further work to scale up the process, the researchers acknowledge, since it presently takes an hour to create the patterns on a 1-inch square sample of metal.
