Water Repellent Metal - Nanotechnology Makes Metal Rust Free

Laser-generated surface structures create extremely water-repellent metals. Super-hydrophobic properties could lead to applications in solar panels, sanitation and as rust-free metals. Scientists at the University of Rochester have used lasers to transform metals into extremely water repellent, or super-hydrophobic, materials without the need for temporary coatings....Super-hydrophobic materials are desirable for a number of applications such as rust prevention, anti-icing, or even in sanitation uses. However, as Rochester’s Chunlei Guo explains, most current hydrophobic materials rely on chemical coatings.

In a paper published in the Journal of Applied Physics, Guo and his colleague at the University’s Institute of Optics, Anatoliy Vorobyev, describe a powerful and precise laser-patterning technique that creates an intricate pattern of micro- and nanoscale structures to give the metals their new properties. This work builds on earlier research by the team in which they used a similar laser-patterning technique that turned metals black. Guo states that using this technique they can create multifunctional surfaces that are not only super-hydrophobic but also highly-absorbent optically.

Guo adds that one of the big advantages of his team’s process is that “the structures created by our laser on the metals are intrinsically part of the material surface.” That means they won’t rub off. And it is these patterns that make the metals repel water.

“The material is so strongly water-repellent, the water actually gets bounced off. Then it lands on the surface again, gets bounced off again, and then it will just roll off from the surface,” said Guo, professor of optics in the University’s Hajim School of Engineering and Applied Sciences. That whole process takes less than a second.

The materials Guo has created are much more slippery than Teflon—a common hydrophobic material that often coats nonstick frying pans. Unlike Guo’s laser-treated metals, the Teflon kitchen tools are not super-hydrophobic. The difference is that to make water to roll-off a Teflon coated material, you need to tilt the surface to nearly a 70-degree angle before the water begins to slide off. You can make water roll off Guo’s metals by tilting them less than five degrees.

As the water bounces off the super-hydrophobic surfaces, it also collects dust particles and takes them along for the ride. To test this self-cleaning property, Guo and his team took ordinary dust from a vacuum cleaner and dumped it onto the treated surface. Roughly half of the dust particles were removed with just three drops of water. It took only a dozen drops to leave the surface spotless. Better yet, it remains completely dry.

Guo is excited by potential applications of super-hydrophobic materials in developing countries. It is this potential that has piqued the interest of the Bill and Melinda Gates Foundation, which has supported the 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.”

Latrines are a challenge to keep clean in places with little water. By incorporating super-hydrophobic materials, a latrine could remain clean without the need for water flushing.

Funding was provided by the Bill & Melinda Gates Foundation and the United States Air Force Office of Scientific Research.

The article, “Multifunctional surfaces produced by femtosecond laser pulses,” was published in the Journal of Applied Physics on January 20, 2015 (DOI: 10.1063/1.4905616). It can be accessed at: http://scitation.aip.org/content/aip/journal/jap/117/3/10.1063/1.4905616

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