Super-hydrophobic metal ‘bounces’ water

Scientists from University of Rochester, New York (USA) have created a super-hydrophobic metal surface that completely repels water. The surface could be used for numerous applications ranging from airplane wings on which ice cannot form, to self-cleaning toilets. The findings were published last week in the Journal of Applied Physics.

Water bounces off super-hydrophobic metal surface (credit: University of Rochester/J. Adam. Fenster)

Water bounces off super-hydrophobic metal surface (credit: University of Rochester/J. Adam. Fenster)

The team of researchers created the water-repellent material by etching micro- and nano-structures on the metal surface by means of super short femtosecond (a quadrillionth of a second) laser pulses. “The water falls towards the surface, and is repelled and bounces off the surface” – leading author Chunlei Guo said. “This is achieved by creating a unique pattern of surface structures at micro- and nano-scales with our laser processing technology”.

The laser-etched patterns make the surface much more repellent than traditional chemical coatings – such as the well-known Teflon of non-stick fry pans – and unlike them, this new water-repellent effect does not wear off. The surface treatment was tested on platinum, titanium and brass surfaces.

Electron microscope image of the super-hydrophobic surface (credit: Journal of Applied Physics/c. Guo)

Electron microscope image of the super-hydrophobic surface (credit: Journal of Applied Physics/C. Guo)

The treated metal has also superior self-cleaning properties. These were tested by the team of scientists by applying dust onto the surface. The researchers found that they could remove about half of the dust particles using only three drops of water and all the dust with only a dozen of droplets. The surface remained completely dry and spotless.

The potential applications for the technology are numerous. Laser-etched hydrophobic patterns could be used on airplane wings to prevent ice from building up. They could also be used to keep toilets clean, especially in developing countries where the water is scarce. This particular application has already attracted commercial interest from the Bill & Melinda Gates Foundation which co-sponsored the research.

Interestingly, in previous work the same team of scientists used a similar patterning technique to turn metal surfaces black and hence highly optically absorbent. The combination of light-absorbing and water-repelling surfaces could lead to the fabrication of more efficient, long-life solar panels that would not rust and would require less maintenance.

However, there are still many challenges ahead. For this technology to become commercially viable, the researchers have to scale up the fabrication process. Currently, it takes about an hour to etch a 2.5 by 2.5 centimetres square of metal. The scientists are quite optimist though, as at the moment their instruments are not optimized for large scale production. The researchers are also planning on applying the technique to non-metal surfaces.

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Carlo Bradac

Carlo Bradac

Dr Carlo Bradac is a Research Fellow at the University of Technology, Sydney (UTS). He studied physics and engineering at the Polytechnic of Milan (Italy) where he achieved his Bachelor of Science (2004) and Master of Science (2006) in Engineering for Physics and Mathematics. During his employment experience, he worked as Application Engineer and Process Automation & Control Engineer. In 2012 he completed his PhD in Physics at Macquarie University, Sydney (Australia). He worked as a Postdoctoral Research Fellow at Sydney University and Macquarie University, before moving to UTS upon receiving the Chancellor Postdoctoral Research and DECRA Fellowships.

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