Water Droplets Bounce Off Laser-etched Metal
The science could lead to rust- and ice-free metals and water-repellant electronics.
Coatings that prevent water from soaking into surfaces are common. But generally, they're made with chemicals that eventually wear off. Now researchers from the University of Rochester have used a laser to etch micro-sized and nano-sized structures into metals that make the surfaces permanently repel water. The technique could lead to rust- and ice-free metals and water-repellent electronics.
Professor Chunlei Guo and colleagues used a femtosecond laser, which delivers up to one thousand pulses of light per second to etch tiny grooves into the surface of platinum, titanium and brass. The pattern of the grooves was partly inspired by those in the lotus leaf (above), which is nature's best water-repellent surface.
The pattern in the metal does a remarkable job at repelling the water. Even when the surface was tilted at a slight five-degree angle, the droplets rolled right off.
As the droplets rolled off, they took dust particles with them. In experiments, the scientists dumped ordinary dust from a vacuum cleaner onto the water-repelling metal and then tested to see how many droplets it took to clean the surface. Three droplets removed half of the dust; twelve droplets removed all of the dust.
The grooved pattern also made the surface black from every angle, a great light-absorbing property. A super-black material that stays very clean would be ideal for solar thermal collectors that collect the most amount of sunlight when they're free of dust and dirt. The research appeared in the Journal of Applied Physics. You can see a video