Magazine article Science News

Carpet of Carbon Nanotubes Cleans Itself

Magazine article Science News

Carpet of Carbon Nanotubes Cleans Itself

Article excerpt

The amazing water-shedding ability of the lotus leaf has long inspired materials scientists. The leaf's wax-coated microstructures cause rain droplets to bounce off the surface, carrying away with them dust particles and other contaminants. In trying to reproduce this so-called lotus effect in the lab, chemical engineers have fabricated a similar self-cleaning material out of forests of carbon nanotubes.

Led by Karen Gleason of the Massachusetts Institute of Technology (MIT), the researchers first created arrays of tiny islands of nickel on a surface of silicon. >From these islands, the researchers grew vertically aligned carbon nanotubes. "Sort of like a bed of pins" is how coinvestigator Kenneth Lau describes the result.

The minuscule pillars, each measuring 50 nanometers in diameter and standing 2 micrometers, form a rough surface. Because there are air pockets between the nanotubes, when a drop of water lands on the surface, "it's essentially held up by air," says Lau.

Using a technique called chemical vapor deposition, the researchers coated the top of each carbon nanotube with poly(tetrafluoroethylene), otherwise known as Teflon. Not only did this arrangement stabilize the nanotube forest, but it also boosted the surface's waterrepelling properties. When water droplets squeezed from a syringe hit the Tefloncoated nanotube carpet, the droplets bounced from and rolled off the surface.

Because the spacing between nanotubes was less than a micron, the material could repel tiny droplets of water just a few micrometers in diameter. …

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