Whisking whiskers: nanobrushes sweep up

Science News, June 18, 2005 by P. Weiss

Scientists have finally gotten a handle on carbon nanotubes. By controlling where those tiny hollow fibers of carbon sprout up on ultrafine shafts of silicon carbide, the researchers have made brushes and brooms loaded with bristles and have demonstrated myriad uses for the minuscule tools.

Anyuan Cao of Rensselaer Polytechnic Institute in Troy, N.Y., and his colleagues have shown that they can use their up-to-centimeter-long brushes to tidy up silicon wafers, soak up contaminants from solutions, and provide electric connections for tiny moving parts in microelectromeehanical systems.

The new structures, described in the July Nature Materials, "are really astonishing in the sense that [the researchers have] been able to create something very complex at the microscale using carbon nanotubes," says nanotechnology specialist David L. Carroll of Wake Forest University in Winston-Salem, N.C.

Achieving such structural complexity is "one of the so-called grand challenges of nanoscience," Carroll adds. In time, for example, engineers might create complex devices such as microscale robots. For now, making the brush structures is "a major step forward," Carroll says.

The microbrushes' characteristics go beyond merely mimicking large-scale brushes. For instance, the brushes' bristles, which are a ten-thousandth the diameter of those of a toothbrush, are jammed together so densely that a nanotube brush head packs about 1,oo0 times as much contact surface area into each cubic micrometer as does a conventional toothbrush head, Cao says. The team, led by Rensselaer's Pulickel M. Ajayan, includes researchers at Rensselaer and the University of Hawaii at Manoa.

When immersed in chemical solutions, microbrushes suck up organic chemicals and heavy metal contaminants like "molecular sponges," Cao says. One big challenge, he notes, is to make sure that the bristles adhere strongly to the shafts so that the bristles themselves don't become environmental and health concerns (SN: 4/23/05, p. 266).

Engineer Norman Miles of Gordon Brush Manufacturing in Commerce, Calif., says that he's eyeing the new report with great interest. "The brush industry is inundated with requests to produce ever-smaller brushes for medical use," he notes. "This technology would be a quantum leap forward in the use of brushes in areas previously outside of the capability of the brush-making industry."

Among specific potential uses, Miles notes, is the deposit of repair materials in tiny cracks that form in teeth or even in nuclear reactor cores.