Monday, June 25, 2007

Climbing Walls with Carbon Nanotubes

Continued from page 1

By Kevin Bullis

To make the tape even stronger while maintaining flexibility, the researchers took a tip from the geckos. They grew nanotubes in distinct bundles, much like the bundles of fibers that make up the hairs on gecko feet. Nanotubes are made by exposing catalysts to hydrocarbon feedstocks: gradually, carbon builds up on the catalysts in a distinctive atomic arrangement that forms tubes. The researchers grew nanotubes in bundles by depositing the catalyst material in a pattern of separate squares. They then transferred these bundles of nanotubes to a flexible plastic to make the tape.

The tape can still be improved in a number of ways. Right now, it takes a significant amount of pressure to get good contact between the nanotubes and the surface, says Metin Sitti, a professor of mechanical engineering at Carnegie Mellon University, who is developing similar materials. Chaudhury says that ultimately, it would be nice to have a material that sticks with little or no pressure, particularly for use with wall-climbing robots. Ali Dhinojwala, a professor of polymer science at the University of Akron, who led the work, says that the attachment pressure might be decreased by doing things like softening the tape's backing.

The researchers also want to make the tape stronger. Right now, when pulled parallel to a surface, the tape releases not because the carbon nanotubes come off the surface, but because the nanotubes themselves break. The researchers are currently working on a number of ways to strengthen the nanotubes to take advantage of this strong adhesion. They are also working to make the tape reusable thousands of times, rather than the dozens of times it can be used now. To achieve this goal, Dhinojwala and his team will have to make the tape self-cleaning, like gecko feet.

To commercialize the tape, the researchers will also need to make bigger patches of tape. So far, they've only made pieces of tape that are far smaller than a dime.