Sep 16 2009
Spiderman's gecko-like ability to climb walls may someday leap from fiction to reality, courtesy of recent nanoscience research showing the exceptional adhesive properties of carbon nanotubes. Complementary to adhesion and equally intriguing is nanotube friction, highlighted in work such as that appearing in the 13 September advanced online publication of Nature Materials.
In a joint experimental and theoretical study of frictional forces on carbon nanotubes, ICTP researcher Erio Tosatti, along with an international team of physicists, discovered a difference in friction depending on which way the tube was stroked by a very small tip. A motion perpendicular to the nanotube produced much more friction than a parallel motion.
"When our experimental colleagues in Atlanta and Hamburg set out to measure friction forces of nanotubes, they expected to find the same amount of friction from parallel and perpendicular movements. Results showed this was not the case," said Tosatti, a theorist with ICTP's Condensed Matter section (also with SISSA and CNR-Democritos). Simulations performed in Trieste then showed that the increased perpendicular friction is caused by a "hindered rolling" of the nanotube on its substrate. More than that, the amount and the left-right friction asymmetry is predicted to depend on the nanotube “chirality” – the generally unknown twist sense of carbon chains that make up each tube. The friction felt by a stroking nanotip should be able to “read” the underlying tube texture, much as a blind man can read a Braille text.
The research findings could lead to improved nanotube selection for assembly in nanotube-based composite materials and devices. And for those of you aspiring to climb walls like Spiderman, the research might perhaps help in improving the design of nano-adhesives that allow for super-gripping powers.
The title of the article is "Hindered rolling and friction anisotropy in supported carbon nanotubes".