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".
Posted September 16th, 2009
