TROY, N.Y., May 2 (UPI) -- A relatively simple method for transforming microscopic carbon tubes into "ropes" several inches long could result in super-strong lightweight materials, researchers at Rensselaer Polytechnic Institute have discovered.
Scientists have been making so-called "nanotubes" -- structures hundreds of times thinner than a human hair with walls one atom thick -- for years, said Pulickel Ajayan, a professor at RPI who led the team in collaboration with researchers at Tsinghua University in Beijing. The team reports its findings in the May 3 issue of the journal Science.
"Carbon nanotubes are generally (millionths of an inch long), which is not enough for any practical purpose," Ajayan said. "We have created strands with nearly aligned nanotubes that are as long as 20 centimeters (eight inches)."
The RPI process adds slight impurities, including a stream of hydrogen gas, to a standard nanotube fabrication method called chemical vapor deposition. The changes induce the tubes' long growth and strand development, resulting in bundles of tubes about as wide as a human hair. Some individual tubes in a strand reach the centimeter range in length, Ajayan told United Press International Thursday.
Although the strand length is limited by the size of the deposition chamber, the ability to make real-world quantities of nanotubes could be a boon for industries seeking strong yet light fibers. The strands display a lower limit of tensile strength roughly equivalent to steel, Ajayan said.
The best real-world analog for the strands, Ajayan said, is spider silk, which is incredibly strong for its weight. The strands could turn out to be even stronger if the process is improved to reduce the amount of empty space inside them, he explained.
"Nanotube films and fibers have been considered for use as artificial muscle ... but they haven't been mechanically strong enough," Ajayan said. "These kinds of developments could provide the basic backbone of that kind of structure."
The RPI discovery is particularly noteworthy because of the length of the strands, said David Carnahan, president of Nano-Lab, based in Brighton, Mass., which manufactures nanotubes. Materials scientists will have an easier time incorporating the strands into other compounds in order to test their composite qualities, he said.
"(The process) looks like it would scale up (to production levels) quite nicely," Carnahan told UPI. "This is really promising in that sense."
Even though researchers have yet to achieve anything close to the theoretical strength of nanotubes, creating the strands is as important in making the technology usable as it was to figure out how to create yarn from cotton, Carnahan said. Individual cotton fibers are only an inch or so long, but when spun into yarn they are stable and strong enough to create entire garments, he said.
Carrying the analogy to the idea of steel cable is also intriguing, because individual steel wires overlap and merge in the same way the nanotubes appear to do in the strands, Carnahan said.
Once the process is perfected and researchers learn how to weave the strands, it is easily conceivable that a "pencil-thin" carbon filament could take the place of the inch-thick steel cables found in ski lifts and elsewhere, he said.