Nanoropes Move Nanoscience Closer to Marketplace

CONTACT: Lia Unrau
(713) 831-4793, unrau@rice.edu

Richard Smalley
(713) 527-4845

NANOROPES MOVE NANOSCIENCE CLOSER TO MARKETPLACE

Rice researchers have produced defect-free nanoropes in useful quantities, the next step toward bringing products to market made from nanoscale materials.

For the first time, nanoropes made up of conductive carbon nanotubes, resembling bundles of long drinking straws, can be produced in high yields-more than 70 percent-according to research led by professor Richard Smalley at the Center for Nanoscale Science and Technology at Rice University.

A key to developing applications based on nanoscale science and technology is having enough material to work with, and until now, nanotube production has been inefficient at producing tubes with few or no defects. The advance allows for a systematic, clean study of the strongest and most conductive class of nanotubes, Smalley says. The
nanotube fibers that pack together to make ropes are predicted to be 100 times stronger than steel, and boast an electrical conductivity similar to copper and the thermal conductivity of diamond.

A paper describing the production of uniform diameter single-wall nanotubes, which self-organize into tightly packed ropes, appears in the July 26 issue of Science. “Crystalline Ropes of Metallic Carbon Nanotubes,” is authored by a team of researchers led by Smalley, Gene and Norman Hackerman Professor of Chemistry and professor of physics at Rice.

Nanotubes, which were discovered in 1991, are relatives of C60, or a carbon soccer ball-shaped fullerene cage known as a buckyball, discovered at Rice in 1985. Nanotubes are tubular versions of the buckyball, resembling rolled-up chicken wire and coming in various configurations. The class of singe-wall nanotube known as (10,10) due to its geometry and symmetry, is the dominant form of tube made at Rice with the new production method.

“The (10,10) single-wall nanotube is to the family of tubes what the buckyball is to the family of fullerene cages,” Smalley says.

Another interesting point, he adds, is that the diameter of this nanotube is precisely the right size to allow a buckyball to roll down its inner core. The single-wall nanotubes, which grow in tightly packed ropes of many parallel tubes, have a diameter of 1.4 nanometers, about 100,000 times smaller than a human hair. They grow hundreds of
thousands times longer than their diameter. The preferred form happens to be metallic, and because its diameter is of atomic dimension, it may serve as an electron waveguide, transporting electrons much the same way that fiber optic glass behaves as a light pipe. Preliminary studies show that the (10, 10) nanotube, and therefore ropes, have the best conductivity of any carbon fiber ever made.

“If we can understand why these (10,10) nanotubes are made, perhaps we can control the growth, and make them grow forever,” Smalley says, a feat which would be today’s holy grail of nanotube research, inspired by the predicted applications for such nanotube fibers.

One potential application includes using one (10,10) nanotube as a probe, giving superpowers to current imaging microscopes by acting as a tiny finger to examine nanoscale material. Other possible applications include using nanoropes in composite materials to create extremely strong but light bicycles, tennis racquets and
airplane wings. High-temperature superconducting material and a new type of electrical fiber cable are more possibilities.

“This would be a fantastic material to transmit electricity across vast distances,” Smalley says.

“Nature has been kind to us again,” says Gustavo Scuseria, Rice professor of chemistry and a co-author of the paper. Scuseria specializes in theoretical calculations to predict and determine behavior of molecular systems. His quantum chemistry simulations confirmed that the conducting (10,10) tubes produced in Smalley’s laboratory are the energetically preferred form compared to other possible tubes that form at the stage in growth when the tube diameter is established.

“This is a real breakthrough,” Scuseria says. “Theory has a large role to play in understanding the growth of these tubes, and this knowledge will let us improve and control production.”

Smalley and his team use graphite mixed with catalytic metals cobalt and nickel, and laser vaporization to spur the high yield of these special nanotubes. Although it is not yet fully understood how the metal catalyst works, they suspect that it acts to promote an energetically balanced, or stable condition to keep the nanotube, which would otherwise quickly close into a sphere, open for extended growth into a tube. As it reaches a critical size, the tube adopts the favored (10,10) structure and diameter, and may continue to grow thousands to millions of times longer. Growth concludes when the catalytic metal cluster at the end of the tube either leaves the single-wall nanotube by evaporation or, if the growing metal cluster at the end gets large enough, by helping to close the end of the nanotube with a hemispherical cap.

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A copy of the Science paper, along with images, is located on the World Wide Web at http://cnst.rice.edu/ropes.html.