Scientists spin thread from nanotubes

By Eric Smalley, Technology Research News

If Spiderman wanted an upgrade for the 21st century, he could make his webs from carbon nanotubes.

These microscopic rolled-up sheets of graphite are among the strongest objects known. They also make good electrical wires. The problem is, nanotubes are so small -- about 10 carbon atoms in diameter -- that it's difficult to produce anything made from them.

Researchers looking for ways to make bulk materials from nanotubes have formed microscopic ropes, pressed sheets and tiny fibers. But these materials tend to be small, fragile or both.

Researchers from Rensselaer Polytechnic Institute and Tsinghua University in China have found a way to work on a larger scale, producing thread-like strands of carbon nanotubes as long as 20 centimeters. The strands could eventually be used to make very strong fabrics, cables and wires.

To date, scientists have made nanotube fibers using a relatively time-consuming process that involves combining nanotubes as they are suspended in a liquid, said Pulickel Ajayan, an associate professor of materials science and engineering at RPI.

The researchers sidestepped the issue by getting bundles of nanotubes to line up into strands during the process that produces the individual nanotubes. "Our approach produces these large strands directly," he said.

The researchers made 10- and 20-centimeter strands that were a third to half a millimeter in diameter, or around five times the diameter of a human hair.

The carbon nanotube strands are as much as 25 times stronger than spider silk, 15 times stronger than nylon fibers, and one-third the strength of steel. The strands are still at least 13 times weaker than individual nanotubes, however.

The strands could be used as electrical cables, strong mechanical devices, and electrochemical actuators, said Ajayan. Electrochemical actuators are electrically powered devices, like valves, whose movements are triggered by chemical reactions.

Nanotubes, a natural component of soot, are commonly made in high concentrations by condensing a hot chemical vapor that includes carbon atoms. The researchers got their nanotubes to form in strands by producing them at very high temperatures and by injecting the carbon vapor into a gently flowing stream of hydrogen gas. The nanotube strands grew in the direction of the flow.

The research is a significant advance, said Philippe Poulin, a materials scientist at Paul Pascal Research Center, a national laboratory in France. "This work is very nice, and fascinating," he said. Poulin's research team has also developed a process for making nanotube fibers.

"The strands they have obtained by direct synthesis are the longest and strongest assemblies made only of carbon nanotubes," said Poulin. "The nanotube strands [have] better physical properties than [our] fibers," he said.

The nanotube materials developed by the two teams are different and are likely to have different applications, Poulin added.

The nanotube strands could be used in practical applications in two to five years, said Ajayan. "More optimization is necessary to improve [their] mechanical properties," he said.

Ajayan's research colleagues were Hongwei Zhu, Cailu Xu and Dehai Wu of Tsinghua University in China, and Bingqing Wei and Robert Vajtai of Rensselaer Polytechnic Institute. They published the research in the May 3, 2002 issue of the journal Science. The research was funded by the National Science Foundation (NSF) and the Ministry of Science and Technology in China.

Timeline:   2-5 years
Funding:   Government
TRN Categories:   Materials Science and Engineering; Nanotechnology
Story Type:   News
Related Elements:  Technical paper, "Direct Synthesis of Long Single-Walled Carbon Nanotube Strands," Science, May 3, 2002


June 12/19, 2002, 2002

Page One

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