Nanotubes show their strength in numbers

WASHINGTON - Carbon nanotubes, the wunderkind molecules of the nanoworld, are finally showing strength in numbers. Researchers have now made large nanotube sheets that have many of the same star qualities as the prima donna-like single molecules, bringing the promises of nanotechnology a step closer to reality.

The flexible, transparent sheets can conduct electricity and emit light or heat when a voltage is applied, leading their creators to propose that our car windows and the canopies of military aircraft could contain nearly invisible antennae, electrical heaters for defrost, or informative optical displays.

These sheets, which are presently several meters long but could potentially be much larger, might also be useful in everything from flexible computer screens that could be rolled into a sack, to light bulb-like devices providing uniform lighting, to strong sails that could be propelled in space by sunlight.

“When you have a remarkable material, it’s easy to make advances in terms of applications,” said Ray Baughman of the University of Texas, Dallas, who led the research team that made the nanotube sheets. The scientists report their findings in the 19 August issue of the journal Science, published by AAAS, the nonprofit science society.

Growing a nanotube forest
Individual carbon nanotubes, long, cylindrical sheets of carbon atoms, are like minute bits of string, and researchers must assemble many trillions of these strings to make useful objects, including wide sheets and long yarns.

Until now, nanotube sheets have usually been made using versions of the ancient art of paper making, by filtering solutions of nanotubes and then peeling the nanotubes off the filter once they’re dry, which can take about a week. Baughman’s group has been working instead with nanotube “forests” that consist of nanotube bundles standing vertically.

The researchers have now shown that by teasing nanotubes away from one side of a forest and attaching them to a strip of sticky tape they can draw the nanotubes into a continuous sheet. With this method they can produce nanotube sheets at up to seven meters per minute, which is fairly close to the rate of commercial wool spinning.

“It’s so surprising that this works,” Baughman said. “A trillion nanotubes must be automatically rotated by about 90 degrees and self-assembled in a parallel fashion for every meter-long, 7 centimeter-wide sheet that we make.”

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