Nanoknot. A thread made out of nanotubes.

Rumpelstiltskins of the Nanoworld

Laboring like modern-day Rumpelstiltskins, scientists have successfully spun submicroscopic carbon nanotubes into nearly pure carbon thread. The precious strands may one day be woven into energy-storing bulletproof vests for Robocop-like soldiers or lightweight cables that tether satellites to Earth.

To make a nanotube, take a hexagonal mesh sheet of carbon atoms and roll it up like a sheet of paper into a tube a few micrometers long and about 1 nanometer wide. Then cap each end with one-half of a buckyball, the spherical 60-atom carbon balls that resemble Buckminster Fuller's geodesic dome. This surprisingly simple cigar-shaped structure is pound for pound the strongest material known. "On a weight basis, a single carbon nanotube is at least 50 times stronger than steel wire," says chemist Philippe Poulin of the Research Center Paul Pascal--CNRS in Pessac, France. When a solution of nanotubes dries out, the tubes stick together and form sheets called "buckypaper." But buckypaper retains only a small fraction of the remarkable strength of the individual tubes. And you can't weave sheets of paper--for that you need thread.

Now, Poulin and his collaborators have found they can spin out silklike strands of carbon by injecting a carefully prepared solution of nanotubes into a rotating solution containing polyvinyl alcohol. If the initial concentration of nanotubes is just right, the stream turns into a mesh ribbon that later collapses into a thread when removed from the spinning bath. Although these fibers don't match individual tubes, Poulin says, they're about three times more difficult to stretch than high-strength nylon fibers.

The fibers should get much stronger as researchers improve the process. "We are not anywhere close to [having] the fibers that will eventually come out," says physicist Richard Smalley of Rice University in Houston, the co-discoverer of buckyballs. "The next year will see a lot of excitement in this field." Already, materials scientist Ray Baughman's group at Honeywell International in Morristown, New Jersey, has spun more durable fibers with a modification of the Poulin group's method; several other teams have also started producing nanotube threads.

Related sites
A carbon nanotube page
The nanotube site
Nanotube images at Richard Smalley's site

Posted in Technology