Nanotubes: the new little high rollers

Tomorrow’s cancer weapon, television screen and space shuttle may all hang on a carbon thread

 By Anita Martin

Carbon, like all elements, got its start among the stars (or rather, within them). But, the ham that it is, carbon has remained in the spotlight. Sure, water, an oxygen-rich atmosphere and moderate climate set the stage for planet Earth, but it was carbon who stole the show with its tendency to form the long chains and rings and its limited abilities to self-replicate—making carbon the basis for life as we know it.

But carbon didn’t stop there. Once it set the foundations for life, it commenced to wow its new organic audience with everything from coal to pencil tips to diamonds. Carbon, depending on its molecular mood, may fuel the world’s electricity and help produce its steel, or even symbolize eternal love. According to Marilyn Monroe, a girl can’t find a better friend.

And just when we thought it was curtain time, carbon comes out for a grand finale: scientists have figured out how to construct pure carbon into the strongest material ever made, which can also conduct electricity and heat, and may change everything from electronics, to plastics to medicine. Introducing nanotubes, starring everyone’s favorite celestial celebrity, the carbon atom.

Bound for success

In 1985, scientists Robert Curl, Harold Kroto and Richard Smalley discovered nanoscopic hollow spheres of pure carbon, while trying to simulate a small-scale Big Bang. They termed them buckminsterfullerenes, or “bucky balls.”

Then, in 1991, Sumio Iijima of the NEC Corporation spotted threads of pure carbon. Upon closer inspection, Iijima saw that these threads take the bucky ball blueprint, and stretch it out—from a sphere to a closed cylinder of pure carbon. Called nanotubes, these carbon cords are both 100 times stronger and six times lighter than steel at the same scale. What’s more, depending on their construction, nanotubes can be either metals or semiconductors.

“Nanotubes are cousins of graphite,” says Liwei Chen, assistant professor of chemistry at Ohio University, who teaches a class on nanoelectric materials. “Graphite, like the diamond, is made of pure carbon atoms connected by very strong covalent bonds.”

But whereas in diamonds carbon atoms are bonded in all directions, graphite atoms bond only along one layer, called a graphene sheet.

“There are no interlayer chemical bonds,” Chen says, “that’s why graphite can be used in a pencil, because the layers are not bonded, so they can break off.”

On a roll

Nanotubes form like carbon layers, or graphene sheets, rolled into tubes, and then sealed together at both ends to make carbon nanotubes (CNT). Composed of hexagonal carbon atoms, they resemble cylinders of nanoscale chicken wire.

“What makes them so versatile is this,” Chen explains, “depending on how you roll it, you get different properties. Some nanotubes are metallic; some are semiconductors. This is a very rich property: a great opportunity and challenge.”

There are three angles at which a CNT can roll itself up, and each one presents unique opportunities and challenges. If each row of hexagons along the tube’s axis forms a helix pattern, for example, the tube acts as a semiconductor. If, instead, the rows are straight, the tube conducts electricity and heat like a metal.

“Because they’re made of carbon, nanotubes are very light,” Chen says. “But, they’re very strong because of their strong bonds and their cylindrical shape, and because of their resiliency and very small diameter, they can bend like a straw.”

Despite this enormous versatility, Chen laments what he calls a “bottleneck position” when it comes to nanotube technology research. “There are many challenges right now in terms of production, purification and processing of nanotubes.”

For one thing, scientists cannot yet selectively control which kind of nanotube they grow. For another, the tiny scale limits the length of CNT. The world record CNT length is four centimeters, achieved by Yuntian Zhu, of Los Alamos National Laboratory.

“The biggest obstacle today,” according to Zhu, “is controlling the type and quantity of nanotubes made.”

Jack of all trades

Despite these drawbacks, companies are scrambling to implement CNTs into their products.

“CNT is a very fantastic material,” Chen says; “you can invent many applications.”

These days, it seems everyone has big plans for these little tubes, from NASA engineers to sports suppliers to cancer researchers. And while some applications remain fantasy, not all are pipe dreams.

Nanotubes are already in use as a light and sturdy reinforcement in plastic composites such as automotive body parts, computer disc drives and even sporting goods. Easton Sports recently teamed up with Zyvex to introduce CNT technology to baseball bat design. CNTs even biked the 2005 Tour du France imbedded into the frames of Team Phonak’s bicycle.

Nanotubes may even enter the realm of the boob tube. Motorola Labs announced its “nano emissive display” model for flat panel television screens this summer. Motorola plans to develop affordable flat panel technology by exploiting CNT’s ability to emit light.

“We believe the market is ripe for disruptive technology, such as carbon nanotubes,” says Bob O’Donnell, director, personal technology at IDC (International Display Corp.), “that provides a CRT [cathode ray tube] quality image at a cost that is significantly lower than current plasma and LCD offerings.”

While nanotubes may “disrupt” flat panel technology and other electronics, prompting corporate readjustment, they may also help save lives. The August 2005 issue of Scientific American featured nanotube lasers, which may be used to selectively destroy cancer cells. Other headlines are popping up posting nanotube possibilities in medicine such as drug delivery and bone reinforcement.

For now, nanotubes remain yet another rising star among nanotechnology research conducted at Ohio University.

“From space shuttles to conductive plastics to nanoelectronics,” Chen says, "the impact of this material is potentially huge. It could impact every aspect of our lives.”