Nanotubes Cut into Pipes: Vital Step

Nanotubes Cut into Pipes: Vital Step

BY LIA UNRAU
Rice News Staff
June 25, 1998

Rice News Staff

Nearly endless tangles of fullerene nanotubes, tiny tubular fibers of carbon,
have been converted into short, open-ended pipes, a form which allows scientists
to manipulate the nanotubes chemically for the first time. This is a vital step
in developing useful nanotechnologies and materials.

A Rice team of researchers, led by chemist Richard Smalley, has brought carbon
nanotubes officially into the world of chemistry by cutting them into pipes
and attaching molecules to their open ends, providing the ability to bind nanotubes
to a variety of other chemical groups or surfaces.

Smalley and his team have demonstrated this ability by tethering the pipes
to gold particles 10 nanometers in diameter. A nanometer is one-billionth of
a meter.

The research was published in the May 22 issue of Science in a paper titled
"Full-erene Pipes."

Since nanotubes were discovered in 1991, scientists have been working to develop
ways to unlock the potential of these carbon fibers that are 100 times stronger
than steel, yet only one-sixth the weight, and that possess interesting electrical
properties.

Two areas that stand to gain by the development of nanotubes are molecular
electronics and high-strength composite materials. Both areas require knowing
how to manipulate the nanotubes.

Molecular electronics involves shrinking components to the molecular level,
increasing density and speed, thereby vastly increasing computing power. Fullerene
pipes, with their molecular nature and electrical properties, might be used
as connectors and components for molecular electronics. With their newly demonstrated
controlled chemistry, nanotubes might also be integrated with other polymers
to make super-strong composite building materials.

To create the fullerene pipes, Smalley and the researchers first purify the
raw nanorope material in large batches using nitric acid, followed by a filtration
technique similar to dialysis, yielding about 10-20 percent pure nanoropes by
weight. Then the nearly endless ropes, which are made of several nanotubes nestled
parallel to one another, are separated and cut into individual open-ended pipes
ranging in length from 100 to 300 nanometers.

The cutting method involves sonic bombardment with high-energy sound waves
in combination with concentrated sulfuric and nitric acids. The walls of the
nanotubes are attacked by the sonication, creating a hole, and the oxidizing
acids etch around the remainder of the tube. The cutting takes place over a
period of one to three hours. The acid treatment leaves the open edge of the
pipe with carboxylic acid groups hanging onto the end, which can easily be converted
to the acid chloride.

When mixed with water and soaplike molecules to keep them separated, the cut
pieces, which are molecularly perfect and chemically clean, are in a form which
allows them to be sorted by length using a type of chromatography. They can
then be manipulated by exposing the ends to additional chemicals, such as alkane
thiol chains attached by amide links. The alkane thiol chains for this research
were provided by chemist Randall Lee’s research group at the University of Houston.

The thiol group on the end of a fullerene pipe was used to create a chemical
bond with a gold sphere, a connection easily and conveniently imaged by atomic
force microscopy.

The attachment of the thiol group and the gold sphere are merely examples of
much richer possibilities for the chemistry of fullerene pipes.

This research was supported by the National Science Foundation, the Office
of Naval Research, the Advanced Technology Program of Texas and the Robert A.
Welch Foundation.

For related information visit the following Web sites:
The Department of Chemistry: http://pchem1.rice.edu/dept.html
The Center for Nanoscale Science and Technology: http://cnst.rice.edu/