Scientists Cut Nanotubes into Pipes: a Usable Form

CONTACT: Lia Unrau

PHONE: (713)
831-4793

E-MAIL: unrau@rice.edu

SCIENTISTS CUT NANOTUBES INTO PIPES: A USABLE
FORM

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
nanotechnolgies and materials.

A team of researchers at Rice University, led by chemist
Richard Smalley, have 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 is published in the May 22 issue of Science in a
paper titled, “Fullerene 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 100-300 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 soap-like 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.

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