Source: Rice University
Rice University's Chemical 'Scissors' Yield Short Carbon Nanotubes; New
Process Yields Nanotubes Small Enough To Migrate Through Cells
HOUSTON-- July 22, 2003 -- Chemists at Rice University have identified a
chemical process for cutting carbon nanotubes into short segments. The new
process yields nanotubes that are suitable for a variety of applications,
including biomedical sensors small enough to migrate through cells without
triggering immune reactions.
The chemical cutting process involves fluorinating the nanotubes,
essentially attaching thousands of fluorine atoms to their sides, and then
heating the fluoronanotubes to about 1,000 Celsius in an argon atmosphere.
During the heating, the fluorine is driven off and the nanotubes are cut
into segments ranging in length from 20-300 nanometers.
"We have studied several forms of chemical 'scissors,' including other
fluorination methods and processes that involve ozonization of nanotubes,"
said John Margrave, the E.D. Butcher Professor of Chemistry at Rice
University. "With most methods, we see a random distribution among the
lengths of the cut tubes, but pyrolytic fluorination results in a more
predictable distribution of lengths."
By varying the ratio of fluorine to carbon, Margrave and recent doctoral
graduate Zhenning Gu can increase or decrease the proportion of cut
nanotubes of particular lengths. For example, some fluorine ratios result in
nearly 40 percent of cut nanotubes that are 20 nanometers in length. That's
smaller than many large proteins in the bloodstream, so tubes of that length
could find uses as biomedical sensors. By varying the process, Margrave
hopes to maximize the production of lengths of nanotubes that are useful in
molecular electronics, polymer composites, catalysis and other applications.
Carbon nanotubes are a type of fullerene, a form of carbon that is distinct
from graphite and diamond. When created, they contain an array of carbon
atoms in a long, hollow cylinder that measures approximately one nanometer
in diameter and several thousand nanometers in length. A nanometer is one
billionth of a meter, or about 100,000 times smaller than a human hair.
Since discovering them more than a decade ago, scientists have been
exploring possible uses for carbon nanotubes, which exhibit electrical
conductivity as high as copper, thermal conductivity as high as diamond, and
as much as 100 times the strength of steel at one-sixth the weight. In order
to capitalize on these properties, researchers and engineers need a set of
tools -- in this case, chemical processes like pyrolytic fluorination --
that will allow them to cut, sort, dissolve and otherwise manipulate
Margrave said his team is already at work finding a method to sort the cut
tubes by size. One technique they are studying is chromatography, a complex
form of filtering. Margrave hopes to re-fluorinate the cut tubes, mix them
with a solvent and pour the mixture through a column of fine powder that
will trap the shorter nanotubes. Another sorting method under study is
electrophoresis, which involves the application of an electric field to a
Margrave's group is researching other ways that fluorination can be used to
manipulate carbon nanotubes, which are chemically stable in their pure form.
The highly-reactive fluorine atoms, which are attached to the walls of the
nanotubes, allow scientists to create subsequent chemical reactions,
attaching other substances to the nanotube walls. In this way, the group has
created dozens of "designer" nanotubes, each with its own unique properties.
Do Wah Ditty
"Now, there are some who would like to rewrite history - Revisionist
Historians is what I like to call them."
- Elizabeth, N.J., June 16, 2003 - President Bushisms