As you probably know, carbon nanotubes have typically a diameter of approximately one nanometer while their lengths can reach several thousand nanometers. This is too long to be really useful. So what to do to cut them into shorter ones? Build 'scissors.'
This is what just did a team of chemists at Rice University.
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.
By varying the ratio of fluorine to carbon, John Margrave, Professor of Chemistry at Rice University 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.
Thatís 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, including biomedical sensors small enough to migrate through cells without triggering immune reactions.
It's also important to obtain nanotubes of specified lengths, which is not obvious with this method. So the chemists are searching a method to sort the nantubes by length.
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 solution.
For more information on this subject, please visit the very well-documented Nanotube Site.
Source: Rice University, July 22, 2003
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