People can be startled by camera flashes. Carbon nanotubes are far more sensitive: A flash can make them burn up.
Carbon nanotubes–carbon atoms arranged in hollow cylinders just nanometers wide–have many unusual properties that chemists and materials scientists hope to exploit in future generations of tiny electronics, biomedical therapies, or other applications. However, it was unexpected that nanotubes could burst into flames, says Pulickel Ajayan of Rensselaer Polytechnic Institute in Troy, N.Y. He and his colleagues describe their observations in the April 26 Science.
Andres de la Guardia, an undergraduate student in Ajayan’s lab, made the discovery after he snapped a close-up of a fluffy mass of nanotubes. When the photographic flash went off just a centimeter or so from the structures–a variety known as single-walled carbon nanotubes–de la Guardia heard a loud popping sound and saw the tubes ignite. Although the freshman was new to the study of carbon nanotubes, “he had the presence of mind to come and tell me,” says Ajayan.
Investigating further, Ajayan and his colleagues found that several other forms of carbon don’t ignite when exposed to a photographic flash. These include graphite powder; multiwalled, or nested, carbon nanotubes; and nanometer-size cages of exactly 60 carbon atoms.
Purified samples of single-walled carbon nanotubes didn’t ignite, either, Ajayan says. Only fluffy, unpurified material ignited when flashed. It’s not clear what caused the ignition, but it might be related to the densities of the samples. The unpurified material is less densely compacted than are purified nanotubes, he says.
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In further studies, the researchers exposed single-walled carbon nanotubes to flashbulb light in inert atmospheres and in a vacuum. In these oxygenfree environments, the researchers were surprised to find that while the nanotubes didn’t ignite, their carbon atoms did rearrange into new structures.
The newly observed nanotube behaviors might prove useful for creating light-induced ignition systems, sensors, and other gadgets, says Ajayan.