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Controlling the Shape of Nanotube Structures

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TROY, N.Y., March 25 -- Researchers at Rensselaer Polytechnic Institute (RPI) are reporting the discovery of a simple method for rapidly creating different shapes of carbon nanotube structures. To produce the minuscule structures on a commercial scale, manufacturers are looking for such techniques that make it possible to work with materials several billionths of a meter in size.

The new findings appear in the Proceedings of the National Academy of Sciences March 23 issue in a paper titled "Capillarity-driven assembly of two-dimensional cellular carbon nanotube foams."

Since their discovery in 1991, nanotubes have tantalized researchers because of their exceptional combination of size, strength and physical properties. They conduct electricity and channel heat efficiently, and their tiny dimensions raise hopes for a new generation of semiconductors and a host of other applications in medicine and materials science. But researchers must first develop techniques that allow for the commercial manufacture of precise structures.

Close-up of nanotube foam (Photo: Chakrapani et al., courtesy RPI)

"To make use of the outstanding properties of carbon nanotubes, it is important to devise techniques for assembling these nanoscale materials into macroscopic objects," said Ravi Kane, an assistant professor of chemical and biological engineering at RPI. "We have developed a very simple method for controlling the assembly of nanotube structures."

The method provides control over the shaping process. Employing a commonly used chemical vapor deposition method, researchers grow a carpetlike film of multiwalled nanotubes on a specially patterned silica base and bake it at 800 degrees centigrade. Then the nanotube film is oxidized and immersed in liquid. As the liquid evaporates, the nanotubes cling together and form predictable shapes based on the patterns of the underlying silica base. Once assembled, the resulting foamlike structures are stable and elastic.

The paper was written by Rensselaer researchers Nirupama Chakrapani, a graduate student; Bingqing Wei, a post-doctoral student; Alvaro Carrillo, a graduate student; Pulickel Ajayan, a professor of materials engineering; and Kane.

"This method can be used to make stable nanotube foams that can be twisted, transferred to other substrates or floated out to form free-standing macroscopic fabrics," Ajayan said. "The assembly process provides a simple and rapid technique for fabricating nanocomposites, with great control over the length, orientation and shape of the cellular structures."

Kane added, "The resulting lightweight cellular foams made of condensed nanotubes could have applications as shock-absorbent structural reinforcements and elastic membranes."

Researchers believe the foams could potentially be used in a great variety of applications, including new microchips and wherever strength and flexibility are needed, from repairing joints to reinforcing carbon-fiber-based aerospace products.

Ajayan and Kane plan to continue studying and measuring the mechanical properties of nanotube foams and related nanocomposites. Their work is part of the ongoing research at the Rensselaer Nanotechnology Center, which integrates research, education and technology dissemination and serves as a national resource for fundamental knowledge and applications in the assembly of nanostructures.

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Mar 2004
Sizable enough to be perceived by the unaided eye.
chemical vapor depositionmacroscopicnanoscalenanotubesNews & FeaturesRensselaer Polytechnic InstituteRPI

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