BuckyPaper has counterintuitive properties-gets thicker when stretched or a negative Poisson’s ratio
When most materials are pulled in one direction, they get thinner in the other direction, similar to how a rubber band behaves when it is stretched.
The April 25 issue of the journal Science (see Sign Change of Poisson's Ratio for Carbon Nanotube Sheets Lee J. Hall, Vitor R. Coluci, Douglas S. Galvão, Mikhail E. Kozlov, Mei Zhang, Sócrates O. Dantas, and Ray H. Baughman Science 25 April 2008: 504-507.DOI: 10.1126/science.1149815) reports that a team of American, Brazillian, Ukrainian and Chinese scientists have unexpectedly discovered that self-assembled sheets of carbon nanotubes [a mixture of carbon single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs)] can produce bizarre mechanical properties when stretched or uniformly compressed-they get thicker when stretched - switching from a positve to a negative Poisson’s ratio. These highly useful properties could be used for such applications as making composites, artificial muscles, gaskets or sensors.
Among the possible uses for buckypaper that are being researched:
- If exposed to an electric charge, buckypaper could be used to illuminate computer and television screens. It would be more energy-efficient, lighter, and would allow for a more uniform level of brightness than current cathode ray tube (CRT) and liquid crystal display (LCD) technology.
- As one of the most thermally conductive materials known, buckypaper lends itself to the development of heat sinks that would allow computers and other electronic equipment to disperse heat more efficiently than is currently possible. This, in turn, could lead to even greater advances in electronic miniaturization.
- Because it has an unusually high current-carrying capacity, a film made from buckypaper could be applied to the exteriors of airplanes. Lightning strikes then would flow around the plane and dissipate without causing damage.
- Films also could protect electronic circuits and devices within airplanes from electromagnetic interference, which can damage equipment and alter settings. Similarly, such films could allow military aircraft to shield their electromagnetic "signatures," which can be detected via radar.
The breakthroughs resulted from the diverse expertise of the article’s co-authors, who come from around the world: Dr. Lee Hall and Dr. Ray Baughman from the U.S., Dr. Vitor Coluci, Dr. Douglas Galvão, and Dr. Sócrates Dantas from Brazil, Dr. Mikhail Kozlov from Ukraine and Dr. Mei Zhang from China.
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