Nanotubes take the heat

Researchers at the University of Pennsylvania have created a fortified epoxy doped with nanotubes that shows a 125 percent increase in thermal conductivity at room temperature.

University of Pennsylvania scientists have determined that adding a relatively small number of carbon nanotubes to epoxy yields a compound three-and-a-half times as hard and far better at heat conductance than the product found in hardware stores.

Led by Penn physicist Alan T. ‘Charlie’ Johnson, the team is said to have created a composite of 95 to 99 percent common epoxy mixed with 1 to 5 percent carbon nanotubes.

Johnson’s group determined that epoxy doped with nanotubes showed a 125 percent increase in thermal conductivity at room temperature.

For some time, scientists have been intrigued by nanotubes, which are pure carbon cylinders with walls just one atom thick. First created by firing lasers at graphite, the structures have become one of the marvels of nanotechnology because they are 100 times as strong as steel and capable of far greater electrical conductivity than other carbon-based materials.

Researchers have envisioned the miniature strands bulking up brittle plastics and conducting current in ever-smaller electrical circuits and have made significant advances in the large-scale synthesis of nanotubes.

The Penn research is said to build upon a paper published in 2000 in the journal Science. In that paper, Johnson and Penn materials scientist John E. Fischer identified carbon nanotubes as the best heat-conducting material ever recorded, the first suggestion that the exotic strands might someday find applications as miniature heat conduits in a host of devices and materials.

Epoxy is an attractive target for fortification with carbon nanotubes, Johnson said, because it’s relatively easy to mix the minuscule filaments into it, and there are clear industrial benefits in a harder, better-conducting epoxy.

‘These findings add considerably to carbon nanotubes’ lustre as possible additives to a variety of materials,’ said Johnson. ‘In addition to adhesives such as epoxy, we are looking at nanotube-based greases that might be used to carry heat away from electronic chips.’

Other scientists have attempted to fortify epoxy with carbon nanotubes, but Johnson’s group succeeded in dispersing the nanotubes more evenly.

‘This is the first published report of enhanced thermal conductivity in a material owing to the addition of carbon nanotubes and the first demonstration of simultaneous thermal and mechanical enhancement of a real-world material,’ Johnson said.

The researchers report their successful experimentation with the commonplace adhesive in the April 15 issue of the journal Applied Physics Letters.