Adding Carbon Nanotubes to Epoxy Yields a Composite Three Times Harder and Far Better at Conducting Heat

Ever since carbon nanotubes debuted a decade ago, scientists have touted the strength attainable by ordinary materials reinforced with these strands of pure carbon. Subsequent studies have added superior heat-conducting properties to the futuristic fibers’ portfolio of benefits.

Now this longstanding promise of superfortified heat-conducting materials has become a reality. 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.

The researchers report their successful tinkering with the commonplace adhesive in the April 15 issue of the journal Applied Physics Letters. Led by Penn physicist Alan T. "Charlie" Johnson, the team created a composite of 95 to 99 percent common epoxy mixed with 1 to 5 percent carbon nanotubes, filaments of carbon less than one-ten-thousandth the width of a human hair.

"These findings add considerably to carbon nanotubes’ luster as possible additives to a variety of materials," said Johnson, an associate professor of physics and astronomy at Penn. "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."

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

"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.

For some time, scientists have been intrigued by nanotubes, pure carbon cylinders with walls just one atom thick. First created by zapping graphite with lasers, the structures have become one of the marvels of the nanotechnology world: 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, among other possibilities, and have made significant strides in the large-scale synthesis of nanotubes.

The Applied Physics Letters paper builds 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. Other scientists have attempted to fortify epoxy with carbon nanotubes, but Johnson’s group succeeded in dispersing the nanotubes more evenly.

Johnson was joined in the Applied Physics Letters paper by Fischer, of Penn’s Department of Materials Science and Engineering; Michael J. Biercuk of Harvard University; Marc C. Llaguno and Marko Radosavljevic of IBM’s T.J. Watson Research Center; and Jerome K. Hyun of Columbia University. The work was funded by the National Science Foundation, the U.S. Department of Energy and Penn’s Laboratory for Research on the Structure of Matter.

Penn is seeking corporate partners and investors to commercialize this patented technology. Additional information is available by contacting Gennaro Gama in Penn’s Center for Technology Transfer at 215-898-9273.