Nanotechnology feels the heat

Research from the University of Pennsylvania indicates that carbon nanotubes – filaments of pure carbon less than one ten-thousandth the width of a human hair – may be the best heat-conducting material ever known.

The findings suggest that these strands, already lauded for their unparalleled strength and unique ability to adopt the electrical properties of either semiconductors or perfect metals, may someday also find applications as miniature heat conduits in a host of devices and materials.

First created a decade ago by firing at graphite with lasers, the structures have become one of the unique discoveries 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 dozens of other possibilities.

The ability of carbon nanotubes to conduct heat suggests applications far beyond those that call on their strength and electrical conductivity, said Dr. Johnson, an assistant professor of physics at Penn State University. As computing power has increased, the heat generated by each circuit on a microchip has proved problematic for computer designers and manufacturers.

Next-generation computer designs might avoid this problem with judiciously placed carbon nanotubes to direct heat away from sensitive circuitry.

Similarly, carbon nanotubes used as heat sinks in electric motors could allow for the introduction of plastic parts that might otherwise melt under a motors intense heat. The tiny structures could also be embedded in materials regularly called upon to withstand extreme heat, such as those that form the exterior panels of airplanes and rockets.

Drs Fischer and Johnson found that sound waves bearing thermal energy travel straight down individual carbon nanotubes at roughly 10,000 metres per second. But they also unexpectedly determined that even when carbon nanotubes are bundled together the bonds between the individual nanotubes remain so weak that heat essentially doesn’t transcend them.

In an ironic twist, the same weak linkages that make carbon nanotubes superior for heat conductance could deflate scientists’ earlier expectation that bundles of them would provide unrivalled mechanical strength. While the individual nanotubes are extremely strong, the weak bonding Drs. Fischer and Johnson observed between nanotubes would need to be overcome to translate this strength to a thicker structure.