New Rubber Beats Heat And Cold

Carbon nanotubes are taking rubbery behavior to new extremes. A novel rubberlike material made from long, tangled strands of single-, double-, and triple-walled carbon nanotubes (CNTs) maintains its viscoelasticity at temperatures as low as –196 °C and as high as 1,000 °C in an oxygen-free environment (Science, DOI: 10.1126/science.1194865).

Most rubbery materials, in contrast, turn brittle in the cold and degrade when things heat up. Because of its temperature-invariant viscoelasticity, the CNT-based material could find use in vehicles that travel to the cold reaches of interstellar space. It could also be used inside high-vacuum furnaces, where it could take the heat without running the risk of reacting with oxygen.

A team led by Don N. Futaba, Kenji Hata, and Ming Xu of the Nanotube Research Center at Japan’s National Institute of Advanced Industrial Science & Technology (AIST) created the CNT-based material using a combination of water-assisted chemical vapor deposition, reactive ion etching of the catalyst film used to grow the nanotubes, and compression.

When the researchers characterized the material, they observed that the tubes are tangled in such a way that they make numerous short contacts with one another. The scientists believe that the material’s thermal stability arises from the fact that the tubes can zip and unzip at those contact points.

In polymeric rubbers, viscoelasticity is typically governed by the arrangement of polymer chains. High temperature breaks these arrangements, and the materials degrade. The researchers believe that in the CNT-based material, the energy from heat goes into overcoming the large van der Waals attraction between the CNTs, resulting in an unzipping of the contact points. Virtually no energy, however, is required for zipping, so this process acts like a heat pump.

Yury Gogotsi, an engineering professor at Drexel University, calls the results “exciting.” Although carbon-based materials possess many extreme properties, he says, “this work uncovers another example of extreme performance of a carbon material that no other solid has shown so far.”