Lower Conductivity in Nanotubes Composites

16 November 2003

A research team at Rensselaer Polytechnic Institute has discovered that the nanotubes’ role as thermal superconductors is greatly diminished when mixed with materials such as polymers.

“Carbon nanotubes are superior thermal conductors by themselves. But, that doesn’t mean they will exhibit the same level of high conductivity when integrated into other materials,” says Pawel Keblinski, assistant professor of materials science and engineering and head of Rensselaer’s research team. His team’s research is published in this month’s issue of Nature Materials.

A global team of researchers was optimistic when a one-percent fraction of carbon nanotubes was added to epoxy and other organic materials, and the thermal conductivity of the newly created composites increased two- or threefold. But, using conventional engineering estimates, Keblinski noted that the composites’ conductivity should have had 50-fold increases.

Why such disparity between the experiment and the expectations?

“Atoms forming stiff carbon nanotubes vibrate at much higher frequencies than the atoms in the surrounding material. This leads to high interfacial resistance for the heat flow between the tubes and the other elements,” Keblinski says.

Energy exchange between two different elements is immediate and plentiful when frequencies in both are similar. Interfacial resistance happens when the frequencies are different, and the heat energy has a difficult time taking the leap from one element to the next.

To test the magnitude of the problem, Keblinski and his Rensselaer collaborators performed computer simulations on a model nanotube composite. Meanwhile, another research group headed by David Cahill at the University at Illinois at Urbana Champaign, heated real carbon nanotubes with a laser.

From the rate of cooling, in both the simulation and the physical experiment, the researchers derived the value of the interfacial resistance. In both instances, they found the resistance is so high that it limits the thermal conductivity of the nanotubes.

One way to reduce the interfacial resistance in such nanocomposites is to induce a stronger bond between the nanotube and other materials to make it easier for heat to cross from one element to the next. However, extensive bonding may distort the original nanotube structure that allows the tubes to be a superconductor of heat in the first place.

Still, Keblinski is optimistic about the use of carbon nanotubes to improve insulating materials. “By adding a small fraction of carbon nanotubes to such materials, we can still increase the thermal as well as electrical conductivity. So, although we may have to lower our expectations, we have not given up hope quite yet that nanotubes will improve materials for a number of applications,” Keblinski says.

Related / You might like...

Electric GT’s Tesla P100DL Features Bcomp Flax Fibre Technologies

Electric GT Holdings and SPV Racing recently unveiled the race-ready version of the EPCS V2.3 Tesla P100DL at Circuit de Barcelona-Catalunya. The car features lightweight body parts made using Bcomp's ampliTex and powerRibs natural fibre composite reinforcement products, contributing to a 500 kg weight reduction over the road edition.

Codem Composites Supports Sahara Force India F1 Team

UK company Codem Composites has provided key bodywork components to support the F1 team Sahara Force India.

EconCore Highlights Lightweighting Benefits of Honeycomb Panels in Transportation

ThermHex Waben and EconCore will exhibit at the IAA Commercial Vehicles exhibition in Hannover, Germany, on 20-27 September 2018.