The purity of carbon nanotubes has a significant affect on the thermal conductivity of composite materials
The thermal conductivity of single-walled carbon nanotubes (SWNT) is much higher than conventional materials — such as copper and carbon black — and so they could be used to dissipate heat in electronic circuits. Studies on SWNT/polymer composite materials report widely different thermal conductivity enhancements, ranging from almost zero to greater than 100%. The thermal properties depend on many factors, such as how well the nanotubes are dispersed and aligned.
Now, Robert Haddon and colleagues1 at the University of California, Riverside, in the USA have studied how the purity of SWNTs affects the thermal properties of a composite material. Initially, SWNTs prepared by arc discharge were purified by treatment with nitric acid. These nanotubes were dispersed in an epoxy resin and the material was cured at high temperature. For comparison purposes, an epoxy composite was also prepared using unpurified ‘as-prepared’ nanotubes.
Composites made with purified SWNTs showed a fivefold enhancement in thermal conductivity. Interestingly, however, the electrical conductivity properties were reversed and the material made from unpurified SWNTs was the better conductor. This contrast is thought to reflect changes in how the nanotubes disperse when purified and also the different nature of thermal and electrical transport processes.
Yu, A. et al. Appl. Phys. Lett. (2006). 10.1063/1.2357580