Nanotubes boost epoxy properties

Researchers routinely add carbon fibers to epoxies and other polymers to produce strong, tough, high-performance materials. Carbon nanotubes (CNTs) are even stronger than carbon fibers, but when they were first added to polymers a few years ago, the expected gains in strength didn’t show up. Poor bonding between the CNTs and the polymer was suspected. Having discovered in 2000 that CNTs are tremendous heat conductors, the University of Pennsylvania’s A. T. “Charlie” Johnson and his collaborators sought, by incorporating CNTs, to boost epoxy’s thermal conductivity, which they reasoned wouldn’t be as sensitive as mechanical strength to the bonding. To their surprise, the CNT-enhanced sample was not only a better thermal conductor, but was also significantly stronger. Johnson doesn’t know exactly why his samples are so strong. One reason might lie in the method his team used to thoroughly disperse the CNTs in the epoxy. If that’s the case, poor CNT dispersal, rather than weak CNT-polymer bonding, could have frustrated previous attempts to boost mechanical strength. CNT-enhanced epoxies or polymers could end up conducting heat away from high-performance integrated circuits. (M. J. Biercuk et al., Appl. Phys. Lett. 80 , 2767, 2002 http://dx.doi.org/10.1063/1.1469696 .)