Improving electrical conductivity and thermal properties of polymers by the addition of carbon nanotubes as fillers

The remarkable electrical and thermal conductivities of isolated carbon nanotubes have spurred worldwide interest in using nanotubes to enhance polymer properties. Electrical conductivity in nanotube/polymer composites is well described by percolation, where the presence of an interconnected nanotube network corresponds to a dramatic increase in electrical conductivity ranging from 10(-5) S/cm to 1 S/cm. Given the high aspect ratios and small diameters of carbon nanotubes, percolation thresholds are often reported below 1 wt%, although nanotube dispersion and alignment strongly influence this value. Increases in thermal conductivity are modest (similar to 3 times) because the interfacial thermal resistance between nanotubes is considerable and the thermal conductivity of nanotubes is only 104 greater than the polymer, which forces the matrix to contribute more toward the composite thermal conductivity, as compared to the contrast in electrical conductivity, > 10(14). The nanotube network is also valuable for improving flame-retardant efficiency by producing a protective nanotube residue. In this article, we highlight published research results that elucidate fundamental structure-property relationships pertaining to electrical, thermal, and/or flammability properties in numerous nanotube-containing polymer composites, so that specific applications can be targeted for future commercial success.