On the lack of thermal percolation in carbon nanotube composites

Recent experiments demonstrated very low percolation thresholds for carbon nanotube composites signified by steep increases in electrical conductivity at very low nanotube loadings. By contrast, thermal transport measurements, even on the same samples, showed no signature of the percolation threshold. These contrasting behaviors are particularly intriguing considering that both transport processes are described by the same continuum equation. In this letter we present a theoretical analysis based on finite element calculations that expose the underlying reasons for markedly different behaviors of electrical and thermal transport in high aspect ratio fiber composites.