Charge carrier transport and low electrical percolation threshold in multiwalled carbon nanotube polymer nanocomposites

Electrical transport properties of multiwalled carbon nanotube (MWCNT) polymer nanocomposites based on epoxy and high density polyethylene (HDPE) as matrices have been studied. The composites have been prepared from masterbatches by dilution. Low electrical percolation thresholds of 0.05 and 0.4 vol.% of carbon nanotubes in epoxy and HDPE matrices were found respectively. The analysis of the temperature dependence of dc-conductivity shows that the charge transport is fully described as the combination in series of one-dimensional (1-D) and three-dimensional (3-D) variable range hopping (VRH) regimes. The transport is limited by the 1-D VRH regime in the low temperatures limit and by the 3-D VRH regime at room temperature. The analysis of the VRH parameters when the overall volume fraction of MWCNT decreases reveals two distinct situations. In the epoxy the local characteristics of the masterbatch remain practically unchanged and a percolating network is maintained even at very low volume fractions; in the HDPE matrix, the density of the MWCNT bundles packing decreases as revealed by the strong variation of the Mott temperature parameter. Our results indicate that amorphous polymers matrices give lower percolation thresholds than semicrystalline ones when a masterbatch dilution process is used.