Electrical conductivity, percolation threshold and dispersion properties of PMMA nanocomposites of hybrid conducting fillers

The present study investigated the effects of the mixture of multiwalled carbon nanotubes (MWCNT) and carbon black (CB) on the electrical and dispersion properties of nanocomposites of PMMA polymerized in situ. These systems are named as mixed-carbon-filler filled systems (MCFFS). The electrical conductivity was measured by the four point probe and the dispersion was analyzed by High Resolution Transmission Electron Microscopy (HR-TEM). It has been shown that the addition of MWCNT and CB in PMMA promoted the electrical conductivity of the composite as a percolation critical concentration is reached. The percolation threshold values were 0.2 vol. (%) for MWCNT and 1.5 vol. (%) for CB, showing that this difference for the two fillers was associated with their geometric shapes, aspect ratios and dispersion characteristics. In addition, MCFFS of MWCNT and CB, varying the concentration of each filler were also prepared. For these systems it was applied the Sun model in order to calculate the theoretical values and compare them to the experimental data. It was observed the synergic effect regarding to the electrical percolation threshold concentration. The MCFFS showed lower critical concentrations (considering the sum of each single filler concentration, MWCNT and CB) and similar conductivities as compared to the single fillers. Despite the presence of aggregates, the microscopy analysis showed that both fillers were well dispersed in the polymer matrix, although the dispersion characteristics of the MWCNT were more effective than CB. In the MCFFS the MWCNT act as filaments linking clusters of the CB, what can explain the synergic effect observed for the lower percolation threshold concentration.