Characteristics of the electrical percolation in carbon nanotubes/polymer nanocomposites

We study the onset of electrical percolation in multiwalled carbon nanotubes (MWNTs)/epoxy nanocomposites. Experiments show a threshold value of 3.2 wt % of MWNTs for percolation to occur. Simulations based on two varied approaches are carried out to evaluate the conductivity characteristics resulting from increasing MWNT content. Simple Monte Carlo simulations in which MWNTs are modeled as either 1D sticks or 2D narrow rectangles dispersed in a 2D simulation volume are shown to yield a percolation threshold in close agreement with experiments. We find that a higher degree of anisotropy in the orientation of nanotubes or of the waviness leads to an increase in the percolation threshold. A more insightful approach encompassing the quantum tunneling effect is also undertaken using the tight-binding simulations. Consideration of the tunneling effect is found to be particularly important when the nanotube aspect ratio is small, the case in which simpler Monte Carlo simulations overestimate the percolation threshold.