Effect of Carbon Nanotube Alignment in Polymer Nanocomposites on the Electrical Conductivity

We studied the effects of nanotube alignment on the electrical conductivity of the nanotube / polymer nanocomposites. Nanocomposites with single-walled carbon nanotubes (SWNTs) and poly(methyl methacrylate) (PMMA) were prepared via our coagulation method. The nanotubes were subsequently aligned to various extents by melt fiber spinning and the degree of alignment was quantified by x-ray scattering. Electrical percolation in the nanocomposites with isotropic nanotubes occurs at $\sim $0.39wt{\%} SWNT. At all nanotube loadings investigated (0.5 to 3 wt{\%}), the electrical conductivity exhibits percolation behavior with decreasing nanotube alignment. At nanotube loadings just above the concentration threshold for percolation, a maximum electrical conductivity is observed at intermediate level of alignment. We attribute the existence of this optimal nanotube alignment to the competition between the number of tube-tube contacts and the distance between these contacts. A two-dimensional Monte Carlo simulation of sticks in a unit square was developed to mimic these nanotube/polymer nanocomposites and shows similar trends. In sum, we observed percolation behavior with respect to nanotube alignment and obtained the maximum electrical conductivity by partially aligning the nanotubes.