Analysis of clustering, interphase region, and orientation effects on the electrical conductivity of carbon nanotube-polymer nanocomposites via computational micromechanics

A multiscale model based on computational micromechanics techniques is developed for determining the effective electrical conductivity of carbon nanotube-polymer nanocomposites containing bundles of SWCNTs at a wide range of SWCNT volume fractions above and below the observed percolation concentrations. The model is applied for both randomly oriented and fully aligned nanotube bundle orientation distributions, with emphasis on the latter in elucidating the relative impact of clustering and nanoscale effects on the effective electrical conductivity of nanocomposites. Nanocomposites consisting of aligned, well-dispersed and clustered/bundled SWCNTs are studied to indicate the influence of clustering on the effective electrical conductivity. A parametric study in terms of interphase thickness and interphase conductivity for both the well-dispersed and clustered arrangements is conducted to allow for the assessment of both the independent influence of the interphase layer and of the combined effects of clustering and interphase regions on the effective electrical conductivity of nanocomposites with aligned SWCNTs. Effective nanotube bundle properties obtained from clustered nanotube arrangements both with and without interphase regions are subsequently applied in an orientation distribution homogenization technique in order to obtain the effective electrical conductivity of nanocomposites consisting of randomly oriented SWCNT bundles. The resulting nanocomposite electrical conductivities are compared with characterization data available in the literature, and are discussed in terms of two mechanisms proposed in the literature for the low volume fraction electrical percolation observed in nanocomposites.