Computational Micromechanics: Effective Electrical Conductivity of Carbon Nanotube-Polymer Nanocomposites

Nanocomposite development in the aerospace industry has been encouraged due to their considerable structural enhancements, particularly for material composed of carbon nanotubes included in a polymer matrix. In an effort to explore the nanocomposites’ material properties, previous works have made use of a computational micromechanics model for the analysis of the effective electrical conductivity for well dispersed configurations and a few clustered configurations. In the present work, the clustering impact is studied in detail using configurations with a varying degree of bundle packing. This study also completes previous works by examining the effect of interphase thickness, interphase conductivity and a detailed analysis of the percolation region as a function of the interphase layer thickness. In the present study, a multiscale model has been developed to analyze the nanocomposite electrical enhancements using a computational micromechanics analysis. Periodic arrangements of well dispersed and bundled nanotubes have been studied using the commercially available finite element software COMSOL v3.4. The computation of the effective electrical conductivity is completed for two different SWCNT (Single Walled Carbon Nanotube) representations, one where they have their actual hollow shape and one where the nanotubes are approximated by a solid shape. The properties of the nanotubes depend on whether the hollow or the solid representation is used since the hollow has an isotropic behavior while the solid is transversely isentropic. However, the same periodic conditions are applied to both Representative Volume Elements (RVEs) with solid nanotubes and RVEs with hollow nanotubes, and the results are compared to assess the quality of the solid approximation. A transversal change in electric potential is applied across the RVE to obtain the effective electrical conductivity of the nanocomposite and the volume averaged electric field and the temperature gradient are obtained. From the results, it appears that effective and hollow representations yield nearly identical results for low SWCNT volume fractions among the RVE. The influence of the presence of an interphase region on the effective transverse conductivities is considered in a parametric study in terms of both interphase thickness and conductivity. The effect of clustering is investigated using RVEs with four different degrees of bundle packing. Finally, the results of each of the clustered arrangements are compared to the well dispersed with and without interphase results, and the percent difference relative to the well dispersed case is calculated. The resulting metric indicates that when comparing the impact of clustering and the effect of adding an interphase region, clustering has less impact than the addition of an interphase region on the effective electrical transverse conductivity of the nanocomposite. 1 Virginia Polytechnic Institute and State University, [email protected] 2 Virginia Polytechnic Institute and State University, [email protected]