Computational micromechanics analysis of electron hopping induced piezoresistive response in carbon nanotube-polymer nanocomposites

Abstract

In this study, a multiscale micromechanics based computational model is developed to capture the effect of electron hopping induced formation/disruption of conductive paths at the nanoscale which govern the effective macroscale conductive and piezoresistive response of the CNT-polymer nanocomposite. The local nanoscale conductivity at the nanoscale is allowed to evolve by tracking the position of the nanotubes under applied deformations and modifying the conductivity of the intertube region depending on the relative proximity of individual pairs of nanotubes. The formation and disruption of the high conductivity bands are highly dependent on the applied strain and yield odd microstructural symmetries for the effective electrical properties, emphasizing on the need of a computational micromechanics model. The effect of local CNT volume fractions and maximum electron hopping range on the effective macroscale gauge factors is studied for different cases of microstructure morphology i.e. CNT-polymer nanocomposites uniformly dispersed aligned CNTs and aligned/randomly oriented microscale bundles composed of aligned CNTs. Random orientation of macroscale bundles is taken into account using micromechanics based techniques by averaging over a discrete number of orientations of microscale bundles in a consistent manner. The results presented herein indicate that the effective gauge factors follow a strain dependent nonlinear response with asymmetry on application of tensile/compressive strains. In addition, the effective gauge factors were observed to be smaller for a microstructure with aligned microscale bundles as compared to randomly oriented microscale bundle. The gauge factors obtained from the current work are of comparable magnitude with those reported in the literature based on experimental investigation indicating that electron hopping could be the dominant mechanism governing the macroscale piezoresistive response of CNT-polymer nanocomposites.