Predicting the piezoresistance contribution of carbon nanotubes in a polymer matrix through finite element modeling

The change in electrical resistance due to mechanical deformation of carbon nanotube (CNT)/polymer composites can be rationalized in terms of two main effects: i) changes in the composite electrical resistivity due to changes in the CNT network configuration, and ii) deformation of the CNTs themselves. The contribution of CNT dimensional changes (ii) to the piezoresistivity of CNT/polymer composites is investigated here. A model based on a representative volume element which describes the CNT geometrical contribution to the composite electromechanical response (piezoresistivity) in terms of the CNT and matrix deformations is proposed. Finite element analysis is performed to correlate the macroscale composite strain to the individual CNT strain. The CNT geometric contribution to the piezoresistivity of the composite is quantified for a range of matrix elastic modulus and different CNT orientations. Based on the model predictions and previous experimental results, it is estimated that the contribution of the CNT deformation to the composite piezoresistivity is only about 5%, indicating that the dominant effect in the piezoresistivity of CNT/polymer composites is the change in the CNT network configuration.