A technique for spatially-resolved contact resistance-free electrical conductivity measurements of aligned-carbon nanotube/polymer nanocomposites

Abstract

The use of carbon nanotubes (CNTs) as an additive in polymer nanocomposites (PNCs) is being driven by a need to improve the mechanical, electrical, and thermal properties of composite materials for a variety of applications including advanced aerospace vehicles. The magnitude of electrical conductivity in CNT-containing PNCs is primarily influenced by the volume fraction, dispersion, interconnectivity and alignment of CNTs as well as the individual CNT properties, which are a function of diameter, chirality, and defects. Measurement techniques used to quantify the electrical conductivity of composites containing CNTs suffer from a host of issues including the influence of contact resistance, poor sample preparation leading to inadequate electrical contact of all concentric shells in aligned multi-walled CNT PNCs, and poor spatial resolution, which can obscure the micrometer- to millimeter-scale effects of inhomogeneities. In this study we demonstrate a new technique for measuring the local (∼100 μm resolution) conductivity of PNCs fabricated by infusing aligned CNT arrays with a non-conductive polymer, where the CNTs are continuous through the thickness of the composite. The technique involves the use of improved surface preparation processes, prior to the formation of electrical contacts, to ensure good electrical engagement of the CNTs. Furthermore, this technique provides a systematic process to remove the contribution of contact resistance and therefore measure the conductivity of the polymer nanocomposite alone. Using this technique we have measured a conductivity of 2.2 × 104 S/m for aligned CNTs (20% volume fraction) in RTM-6 aerospace epoxy.