Microwave properties of graphite nanoplatelet/epoxy composites

The complex permittivity spectra and conductivity of graphite nanoplatelet (GNP)/epoxy composites were measured to assess the application potential of these materials as conductive coatings and/or microwave absorbers with high structural integrity. The frequency used ranged from 0.05 to 18.0 GHz. The measured static conductivity was in fairly good agreement with the prediction from the Neelakanta equations. For the complex permittivity, however, the measured values were much higher than those predicted. A better prediction required the use of the order function as a semiempirical parameter to account for the particle loading effect. The surface treatment using nitric acid was found to increase both the conductivity and permittivity of the GNP/epoxy composites although the effect was small, which led to the decrease in the matching thickness of microwave absorbers. (c) 2008 American Institute of Physics.