Dielectric relaxation in carbon black-epoxy composite materials

Abstract

Filled polymers have been a fertile area for modeling studies of microwave dynamics, percolation, and elasticity network formation to mention but a few. To better understand the basic concepts relevant to wave transport in filled polymers, an experimental validation is paramount for theories that predict the dielectric response and, hence, the polarization mechanisms of these heterostructures. Reproducible measurements of the effective complex permittivity, at ambient temperature, are reported in the frequency range of 200 Hz–15 MHz for series of carbon black (CB)-epoxy composites that provide a detailed and quantitative characterization of the dielectric relaxation behavior. We provide observational evidence showing that dipolar relaxation and anomalous low-frequency dispersion are likely the transport mechanisms in these samples below and above percolation, respectively. The various fractional exponents of the power-law decay of these spectral models are analyzed, and Hill plots can be used to rationalize the effective complex permittivity observations for these series of samples. Our results have important implications for designing and optimizing engineered CB/polymer materials for a broad spectrum of engineering applications, e.g., solid broadband tissue simulant materials and electromagnetic absorbers.