Temperature effect on dielectric properties of carbon black filled epoxy polymer composites

The complex permittivity of carbon black/epoxy composites containing different amounts of conductive carbon black particles was reported in the frequency range 100 Hz-15 MHz and over the temperature range 23-80 degrees C. The shape of experimental spectra of these heterogeneous media gives evidence of a typical dielectric relaxation process below the threshold percolation. The temperature dependence of the dielectric response has been analysed below and at near the epoxy glass transition temperature (T-g congruent to 80 degrees C), for various carbon concentrations. Jonscher's phenomenological model has been used for modelling this relaxation process. The activation energy, deduced from Arrhenius equation, is found to be insensitive to the carbon black concentration. This behavior is discussed in term of the interfacial interaction between the carbon particles and the polymer. Besides, the increase of both parts of the complex permittivity with increasing the carbon black concentration and the temperature is compared to the recently proposed Shin's mixture law.