Polarization Mechanism Underlying Strongly Enhanced Dielectric Permittivity in Polymer Composites with Conductive Fillers

Polymer composites filled with conductive fillers can demonstrate ultrahigh effective dielectric permittivity, which is generally attributed to an enhanced Maxwell-Wagner-Sillars interfacial polarization associated with the formation of microcapacitor networks. Here, we explore a composite of the ethylene-propylene-diene elastomer with carbon-black (CB) nanofillers and investigate its dielectric response over wide ranges of temperature and frequency. The dielectric relaxation exhibits atypical (counter-Arrhenius) temperature dependence, contradicting the widely assumed interfacial polarization mechanisms. It is shown that the relaxation/polarization is actually determined by electron displacement─primarily via e-conduction and tunneling within CB clusters─and that the composites' dielectric response can be quantitatively correlated with the CB cluster morphology via a set of scaling laws. Considering the selected composite as a paradigmatic system, the physical origins of the dielectric relaxation and the associated scaling relations seem to be generally applicable and expected to also pertain to other dielectric polymer/conductive-filler composites near percolation.