Maxwell-Wagner-Sillars mechanism in the frequency dependence of electrical conductivity and dielectric permittivity of graphene-polymer nanocomposites

The Maxwell-Wagner-Sillars (MWS) effects have been reported in various experiments of graphene-polymer nanocomposites under AC loading. It is considered to be the source of the observed high dielectric constant for this class of nanocomposites. But at present no theory seems to exist to provide a physical description of this mechanism, and to transform this effect into the reported high electrical conductivity and dielectric permittivity. In this work we start out from consideration of high disparity of electrical conductivity between graphene and polymer phases to present such a description, and then integrate it into an effective-medium theory to illustrate how it affects the overall properties of the nanocomposite. We model this mechanism with numerous nanocapacitors at the graphene-polymer interfaces, whose charge accumulation is taken to be directly proportional to the difference of conductivities of graphene fillers and polymer matrix. In the context of complex conductivity, this formulation gives rise to an added frequency-dependent conductivity and permittivity of the interface regions. We highlight this theory with an application to reduced graphene oxide/polypropylene (rGO/PP) nanocomposites, and demonstrate that the calculated conductivity and permittivity are in close agreement with experimental data over the frequency range from 103 to 107 Hz. This study clearly demonstrates that the MWS mechanism is principally responsible for the frequency dependence of electrical conductivity and dielectric constant of graphene-polymer nanocomposites.