Confinement effects on electrical conductivity and dielectric permittivity of graphene and reduced graphene oxide dispersed polymer nanocomposite films*

Many recent research efforts have studied how the incorporation of graphene oxide (GO) and reduced graphene oxide (rGO) impact the frequency-dependent dielectric properties in polymer nanocomposite materials. However, few studies explore the effect of film confinement in the micron to sub-micron range of the thin film regime. In this film thickness range, which is comparable to the lateral dimensions of the platelet GO and rGO nanomaterials, we can expect film confinement effects on platelet orientation, which also impacts its relative projection area to the applied electric field. Pristine graphene can be achieved by reducing graphene oxide, which has a similar honeycomb structure with both sp² and sp³ carbon imbuing the surface with limited oxygen-based functional groups that can interact with the polymer matrix via a nanometric interfacial zone.  In this work, we present the nanomaterial loading-frequency dependence of these two fundamental properties, in thin polyvinylidene fluoride (PVDF) film containing GO and rGO of thicknesses ranging from 1 µm to 100 µm. A controlled microwave was used for reducing graphene oxide in a laboratory environment. We will discuss the film finite size effects on the relative response of GO vs. rGO vs. pristine PVDF in terms of their dielectric constant, loss tangent, and AC conductivity data over the frequency range of 1 kHz to 1 GHz using a dielectric spectrometer. We observed that the AC electrical conductivity tends to increase with frequency, but the dielectric permittivity tends to decrease in general and that the dielectric properties are more frequency sensitive for the 1 µm film than the 100 µm films. AFM and SEM were used to ascertain the film morphology and quality of these nanocomposite films. This study may provide insight into the development and utilization of GO and rGO-based polymer thin films in future electronics.