Chlorine-doped graphene oxide/poly (vinylidene fluoride) nanocomposites: Exceptional dielectric properties

This paper reports our recent work [1] on developing a facile and controllable method to fabricate chlorinated reduced graphene oxide (Cl-rGO)/poly (vinylidene fluoride) (PVDF) composites with exceptional dielectric constants and low loss tangents. The observed results are explained in terms of the modifications in structure, elemental composition, electrical conductivity, Cl-rGO/PVDF interfacial interaction and PVDF phase transformation. GO sheets are doped with chlorine by mixing thionyl chloride into the GO dispersion, resulting in the formation of both charge transfer complexes and covalently bonded chlorine on GO sheets. Cl functions as an electron acceptor, i.e. p-type dopant, and an optimal chlorination gives rise to a maximum ionic Cl along with the highest charge carrier density of GO and the highest electrical conductivity of the composites. Strong interfacial interactions exist between the Cl-rGO sheets and PVDF chains due to chlorination, allowing the adsorption of F atoms onto the basal plane of GO sheets to form β-phase PVDF, to the benefit of enhanced dielectric constants of the composites. The Cl-rGO/PVDF composites with 0.2-0.4 vol% graphene present high dielectric constants and moderate loss tangents: e.g. a dielectric constant of 364 - equivalent to 13 times that of the neat PVDF - with a moderately increased loss tangent of 0.077 at 1 kHz with 0.2 vol% graphene. These values are among the best dielectric performance ever reported to date for composites containing graphene, CNTs and other carbon fillers. The synergy stemming from chlorination of GO sheets on the dielectric properties of Cl-rGO/PVDF are identified. Materials with high dielectric constants are broadly employed in electronics and electromechanical systems, such as embedded capacitors in microelectronics, electromagnetic interference shielding and energy-storage devices.