Enhanced dielectric permittivity and suppressed electrical conductivity in polyvinylidene fluoride nanocomposites filled with 4,4'-oxydiphenol-functionalized graphene.

Plastic film capacitors suffer from low charge storage capacity due to the low dielectric constant of the polymer (<10). We have devised a polyvinylidene fluoride (PVDF) composite film filled with small-size graphene oxide (GO) sheets that have aromatic molecules attached to their surfaces. The use of 4,4'-oxydiphenol molecules to functionalize graphene sheets is found to have a remarkable effect on enhancing the dielectric permittivity as well as reducing the electrical conductivity of the nanocomposite. When under electric field, these molecules with an angled molecular geometry act as aligned electric dipoles to largely enhance the dielectric permittivity of the composite, reaching a level two orders of magnitude higher than that of the counterpart filled with blank graphene sheets. Also, the aromatic molecules in graphene surface act as resistive barriers that block charge transfer between inter-connected graphene sheets. As a consequence, the electric conductivity of the composite can be decreased by two orders of magnitude. The PVDF composite filled with functionalized graphene shows a percolation threshold of 13 wt% and a high dielectric constant of 1091 at 100 Hz at this point.