Dielectric properties of electrospun barium titanate fibers/graphene/silicone rubber composites

The ability to increase the dielectric constant of an insulator by embedding spherical particles is limited at low volume fraction as described by the rule of mixtures. High aspect ratio fillers are predicted to be able to increase the dielectric constant more efficiently than spherical fillers. In this work, barium titanate fibers were synthesized by electrospinning a sol-gel, followed by a heat treatment to obtain a perovskite crystal structure. Graphene platelets were synthesized by a thermal shock method. Dielectric spectroscopy showed that a larger dielectric constant increase was achieved by this means, and a combination of barium titanate and graphene platelets yielded the highest value when used in a polydimethyl siloxane matrix. The increase in dielectric loss over the pure matrix was small when the volume fraction was below the percolation threshold of graphene platelets. The electric flux density-electric field (D-E) measurements showed a linear dielectric constant in barium titanate filled composites and higher loss when graphene was added. The mechanisms that lead to those phenomena are discussed in this work. This is a promising route for creating high dielectric constant, low loss materials, for use as capacitor and electric field grading materials.