Inserting insulating barriers into conductive particle channels: A new paradigm for fabricating polymer composites with high dielectric permittivity and low dielectric loss

A longstanding challenge in fabricating high dielectric polymer composite is how to rationalize structure design to improve dielectric permittivity while minimizing dielectric loss. Typically, adding conductive particles in to the composite often leads to an increase in the dielectric loss caused by leakage current due to ‘insulator-conductor’ transition at the percolation threshold. This work presents a strategy for simultaneously assembling conductive and insulating particles to form chainlike structures, based on dipole-dipole interactions induced by electric fields. Specifically, insulating barium titanate (BaTiO3) particles can be subtly embeded in the conductive graphite channels to serve as barriers. The formation of such morphology plays an important role for balancing the high dielectric permittivity and relatively low dielectric loss for conductive fillers/polymer composite systems. With only 2.5 wt% graphite, the dielectric permittivity can be enhanced significantly upon electric field induced assembly, while the dielectric loss also inevitably increases to 396. By incorporating additional 5 wt% BaTiO3 (barriers), we are able to reduce the dielectric loss to as low as 0.19 while the dielectric permittivity still remains relatively high (73.5). This work provides a critical material design concept for high-performance flexible dielectric materials based on creating barriers through the assistance of electric fields in ternary composites, which prevents the generation of leakage current between conductive fillers interfaces.