Significantly Suppressed Dielectric Loss and Enhanced Breakdown Strength in Core@Shell Structured Ni@TiO₂/PVDF...

An insulating shell on the surface of conductive particles is vital for restraining the dielectric loss and leakage current of polymer composites. So as to inhibit the enormous loss and conductivity of pristine nickel (Ni)/poly(vinylidene fluoride)(PVDF) composites but still harvest a high dielectric permittivity (ε_r) when filler loading approaches or exceeds the percolation threshold (f_c), pristine Ni particles were covered by a layer of titanium dioxide (TiO₂) shell via a sol-gel approach, and then they were composited with PVDF. The impacts of the TiO₂ coating on the dielectric performances of the Ni/PVDF composites were explored as a function of the filler concentration, the shell thickness and frequency. In addition, the dielectric performances were fitted using the Havriliak-Negami (H-N) equation in order to further understand the TiO₂ shell's effect on polarization mechanism in the composites. The Ni@TiO₂/PVDF composites exhibit high ε_r and enhanced breakdown strength (E_b) but remarkably suppressed loss and conductivity when compared with pristine Ni/PVDF because the TiO₂ shell can efficiently stop the direct contact between Ni particles thereby suppressing the long-range electron transportation. Further, the dielectric performances can be effectively tuned through finely adjusting the TiO₂ shell' thickness. The resulting Ni@TiO₂/PVDF composites with high ε_r and E_b but low loss show appealing applications in microelectronics and electrical fields.