Influence of copper calcium titanate nanoparticles designed with hierarchical interface structure on dielectric polarization and strength of polyvinylidene fluoride nanocomposites

Interface modification of nanofillers is an effective method to improve the dielectric property of the polymer composites constructed with different core-shell structured fillers. However, there are differences in the improvement and the dielectric response mechanisms are not clear. Herein, CaCu3Ti4O12 spherical nanoparticles (CCTO, marked as C), core-shell structured CCTO-SiO2 (CS), core-satellite structured CCTO-Ni (CN), and core-satellite-shell structured CCTO-Ni-SiO2 (CNS) nanoparticles are synthetized and used as fillers to investigate their effects on the dielectric polarization and strength of the PVDF-based nanocomposites. The results show that Ni nanoparticles are embedded within a 10 nm thick SiO2 shell and deposited on the surface of CCTO core with a diameter of 160 nm to form the hierarchical interface structured CNS fillers. Additionally, different interface structures of C, CS, CN, and CNS nanofillers play different roles in inducing interfacial polarization of the PVDF-based composites, which are weakened and enhanced by coating amorphous SiO2 shell and depositing Ni nanoparticles, respectively. Specially, the dielectric constant of the P-CN with a 1.5 vol% loading is 19.44 at 102 Hz, which is 69.8 % higher than that of PVDF. Significantly, the CNS fillers increase the dielectric constant and strength of the P-CNS composite to 15.05 and 147.2 kV/mm, respectively, and decrease leakage current density of 8.44 x 10- 7 A/cm2, due to the hierarchical interfacial polarization effect of core-satellite-shell structured CNS and the restriction of the conductive path. This study provides more insight into the controlling of interface structure design on the dielectric polarization and strength, and offers a theoretical basis for designing polymer nanocomposites with high dielectric property.