Gaoru Chen

Nano-KTN@Ag/PVDF composite films with high permittivity and low dielectric loss by introduction of designed KTN/Ag core/shell nanoparticles

A designed nano-KTN/Ag core/shell structure endows nano-KTN@Ag/PVDF composite films with excellent properties of remarkably enhanced dielectric permittivity, low loss tangent and flexibility. It has been found that the incorporation of KTN@Ag nanoparticles can increase the average crystallite size of the β phase in a polymer matrix, which elevates the polarization level of the polymer matrix and increases the dielectric permittivity of the nanocomposites. 25 vol% composites own a remarkably enhanced dielectric permittivity (er = 230) at 100 Hz, which is due to MWS polarization at the internal interface between nano-KTN@Ag and the PVDF matrix, the increased induced polarization of the nanoparticles and the “boundary layer capacitor effect”. The low loss tangent is achieved because of an enhanced polarization reverse speed by the Ag shells and a blockage of charge transfer by PVDF chains. The percolation threshold of the composite films (fc = 0.317) was predicted by the percolation theory, and the theoretical results were in good agreement with the experimental data.

Geometrical shape adjustment of KTa0.5Nb0.5O3 nanofillers for tailored dielectric properties of KTa0.5Nb0.5O3/PVDF composite

This paper indicates that rational design and precise control for the structure and shape of nanofillers are effective for achieving the desired permittivity and breakdown strength for high energy densities of polymer nanocomposites. Two types of KTa0.5Nb0.5O3 (KTN) nanoparticles with different shapes (NC-KTN and NR-KTN) were introduced into the PVDF matrix. The molecular dynamic simulation and the Brunauer–Emmett–Teller (BET) surface area proved that the nonbonding interaction energy is stronger in the NR-KTN/PVDF composite films due to the larger surface area of NR-KTN (30.96 m2 g−1). In addition, the interfacial polarization related to the shape of nanofillers further improved the dielectric permittivity of NR-KTN/PVDF composite films. Through the comparison between the experimental data and various theoretical models, we concluded that the geometric shape of fillers has a significant impact on the dielectric constant of composite films.