Size Effect of Boron Nitride Nanosheets on Dielectric Properties of BNNSs/P(VDF-HFP) Composite Films

Boron nitride nanosheets (BNNSs) is an insulating material with high breakdown strength (800 kV/mm), which is an ideal candidate for the enhancement of breakdown strength of polymer-based composites. Generally, the lateral size of BNNSs has a significant influence on thermal conductivity and mechanical properties of composites. Thus, it is worthy to further study the size effect of BNNSs on dielectric properties of composites. In this study, edge-hydroxylated BNNSs with large lateral size (l-BNNSs) and small lateral size (s-BNNSs) were respectively added into poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) to prepare BNNSs/P(VDF-HFP) composite films. The breakdown strength and dielectric constant of the composite films are tested by dielectric strength tester and broadband dielectric spectrometer to reveal the size effect of BNNSs on dielectric properties of polymer-based film capacitors. Due to the better crystal lattice of l-BNNSs and higher degree of in-plane orientation compared with s-BNNSs, the insulating network of l-BNNSs/P(VDF-HFP) composite film is more compact and perfect, which can effectively prevent the occurrence of conduction and electrical breakdown in composite films. When the mass fraction of BNNSs is 10%, P(VDF-HFP)/l-BNNSs composite films reach the highest breakdown strength (644 kV/mm). Compared with s-BNNSs/P(VDF-HFP) composite films, the breakdown strength of l-BNNSs/P(VDF-HFP) composite films has an increase of 7.65%.