Few-layer boron nitride nanosheets/poly (vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) dielectric nanocomposite functionalized with grafting POSS copolymer

The development of advanced film capacitors for the energy storage and conversion has attracted tremendous attentions to fulfill the applications of electrical power supplies. The polymer-based composite with large dielectric property and discharged energy capability is promising candidate for film capacitor. Here, polymer composite film with high polarization was prepared by blending poly(vinylidene fluoride-trifluoroethylene-chlorofluoroethylene) (P(VDF-TrFE-CFE)) terpolymer and functionalized few-layer boron nitride nanosheets (BNNSs). The hyperbranched polyethylene-grafting-polyhedral oligomeric silsesquioxane (HBPE-g-POSS) copolymer was synthesized to exfoliate BNNSs from h-BN bulk in chloroform with assistance of ultrasonication. The morphologies of BNNSs have been characterized by high-resolution transmission electron microscopy and atomic force microscopy, which confirm the resultant nanosheet with lateral size of 100–200 nm and thickness of 1.2–1.8 nm. The presence of Si peak in X-ray photoelectron spectroscopy indicates that the hyperbranched copolymer is attached on surface of nanosheets. The received few-layer BNNSs were incorporated into P(VDF-TrFE-CFE) matrix via solution casting method. The relative content of electroactive phase in nanocomposite is enhanced because of strong interaction between fluoropolymer and HBPE-g-POSS during crystallization. The dielectric constant increases to 21.2 with dielectric loss of 0.04 at 100 Hz for 0.5 wt% nanocomposite, and released energy density of 8.3 J/cm3 with charge–discharge efficiency of 52% at 325 MV/m is also achieved in current film, which is attributed to large interfacial polarization with HBPE-g-POSS neighboring layer between nanosheet and polymer matrix. This work on few-layer BNNSs/fluoropolymer nanocomposite with hyperbranched copolymer interface establishes an effective route to develop polymer composite with high energy capability for flexible film capacitor.Graphical abstract