Chemical bonding-induced low dielectric loss and low conductivity in high-K poly(vinylidenefluoride-trifluorethylene)/graphene nanosheets nanocomposites

Blending high-permittivity (ε_r) ceramic powders or conductive fillers into polymers to form 0-3-type composites has been regarded as one of the most promising processes to achieve high-dielectric-permittivity materials with excellent processing performance. The high dielectric loss and conductivity induced by the interface between the matrix and fillers as well as the leakage current have long been a great challenge of dielectric composites, and the resolution of these challenges is still an open question. In this work, poly(vinylidenefluoride-trifluorethylene with double bonds)/graphene nanosheets (P(VDF-TrFE-DB)/GNS) terpolymer nanocomposites were fabricated via a solution-cast process. GNSs were functionalized with KH550 to improve the dispersion in the terpolymer matrix solution and crosslinked with P(VDF-TrFE-DB) by a free-radical addition reaction in the nanocomposites. Compared with neat terpolymer, significantly increased dielectric permittivity and a low loss were observed for the composites. For instance, at 1 kHz the P(VDF-TrFE-DB)/GNS composites with 4 vol % GNS possessed a dielectric permittivity of 74, which is over seven times larger than that of neat terpolymer. However, a rather low dielectric loss (0.08 at 1 kHz) and conductivity (3.47 × 10^-7 S/m at 1 kHz) are observed in the P(VDF-TrFE-DB)/GNS composites containing up to 12 vol % GNS. The covalent bonding constructed between P(VDF-TrFE-DB) and GNS is responsible for the reduced aspect ratio of the GNS and the crystalline properties of P(VDF-TrFE-DB) as well as the improved compatibility between them. As a result, the high-dielectric-loss conductivity of polymer composites, mainly induced by conduction loss and the interface polarization between the matrix and filler, were effectively restricted. Meanwhile, the 3D network established between P(VDF-TrFE-DB) and GNS endows the P(VDF-TrFE-DB)/GNS composites at high temperature with excellent mechanical and dielectric properties. Besides preparing high-performance dielectric composites, this facile route may also be utilized to fabricate high-performance nanocomposites by inhibiting the poor compatibility between fillers and polymeric matrix.