Enhanced breakdown strength and suppressed dielectric loss of polymer nanocomposites with BaTiO3 fillers modified by fluoropolymer

Abstract

The introduction of ceramic fillers into a polymer matrix is an effective way to obtain dielectric nanocomposites with high energy storage density. However, the inorganic fillers are difficult to disperse evenly into the polymer matrix because of the poor compatibility, which stems from the large surface energy difference and the mismatch in dielectric constant between the fillers and polymer matrix. Polymer nanocomposites with high dielectric constant while maintaining high breakdown strength have great potential to achieve high energy storage density. In this work, poly(dodecafluoroheptyl methacrylate) terminated with a thiol end group (PDFMA-SH) was synthesized via a two-step process including Reversible Addition-Fragmentation Chain Transfer (RAFT) polymerization and subsequent aminolysis reaction. The polymer was then grafted into the surface of BaTiO₃ (BT) nanoparticles by a “thiol–ene” click reaction to reduce the surface energy of BT nanoparticles. A novel nanocomposite consisted of the core–shell structured PDFMA@BT hybrid nanoparticles and poly(vinylidene fluoride–chlorotrifluoroethylene) (P(VDF–CTFE)) matrix was prepared. The influence of the fluoropolymer shell on the dispersion of fillers, the compatibility between the fillers and polymer matrix, dielectric properties and breakdown strength were investigated systematically. The results indicate that the strong interfacial adhesion between the hybrid nanoparticles and P(VDF–CTFE) matrix makes the fillers uniformly dispersed in the polymer matrix. Meanwhile, the excellent compatibility between the two components is favorable for enhancing the breakdown strength and suppressing dielectric loss, providing a condition to prepare dielectric materials with high energy storage density.