Increased dielectric permittivity of poly(vinylidene fluoride-co-chlorotrifluoroethylene) nanocomposites by coating BaTiO3 with functional groups owning high bond dipole moment

Polymer nanocomposites with high dielectric permittivity (epsilon) are urgently demanded for power energy storage. In this research, in order to prepare nanocomposites with strong interfacial interactions and higher epsilon, a novel surface modification molecule, 3,4,5-trihydroxybenzoic acid (or Gallic acid, GA), was developed. There are two main advantages for selecting GA as the coating molecule. Firstly, the polar groups, such as hydroxyl and carboxyl groups in GA, could form hydrogen-bonding interaction with poly(vinylidene fluoride-co-chlorotrifluoroethylene) (PVDF-CTFE). Therefore, though thickness of coating layer is only 1.6 nm, nanocomposites with better dispersion were prepared by strengthening hydrogen-bonding interaction at polymer-nanoparticle interface. Secondly, functional groups with high bond dipole moment, such as carboxyl groups and phenolic groups, are beneficial to obtain high epsilon in PVDF-CTFE + BT@GA. epsilon is 25.6 at 1 kHz with 12.9% BT@GA. This is about 2.5 times higher than that of PVDF-CTFE matrix (10.4 at 1 kHz). The hypothesis in this research might offer a feasible approach to prepare capacitors with higher epsilon and higher energy density by regulating bond dipole moment of functional groups in the coating molecules.