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High dielectric constant polymer composites capable of withstanding a high electrical field have much application in electronic devices and electrical equipment because of their ease of processing, flexibility, and low cost. Conventional polymer composites with a high dielectric constant, namely ceramic particulate composites and conductive filler based percolative composites, either show low dielectric enhancement or cannot withstand high electric field. Here we report a new strategy for preparing high dielectric constant polymer composites by using novel three-dimensional zinc oxide (3D ZnO) superstructures as fillers. Two kinds of 3D ZnO (flower-like and walnut-like) superstructures were prepared via a template-free solvothermal method. Their poly(vinylidene fluoride) (PVDF) composites as well as commercial ZnO filled PVDF composite were investigated by a broadband dielectric spectroscopy at a wide temperature range (−50 to +150 °C). Our results showed that, compared with the commercial ZnO, the newly synthesized ZnO superstructures not only significantly increase the dielectric constant of their PVDF composites but also show similar effect on the breakdown strength of their composites. For instance, the dielectric constants (100 Hz) of the composite samples with commercial ZnO, flower-like, and walnut-like ZnO superstructures are 19.4, 221.1, and 104.9, respectively, whereas their breakdown strengths are 45, 42, and 40 kV/mm, respectively. The dielectric investigation evidenced that the higher dielectric constant in the composites with ZnO superstructures should be attributed to the formation of a ZnO percolation network.

The Ag@TiO 2 core@shell nanoparticles filled ferroelectric poly(vinylidene fluoride) (PVDF)-based composites (0-3 connectivity) were prepared in order to study the effect of core@shell structure on dielectric permittivity in the Ag@TiO 2 /PVDF nanocomposites. The Ag@TiO 2 core@shell nanoparticles were synthesized via a water-thermal meting route. Transmission electron microscope (TEM) images showed the nanoparticles were about 60-120 nm in diameter and the thickness of the shell layer was about 6-12 nm, which can be adjusted by changing the fabrication conditions. Results of dielectric measurements showed that the shell-layer thickness of the Ag@TiO 2 core@shell nanoparticles played a key role in deciding the final values of the dielectric properties of the nanocomposites. The variation of dielectric properties of the nanocomposites with temperature also depends on the shelllayer thickness of the Ag@TiO 2 core@shell nanoparticles.

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