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For practical application, studying the mechanism governing the macroscopic dielectric properties of polymer composites at low concentration is of great significance. A three-dimensional (3D) representative model with randomly dispersed grains in polymer matrix has been established and calculation results of effective permittivity of BT/PVDF composites with finite element method (FEM) show good consistency with experimental measurements, which demonstrate that the distribution of electric field in ceramic particles/polymer composites at low concentration can be approximated by the electrostatic field. Furthermore, the relationship between the internal electric field and dielectric properties of composites has been established. The effect of grain size in submicron and its dielectric constant to the effective permittivity of composites are fully investigated. The former shows of negligible significance compared with the evident effect of volume fraction, while the latter presents saturation as increasing the permittivity ratio between ceramic particle and polymer. [ABSTRACT FROM AUTHOR]

Recent advances in the electrospinning technique offer significant opportunities for improved fiber reinforced polymer composites of interest for capacitor applications. Classical effective medium approximation may fail to reach exact solutions due to the intricately inhomogeneous distribution of the depolarizing field in fibers with arbitrary orientation degrees. In this work, a three-dimensional finite element method (FEM) model has been developed to in-depth study the effects of fiber alignment on the dielectric response in fiber/polymer composites. A quantitative relationship between the effective permittivity of composites and the alignment degree of fiber has been initially established. Furthermore, we define a parameter of the effective angle which has the equivalent contribution on the effective permittivity with the actually distributed multiple alignment angles of fibers in practical composite materials. The calculation results with FEM show good agreement with the experiment measurements delivered recently. [ABSTRACT FROM AUTHOR]