Improved dielectric properties of surface modified BaTiO₃/polyimide composite films

Polyimide was chosen as matrix, and barium titanate/polyimide nanocomposite films were prepared by in situ polymerization process. In order to improve the interfacial compatibility of two phases, barium titanate was modified with 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTCA) and TH-615 acrylic-acrylate-amide copolymers. The modified BaTiO₃/polyimide nanocomposite films were also prepared. X-ray diffraction (XRD) analysis, Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) were applied to characterize the samples, and the dielectric properties of the composites were tested in detail. The effects of dispersants on the dielectric properties of the composite film were investigated. The results show that surface modification would give better dispersion uniformity of the filler particles in the matrix, and the interfacial compatibility between two phases was improved. By 8% PBTCA modification, the dielectric constant of BaTiO₃/polyimide film was 23.5 (at frequency 10³ Hz), the loss tangent 0.00942, breakdown strength 80 MV m^{- 1}, and energy storage density 0.67 J cm^{- 3}. When BaTiO₃ was modified by 6% TH-615, the dielectric constant was 20.3 (10³ Hz), the loss tangent 0.00571, breakdown strength 73 MV m^{- 1}, and energy storage density 0.68 J cm^{- 3}. The study shows that appropriate modification of the ceramic filler could improve its dispersion in the polymer matrix and the compatibility between them.