Fabrication and enhanced dielectric properties of polyimide matrix composites with core–shell structured CaCu3Ti4O12@TiO2 nanofibers
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Core–shell structured CaCu3Ti4O12@TiO2 (CCTO@TiO2) nanofibers were prepared via a normal coaxial electrospinning technique with sol precursors. Polyimide (PI) nanocomposite films containing the core–shell structured CCTO@TiO2 nanofibers were fabricated by the solution casting method. The core–shell structure of the CCTO@TiO2 nanofibers was confirmed through transmission electron microscope. The percolation of the CCTO/TiO2 interfaces leads to much enhanced interfacial polarization of the CCTO@TiO2 nanofibers, which gives rise to substantially increased dielectric constant of the nanocomposites. Compared to the nanocomposites with CCTO nanofibers, the breakdown strength of the nanocomposites with CCTO@TiO2 nanofibers is also increased due to the charge shifting is limited to the interfacial zone of CCTO/TiO2 interfaces, instead of in the PI matrix to form a percolation path. For the nanocomposites with 5 vol% nanofibers, the dielectric constant of 5.55 was enhanced to 5.85 and the breakdown strength of 201 kV/mm was increased to 236 kV/mm by utilizing the TiO2 coated CCTO nanofibers, while the dielectric loss shows no obvious change. Meanwhile, the PI nanocomposite film filled with 1 vol% CCTO@TiO2 nanofibers exhibits a maximal energy density of 1.6 J/cm3. The core–shell structured nanofibers open up an effective way to optimize the dielectric properties of polymer nanocomposites with high energy density.
This study was financially supported by National Natural Science Foundation of China (21304018 and 21374016), Jiangsu Provincial Natural Science Foundation of China (BK20130619 and BK20130617) and a project funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions.
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