Flexible polymer composite films are prepared by a solution cast method with polar polyvinylidene fluoride (PVDF) or non-polar epoxy as the polymer matrix. BaTiO 3 nanoparticles and BaTiO 3 nanofibers with large aspect ratio are used as dielectric fillers after surface modification by polydopamine. The effects of filler shape, surface modification and polarity of polymer matrix on the microstructure, dielectric constants and breakdown strength of polymer composites are investigated in detail. Surface modification by polydopamine improves the compatibility between BaTiO 3 and polymer as well as passivating the surfaces of BaTiO 3 . At the same volume fraction, composites filled with BaTiO 3 nanofibers exhibit greater dielectric constants than the composites filled with BaTiO 3 nanoparticles. The polydopamine layers on BaTiO 3 nanofibers give rise to stronger interfaces between the fillers and polymer matrices. Improved breakdown strengths are achieved in both composites. This work may provide a general strategy for flexible polymer nanocomposites with greatly enhanced dielectric constants and breakdown strength.

A carbon nanotube (CNT)/polymer composite is prepared with a CNT array using an electrospinning method and hot‐pressing technology. This composite exhibits a stable high dielectric permittivity and low dielectric loss over a wide frequency range, in addition to a large energy density.

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