All organic polyimide‐based composite films with high intrinsic polarization for superior energy density and low dielectric loss

Abstract A simple and low‐cost approach was proposed to fabricate poly(vinylidene fluoride) (PVDF) and polyimide‐poly(amidic acid) (PI‐PAA) all‐organic hybrid films with excellent dielectric performance by solution casting and thermal imidization process. The results showed that the introduction of PVDF and PAA molecular chains into PI matrix significantly enhanced the dielectric permittivity and energy density of PI‐based composites. The permittivity and energy density of 15 wt% PI‐PAA/PVDF composites were 4.83 at 10 3 Hz and 5.55 J cm −3 , which were 52% and 107% higher than that of PI (3.18 at 10 3 Hz, 2.68 J cm −3 ). In addition, the dielectric loss of 15 wt% PI‐PAA/PVDF composites was still maintained at a low level (0.009 at 10 3 Hz). The molecular dynamics results showed that the polarization strength of composites mainly originated from the intrinsic polarization strength. The intrinsic polarization strength of PI‐PAA/PVDF in the composites was 10 10 times higher than interfacial polarization strength, and interfacial polarization was negligible. There was no significant difference between the self‐diffusion coefficients of 15 wt% PI‐PAA/PVDF and PI‐PAA, indicating that the relaxation polarization of polymer molecular chains was suppressed. This work provides an effective way for the preparation of dielectric for all organic high voltage direct current system.