▎ 摘　　要

Polymer dielectrics possess excellent flexibility compared with inorganic ceramic materials. However, the relatively low dielectric constant and working temperature significantly constrain their widespread application. Here, we report a low-cost facile strategy to develop flexible polymer-based composite films with high dielectric constant over a broad temperature. Polyacrylonitrile (PAN) nanofiber mats containing graphene oxide (GO) with core-shell microstructure were first prepared via coaxial electrospinning and then hot-pressed into dense composite films. It was revealed that hot-pressing assisted by a stretching force under appropriate temperature and pressure can generate local conformational changes of PAN, leading to the formation of an electroactive phase with increased dielectric constant. Meanwhile, the GO transformed into reduced graphene oxide (rGO) under heat reduction, serving as conductive nanofillers to further promote the increase of dielectric constant. Consequently, the optimized rGO/PAN composites displayed thermally stable dielectric properties with a high dielectric constant (epsilon ' = 23, 80 degrees C; epsilon ' = 40, 150 degrees C) and low loss (tan delta = 0.13, 80 degrees C; tan delta = 0.55, 150 degrees C) over a broad temperature range. This work offers an efficient method for the synthesis of flexible composite dielectric films that hold great potential in high-temperature electronic applications.