Sandwich-structural PVDF nanocomposites with high thermal conductivity and excellent dielectric properties

Polymeric dielectric composites have been widely used in the fields of sensing and energy storage fields because of their excellent properties. However, the performance of dielectric composites is not sufficiently aligned with the requirements of application due to low thermal conductivity. Therefore, the investigations of the new methods as the design of structure and modification of the fillers to prepare excellent comprehensive performance of materials have attracted great attention. In this work, Poly(vinylidene fluoride) (PVDF) is used as matrix to prepare dielectric materials due to its high dielectric permittivity and favorable flexibility. Boron nitride (BN) with high thermal conductivity and a wide band gap is adopted as fillers. Meanwhile, the modified BN (m-BN) was prepared by coating with polydopamine (PDA) to improve the compatibility between the matrix and the fillers. The multi-layer polymeric composites based on PVDF and m-BN was fabricated via layer by layer spin coating technique. The morphology of fracture surface of PVDF/m-BN composites was investigated by scanning electron microscope. Clear interfaces can be observed in the PVDF/m-BN composites. The influence of both structures and m-BN concentration on the dielectric properties and thermal conductivity of nanocomposites were also discussed. Compared with single-layer, multi-layer exhibited obvious improvement in dielectric constant. The dielectric constant of sandwich-layer nanocomposites with 10 wt% m-BN loading reached 16, which is 30% higher than that of single layer. These enhancements may be attributed to Maxwell-Wagner interfacial polarization, which was generated from the multi-layer structure. In addition, the thermal conductivity of sandwich layer is 4 folds of single layer and the breakdown strength of the composites has increased by 30% due to the well-organized m-BN. Therefore, this works offers a new method for the potential usage of sandwich-structural PVDF nanocomposites in electric power field.