Simultaneously improving in-plane and through-plane thermal conductivity of insulted PVDF composite film using multi-layer and multi-filler strategies

Abstract

In this paper, a multi-filler synergistic strategy combined with multi-layer hot pressing technology was developed to optimize the thermal conductivity and insulation properties of composite materials. Boron nitride nanosheets (BNNS), aluminium oxide (Al₂O₃) microspheres and silver (Ag) nanoparticles were incorporated to construct a three-dimensional thermal conduction network within a polyvinylidene fluoride (PVDF) thermally conductive composite film. An electrospun PVDF fiber film was first prepared to be used as a template. BNNS and Al₂O₃ were then electrostatically assembled on the surface of the PVDF fiber and in the film to obtain continuous BNNS/PVDF fiber film and Al₂O₃/PVDF fiber film, respectively. Ag nanoparticles were then prepared in situ on the Al₂O₃/PVDF fiber film to obtain an Ag-enhanced Al₂O₃/PVDF fiber film. A sandwich structured PVDF composite film (B-A@Ag-B/PVDF) was finally prepared by hot pressing, using the BNNS/PVDF fiber films as the top and bottom layers and the Ag-enhanced Al₂O₃/PVDF fiber film as the middle layer. The resulting B-A@Ag-B/PVDF composite film, with a total filler mass fraction of 32.1 %, had in-plane and through-plane thermal conductivities of 4.13 W m^–¹ K^–¹ and 1.05 W m^–¹ K^–¹, respectively, improvements of 1620 % and 452 % compared to those of pure PVDF. In addition, the through-plane electrical conductivity was as low as 5.38 × 10^–¹¹ S/cm, matching the standards for insulating materials. The B-A@Ag-B/PVDF composite film demonstrates significant potential for advanced thermally conductive polymer composites.