Enhancing out-of-plane thermal conductivity of polyimide-based composites via the construction of inter-external dual heat conduction network by binary fillers

Polyimide (PI) materials have found widespread utilization in advanced electronic systems. PIs with enhanced out-of-plane thermal conductivity ( K ⊥ ) are urgently required to address the rising need for heat dissipation. However, their production remains a formidable challenge due to the difficulty of constructing heat transmission channels along the thickness direction. This study introduces an innovative approach to enhance the K ⊥ values of PI-based composites by utilizing binary fillers to construct an inter-external dual heat conduction network. To achieve this, we first prepared PI/reduced graphene oxide (rGO) hybrid microspheres via solution mixing and precipitation. The microspheres were then coated with boron nitride nanosheets (BNNS) by self-assembly to form a core-shell architecture. This assembly undergoes further refinement via cold-pressing and subsequent densification through hot-pressing, ultimately producing the (PI/rGO)@BNNS composites. This strategy improved K ⊥ values significantly, with a 13-fold and 3-fold increase in the K ⊥ value (3.98 W m −1  K −1 ) in comparison to pure PI (0.31 W m −1  K −1 ) and the random distribution composite (1.45 W m −1  K −1 ), respectively. The finite element analysis confirmed that the synergistic effect of rGO inside the PI phase and BNNS outside the PI phase greatly increased the heat transfer in PI-based composites. When utilized as a thermal interface material (TIM) for LED bulbs, the (PI/rGO)@BNNS composites exhibit an excellent heat dissipation capacity. Additionally, the prepared composites also maintain electrical insulation and present a reduced coefficient of thermal expansion . Overall, our work provides a simple and efficient technique for enhancing the out-of-plane thermal conductivity and maintain the electrical insulation of high-performance PI-based materials, which could have broad application potential in next-generation electronic devices.