Hydrogen bonding and π-π interaction enhanced high thermal interface design with low dielectric loss of BN/PI/epoxy for high voltage-high frequency insulating application

The formation of thermally conductive pathway is the key to improve thermal conductivity (TC), and the interface design of filler/polymer is the key to balance the increase of dielectric loss caused by the introduction of fillers. Herein, inspired by the lowest packing efficiency of simple cubic packing in the crystal structure, the spherical boron nitride agglomerates/epoxy composites enhanced by intra-interfacial hydrogen bonding and π-π interaction were prepared by polyimide-assisted unidirectional freeze-drying strategy. The introduction of polyimide increased the number of hydroxyl groups on the polymer side near the interface, increasing the number of hydrogen bonds at the filler/polymer interface from 24 to 33 and changing the van der Waals interaction energy from − 1141.35 to − 1631.21 kcal/mol, thus increasing the overlap of phonon density of states from 0.1821 to 0.2640 and decreasing the filler/polymer interface thermal resistance from 6.20 × 10 −10 to 4.28 × 10 –10 m 2 K/W. The 3D-interconnected packing network and the interface design contribute to the improvement of isotropic TC (comprehensive TC 2.72 W/(m·K), through-plane TC 3.23 W/(m·K) and in-plane TC 2.19 W/(m·K)) and reduction of dielectric loss (0.00701, 29.0% lower than EP) at the spherical boron nitride agglomerates loading of 24.6 vol%, thus helping to balance the heat generation and dissipation. At 13 kV and 44 kHz, the thermal breakdown time is 531% higher than EP. This work develops a practical approach to fabricate epoxy composites with isotropic thermal conductivity, which is expected to be applied in electrical and electronics industry under high voltage-high frequency conditions.