Mechanism of the size factor of heterostructured fillers on the thermal conductivity and dielectric properties of epoxy resins composites

To resolve the insufficient thermal conductivity (TC) of traditional epoxy resin (EP) potting compounds in high-power-density electric vehicle drive motors, this study employed a hydrogen-bonded self-assembly strategy to prepare Diamond-Boron Nitride (ND-BN) heterostructure fillers with varying BN particle sizes (5, 20, 30 μm). The ND-BN/EP composites were fabricated with a fixed filler content of 20 wt.% and an ND:BN ratio of 1:2. The TC and dielectric properties of ND-BN/EP composites were investigated and compared with BN/EP composites. The characterization results confirm the successful attachment of ND particles onto the BN sheet surfaces and the formation of hydrogen bonds between them. The heterostructure filler exhibits good dispersion within the EP matrix. When the BN particle size was 20 μm, the ND-BN/EP composite achieves an optimal thermal conductivity of 1.3 W·m⁻ 1 ·K⁻ 1 . Smaller BN particles struggle to form continuous thermal pathways, while larger BN particles tend to stack, hindering heat transfer. Smaller filler particles exhibit stronger interfacial polarization, leading to increased dielectric constants and dielectric loss tangent. Concurrently, the number of interfacial defects increased, introducing more localized electric field concentration points and consequently reducing the breakdown electric field strength. The filler size has little effect on the volume resistivity of the composites. This study clarified the regulatory mechanism of heterostructure filler size factors on the TC and dielectric properties of EP composites, providing a theoretical basis for the development of highly thermally conductive and insulating EP potting compounds.