Highly thermal conductive and insulating performance of epoxy/BN composite with BN orientation induced by high-frequency bipolar square wave field

Electric field-induced orientation of fillers has emerged as an effective strategy for enhancing thermal conductivity of epoxy (EP) composites at low filler loading contents. However, in-depth explorations of the alignment impacts, exerted by high-frequency electric fields, on thermal conductivity and breakdown strength of epoxy composites are still lacking. This research introduces a novel approach for fabricating EP/boron nitride (BN) composites by applying a high-frequency bipolar square wave electric field in situ during the curing process. By utilizing dielectrophoretic forces arising from orientation polarization, the viscous resistance can be effectively overcome, which facilitates the alignment of BN in the direction of applied electric field. This alignment leads to a synergistic enhancement in both thermal conductivity and breakdown strength of EP/BN composite. The composites achieve thermal conductivity of 1.085 W/(m·K) when h-BN loading reaches 25 wt%. This indicates 69.5 % enhancement compared to their counterparts with random dispersion. Moreover, the breakdown strength of electric field-oriented EP/BN is increased by 5.0 % and 4.3 % respectively under fields with 50 Hz and 10 kHz compared to that of random EP/BN. This study has an insight into the effect of filler orientation induced by bipolar square-wave field with high-frequency and high voltage on thermal conductivity and breakdown strength of EP composites.