Interfacial Engineering of Graphene-Derived Shells on Spherical Boron Nitride Fillers for Thermally Conductive and Electrically Insulating Epoxy Composites.

Spherical boron nitride (BN) particles offer geometric advantages for three-dimensional thermal network formation, yet their large filler-matrix interfacial area amplifies interfacial thermal resistance, limiting practical thermal conductivity enhancement. To address this limitation, an inverse core-shell hybrid filler strategy was developed in which graphene oxide-coated BN (GO-BN) and partially reduced graphene oxide-coated BN (prGO-BN) serve complementary and distinct functional roles within an epoxy matrix. The prGO-derived shell acts as a phonon-bridging interlayer that reduces interfacial thermal resistance and promotes thermally conductive pathway formation, while the oxygen-rich GO shell of GO-BN improves filler dispersibility and suppresses electrical percolation among prGO-BN particles at high filler loadings. Comprehensive characterization confirmed that the two fillers differ exclusively in the chemical state and surface polarity of their outer shells, enabling systematic decoupling of thermal and electrical transport pathways within the composite. The optimized GO-BN/prGO-BN hybrid composite simultaneously achieves a thermal conductivity of 6.25 W m-1 K-1 and a volume resistivity of 1.3 × 1012 Ω cm at 60 wt.% total filler loading, demonstrating that precise interfacial engineering of graphene-derived shell chemistry constitutes an effective strategy for next-generation electrically insulating thermal interface materials.