Core-shell BN/SCF architecture with phonon-electronic dual conduction pathways for synergistic enhancement of thermal conductivity, EMI shielding and mechanical properties in CF/EP composites

The urgent demand for reliable thermal management, electromagnetic interference (EMI) shielding and mechanical properties in aerospace electronics operating under extreme conditions drives the development of advanced multifunctional composites. Herein, the core-shell boron nitride/short carbon fiber (BN/SCF), synthesized via diazonium coupling and electrostatic assembly, is strategically aligned onto CF felts using a high-voltage electric field. Subsequent lamination with CF cloth and vacuum-assisted resin infusion (VARI) molding to fabricate multifunctional carbon fiber/epoxy resin (CF/EP) composites. The three-dimensional CF felt establishes thermal conduction bridges within EP interlayers, effectively mitigating the intrinsic limitation of out-of-plane thermal conductive. Concurrently, the BN nanoplates coated onto SCF enhance EP phonon transport via architecturally ordered crystalline lattice alignment, while oriented SCFs extend phonon pathways, collectively establishing phonon-electron dual thermal channels. Consequently, the CF/EP composites achieved optimal out-of-plane and in-plane thermal conductivities of 1.20 and 14.08 W m⁻¹ K⁻¹. The unique core-shell BN/SCF promotes multiple reflections of electromagnetic waves (EMWs) through an energy band structure mismatch between the wide bandgap BN and conductive SCF, and BN dielectric polarization, achieving exceptional shielding effectiveness (SE) of 50.06 dB, which was a 63.33 % improvement over the original CF/EP composites (30.65 dB). Moreover, the core-shell BN/SCF acts as rivet-like reinforcements, suppressing crack propagation through synergistic mechanical interlocking and chemical bonding, achieving 35.50 % and 97.35 % enhancement in ILSS and mode II toughness compared to original CF/EP. This multiscale structural engineering strategy demonstrates a material-level solution to fulfill the multifunctional requirements of next-generation aerospace systems operating under extreme environment conditions.