Interfacial Engineering of Polydopamine-Coated Boron Nitride Nanoparticles for Enhanced Dielectric and Breakdown Performance in Epoxy Nanocomposites

This study demonstrates enhanced dielectric properties and breakdown strength in epoxy resins (EP) through the incorporation of polydopamine-modified boron nitride nanoparticles (h-BN@PDA) as a functional nanofiller for next-generation power electronics insulation. We fabricated h-BN@PDA/EP nanocomposites with filler loadings ranging from 1 to 5 wt %. The microstructure, trap characteristics, and dielectric behavior were systematically investigated using SEM, FTIR, DSC, conductivity measurements, space charge characterization, and breakdown tests. The 1 wt % h-BN@PDA/EP composite demonstrated superior performance, exhibiting a deep trap energy level of 1.078 eV, significantly deeper than that of pure epoxy (1.02 eV), and a maximum DC breakdown strength of 217.9 kV/mm, compared to 201.9 kV/mm for pure EP. This improvement is attributed to the well-dispersed nanofillers and their effective charge-trapping capability. In contrast, composites with 3–5 wt % loading showed increased space charge accumulation and a marked reduction in breakdown strength (down to 139.4 kV/mm). This degradation is attributed to filler agglomeration, which induces localized field distortion and disrupts the composite microstructure, outweighing any potential benefits from increased interfacial area. The dielectric performance evolves with filler concentration due to a decisive shift in the dominant mechanism: the charge-trapping mechanism at low concentrations (1 wt %) suppresses charge migration, while interfacial polarization dominates at high concentrations (3–5 wt %), promoting charge transport. This work elucidates the interplay between charge trapping and interfacial polarization, providing a guideline for designing high-performance nanodielectric materials for encapsulating wide-bandgap power devices.