Multi-mechanism synergistic regulation of charge dynamics in epoxy composites via plasma-assisted polydopamine interface engineering

The accumulation and migration of space charges severely limit the application of polymer insulation in high-voltage direct current systems. This study investigates epoxy resin composites modified with polydopamine-functionalized boron nitride nanosheets (PDA@BNNS), where a two-step process involving plasma hydroxylation and subsequent polydopamine coating was employed to enhance the filler-matrix interface. The composites were characterized using pulsed electro-acoustic measurements, direct current (DC) conductivity tests, surface potential decay, and broadband dielectric spectroscopy. Results show that the 3 wt. % PDA@BNNS composite exhibits optimal performance, suppressing space charge accumulation and reducing the stored charge amount by approximately 36% at 20 kV/mm compared to pure epoxy. The effective charge injection barrier at 20 kV/mm increases from 1.12 eV (pure epoxy) to 1.35 eV (3 wt. % composite), and the conduction activation energy rises to 0.70 eV. The introduction of deep traps not only modifies the trap-limited space charge-limited current but also fundamentally alters the bulk conduction mechanism. To further elucidate this, the temperature-dependent conductivity was analyzed. Charge transport transitions to a three-dimensional variable-range hopping mechanism dominated by deep traps. A multi-mechanism synergistic model is proposed, encompassing barrier enhancement, deep trapping, potential quantum confinement, field homogenization, and relaxation optimization. This interface engineering strategy provides an effective approach for developing high-performance DC insulation materials.