A Comparative Study of Gas-phase Fluorination and Nano-Al2O3 Doping on Space Charge Behavior and Trap Level in Epoxy Resin

In this work, the effect of gas-phase fluorination concurrent with nano-Al ₂ O ₃ doping on space charge distribution, as well as trap level and density of epoxy resin, is investigated. Epoxy resins with different concentrations of Al2O3 nano-fillers (0, 1, 3, and 5 wt%) are prepared and fluorinated by a gas mixture of F2/N2 (20/80 v/v) for 30 min at 40 °C and 0.05 MPa. Fourier-transform infrared (FTIR) spectroscopy confirms the breakage of molecular-chain during the gas-phase fluorination process. The space charge behavior is observed by the pulsed electroacoustic (PEA) method before and after fluorination. PEA results indicate that 30-minute fluorination is useful against space charge injection into the bulk of epoxy resin/Al ₂ O ₃ nanocomposites. The trap density and trap energy level distribution are determined by isothermal surface potential decay (ISPD) measurement. The results indicate that fluorination introduces shallow traps on the surface, which can increase the conductivity of surface, and, thus, the trap depth is considerably reduced after fluorination. Moreover, it is found that incorporating 1 wt% nano-Al ₂ O ₃ particles into epoxy resin can level up the energy level of deep traps. However, further increasing the nano-Al ₂ O ₃ concentration, e.g., 3 and 5 wt%, promises the overlap of interaction zones between polymer matrix and nanoparticles, reducing the trap energy level.