Mesoscopic trap and elastic properties of polyetherimide nanocomposites with improved energy storage performance

Polymer nanocomposites (PNCs) are important energy storage dielectrics for capacitors. However, the lack of quantitative research on the properties of mesoscopic scale conductivity, traps, and Young's modulus in interfacial regions between polyetherimide and nanofillers results in an unclear understanding of the relation between the structure and properties. Polyetherimide/Al₂O₃ PNCs are prepared by in-situ polymerization, and the dielectric, thermal, and mechanical properties are measured. The experiments show that the film doped with 3 wt% nanofillers has the highest resistivity, Young's modulus, breakdown strength, and energy storage density. Then, the mesoscale distributions of the conductivity and Young's modulus in interfacial regions are solved as the inversion problem of electric and stress fields, and the macroscopic conductivity and Young's modulus of PNCs are obtained by high-throughput simulations. The conductivity, trap, and Young's modulus distributions are obtained by comparing the simulation and experimental results. It shows that the molecular chains in interfacial regions are bounded by nanofillers to form a tighter aggregated structure, hindering the molecular motion. Accordingly, the charge transport between molecular chains slows down, the trap energy increases and the conductivity decreases. The tighter aggregated structure makes PNCs have higher breakdown strength, energy storage density, and lower energy loss.