The role of interfaces in PI matrix nano composite films on electrical properties

Polyimide (PI) matrix nano composite films have been studied extensively and been taken as field-grading materials in aircraft, flexible circuit boards, new energy batteries and so on. In present paper, the composite films doped with different weight content of fumed Al2O3 were prepared by in-situ polymerization (the contents of Al2O3 in the composite films are 5%, 10%, 15%, 20%). TEM and SAXS were applied for presenting the microstructure of the interface between Al2O3 and PI. The results indicated that Al2O3 particle absorb lots of PI molecular chains to reduce own high surface energy, produce at least two regions with different electron cloud density and electron absorption capacity in the interface, which promoted the dielectric constants and conduction current prominently. The trap distribution was depicted by isothermal decay current test. It was shown that shallow trap and deep trap were produced in the composite films, and the shallow trap always predominated in all composite films, which is favorable transport carrier, explaining the promoted dielectric constants and conduction current. It was suggested that the shallow trap can capture and produce carrier, prevent charge accumulation and enhance the corona resistance property. The figures represented that the composite films have better than that of pure PI film, the corona aging life of PI/Al2O3 20% is about 25 times the life of pure PI.