High-dielectric-constant graphite oxide-polyimide composites as embedded dielectrics

Microstructure and dielectric performance of graphite oxide (GO)/polyimide (PI) composites were investigated. Graphite oxide was prepared by hummer method([1]) through which graphite flakes were oxidized by concentrated sulfuric acid, potassium permanganate and hydrogen peroxide. Polyimide was synthesized with pyromellitic dianhydride (PMDA) and 4,4-diamino-diphenyl ether (ODA) in N,N-dimethylformamide (DMF) solution. GO/PI composite film was fabricated via coating process. The experimental results showed that the dielectric constant epsilon(r) increased gradually with GO content before reaching the percolation threshold. The value of dielectric constant epsilon(r) was 68 at 1000 Hz for the composite containing 1wt% of GO, which was 19 times larger than that of the pure PI. The dielectric loss tan delta was 0.6 for the composite containing 1 wt% GO. When the GO content reached 2 wt%, both of the epsilon(r) and tan delta values increased substantially, indicating formation of conducting pathway between GO particles. The results implied that when GO content was at a low level, the insulating PI served as electrons barrier layer between GO and prevented electrons from transferring from one GO to another under an external field. As a result, the measured epsilon(r) value increased with GO content, while the tan delta remained low. However, when GO filler loading reached a higher level and was in the vicinity of a critical concentration, GO was so close to each other and the conducting pathway could be developed in PI, leading to remarkable growth of epsilon(r) and tan delta.