Dielectric properties of graphene–iron oxide/polyimide films with oriented graphene

The preparation of high-dielectric-constant (k) materials is important in the field of electronics. However, how to effectively use the function of fillers to enhance k is still a challenge. In this study, anisotropic graphene (GNS)–iron oxide (Fe3O4)/polyimide (PI) nanocomposite films with oriented GNSs were prepared by the in situ polymerization of 4,4′-oxydianiline and pyromellitic anhydride in the presence of GNS–Fe3O4. Films of the precursors were fabricated, and this was followed by stepwise imidization under a magnetic field at a higher temperature to orient the magnetic sheets. The orientation of GNS–Fe3O4 and the relationships of the GNS–Fe3O4 content and measurement frequency with the dielectric properties of the GNS–Fe3O4/PI films were studied in detail. The dielectric property differences of the GNS–Fe3O4/PIs with GNS–Fe3O4 parallel or perpendicular to the film surface were not obvious, when the content of GNS–Fe3O4 was lower than 5 wt %. However, at the percolation threshold, the k values of GNS–Fe3O4/PI films with horizontal GNS–Fe3O4 were much higher than those of the other two kinds of films at 103 Hz; this was derived from the contribution of more effective microcapcitors parallel to the film surface. So, making the GNS–Fe3O4 parallel to the film surface greatly enhanced k of GNS–Fe3O4. However, switching the charges on the large lateral surface of the parallel GNSs with the electric field also caused a higher dielectric loss and the frequency dependence of k and the dielectric loss at low frequency. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43041.