Effect of nano-Al 2 O 3 on the polarization of polyimide nanocomposite films with tri-layer structures

Polyimide (PI)/Aluminum oxide (Al 2 O 3 ) nanocomposite films wtih tri-layer structures (PI-Al 2 O 3 /PI/PI-Al 2 O 3 ) are manufactured from pyromellitic dianhydride (PMDA) and 4,4'-oxydianiline (ODA) via in-situ polymerization method. Microstructure, dielectric property and electrical conductivity of the nanocomposite films are characterized in this paper. Transmission Electron Microscope (TEM) and X-Ray Diffraction (XRD) results show that nano-Al 2 O 3 particles are successfully introduced into target tri-layered structure and are homogeneously dispersed in the polyimide matrix. Compared with pure films, the obtained composite films perform lower relative permittivity at low nano-Al 2 O 3 doping content (0–8wt%) and higher relative permittivity at high nano-Al 2 O 3 doping content (>8wt%). The dielectric loss (loss tangent) of the composite films is higher than that of the pure films at the same frequency, and increases consistently with the increase of nano-Al 2 O 3 content, especially in low frequency range. Furthermore, at the same nano-Al 2 O 3 concentration, the dielectric loss of the composite films reduces at frequencies 103 Hz. The effect of nano-Al 2 O 3 on electrical conductivity is only observed clearly at low frequency region ( 2 O 3 particles, respectively.