Preparation and Characterization of Polyimide/Alumina Composite Films as Improved Solid Dielectrics

Abstract

Polyimide/alumina (PI/Al₂O₃) nanocomposite films were prepared by incorporating different nano-sized Al₂O₃ contents into PI which derived from pyromellitic dianhydride (PMDA) and a flexible diamine 4,4-bis(3-aminophenoxy) biphenyl (4,3-BAPOBP). The micromorphology, chemical structure, dielectric, mechanical properties and glass transition temperatures (T g ) of prepared films were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), LCR metry, electronic tensile testing and differential scanning calorimetry (DSC). SEM images show uniform distribution of Al₂O₃ nanoparticles in matrix. FTIR spectra indicate that Al₂O₃ nanoparticles are functionalized with γ-aminopropyl triethoxysilane (γ-APS) and the imidization was complete. XRD patterns reveal the peaks of PI/Al₂O₃ composite films were similar to those of Al₂O₃, indicating that the crystal structure of Al₂O₃ remains unchanged and stable after being doped into PI matrix. Meanwhile, the effects of additives on the dielectric and mechanical properties of composite films were also studied. The results show the dielectric constant and dielectric loss of hybrid materials increase with the addition of Al₂O₃ nanoparticles. The electrical breakdown strength and tensile strength of PI/Al₂O₃ can be markedly improved by the addition of appropriate amounts of Al₂O₃ to the PI matrix.