Effect of surface charged SiO2 nanoparticles on the microstructure and properties of polyimide/SiO2 nanocomposite films

Polyimide (PI)/silicon dioxide (SiO2) films have been fabricated by in-situ polymerization method. The average diameter of the SiO2 nanoparticles is determined to be about 7 nm, which are modified by surface treatment to create surface charges (e-SiO2). Their microstructures are investigated using small angle X-ray scattering (SAXS) technique, Raman Spectroscopy and Scanning Electron Microscopy (SEM). The morphology of the composite films shows better and more uniform dispersion of the e-SiO2 nanoparticles in PI matrix than SiO2 nanoparticles due to the coulomb repulsion among surface charged nanoparticles. Our study shows that the resulted uniform dispersion of e-SiO2 in PI has direct impact on the dielectric constant, dielectric loss, corona aging time and thermal stability of PI/e-SiO2 composite films and our studied result is presented. The corona aging time of a PI/e-SiO2 composite film with 20 wt% doping is increased to 128 h, which is forty times more than that of a pure PI film (3 h). In addition, the thermal stability and tensile strength of composite films are also enhanced.