Dielectric properties of polyimide-mica hybrid films

Polyimide-mica hybrid films were prepared via ultrasonic dispersion and in situ polymerization process from a solution of a polyimide precursor and mica in N,N-dimethylacetamide, and their structure was characterized by FTIR and XRD techniques. The dependence of dielectric properties, such as dielectric constant and electrical break-down strength, of the hybrid films on the content of mica was studied at room and cryogenic temperatures. The results show that the dielectric constant of PI-mica hybrid films decreases with the increase of the mica content at temperatures from -150 to 150°C and at frequency range from 1 kHz to 1 MHz. It was found that the cryogenic electrical breakdown strength of the PI-mica hybrid films could meet the requirements of cryogenic insulating materials. KGaA, Weinheim.