Dielectric and mechanical properties of polyimide-barium titanate nanocomposites

A polymer-ceramic nanocomposite is studied as a candidate for structural dielectric devices in aerospace applications. A pre-imidized polyimide powder was chosen for its excellent mechanical properties at elevated temperatures, while barium titanate (BaTiO₃) nanoparticles with a nominal diameter of 60 nm were dispersed in the matrix for the intended purpose of increasing the permittivity of the composite. Film samples with nanoparticle loadings of 0 to 20 vol% were created by solvent casting, and characterized using dielectric spectroscopy, dynamic mechanical analysis, and scanning electron microscopy (SEM). The addition of 20 vol% BaTiO₃ was observed to increase the real part of the permittivity from 3.9 to 8.9 at 100 Hz, and the room temperature storage modulus from 2.6 GPa to 4.4 GPa, as compared with neat polyimide. On the other hand, the breakdown strength was observed to decrease with the addition of nanoparticles. SEM images suggest that nanoparticle agglomeration and settling may cause the observed decrease in breakdown strength. Processing changes, such as nanoparticle surface modification, should be considered in order to improve the particle-matrix interface and in turn the dielectric and mechanical properties of the composite.