Fabrication And Dielectric Characterization Of Advanced BaTiO₃/Polyimide Nanocomposite Films

Ceramic/polymer composite is a kind of most promising electric materials, which combines the virtues of both ceramic materials and polymer materials. Via optimization of technical crafts, it is hopeful to get high-dielectric-permittivity composite materials with good mechanical properties and molding easiness.In this work polyimide (PI) with excellent thermal properties is chosen as the matrix of the composites. Barium titanate/polyimide (BT/PI) nanocomposite films with high thermal stability are prepared with PI and BT and the properties of the composites are characterized in detail. The main points studied in the paper are listed as following:(1) Without any coupling agents or surfactants, BT/PI nanocomposite films are synthesized by solution mixing technique and in-situ polymerization technique, respectively. The influences of the technical crafts on the dielectric properties of the composites are also studied.(2) The microstructure of the BT/PI nanocomposite films by in-situ polymerization technique is examined, and the mechanism of the resulting core-shell-like structure in the composites is analyzed. The effect of such special microstructure on the dielectric permittivity and the breakdown strength of the composite materials are also discussed.(3) The frequency dependence of the dielectric properties of the BT/PI nanocomposite films by in-situ polymerization technique is studied, together with the influence of loading concentration of the ceramic fillers on the dielectric properties of the composite films. Here the relationship between the loading concentration of BT and the dielectric permittivities of the composite films is simulated as a linear model.(4) The thermal properties and the temperature dependence of dielectric permittivities of the BT/PI nanocomposite films by in-situ polymerization technique are investigated, indicating that the thermal stability of the PI matrix has some effect on the properties of the composite films.(5) The effect of the imidation processes is studied on the dielectric properties of the BT/PI composite films, and the imidation process is optimized. The reason why the optimized imidation process can improve the dielectric permittivities of the composite films and reduce the loss tangent is demonstrated here.