Effect of Nanoparticles on the Dielectric Properties of Polyimide

As part of a search for a better dielectric for use in high energy density capacitors, polyimide PI films containing a layered material, zirconium orthophosphate, ZrOH2PO42xH2O alpha-ZrP, were fabricated. PI has the advantage that it can be used to very high temperatures. To characterize the materials, x-ray diffraction XRD, differential scanning calorimetry DSC thermogravimetric analysis TGA, and dielectric measurements permittivity, loss and breakdown strength were made. The permittivity and loss studies were also carried out on both neat PI films and alpha-ZrP. The XRD, DSC and TGA results are consistent with amorphous composites. The effects of water or other impurities were observed in all three kinds of dielectric studies on all three types of material. For example, the relative permittivity of the composites decreased strongly when water was removed from the materials. Nonetheless, some increase in the relative permittivity of the dry nanocomposites was observed. Impurity or water-associated loss peaks were observed in all three types of material. The frequency and temperature dependences of the loss peaks made it possible to identify which were true relaxations. The effect of water is to decrease the dielectric strength of the composites. However, in both the wet and dry materials, the dielectric strength exhibits a maximum at a loading of about 5 wt alpha-ZrP.