Fabrication And Characterization Of Polyimide/Potassium Sodium Niobate Composite Films

Polyimide (PI) is widely used in various fields for its excellent performance.However, with the rapid development of technology, the traditional and pure PImaterial has been difficult to meet the requirements. In recent years, in order toimprove the application performance of PI, the research about PI matrix compositeshas become a hot in academic and industry fields.In this paper, the pyromellitic dianhydride (PMDA) and4,4′-Diaiminodiph-enylether (ODA) were used as raw materials to synthesize the polyamic acid (PAA), inwhich the DMAC was solvent. Then, the PI films with different molecular weightswere prepared by thermal imidization from PAA. In addition, a series ofwell-dispersed polyimide/potassium sodium niobate (PI/KNN) with different KNNcontents were prepared through in situ polymerization with the help of ultrasonicdispersing technology.The viscosities of the PAA, ultraviolet-visible spectra and fluorescence spectraof the PI films were measured. The results showed that, as the mole ratios(PMDA:ODA) increased, the inherent viscosity of PAA decreased first, thenincreased. The inherent viscosity reached the maximum value (1.57dL/g) when themole ratio was1.015, at the same time; the molecular weight of the PI reached themaximum value. In addition, the ultraviolet absorption spectra and fluorescenceemission spectra showed a red-shift with the increase of inherent viscosity, whichwas mainly due to the increase of conjugated effect.The structure, morphology, dielectric and thermal stability properties of thePI/KNN films were characterized and analyzed through the measurements of X-raydiffraction, scanning electron microscopy, dielectric and thermogravimetric. The testresults showed that KNN filler was well dispersed in PI matrix, and the size of KNN filler was estimated to be about1~3μm. Moreover, an internal boundary layercapacitance (IBLC) structure was formed in PI/KNN composite films. Comparedwith the pure PI film, the dielectric properties of the PI/KNN films were significantlyimproved. When the volume concentration of KNN reached40%, the dielectricpermittivity of the composite film was22at102Hz. And the loss tangent of thehybrid film was still lower than0.05at102Hz. At the same time, the conductivity ofthe hybrid film was still lower than10-8Sm-1at102Hz, which showed the excellentinsulation performance. In addition, the thermal stability of the hybrid films wasgood, and the initial thermal decomposition temperatures were about450～500℃.