The Impact Of Thickness Distribution On Dielectric Properties Of Nano-Hybrid Three-Layer Composites PI Films

The thickness distribution of the nano-hybrid three-layer composite polyimide(PI)films has an important influence on the dielectric properties of the material.This research not only can further improve the dielectric properties of the films,it is also has the significance to perfect the dielectric physics theory of multilayer structure material.However there is a few study reported about the relationship between composite structure of three-layer and dielectric properties,furthermore,in-depth reports is rare.In this paper,micro emulsion-hydrothermal method was used in preparing a series of A and B three-layer PI composite films with different thickness distribution.The nano dispersion liquid and nano-hybrid three-layer composite PI films were systematically investigated by means of XRD,TEM,FT-IR and UV-VIS.The composite films were characterized by conduction current test,resistance,dielectric spectroscopy,breakdown strength test and corona-resistant test under the same environmental condition.XRD and TEM test results showed that the size of inorganic particles and inorganic nano dispersion phase is nanometer level.The results of FT-IR show that the imidization of nano-hybrid PI composite films have been completely achieved.The results of UV-VIS show that the nano-hybrid PI composite films have excellent transparency.According to the results of TEM,the structural proportion of three layer compound film conformed to the requirements of the design.The average size of silicon/aluminum oxide nano-particles in the hybrid PI films is less than 30 nm,and they formed composite structure.Electric conduction current tests showed that,with the dielectric strength increasing,the conduction current of three-layer composite PI film was gradually increased,while the gradient of the space charge limited current curve decreased along with the increase of hybrid PI layer thickness proportion.When the intermediate PI layer thickness is fixed,with increasing of the thickness of hybrid PI layer,the electrical aging threshold of three layer PI films shows a downward trend.When the hybrid PI layer thickness is constant,with increasing of the thickness of intermediate PI layer,the electrical aging threshold rises.Through breakdown strength test analysis,variation of two kinds of sample dielectric strength is similar to the variation of the electrical aging threshold.The permittivity and dielectric loss of nano-hybrid three-layer composite PI films are between the pure PI films and thin hybrid PI films,and increased with the relative proportion of hybrid PI layers increasing.Compared to pure PI,resistivity of the nano-hybrid three-layer composite PI films is lower.When the intermediate PI layer thickness is fixed,the corona resistance property showed slow decrease after the rapid increase with the thickness of hybrid PI layer increasing.When the hybrid PI layer thickness is constant,with the thickness of middle PI layer increasing,the corona resistance decreased.