Effect Of Surface Modification Of Gas Phase SiO₂ On The Properties Of PI/SiO₂

Polyimide?PI? became an important insulating material due to the advantage in the synthesis and performance. With the development of technology, polyimide films doped with SiO₂ possess good mechanical properties, electrical properties and thermal properties. Thus they have wide application prospect in the field of electrical insulation. The gas phase SiO₂ nano particles, as a kind of nano particle with surface charged, can modify the performance of PI very well. However, the activity hydroxyl,absorbed water and the surface acid area caused by preparation make the gas phase SiO₂ became hydrophilic and hard to disperse in organic phase. In this paper, PI/SiO₂ doped with the same size of nano gas phase SiO₂ and six methyl two silazane?HDMZ?treated SiO₂ are prepared by in situ polymerization method to study the surface charge of SiO₂ and the effect of surface modification on the performance of PI/SiO₂.Characterize the morphology of two kinds of nano particles by using TEM, the organization structure by using XRD, the surface electric potential by Zeta potential test. Structure characterization of composite films are characterized by small angle X ray scattering technique, infrared absorption spectroscopy FTIR. Test the dielectric spectroscopy, dielectric loss tangent, corona aging life time and DSC curve of films.The experimental results show that: 1,The surface of hydrophilic Aerosil-380 SiO₂gas phase particles is with negatively charge, and the surface of HDMZ treated hydrophobic TS-630 SiO₂ is uncharged. The size of two kinds gas phase SiO₂ particle were both 7-10 nm, both SiO₂ were amorphous. The surface of hydrophobic SiO₂ particles were coated with a clear layer. 2, Fractal characteristics and phase interface were observed in both two kinds of films; With the increase of SiO₂ component, the fractal structure of composite films change from mass fractal dimension to mass-surface fractal. With the develop of the frequency, the dielectric loss of two kinds of composite films increased significantly. Compared with system A, the dielectric constant and dielectric loss of system B were inter with the doping component of SiO₂. 4, Two kinds of SiO₂ can both improve the corona aging performance of composite films, when the component of SiO₂ is 15%, corona aging time of A and B were 88.2 and 87.5 hours respectively, 22.5 times of pure PI films. 5,The introduction of system B SiO₂ can enhance the glass transition temperature of composite films.In conclusion, the introduction of two types of SiO₂ can both increase various ofproperties of PI/SiO₂. But the performance improvements showed differences. This is mainly due to the interface structure, polymerization mechanism of complex changeable factors, leading to the material performance exhibiting the contradictory macroscopic properties. Therefore, when we expect to modify polyimide by using SiO₂, we should select nanoparticles corresponding different performance requirements.