Structure And Property Analyse Of The Nano-Organic-Silica/PI Films

Nano material is known as especial structure and properties, which becomes playing an important role in increasing the materials'performance. Polyimide (PI), as a typical kind of engineering materials with the highest thermal stability hitherto, has been widely used in the aeronautic and electronic industries because of its outstanding performances such as excellent thermal and electric properties and mechanical properties. Its high thermal stability and glass transmission temperature are beneficial to the distribution of the nano-particles in the synthesis process of the polyimide.In recent years, more and more papers were reported about SiO2/polyimide hybrid materials, which mainly focused on preparing nano SiO2 power or organic silica sol and hybrid process, and researching the thermal stability, dielectric properties and mechanical properties of hybrid films. But there are few articles about how the structure of organic silica sol influencing on the film's properties. In this paper, by changing the mol ratio of the diphenyldimethoxyssilane(DDS) and the tetraethoxysilane(TEOS), the nano-organic-silica/polyimide films were prepared by sol-gel method. The surface topography of the PI films were characterized via scanning electron microscope, and the electric properties and thermal stability were measured via breakdown strength measurement, corona discharge measuring equipment, dielectric spectrometer and TG. The effect on properties of PI made by structure of nano-organic-silica were also analyzed.The results showed that there was the -Si-O-Si- net structure, which was well-proportioned in the interior and surface of films. Different nano-organic silica structure has different influence in the films'performances. Based on 20wt% content in PI film, the effects of different network sizes, the dimension and the network weaknesses of organic silica structure make the breakdown strength of the hybrid films increase firstly and slowly decrease later following as DDS mol content rising in the organic silica sol. And when the DDS molar was 25%, the breakdown strength of the hybrid PI films was highest, which is 311kV/mm. In low frequency region, when the DDS molar of the hybrid films were 37.5% and 50% , the dielectric constantεr was less than that of pure PI film. With the DDS molar in the hybrid films increasing, the dielectric loss tanδdecreased and the thermal stability increased, but its increasing extent was not big; the corona-resistant time also increased obviously. Under the condition of the same thickness(28μm) between the hybrid films and pure PI films. When the DDS molar of the hybrid PI films was 50%, the corona-resistant time was 46.43h, whose corona-resistant time was 8.57 times longer than that of pure PI film. According to the graph of scanning electron microscopy (SEM), when the DDS molar was 50% , the dispersion of inorganic nano-component in organic matrix was best. On this basis, when the DDS molar was 50% in organic silica sol,the electric properties was studied by changing the content of nano-inorganic-silica. The results shows that the breakdown strength, the corona-resistant time, the thermal stability and the surface topography of PI films adulterated 15wt% were better than ones of PI films adulterated 20wt%.