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

Nano material is known as especial structure and properties, which becomes taking an important role in increasing the materials'performance. Polyimide (PI), as a typical kind of engineering polymer material with 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, accordingly a voiding precipitation among them in the synthesis process of the polyimide.In recent years, more and more papers were reported about polyimide/SiO₂ hybrid materials, which were about preparing nano SiO₂ power and hybrid process of organic silica sol, researching the thermal stability, dielectric properties and mechanical properties of hybrid films. But there were few articles about organic silica sol influencing on the film's properties. In this paper, by adjusting the mol ratio of the Methyl-triethoxysilane(MTEOS) and the tetraethoxysilane(TEOS), were prepared the nano-organic-silica/polyimide films by means of sol-gel method.And their surface, morphology and structure were characterized via FT-IR and AFM. The relationships between the structure of the films and the properties, including the breakdown strength, the dielectric constantε_r and the dielectric loss tanδ, were researched via corona discharge measuring equipment, breakdown strength measuring system, dielectric spectrometer ,TG.The results showed that there was the -Si-O-Si- net structure, which was well-proportioned in the hybrid film. Different nano organic silica has different influence in films'performances. Because of different meshwork size of organic silica and different dimension of that, different meshwork weaknesses maked the breakdown strength of the hybrid films firstly lower and higher later following as increasing of MTEOS mol contents in the organic silica sol. The dielectric constantε_r of the hybrid films was higher than that of pure film because of the incompletely aggregating of the organic silica processor. In low frequency region and intermediate region,when the MTEOS mol content was above 25 mol%, the dielectric loss tanδof hybrid film was the same as that of pure film, as well as frequency. In high frequency region, the dielectric loss tanδof hybrid film increased obviously when the MTEOS mol content was 100 mol%. The big size of the organic silica meshwork contributed to increasing the age of corona resistance and thermal properties. When the MTEOS mol content was 100 mol%, the age of corona resistance was 9.7h which was 1.8 times as that of the pure film and the thermal decomposing temperature was 15.21℃higher than that of pure film.