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Jul 19, 2023
Organic inorganic nanocomposites have shown significant advantages in improving the heat resistance, mechanical properties, and organic size stability of materials. It is an effective means to further improve the heat resistance and high-temperature dimensional stability of PI. Si02 is currently one of the materials with the lowest known coefficient of thermal expansion. Using different methods to composite polyimide and inorganic materials on a nanometer scale and to make the nanoparticles uniformly dispersed in the hybrid membrane are becoming a research hotspot.
The research on polyimide/silica (Pl-SiO2) hybrid membrane materials began in the early 1990s. Extensive research has been conducted on the preparation process, thermal and mechanical properties, and certain results have been achieved.
At present, the sol gel method is mostly used to prepare this Hybrid material. This method usually refers to the process in which the precursor of inorganic silicon source is decomponded to synthesize sol under certain conditions, and then the solution or sol is transformed into a spatial reticulated inorganic oxide gel after solvent volatilization or heating. The thermal and mechanical properties of silicon containing polyimides prepared by this method are improved in varying degrees, and their electrical properties are also changed. The most important thing is that the gas permeability of Pl-S core hybrid membrane is much higher than that of bulk polyimide membrane at room temperature, and its gas separation function has great potential, especially in the process of dehydration and dehumidification of raw materials or products.
The Hybrid material with low content of S core (no more than 10%) has higher thermal stability, better mechanical properties and lower linear expansion coefficient than polyimide, while maintaining the photosensitivity of polyimide; The series of hybrid membranes prepared under acidic conditions have a greater impact on the glass transition temperature than those prepared under alkaline conditions, but both have good gas permeability and hydrophilicity. Their separation coefficients at pressures of 0/Qinhe and 0/C are greater than the theoretical values of Nussen diffusion. However, the synthesis of Hybrid material with high SiO2 content failed to obtain satisfactory results.
People are constantly improving the sol gel method to increase the SiO2 content and reduce the phase separation size. The salt of triethylamine was obtained by the reaction of polyamide acid with triethylamine, and the sol gel reaction was carried out with methanol as the solvent. The morphology and phase separation size of the hybrid membrane were greatly improved, and a transparent film containing 20% SiO2 could be obtained; The functionalized polyamide acid prepared from diamine containing ethoxysilane can form Chemical bond with SiO2, and even if the content of SiO2 reaches 70%, transparent membrane can still be obtained.
Using phenyldiethylsilane (PTEOS) instead of triethoxysilane (TEOS), a transparent film with a SiO2 content of 45% and good compatibility was obtained; In addition, the addition of a small amount of coupling agent in the sol-gel process can also effectively increase the compatibility of the two phases.
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