Preparation By Photoacids Generation And Properties Of Silica Aerogels

Silica aerogel is a kind of porous material with a 3D network of silica particles and it has many excellent properties, such as high surface area, high porosity, low density, low thermal conductivity, low dielectric constant, low refractive index etc.. Because of the excellent performance, silica aerogel has potential applications in many fields, such as aerospace materials,environmental protection, catalyst carrier, energy storage materials, insulation materials and so on. But the application of silica aerogels is not as widely as foaming materials, this is mainly for two reasons: first, due to the structure characteristics of silica aerogel the mechanical properties is very poor, broken easily, difficult as structural support materials; second, silica aerogels require the use of supercritical complex techniques by the traditional preparation method, although the method of drying at atmospheric pressure is developed,but the preparation process is complex, time-consuming and expensive.Therefore, in order to realize the large-scale industrialization of the material, it is necessary to develop a simple and rapid preparation of silica aerogels with excellent mechanical properties.In this thesis, highly flexible silica aerogels were fabricated by using 2-(3-(triethoxysilyl)propylcarbamoyloxy) ethyl acrylate (TESEA) and methyltriethoxysilane (MTES) as co-precursors through photopolymerization and sol-gel process, then followed by ambient pressure drying. Attributing to photolysis of the photoacids generators (PAG), the radical and Bronsted acid(HSbF6) were generated simultaneously under irradiation. The radical initiated the photopolymerization of acrylate which induced the gelation and fixed the shape of the gel quickly, allowing the sol-gel process of silicane gradually. In this paper, the effects of the structure of silicon source, the concentration of precursor and the content of TESEA on the structure and properties of silica aerogels were investigated. The PDMS was added into the gel system to further improve the mechanical properties of the material.The results of the research are as follows: (1) Under UV light, Bronsted acid (HSbF6) and radicals can be produced by PAG. The double bond of TESEA can generate polyacrylates initiated by the radicals and the sol-gel reaction of siloxanes can be catalyzed by Bronsted acid (HSbF6) at the same time. So the gel time can be reduced significantly. (2)The optimum methods kept the mass ratio of the m(TESEA)/(m(TESEA)+m(MTMS)+m(PDMS)) at 18wt%,the mass ratio of m(PDMS)/ (m(TESEA)+m(MTMS)+m(PDMS)) at 8wt%, the weight percent of the silicon source at 25wt%. The sample has excellent mechanical properties and the young's module is 30.8 kPa. The sample remains complete when compressed to 40% of its original height. At the same time the aerogel can be compassed to 60% of its original height for 20 times without being damaged. And after the test the sample can restore the original height in 24 hours. The contact angle of the aerogels sample is 141°.(3) Due to its excellent mechanical properties and hydrophobicity, the material can be applied to oil-water separation. The results of the adsorption test showed that the mass of the aerogel increased to several or ten times of its own quality after absorbed organic solvent and the solvents can be easily separated. The aerogel can be reused for oil-water separation. The mass did not change significantly during the separation experiments repeated for 10 times.