为探究降低二氧化硅气凝胶体积密度的有效途径,以甲基三甲氧基硅烷(MTMS)和二甲基二乙氧基硅烷(DMDES)为硅源合成有机硅氧烷气凝胶,基于Box-Behnken Design响应面设计方法,分析MTMS/DMDES摩尔比、H2O/Si摩尔比、氨水浓度这3个因素及其交互作用对气凝胶体积密度的影响机理与规律,得到最佳制备工艺条件。制备低密度有机硅氧烷气凝胶的最佳工艺条件为MTMS/DMDES摩尔比6/4,H2O/Si摩尔比25,氨水浓度1mol/L。在此优化条件下,气凝胶体积密度为0.148g/cm3,与理论值基本吻合。研究结果表明:各因素对气凝胶体积密度的影响主次顺序为氨水浓度、MTMS/DMDES摩尔比、H2O/Si摩尔比;气凝胶由球形粒子连接组成,粒径为3～4μm;平均孔径约为7.03μm;气凝胶具有良好的疏水性、抗压缩性和热稳定性,接触角高达146.2°,60%应变时应力为25.4kPa,热分解温度达到389.2℃,导热系数为0.0564W/(m·K)。
In order to explore an effective way to reduce the bulk density of silica aerogels,organosiloxane aerogels were synthesized using methyltrimethoxysilane (MTMS) and dimethyldiethoxysilane (DMDES) as silicon sources.Based on the Box-Behnken Design response surface design method,the impact mechanisms and laws of three factors,namely,MTMS/DMDES molar ratio,H2O/Si molar ratio and ammonia concentration,as well as their interactions on the bulk density of silica aerogels were analyzed,and the optimal preparation process conditions were obtained.The optimal process conditions for preparing low-density organosiloxane aerogels were: MTMS/DMDES molar ratio of 6/4,the H2O/Si molar ratio of 25,and the ammonia concentration of 1mol/L.Under this optimized condition,the bulk density of the aerogel was 0.148g/cm3,which was basically consistent with the theoretical value.The results showed that the influence of various factors on the bulk density of aerogel followed the order: ammonia concentration,MTMS/DMDES molar ratio,H2O/Si molar ratio.Aerogel was composed of spherical particles with a diameter of 3～4μm,and the average aperture was 7.03μm.Aerogel had good hydrophobicity,compression resistance and thermal stability,with a contact angle of 146.2°,a stress of 25.4kPa at 60% strain,a thermal decomposition temperature of 389.2℃,and a thermal conductivity of 0.0564W/(m·K).
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基金资助
杰出青年科技人才培养项目(2020Q003);昌吉州科技计划(202110140019)
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