酸碱催化剂浓度对柔性硅气凝胶性能和结构的影响

Effects of acid-base catalysts concentration on structures and properties of flexible silica aerogels

以甲基三甲氧基硅烷(MTMS)和正硅酸乙酯(TEOS)作为混合硅源,甲醇为溶剂,十六烷基三甲基溴化铵(CTAB)为表面活性剂,通过酸碱两步催化溶胶凝胶法制备醇凝胶,经超临界干燥可以制备高弹性疏水块状硅气凝胶。分别采用0.1 mol·L^(-1)和0.01 mol·L^(-1)的草酸作为酸催化剂,5 mol·L^(-1)和10 mol·L^(-1)的氨水作为碱催化剂,研究不同酸碱催化剂浓度对其网络结构的影响。发现高浓度酸和高浓度碱以及低浓度酸和低浓度碱作为催化剂合成的硅气凝胶的网络结构更加均匀,孔径分布更窄。其中,在草酸浓度为0.01 mol·L^(-1)、氨水浓度为5mol·L^(-1)时,所得硅气凝胶密度为0.135 g·cm-3、比表面积为807 m2·g^(-1)、孔隙率约为93%,凝胶最大可压缩至其起始长度的60%,压缩回弹率为100%。

Flexible silica aerogels with super-hydrophobicity and elasticity were successfully prepared via acid-base two-step sol-gel method, followed by supercritical drying process. They were synthesized with tetraethoxysilane（TEOS） and methyltrimethoxysilane（MTMS） as coprecursors, methyl alcohol as solvent and cetyl trimethyl ammonium bromide（CTAB） as surfactant. The influence of acid-base catalysts concentration on silica aerogels was studied in detail. Aerogels prepared with higher base concentration and lower acid concentration were found to have more uniform pore structures and narrower pore size distributions. It was observed that the optimum aerogels can be obtained with 0.01 mol·L^（-1） oxalic acid and 5 mol·L^（-1） ammonia as acid-base catalysts, respectively. The density of the as-prepared aerogel was as low as 0.135 g·cm-3, the porosity was around 93% and the specific surface area was as high as 807 m2·g^（-1）. The maximum compression ratio of the aerogel was as high as 60% with 100% compression resilience ratio.