水玻璃为原料常压干燥制备疏水SiO_(2)气凝胶

Preparation of hydrophobic SiO_(2) aerogel via ambient pressure drying with water glass

采用溶胶-凝胶法,以自制水玻璃为原料、三甲基氯硅烷(TMCS)为疏水改性剂,通过常压干燥制得疏水SiO_(2)气凝胶。研究多步溶剂置换-表面改性和一步溶剂置换-表面改性两种改性工艺对SiO_(2)气凝胶结构与性能的影响,探讨一步溶剂置换-表面改性机制。结果表明:采用乙醇/TMCS/正己烷对凝胶进行一步溶剂置换-表面改性,可快速制备SiO_(2)气凝胶,所制得的气凝胶具有纳米多孔结构,孔洞分布密集、均匀,比表面积为654.24 m^(2)/g,孔体积为2.72 cm^(3)/g,平均孔径为12.38 nm,线收缩率为14.37%。改性后的气凝胶表现出较强的疏水性,接触角达到143°,且382℃左右仍可保持疏水特性。一步溶剂置换-表面改性过程中凝胶表面的Si-OH被Si-OSi(CH_(3))_(3)取代,凝胶的疏水改性和孔隙水的置换是同步完成的,乙醇的存在减缓了TMCS与孔隙水的剧烈反应,避免了改性时凝胶发生破碎。

The hydrophobic SiO_(2) aerogel was produced by sol-gel method using self-made water glass as raw material and trimethylchlorosilane(TMCS)as hydrophobic modifier through ambient pressure drying.The effects of two modification processes,namely multi-step solvent replacement-surface modification and one-step solvent replacement-surface modification,on the structure and properties of SiO_(2) aerogel were investigated,and the mechanism of one-step solvent replacement-surface modification was explored.Results showed that SiO_(2) aerogel could be rapidly prepared by one-step solvent replacement-surface modification of the gels with ethanol/TMCS/hexane.The resulting aerogel had a nanoporous structure with dense and uniform pore distribution,which the specific surface area of 654.24 m^(2)/g,the pore volume of 2.72 cm^(3)/g,the average pore size of 12.38 nm and the linear shrinkage of 14.37%.The modified aerogel exhibited strong hydrophobicity,with a contact angle of 143°,and the hydrophobic properties could still be maintained at 382℃.In the one-step solvent replacement-surface modification process,Si—OH on the gel surface was replaced by Si—OSi(CH_(3))_(3).The hydrophobic modification of the gel and the replacement of pore water were completed simultaneously,and the presence of ethanol slowed down the violent reaction between TMCS and pore water,avoiding gel fragmentation during the modification.