摘要
超临界干燥制备了SiO_2气凝胶,500℃热处理SiO_2气凝胶后与气相六甲基二硅胺烷(hexamethyldisilazane,HMDS)在常温下反应,制备了疏水气凝胶。采用Fourier转换红外光谱、热重-差示扫描量热法、碳元素分析、氮吸附法对气凝胶进行表征。结果表明:热处理使气凝胶表面的乙氧基氧化成羟基,羟基与HMDS反应,生成硅甲基,从而具有疏水性,与水接触角为120°。反应质量增加率最大值为10.5%。疏水气凝胶经受350℃以上高温后变成亲水,可再与HMDS反应,又具有疏水性。随再疏水处理次数增加,平均孔径减小,机械强度增大。每次再疏水处理反应质量增加率为5.5%～8.9%,热处理和疏水处理交替进行20次后,气凝胶的质量增加到303%。
Hydrophobic aerogels were synthesized via heating the supercritical dried aerogels at 500℃, then reacting with hexame- thyldisilazane （HMDS） vapor at room temperature. The hydrophobic aerogels were characterized by Fourier transform infxared spec- troscopy, thermogravimetric-differential scanning calorimetry, carbon elemental analysis, and nitrogen adsorption. The results show that the surface ethoxyl groups were transformed to hydroxyl groups during heating, and the hydroxyl groups reacted with： HMDS vapor to form trimethylsilyl groups, making them hydrophobic. The water contact angle is 120° . The maximum reaction mass gain is 10.5%. The hydrophobic aerogels become hydrophilic when heated beyond 350 ℃; however, they can react with HMDS and become hydrophobic again. When the heating and modification cycle is repeated, the average pore size decreases, and the mechanical strength increases. The mass gain at each modification cycle is 5.5%- 8.9%, and the aerogel mass increases to 303% after 20 cycles.
出处
《硅酸盐学报》
EI
CAS
CSCD
北大核心
2008年第A01期89-94,共6页
Journal of The Chinese Ceramic Society
基金
国防科技重点实验室基金(9140C8203050604)资助项目。
关键词
二氧化硅气凝胶
疏水
六甲基二硅胺烷
吸湿性
silica aerogels
hydrophobic
hexamethyldisilazane
moisture absorption
