Comparison of Hydrophobic Silica Aerogels Prepared by Different Modifiers

Hydrophobic silica aerogels were prepared by tetraethoxysilane(TEOS) and isopropanol (IPA) as raw materials, hexamethyldisilazane (HMDZ) and trimethylchlorosilane(TMCS) as modifier through sol-gel method, derivatization and followed by supercritical drying process, and they were characterized by means of SEM, IR, XRD, TG and so on. The results indicate that the hydrophobic silica aerogels before and after modification both had amorphous silica phase, which consisted of nano-porous continuous three-dimensional network skeleton by Si-O-Si, and the average diameter of skeleton was 3 nm. The silica aerogels after modification virtually had no mass loss before 450 ℃. However, when temperature was increased from 450 ℃ to 600 ℃, the mass loss of the silica arogels modified by TMCS and HMDZ reached 17% and 9.21% respectively. After TMCS modification, the density of silica aerogel reduced from 0.192 g·cm-3 to 0.149 g·cm-3, porous volume increased from 4.70 cm3·g-1 to 6.19 cm3·g-1, contact angle reached 157°, and water absorption was only 1.5%. The density of silica aerogel modified by HMDZ was 0.181 g·cm-3, porous volume was 5.01 cm3·g-1, contact angle was 120°, water absorption was 2.5%, and its hydrophobic effect was lower than modified by TMCS.