Preparation of super hydrophobic silica aerogel and study on its fractal structure

The experimental results on silica aerogels with super hydrophobic property are reported. Silica alcogels were prepared via a two-step acid/base process by keeping the molar ratio of tetraethyoxysiliane (TEOS), ethanol (EtOH), water (H2O), hydrochloric acid (HCl) and ammonia (NH4OH) constant at 1:6:8:1.0 x 10(-3):1.1 x 10(-2), respectively, and varying the molar ratio of N,N-dimethylformamide (DMF)/TEOS (G) from 0 to 1.2. After two aging treatment steps, they were modified by isopropyl alcohol (IPA)/trimethylchlorosilane (TMCS)/n-hexane solution at 60 degrees C. It was found that G Value at 0.8 resulted in low density (similar to 0.2 g cm(-3)) and the minimum volume shrinkage (similar to 6%), with the total water adsorption ratio similar to 5.1% when exposed to water for 3 months and the contact angle 0 approximate to 178 degrees. Besides, the aerogels (G = 0.8) had higher volume fractal dimension (similar to 1.8), which indicted that it possessed better connectivity and more uniform particle sizes. (C) 2008 Published by Elsevier B.V.