Low density and hydrophobic silica aerogels dried under ambient pressure using a new co-precursor method

Hydrophobic silica aerogels were prepared by a fast co-precursor method based on sol-gel process under ambient pressure drying. Organic tetraethoxysilane (TEOS) and inorganic aqueous alkaline silica sol were simultaneously used as starting materials, while trimethylchlorosilane (TMCS) was chosen as surface modification agent. Alkaline silica sol plays a double role of increasing pH value for condensation reactions and as co-precursor. The porosity and hydrophobicity of silica aerogels were in close correlation with the synthesis parameters. The monolithic and crack-free sample with a low density of 0.130   g   ∙   cm −   3 and high water contact angle of 142.8° was obtained by optimized the synthesis conditions (silica sol/TEOS molar ratio, ethanol/silica sol molar ratio, H 2 O/silica sol molar ratio and TMCS/n-Hexane volume ratio were 0.58, 1.32, 5.34 and 1:7, respectively).