Hydrophobic properties of TMOS/TMES-based silica aerogels

Abstract The hydrophobic properties of tetramethoxysilane (TMOS)-based silica aerogels by incorporating trimethylethoxysilane (TMES) as a synthesis component, are described. The molar ratio of TMES/TMOS (M) was varied from 0 to 4.0 by keeping the TMOS, methanol (MeOH), water (H2O) and ammonium hydroxide (NH4OH), molar ratio constant at 1:14:4:3.7×10−3. The hydrophobic properties of the aerogels were studied using contact angle measurements, infrared spectroscopy and thermal analysis. The contact angle, θ increased from 100 to 140° for M=0.5 to 4. While the volume shrinkage of the aerogels increased whereas the bulk density decreased with increased M values. The hydrophobic aerogels are thermally stable up to a temperature of 300°C and above this temperature the aerogels become hydrophilic.