Physical properties of methyltrimethoxysilane based elastic silica aerogels prepared by the two-stage sol–gel process

The experimental results on the physical properties of methyltrimethoxysilane (MTMS) based elastic silica aerogels prepared by the two stage sol–gel process, are reported. The molar ratio of methanol (MeOH)/MTMS, (M), was varied from 14 to 42 and the molar ratios of acidic water/MTMS, (A) and basic water/MTMS, (B) were each varied from 0.8 to 7.2. The acidic water and basic water concentrations were also varied from 0–0.1 M and 6–13.36 M, respectively. The MTMS based superhydrophobic elastic aerogels could be obtained by adding only distilled water without an acid in the first step which would prevent the possible corrosion of the autoclave during the supercritical drying. With an increase in the MeOH/MTMS molar ratio, the aerogels have been found to become flexible which was characterized by the Young’s modulus. The best quality elastic superhydrophobic aerogels in terms of contact angle (160°), density (37 kg/m³), volume shrinkage (6%), porosity (98%) and thermal conductivity (0.057 Wm⁻¹ K⁻¹) have been obtained for the molar ratio of MTMS:MeOH:acidic water:basic water:: 1:35:3.97:3.97, respectively. The hydrophobicity was confirmed by Fourier Transform Infrared (FTIR) spectroscopy and contact angle measurements. The microstructure of the aerogels has been studied by the transmission electron microscopy (TEM).