Hydrophobic silica composite aerogels using poly(methyl methacrylate) by rapid supercritical extraction process

A poly(methyl methacrylate) solution was mixed in an optimized tetraethoxysilane-based silica sol and a silica aerogel was obtained by a rapid supercritical extraction process. The hydrophobicity was enhanced by an addition of poly(methyl methacrylate), the silica aerogel prepared with 6 wt% poly(methyl methacrylate) has the contact angle of 156° with low density (0.067 g/cm³), high surface area (829 m²/g), and low thermal conductivity (0.072 W/m·K). The thermogravimetric-differential thermal analysis also showed that the aerogels were hydrophobic up to a temperature of 393 °C. An extra hydrophobicity could be expected for silica aerogel using poly(methyl methacrylate) through the surface modification of silica aerogel with generated –OCH₃ and –CH₃ radicals by the thermal decomposition of poly(methyl methacrylate) excluding poly(methyl methacrylate) itself. This study provided a simple and cost effective method that used an inexpensive polymer additive without using an expensive surface modification agent nor hydrophobic silica precursor.