Rapid synthesis of MTES-derived silica aerogel monoliths in Cetyltrimethylammonium bromide/water solvent system by ambient pressure drying

Polymethylsilsesquioxane (PMSQ) aerogels are silica aerogels that contain dangling methyl groups and exhibit high strength and flexibility. Common silica precursors trialkoxysilanes have difficulty to form networks in sol-gel processes, preventing monolith formation. Here crack-free PMSQ monolithic aerogels are synthesized from methyltriethoxysilane (MTES) at ambient conditions. The concentrations of cetyltrimethylammonium bromide (CTAB) surfactant in the sol were optimized to delay the phase separation of MTES. Crack-free aerogel monoliths with flat surfaces were obtained from silica sols with a CTAB of 0.692-1.039 mmol/L, while pits, wrinkles, cracks, or complete breakage appeared beyond this range. The Si-CH3 groups on the aerogel skeleton made them hydrophobic up to 400 degrees C for 1 h in air conditions while oxidized into Si-O-Si bonds at 565.0-751.2 degrees C under N2 conditions, making them hydrophilic. The new synthesis method is 1.3-31.8 times faster than conventional processes and contributes to developing next-generation green and scalable production technologies of silica aerogels.