Synthesis of nanoporous silica aerogel by ambient pressure drying

A crack-free silica aerogel monolith was fabricated from a cheap water glass derived silicic acid solution by adding glycerol, which served as a drying control chemical additive (DCCA). The OH surfaces of the wet gel with glycerol were modified using a TMCS/n-hexane mixture followed by solvent exchange from water to n-hexane. The obtained surface modified wet gel was dried at 75 A degrees C under ambient pressure. The addition of glycerol appears to give the wet gel a more homogeneous microstructure (larger pore size and uniform size distribution) as well as enhanced stiffness. However, glycerol also retards surface modification and solvent exchange. The aerogel synthesized with glycerol added to the silica sol maintained a relatively low bulk density compared with the aerogels aged in a mixed ethanol (EtOH)/TEOS solution. The reproducibility of aerogel production was further improved in the aerogel synthesized with glycerol added to the silica sol and aged in a 70%EtOH/30%TEOS solution.