Structural control of ambient drying silica aerogel by drying control chemical additive

The effect of glycerol as a drying control chemical additive for ambient pressure drying of silica aerogel was investigated. Silica hydrosol was prepared by the addition of 0.5-2.0 mass% glycerol to the mixture of metal alkoxide (TEOS) precursor and isopropanol as a solvent. The glycerol additive in silica aerogel is located on the hydroxyls of silica surface and could suppress a formation of crack in silica aerogel during ambient drying. The addition of excess glycerol affected a gelation time and springback effect. Crack-free silica aerogels were obtained. Specific surface area, average pore size, total pore volume, porosity and transparency of the silica aerogel were decreased but bulk density and hydrophobicity were increased as increasing the glycerol contents. Silica aerogel with 1 mass% glycerol addition was showed 0.42 g/cm³ of bulk density, 888 m²/g of specific surface area, 4.6 nm of average pore diameter and 85% of porosity.