Synthesis and characterization of low density and hydrophobic silica aerogels dried at ambient pressure using sodium silicate precursor

The present paper deals with the synthesis and characterization of low density and hydrophobic silica aerogels dried at ambient pressure using low cost sodium silicate precursor. The hydrogels were prepared by sol-gel processing of sodium silicate precursor and acetic acid catalyzed water followed by vapour passing and solvent exchange with methanol. The mixture of MeOH:trimethylchlorosilane (TMCS):hexane was used for the end capping of the silanols present on the silica surface. The process was optimized by varying vapour passing time, gel ageing time, molar ratios of H2O/Na2SiO3, CH3COOH/Na2SiO3 and TMCS/Na2SiO3 and silylation period. The aerogels have been characterized by bulk density, % of volume shrinkage, porosity, Fourier transform infrared spectroscopy, thermogravimetric and differential thermal analysis and contact angle measurements. The best quality silica aerogels in terms of low density (0.073 g/cc), higher porosity (96%) and better hydrophobicity (theta = 146A degrees) have been obtained with the molar ratio of Na2SiO3:H2O:CH3COOH:TMCS at 1:166.6:2.25:11.9.