Effect of different trimethyl silylating agents on the hydrophobic and physical properties of silica aerogels

An essential feature of the ambient pressure dried aerogel manufacturing process is the end-capping of the reactive silanol groups in the silica wet gel. In this report, we have presented the effect of two different trimethyl silylating agents viz. trimethylchlorosilane (TMCS) and hexamethyldisilazane (HMDZ) on the hydrophobic and physical properties of ambient pressure dried silica aerogels. The hydrogels were prepared by sol-gel processing of sodium silicate precursor (Na₂SiO₃) in the presence of acetic acid catalyst followed by vapour passing treatment and different solvent exchanging steps. The silylating agent in hexane was used for end-capping of the silanols present on the silica surface of the gel. To study silylation behavior silylating agent/Na₂SiO₃ molar ratio was varied from 2.4 to 5.6. The aerogels have been characterized by density, % of volume shrinkage, porosity, % of optical transmission, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM), Thermo-gravimetric and Differential Thermal Analysis (TG-DTA) and contact angle measurements.