In this paper, the preparation of tetramethoxysilane (TMOS) based silica aerogels, by sol-gel process with varying the molar ratio of silylating agent are reported. The optimal molar ratio of precursors TMOS: MeOH: NH4OH was kept constant at 5:14.2:0.93 × 10-4, respectively, and concentration of silylating agent, hexamethyldisiloxane (HMDSO) were varied from 2% to 12% of the solvent. The retrieved aerogels have been characterized by apparent density, % porosity, Thermal conductivity, Fourier Transform Infrared Spectroscopy (FTIR), Thermo-gravimetric and Differential Scanning Calorimetry (TGA-DSC) and contact angle measurements. The effect of humidity on silica aerogels has been studied. The thermal analysis indicates thermal stability of hydrophobicity retains up to 329 °C.

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