Preparation and characterization of HMDS modified hydrophobic silica aerogel

Hydrophobic silica aerogel was prepared using sol-gel two-step method and surface post-processing method followed by ethanol supercritical drying, using tetraethoxysilane (TEOS) as silica source, ethanol as solvent, hydrochloric acid and ammonia as catalyst, and hexamethyldisilazane (HMDS) as modifier. The effects were investigated on microstructure of aerogel by changing the HMDS dosage over a range of 4%-40% and modification time over a range of 12-72 h. The hydrophobicity was investigated by video contact angle analyzer and Fourier transform infrared spectroscopy (FTIR). The surface area, pore volume and pore size were measured by N2 adsorption-desorption isotherms. The thermal stability was tested by simultaneous thermo-gravimeter and differential scanning calorimeter (TG-DSC). With the increase of HMDS dosage, the contact angle of hydrophobic silica aerogel increased, ranging from 125°-157°, surface area and pore volume decreased, ranging from 863.59-763.24 m²/g and 3.57-3.04 cm³/g, pore size increased, ranging from 16.53-17.14 nm. The contact angle increased with the increase of modification time, ranging from 120°-152°. The aerogel with good hydrophobicity was obtained, modified with 20% HMDS for 48 h, and stable under 267.3 °C.