Thermal Gelation for Synthesis of Surface-Modified Silica Aerogel Powders.

A spherical silica aerogel powder with hydrophobic surfaces displaying a water contact angle of 147° was synthesized from a water glass-in-hexane emulsion through ambient pressure drying. Water glass droplets containing acetic acid and ethyl alcohol were stabilized in n -hexane with a surfactant. Gelation was performed by heating the droplets, followed by solvent exchange and surface modification using a hexamethyldisilazane (HMDS)/ n -hexane solution. The pH of the silicic acid solution was crucial in obtaining a highly porous silica aerogel powder with a spherical morphology. The thermal conductivity, tapped density, pore volume, and BET surface area of the silica aerogel powder were 22.4 mW·m -1 K -1 , 0.07 g·cm -3 , 4.64 cm 3 ·g -1 , and 989 m 2 ·g -1 , respectively. Fourier transform infrared (FT-IR) spectroscopy analysis showed that the silica granule surface was modified by Si-CH 3 groups, producing a hydrophobic aerogel.