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 -hexane with a surfactant. Gelation was performed by heating the droplets, followed by solvent exchange and surface modification using a hexamethyldisilazane (HMDS)/-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·mK, 0.07 g·cm, 4.64 cm·g, and 989 m·g, respectively. Fourier transform infrared (FT-IR) spectroscopy analysis showed that the silica granule surface was modified by Si-CH groups, producing a hydrophobic aerogel.