Preparation and surface modification mechanism of silica aerogels via ambient pressure drying

Silica aerogels were synthesized via sol-gel processing followed by a two-step surface modification using methyltrimethoxysilane (MTMS) and trimethylchlorosilane (TMCS)/ethanol (EtOH)/n-Hexane as modifying agents via ambient pressure drying. The bulk modification and surface modification of silica network from the alcogels were accomplished in this approach. The obtained silica aerogels exhibited three-dimensional nanoporous structure with the porosities, densities and specific surface areas in the ranges of 87.7-92.3%, 0.27-0.17 g cm(-3), and 852-1005 m(2) g(-1). respectively. The presence of Si-CH3 functional groups on the surface of silica network resulted in hydrophobic property with the contact angle as high as 156 degrees. The promotion of pore water displacement during the surface modification strengthened the backbone of silica aerogels leading to good thermal and hydrophobic stabilities. Possible mechanism of surface modification and solvent exchange by a two-step modification is suggested. (C) 2011 Elsevier B.V. All rights reserved.