Surfaces properties of silica gels modified with hydrophobic groups

Silica gels with trimethylsilyl and long-chain alkyl (C-6-C-18) groups have been synthesized. It has been established that adsorption of water on silica gels modified with trimethylsilyl groups decreases substantially and varies as a function of the modifier and the synthesis method chosen. The most hydrophobic surface (contact angle Theta = 136 degrees) is characteristic of silica modified with trimethyliodosilane vapor at 25 degrees C. It has been shown that the lowest affinity for water (Theta = 110-130 degrees) is characteristic of silica gels modified with hydrocarbon radicals, i.e. of silica gels whose residual silanol groups were end-capped using vapor-phase modification with hexamethyldisilazane or trimethyliodosilane. The results presented account for the differences in hydrophobic properties of surfaces of silica gels modified with trimethylsilyl and long-chain alkyl groups. (C) 1999 Elsevier Science B.V. All rights reserved.