Octadecyl-modified silicas obtained by non-hydrolytic condensation of a C18-hybrid silica sol on a silica surface

Abstract Octadecyl-modified silicas bearing different amounts of octadecyl groups were synthesized by non-hydrolytic condensation of a C18-hybrid silica sol on spheroidal silica. The modified materials were characterized by a set of complementary techniques, including diffuse reflectance infrared spectroscopy (DRIFTS), attenuated total reflectance infrared spectroscopy (ATR), solid-state magic angle spin 1 H, 13 C and 29 Si nuclear magnetic resonance spectroscopy (NMR), thermogravimetric analyses (TGA), N 2 adsorption/desorption porosimetry and scanning electron microscopy (SEM). The octadecyl-modified silicas presented weight loss percentages of octadecyl ranging from 0.5 to 8.5 wt%. An increase in the octadecyl content on the silica surface resulted in an increase in the alkyl chain order and the six-fold siloxane rings. The use of a high C18-hybrid silica sol amount in the synthesis led to the formation of a porous hybrid silica gel layer on the surface of the spheroidal commercial silica.