We present a quantitative study of different parameters of the silanation reaction (grafting of long aliphatic chains on silica surfaces via trichlorosilane group). Some of them, such as temperature or water traces, are shown to be particularly crucial. A mechanism for the reaction, completing the one previously reported, is proposed and optimal experimental conditions to perform high-quality monolayers of long aliphatic chains are deduced. Characterizations were performed with different techniques including X-ray reflectivity experiments and contact angle measurements. Results are consistent with well organized layers in which the chains are densely packed completely extended perpendicular to the surface. In the case of mixtures, the layer comportment reflects the concentration of each species in solution; there does not seem to be any segregation.

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