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.

Common and Newton black films, which are the ultimate stage of thinning of soap films, are investigated by absolute x-ray reflectivity. The challenging and open problem concerning these two systems is the determination of the equilibrium thickness of the aqueous core. X-ray reflectivity provides very detailed and new information about their sandwich structure: The Newton black film appears much thinner than expected. As opposed to the common black film, it does not contain any aqueous core but only a hydration layer. In both cases the amphiphilic structure is the same.

URL: http://www-spht.cea.fr/articles/s94/035International audienceFree standing black films drawn from a diblock copolymer aqueous solution were studied by X-ray reflectivity. Due to the hydrophilic part of the copolymer which is a highly charged polyelectrolyte (PSSNa), such films form two opposing charged brushes. Above a determined threshold the thickness of the double brush weakly decreases as electrolyte is added. These results are in good agreement with recent mean-field theories

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