Abstract
In situ small-angle X-ray scattering (SAXS) measurements, with the aid of a specially-designed cell, have been carried during CH2Br2 adsorption on MCM-41. Ordered mesoporous silicas consist of a 2D hexagonal array of cylindrical mesopores of uniform size. As a result, they exhibit Bragg peaks because of the regular packing of the cylindrical pores. Dibromomethane was selected as a contrast-matching fluid because it has almost the same electron density as silica. The SAXS patterns provide information about both the structural properties of MCM-41 and the adsorption mechanism. The power law observed in the low-Q regime can be ascribed to intergrain interfacial scattering. The intensity decrease and the elimination of the Bragg peaks for the saturated sample suggested that an almost perfect contrast matching was achieved. Finally, information about the growing thickness of the adsorbed film was obtained by analyzing the integrated intensities of the diffraction peaks with a structural model consisting of infinitely long concentric cylindrical shells with four levels of electron density.
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