Structure of silica-based organic–inorganic hybrid xerogel

The short range order in hybrid xerogels obtained by hydrolysis of (MeO)3Si–CC–C6H4–CC–Si(OMe)3 was investigated by X-ray diffraction analysis. Results were correlated to spectroscopic data and porosity measurements. Aside from the signal related to the Si–O–Si units (q=1.60 Å−1), the signals at q1=0.55 Å−1 and q2=1.12 Å−1 were attributed to the presence of organic spacers and their organization within the material. These signals were found to be independent of the porosity of the material as measured by the BET method. Thus, changing the solvent or the concentration used at the polycondensation step leads apparently to a similar structure for the materials, representative of the same local order in the material although the porosity is very different. Copolycondensation with tetramethoxysilane (TMOS) results in a shift of the q1 broad peak towards small angles and a decay of the q2 signal when increasing TMOS ratio. An interpretation by a uniaxial swelling is proposed. Elimination of the organic group by chemical treatment and thermal treatment leads to silica xerogels. While no traces of the former organization were found in the case of chemical treatment, the presence of a signal at about 0.30 Å−1 indicates the possibility of a residual organization in the case of the thermal treatment.