Auto-organization of Nanostructured Organic-Inorganic Hybrid Xerogels Prepared by Sol-Gel Processing: The Case of a "Twisted" Allenic Precursor

Nanostructured hybrid materials prepared by sol-gel hydrolysis-polycondensation of the precursor 1,3-bis (propyltrimethoxysilyl)-1,3-diphenylallene P having a bulky rigid and twisted core with two short flexible arms exhibited a self-organization evaluated by birefringence measurements (micrometric scale) and Xray diffraction studies (nanometric scale). These observations show that the auto-organization of hybrid materials is not limited to rigid-rod or mesogenic spacers. It appears as a more general phenomenon. The twisted geometry of the organic group induced an anisotropic organization, the morphology of which was unprecedented and different from the one observed with the linear or mesogenic hybrid materials previously studied. Moreover, the birefringence pictures were also different from those observed with liquid crystals. In some cases unprecedented wavy parallel cracks showed the extension of the organization over the millimetric scale. It is the same for the X-ray diffraction. In all the cases precedently studied the X-ray diffraction diagrams exhibit diffraction peaks related to the length of the organic spacer. We observed here signals which did not correspond to this distance, suggesting a different nanometric scale organization in the solid.