Insight into the Molecular Self-Assembly and Structural Organization of Mesoporous Hybrid Silica Films with Binary Composition

Despite the large amount of work reported on mesoporous hybrid organic–inorganic films, the organization of functionalities in the pores remains very poorly documented and understood. Comprehension of the molecular self-assembling processes in hybrid mesoporous films is crucial to control the localization of functional groups and functional domains in the pores and, thus, the overall properties of the final material. This work is devoted to the fundamental understanding of the process at the molecular level using model precursors. Ordered mesoporous silica thin films are prepared by the co-condensation sol–gel process between hybrid and nonhybrid precursors. Self-assembly of the mesophase is achieved by the templating method using an ionic surfactant. Bromoalkylsilanes with different chain lengths are chosen as the model molecules because of the weak interactions at the molecular level. The influence of several parameters (length of the alkyl chain, concentration, relative humidity) on the film mesostructure is evaluated by small-angle X-ray scattering (SAXS), environmental ellipsometric spectroscopy (EEP), and transmission electron microscopy (TEM). A relationship between those parameters and the mesophase arrangement, pore size distribution, porosity, and Young’s modulus is established. Moreover, a simple method to estimate the average number of molecules per pore and the number of pores per volume unit is proposed, bringing quantitative insight into the film organization at different scales.