Preparation of highly ordered mesostructured tin oxide film with a microcrystalline framework through vapor-induced liquid-crystal templating

An optically transparent hexagonal mesostructured tin oxide film with a microcrystalline framework was prepared by combining dipcoating and a subsequent treatment with water vapor. After a substrate was coated with an alcoholic precursor solution containing tin tetrachloride and nonionic surfactant, the substrate was subject to a process to form a highly ordered mesostructured film on the substrate. Although the film after the simple drying process was opaque and showed only poor structural ordering, a short post-treatment with water vapor at low temperature significantly improved the transparency and the structural ordering of the film. It was proved that the longer low-temperature post-treatment induces the crystallization of the framework, preserving the ordered channel structure though vertical shrinkage of the periodic structure and degradation of the ordering were concomitantly observed. The post-treatment could not be replaced by the addition of water in the precursor solution. Though water was added to the system, the film was opaque and showed only poor structural ordering without the post-treatment. These results show that the present process cannot be a simple solvent evaporation process. It was shown that the formation of a lyotropic liquid-crystal phase induced by the exposure to water vapor before the completion of the condensation plays an essential role in the preparation process.