A pure aqueous route to mesoporous silica thin films via dip-coating of prefabricated hybrid micelles

Abstract

Mesoporous thin films were prepared by dip-coating with a purely aqueous method, as a substitute for the alcohol-based evaporation-induced self-assembly route. Unlike other aqueous routes that require a very slow pulling rate possible only using high performance dip-coaters, as a result of the high surface tension of water, this new process works with standard dip-coaters and at similar pulling rates as are used for the evaporation-induced self-assembly route. This unique asset is the result of the synthesis of prefabricated self-assembled silicate/organic hybrid micelles. These building blocks are concentrated before use, which provides a gelling edge after moderate evaporation. As a result, defect-free continuous mesoporous films with well-organized hexagonally packed pores were prepared after optimization of both the evaporation rate of the solution of hybrid micelles and the dip-coater pulling rate. The transmission electron microscopy observation reveals the hexagonally packed structure of mesoporous silica film. This nanostructure has already been observed on films prepared with the evaporation-induced self-assembly process, but it is the first time it is obtained with a pure aqueous method, based on prefabricated hybrid micelles, not on controlled evaporation of mesophases.