In situ X-ray reflectivity and GISAXS study of mesoporous silica films grown from sodium silicate solution precursors

An environmentally friendly and inexpensive silica source, sodium silicate solution, was applied to synthesize a free-standing mesoporous silica film at the air/liquid interface, exploiting the co-assembly of cetyltrimethylammonium bromide and polyethylenimine. The effect of the composition of the solution used for the film formation on the mesostructure of the as-synthesized silica films, characterized by small angle X-ray scattering (SAXS), was investigated. The initial film formation time is estimated by the change in surface pressure with time. Additionally, a possible formation process of the mesostructured silica film is proposed using data from in situ grazing incidence small angle X-ray scattering (GISAXS) and X-ray reflectivity (XRR) measurements. A free-standing film with a wormlike structure was formed at the interface and reorganized into a 2D hexagonal ordered structure while drying at room temperature, after removal from the air/solution interface. The ordered 2D hexagonal structure, however, could only be retained to some extent during calcination, in samples where nitrate ions are present in the film formation solution.