Free-Standing Ordered Mesoporous Silica Films Synthesized with Surfactant-Polyelectrolyte Complexes at the Air/Water Interface

Solid cetyltrimethylammonium bromide (CTAB) and polyethylenimine (PEI) films self-assemble at the air/water interface. Small angle X-ray scattering (SAXS) measurements show that dried films maintain the same ordered mesostructure as the films at the air/water interface, and here the effects of PEI concentration and cross-linker (CL) on film mesostructure were investigated. Free-standing silica films were then synthesized by adding tetramethoxysilane (TMOS) to the surfactant-polyelectrolyte solutions. Silica films have been studied by Brewster angle microscopy (BAM) and neutron reflectivity on assynthesized films at the solution surface. Dried films have also been examined by SAXS and thermogravimetric analysis (TGA). On the basis of neutron reflectivity and SAXS data, a phase diagram for the CTAB-PEI-TMOS system has been drawn, and we propose a model for the formation of silica films synthesized with surfactant-polyelectrolyte complexes. The silica films retain their ordered mesostructure after surfactant removal, and polymer remains inside the silica wall when the surfactant has been washed out, which improves the mechanical properties of the films and may be used to add functionality to these membranes in future applications.