Supported mesostructured thin films are of major importance for applications in optical, electrochemical and sensing devices. However, good performance is restricted to mesostructured phases ensuring good accessibility from the film surface, which would be straightforward with cylindrical pores oriented normal to the underlying support, but this remains challenging. Here, we demonstrate that electrochemistry is likely to induce self-assembly of surfactant-templated (organo)silica thin films on various conducting supports, homogeneously over wide areas. The method involves the application of a suitable cathodic potential to an electrode immersed in a surfactant-containing hydrolysed sol solution to generate the hydroxyl ions that are necessary to catalyse polycondensation of the precursors and self-assembly of hexagonally packed one-dimensional channels that grow perpendicularly to the electrode surface. The method is compatible with controlled and localized deposition on heterogeneous supports, opening the way to electrochemically driven nanolithography for designing complex patterns of widely accessible mesostructured materials.

Highly ordered and vertically oriented mesoporous silica films can be generated by electro-assisted self-assembly (EASA). The method involves the electrogeneration of hydroxide ions at an electrode surface immersed in an hydrolyzed sol solution (containing typically tetraethoxysilane, TEOS, and cetyltrimethylammonium bromide, CTAB) in order to catalyze polycondensation of the precursors and self-assembly of hexagonally packed one-dimensional channels that grow perpendicularly to the support. Vertically aligned mesostructures have been demonstrated by TEM imaging and by grazing incidence X-ray diffraction (GIXD), this latter technique enabling characterization of thin films directly on their underlying electrode surface. The influence of the electrosynthesis medium composition (precursor and surfactant concentrations, surfactant chain length) on the mesostructural order and film thickness has been thoroughly examined. It was shown that the highly ordered and oriented mesoporous silica films can be obtained over a wide composition of the starting sol (i.e., 10−200 mM CTAB and 50−350 mM TEOS) and that the lattice parameter can be moderately tuned by changing the chain length of the surfactant template. Thickness of these films can be accurately controlled by applying galvanostatic conditions and by varying the deposition time, which offer the versatility to be applied in the same way to electrodes of different nature without overpotential problems encountered in the potentiostatic mode. Thin mesoporous films are often covered with an additional byproduct made of particulate aggregates arising from bulk gelification at the electrode/solution interface. Getting aggregate-free thin films is possible by working in diluted solutions (i.e., [TEOS] < 125 mM and CTAB/TEOS ratio <0.32) and with a short deposition time (∼10 s). Voltammetric experiments carried out on these films deposited onto planar indium−tin-oxide electrodes, after template extraction, have revealed very sensitive responses to solution-phase redox probes as a result of fast mass transport from the external solution through the film to the electrode surface. Quantitative characterization of these mass transfer processes reveals that apparent diffusion coefficients as high as about 1 × 10−7 cm2 s−1 can be reached but great care should be taken in defining the film synthesis conditions that may lead to some additional limiting effects.

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