Preparation of ordered and oriented mesoporous silica thin films bearing octyl or hexadecyl groups by electrochemically assisted self-assembly and evaluation of their transport properties
Résumé
Well-organized octyl-and hexadecyl-functionalized mesoporous silica thin films are generated onto indium-tin oxide electrodes by combining the electrochemically assisted self-assembly technique and the sol-gel co-condensation route. The electrodeposition is carried out under potential control from mixtures containing various molar ratios of tetraethoxysilane and octyltrimethoxysilane (O-TES) or hexadecyltrimethoxysilane (HD-TES), using cetyltrimethylammonium bromide as surfactant template. Films with hexagonally packed functionalized mesochannels oriented perpendicular to the underlying support are obtained up to, respectively, 20% O-TES and 5 % HD-TES introduced in the starting sol. Electrochemical investigations using various redox probes demonstrate that the films remain porous despite the presence of long carbon chains inside the mesochannels and that, in the presence of such long chain alkyl groups, the physical diffusion through the pores is not sufficient to describe the mass transport issues, which can also imply accumulation effects owing to the hydrophobic character of the medium.