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International audience; The electro-assisted self-assembly (EASA) of tetraethoxysilane (TEOS) and cetyltrimethylammonium bromide (CTABr) in hydro-alcoholic medium is now recognized to be a versatile method to generate highly ordered mesoporous silica films with unique orientation of mesopore channels normal to the underlying surface. In this work, we have evaluated the possibility to extend the method to aqueous media (i.e., without adding a cosolvent) and to determine the parameters affecting the EASA process and the resulting organization/orientation of the mesoporous framework by using electron microscopies and diffraction techniques. Contrary to water/cosolvent-based sols, the nature of the surfactant and supporting electrolyte counteranions (X-) was found to induce drastic variations on both the morphology and the mesostructural order of the deposits formed by electrochemically induced gelification (by pH increase) of CTAX/NaX-based silica sols. These changes are triggered by different surfactant assemblies arising from lower critical micellar concentration when passing from hydro-alcoholic to aqueous medium, and they are affected by the chaotropic-cosmotropic character of the counteranions. To be brief, cosmotropic anions (such as SO42-) promote the formation of thin films but suffering from poor or no ordering, whereas weakly bonded anions (such as Cl-) favor the mesostructuration but mainly in the form of particles or aggregates, while chaotropic anions (such as Br-) lead to rather thick deposits made of poorly organized aggregates. Mixing these anions, to get mixed micelles, enables compromises to be reached between these ``extreme'' behaviors and mesostructured thin films can be indeed obtained with the CTACl/Na2SO4 and CTABr/Na2SO4 media, exhibiting, respectively, some vertical or horizontal orientation of mesopore channels. This can be rationalized by taking into account the CTA(+), X- binding strength variations (Cl- < SO42- < Br-), thus affecting competitive binding of negatively charged silicate species, and sphere-to-rod transition abilities (SO42- approximate to Cl- < Br-) of the CTA(+)-based templates. Cyclic voltammetry was also used to characterize mass transport processes through the films. Finally, a preliminary work aiming at getting swelled pores of such electrogenerated films with mesitylene was carried out to evaluate the potential interest of the water-based EASA process for the entrapment of hydrophobic molecules inside the surfactant-silica phases.

International audience; Thin films with combined macropores (∼100 nm) and mesopores (∼3 nm) can be prepared by the electro-assisted deposition of a mesoporous silica material inside a polystyrene bead assembly. The filling of voids between the polystyrene beads template strongly depends on the deposition time, as demonstrated by systematic SEM analysis. Low deposition time leads only to very thin silica layers on the PS beads. Longer deposition time leads to the complete filling of the macroporous texture and to the growth of an additional overlayer with very well oriented pores normal to the electrode surface. The presence of mesopores into the film has been evidenced with using TEM, grazing incidence X-ray diffraction (GIXD), and Krypton sorption isotherm. The electrochemical characterization demonstrates that the hierarchical material is highly permeable to external reagents, being thereby promising for various applications involving such mass transport processes.

Ellipso-porosimetry and electrochemical techniques were used to characterize porosity and molecular transport into mesostructured porous silica thin films displaying various structures. The films have been prepared by the evaporation-induced self-assembly (EISA) method using cetyltrimethylammonium bromide (CTAB) as the template. According to previous investigations, the structure of the film can be controlled by the fine adjustment of the CTAB concentration and relative humidity during the dip-coating process. Films displaying p6m (2D hexagonal), P63/mmc (3D hexagonal), and Pm3n (cubic) nanoporous structures have been obtained (as revealed by XRD and TEM) and characterized after template removal by ethanol washing. Characterization of the film porosity has been performed on the basis of water adsorption−desorption cycles and ellipso-porosimetry measurements. They revealed significant contraction of the mesoporous structure when contacting water molecules, leading to a decrease in the pore diameter for bot...

Five different ordered mesoporous silica samples displaying various pore sizes and structures (two small-pore MCM-41, two large-pore MCM-41, and one small-pore MCM-48) and one amorphous silica gel have been grafted with either aminopropyl or mercaptopropyl groups. The resulting aminopropyl-grafted silicas (APS) and mercaptopropyl-grafted silicas (MPS) have been studied in solution via protonation of APS and metal ion binding on both APS and MPS. Special attention was given to characterize the accessibility to the binding sites and to the speed at which the reactants are reaching these reactive centers inside the mesoporous materials. Results have been obtained from batch experiments, by monitoring the reactant depletion in suspensions containing APS or MPS particles, and discussed with respect to the structure and porosity of the organic−inorganic hybrids. As a general trend, both accessibility and rate of access to the reactive sites were higher with ordered mesoporous solids than with amorphous material...