Catherine Jacquiod

Phase diagram for mesoporous CTAB–silica films prepared under dynamic conditions

Using θ–2θ and grazing incidence synchrotron X-ray diffraction experiments, the domain of existence of the different phases is established for spin-coated mesoporous silica films as a function of the surfactant/Si molar ratio and the condensation rate of the initial silica sol. These phases derive from three different micellar structures: the 3D-hexagonal structure (P63/mmc), formed from spherical micelles, the cubic structure (Pm3n), made up of ellipsoidal micelles, and the 2D-hexagonal structure (p6m), composed of cylindrical micelles. Electron microscopy investigations show that the organization of films is generally maintained after removal of the surfactant by calcination. However, structural distortions take place in mesoporous films as a consequence of the usual contraction during drying and calcination of films.

Structural study of 3D-hexagonal mesoporous spin-coated sol–gel films

Mesostructured films deposited on glass substrates by spin coating are studied by X-ray diffraction, small angle X-ray scattering using grazing incidence (GISAXS) and high resolution electron microscopy. The films generally present a gradient of ordering from the air/sol interface to the interior of the film, with a 3D-hexagonal mesophase near the surface and a disordered micellar structure at the interior. However, the 3D-hexagonal ordering and the texturing can be extended over all the film thickness by adjusting the composition of the deposited solution. In particular, critical values are clearly observed both for the size of silica units forming the walls in the mesophase and for the film thickness. All these results can be understood from the competition between structuration and gelation of the films during alcohol removal.

Ag nanoparticles synthesised in template-structured mesoporous silica films on a glass substrate

Ag nanoparticles have been synthesised within a mesoporous template-structured silica film by a chemical route which includes ion-exchange with Ag(NH3)2+ followed by reduction.

Synthesis of Transparent Mesoporous and Mesostructured Thin Silica Films

A novel method for obtaining crack-free transparent periodic mesoporous thin films is described. Such films are prepared by a simple sol-gel process using surfactants as templates, with a pre-treatment of the glass substrate. The silicate precursor (tetraethoxysilane) is pre-hydrolyzed under acidic conditions before dissolving directly cetyltrimethylammonium bromide (CTAB). The solution is then spin-coated on pre-treated glass substrate. After the film has been deposited, it is calcined in air. X-ray Diffraction (XRD) has been used to characterize the film before and after thermal treatment. The film consists of a nanocomposite material with a periodic structure. Before calcination the XRD pattern has a sharp peak at d = 3.8 nms which is broadened and shifted by about 3.0 nm after calcination. Infrared transmission spectra have been performed on the films. Analysis of the free OH group stretching vibration indicates the removal of the surfactant after calcination in addition to an enhancement of the specific surface area.

Infrared Evidence for Hoffman Reaction During Calcination of Surfactant-Templated Silica Films and Analysis of the Resulting Surface Sites

Fourier Transform Infrared transmission spectroscopy is used to characterize surfactant-templated silica films on glass. The calcination process is followed in situ and evidence for the removal of the surfactant along the Hoffman reaction is given. Once calcined, the surface of the pores of the mesoporous films is proven by deuteration experiment to be hydroxylated. Bands are attributed to isolated and hydrogen-bonded silanols. Silylation reaction with hexamethyldisilazane only occurs with isolated silanol groups.

New Structure of CTAB Templated Silica Films as revealed by GISAXS coupled to HRTEM

A microstructural study on surfactant templated silica films is performed by coupling traditional X-Ray Diffraction (XRD) and Transmission Electronic Microscopy (TEM) to Grazing Incidence Small Angle X-Ray Scattering (GISAXS). By this method it is shown that spin-coating of silicate solutions with cationic surfactant cetyltrimethylammonium bromide (CTAB) as a templating agent provides 3D hexagonal structure (space group P6 3 /mmc) that is no longer compatible with the often described hexagonal arrangement of tubular micelles but rather with an hexagonal arrangement of spherical micelles. The extent of the hexagonal ordering and the texture can be optimized in films by varying the composition of the solution.