Sophie Besson

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.

Silver nanoparticle growth in 3D-hexagonal mesoporous silica films

The 3D-hexagonal mesoporous films are used as templates to grow uniform silver nanoparticles. The grafting of hydrophobic groups at the pore surface, significantly slows down the silver ion diffusion, anchoring small silver clusters in micropores and leading to organized domains of silver particles in mesopores with a narrow size distribution.

How can nanoparticles change the mechanical resistance of ordered mesoporous thin films

Abstract Nanoindentation was performed on mesoporous thin films in order to investigate their mechanical behaviour. It has been found that the empty mesoporous films behave plastically while films filled with nanoparticles exhibit more elastic deformations. This contrasting behaviour is consistent with the different indent morphologies observed by optical and electronic microscopy.

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.