Muriel Matheron

Highly ordered CTAB-templated organosilicate films

Well-ordered organic–inorganic mesoporous films are prepared using an original two-step synthesis and compositions up to 50 mol% methyltriethoxysilane (MTES). These materials exhibit the three different mesostructures (2D-hexagonal, 3D-hexagonal and cubic) previously observed in the pure silica system with significant modifications of their domain of stability. During deposition and drying of organosilicate films, MTES monomers progressively condense at the internal surface of the silica clusters in agreement with the monomer–cluster growth model, leading to a significant reduction of the microporosity in the silica walls of the mesoporous structure.

Stabilization of well-organized transient micellar phases in CTAB-templated silica and organosilica thin films

The influence of some previously reported critical parameters (aging of the silica sol, humidity, % of trivalent precursor) controlling the nature and the degree of organization of mesophases is studied in detail for CTAB-templated silica and organosilicate films prepared by rapid evaporation techniques. It is shown that all of these parameters directly influence the silica-condensation kinetics. Concerning films with the 2D-hexagonal structure belonging to the CTAB-water phase diagram, the mesophase is mainly stabilized by interactions between cylindrical micelles, and the reactivity of the silica sol does not drastically modify the extent of the order in films. In contrast, the formation of a rigid silica network just after the micellar organization appears to be crucial to prepare well-organized films with the 3D-hexagonal or the cubic transient structure. In the latter case, the size and reactivity of silica clusters have to be controlled to obtain rapid gelation in the deposited sol.

Nanostructured Sol-Gel Coatings for Optical Applications

Well-ordered organosilicate mesoporous coatings with the 3D-hexagonal symmetry are prepared by the sol-gel technique. These films contain high amounts of hydrophobic methyl groups at the pore surface and do not absorb moisture making possible their use as low-index layers in interferential antireflective devices. Besides, these films also appear as good hosts for photochromic dyes leading to coatings for optical switching devices. Methyl groups and mesoporosity offer optimized environments for photochromic dyes dispersed by multiimpregnation technique.

Ordered mesoporous organosilica films

Publisher Summary This chapter demonstrates that the optical and mechanical properties of mesoporous silica films provide the possibility to use them as low-index or low dielectric constant coatings. However, the surface of the pores must be carefully controlled to avoid any introduction of contaminations. This implies a chemical modification of the surface of the pores, which must be performed without ignoring the structure of the porosity (proportion and accessibility of micropores and mesopores). A first possibility consists in a post-synthesis gaffing with a reactive silane (chlorosilane, silazane, or alkoxysilane), but some more work is required to optimize this passivation strategy. Other functionalization processes such as the direct co-condensation of organic/inorganic silica precursors are also investigated. In any case, the functional organic group must be chosen to efficiently block the accessibility of the pores, either because of its bulky nature or because of its hydrophobic and oleophobic nature.

Photochromic mesoporous hybrid coatings

Spirooxazine (SO) photochromic molecules were trapped in sol-gel matrices. In order to increase the colourability and improve mechanical properties of sol-gel photochromic films, we present an original strategy in which SO photochromic molecules were dispersed in mesoporous organized films using the impregnation technique. Well-ordered organosilicate mesoporous coatings with the 3D-hexagonal symmetry were prepared by the sol-gel technique. These robust mesoporous films, which contain high amounts of hydrophobic methyl groups at the pore surface, offer optimized environments for photochromic dyes dispersed by impregnation technique. After impregnation by a spirooxazine solution, the photochromic response is only slightly slower when compared with mesostructured or soft sol-gel matrices, showing that mesoporous organized hybrid matrix are good host for photochromic dyes. Moreover, the molecular loading in films is easily adjustable in a large range using multi-impregnation procedure and increasing the film thickness leading to coatings for optical switching devices.