Showing papers by "Florence Babonneau published in 2002"

An in Situ Study of Mesostructured CTAB−Silica Film Formation during Dip Coating Using Time-Resolved SAXS and Interferometry Measurements

Abstract: Silica thin films with ordered porosity can be prepared by dip coating, combining polycondensation of silicate species and organization of amphiphilic mesophases. This paper reports on the preparation of templated films using cetyltrimethylammonium bromide (CTAB) as the surfactant and tetraethoxysilane (TEOS) as the inorganic precursor. Depending on the CTAB/Si molar ratio, films with different porous networks3D hexagonal (P63/mmc), cubic (Pm3n), and columnar hexagonal (p6m)were obtained. Identification of the structures was accomplished by coupling two-dimensional X-ray diffraction at grazing incidence and TEM investigations on film cross sections. Other experimental parameters (e.g., deposition rate and composition of the starting sol, including its aging time) appeared also to influence the degree of organization of the final films greatly. To obtain a better understanding of the self-assembly mechanism, the structural formation of the films was followed in real time by in situ SAXS. Because of the ver...

In-Situ SAXS Studies on the Formation of Silicate/Surfactant Mesophases with Solubilized Benzene under Acidic Conditions

Abstract: The formation of mesoscopically ordered silica/surfactant composites under acidic synthesis conditions is studied by time-resolved in-situ small-angle X-ray scattering (SAXS) using synchrotron radi...

Directing role of pH and ethanol vapour on the formation of 2D or 3D mesostructured silica and hybrid organo-silica thin films

Abstract: A simple synthetic route leading to ordered mesostructured silica and organo-silica thin films is investigated by in situ X-ray experiments. The mesophase directing role of pH and of ethanol vapour pressure during film formation is demonstrated. Modifications of these two parameters during dip coating results in three different 2D or 3D mesostructures (p6mm, P63/mmc, or Pm3n).

Synthesis and characterization of periodic porous benzene-silica hybrid powders with cubic and hexagonal symmetries

Abstract: Organosilica powders with uniformly distributed bridging benzene groups have been synthesized from the condensation of bis- or tris-(triethoxysilyl)benzene in the presence of cetyltrimethylammoniumbromide. The syntheses were performed under strong acidic conditions and the organic groups were always incorporated without cleavage of the Si-C bonds as indicated by solid state MAS NMR studies. Depending on the nature of the precursors, materials with different ordering were obtained: a 2D-hexagonal (p6m) phase was formed from the 1,3-bis(triethoxysilyl)benzene, whereas the 1,4-bis(triethoxysilyl)benzene lead to a cubic Pm3n phase. The surfactant was removed either by solvent extraction or by controlled calcination, which did not affect the mesostructure of the materials.

Microstructural evolution and order-disorder transitions in mesoporous silica films studied by FTIR spectroscopy

Abstract: Silica mesoporous thin films have been synthesised with a self-assembling process employing cetyltrimethylammonium bromide as the organic template and tetraethyl orthosilicate as the silica source. Mesoporous films with Pm3n cubic phase phases have been obtained and the films have been thermally treated in air with a progressive heating schedule from asdeposited up to 1000°C. The evolution of the microstructure has been studied with transmission Fourier transformed infrared (FTIR) spectroscopy. FTIR spectra of the as-deposited films have shown the presence of cyclic species, which at temperatures larger than 350°C have been no more observed. In the 1000–1300 cm-1 region several overlapped absorption bands have been detected. In particular, the pair LO3-TO3, the cyclic species absorption bands and the pair LO4-TO4 have been resolved. These last bands, in particular, are associated with disorder-order transitions in the silica microstructure. These disorder-induced optical modes are due to the large interface area and related to bond strains. The evolution of the bands in the 1000–1300 cm-1 region has been followed with the Berreman configuration, performing the transmission FTIR analysis at 45° with respect to the normal incidence angle. The LO3 band, which in silica sol-gel films is indicative of the network condensation and is activated by scattering of the light in the pores, was resolved as a single sharp band from 250°C.