This work describes the detailed structural investigation of mesophase-templated mesoporous silica films by 1D and 2D X-ray scattering techniques and transmission electron microscopy. The films are prepared by sol−gel dip coating with 2D hexagonal templating mesophases, yielding 2D mesoporous structures consisting of cylindrical pores whose axes are aligned parallel to the surface. It is shown that drying and thermal treatments induce an unidirectional shrinkage of the layers in the direction of the normal of the film. The true rectangular symmetry is only evidenced by 2D X-ray scattering in two different scattering geometries. 1D diffraction gives only an apparent hexagonal symmetry. It is furthermore shown that although the cylinder axes are randomly orientated within the plane parallel to the surface, there are large domains with well aligned 2D planar unit cells perpendicular to the surface. It is demonstrated that this preferential ordering is destroyed by nanoparticle seeding with amorphous silica or maghemite particles.

Hexagonal mesoporous silica layers were prepared by the sol±gel route using silicon alkoxides as silica precursors and alkyltrimethylammonium bromides to form the templating liquid crystal mesophase. The synthesis conditions required to obtain well-ordered crack-free layers were investigated. Thin layers exhibiting these properties were deposited from diluted sols. X-Ray diffraction enabled characterisation of the thermal evolution of their ordered structure and crystalline texture. Their porosity was experimentally measured from nitrogen adsorption±desorption analyses carried out directly on the thin layers. Two main synthesis parameters were identi®ed. The ®rst is the ageing time of the sol before deposition: 29 Si NMR showed that the disappearance of the ordered structure in the layers is related to the appearance of the Q 3 species in the sol. The second important synthesis parameter is the surfactant volume fraction in the medium after the removal of the volatile components. Using hexadecyltrimethylammonium bromide, well-ordered hexagonal layers were obtained for surfactant volume fractions ranging from 0.5 to 0.65, as expected from the corresponding water± surfactant binary diagram. For surfactants with shorter alkyl chains, the domain of existence of the hexagonal layers shifts to higher surfactant volume fractions in agreement with the evolution previously observed on the water±surfactant binary diagrams.

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We study the interplay between transport and adsorption in porous systems under a fluid flow, based on a lattice Boltzmann scheme extended to account for adsorption. We performed simulations on well-controlled geometries with slit and grooved pores, investigating the influence of adsorption and flow on dispersion coefficient and adsorbed density. In particular, we present a counterintuitive effect where fluid flow induces heterogeneity in the adsorbate, displacing the adsorption equilibrium towards downstream adsorption sites in grooves. We also present an improvement of the adsorption-extended lattice Boltzmann scheme by introducing the possibility for saturating Langmuir-like adsorption, while earlier work focused on linear adsorption phenomena. We then highlight the impact of this change in situations of high concentration of adsorbate.

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Hexagonal mesoporous silica layers were first prepared by the sol-gel route from solutions containing silicon alkoxides as silica precursors and alkyltrimethylammonium bromides to form the templating liquid crystal mesophase. The synthesis conditions required to obtain well-ordered crack-free layers were investigated. Two main synthesis parameters were identified. The first one is the aging time of the sol before deposition which defines the size of the inorganic cluster before the thin layer deposition and the simultaneous phase formation. The second important synthesis parameter is the surfactant volume fraction in the medium after the departure of the volatile components. Well-ordered hexagonal layers were obtained for surfactant volume fractions in agreement with the water-surfactant binary diagram. These synthesis conditions were extended to cubic and lamellar phases and to other types of surfactants, gemini (cationic surfactants with two polar head groups) and non-ionic triblock copolymers. First results concerning the extension of this approach to the preparation of alumina thin layers are finally presented.

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M. Klotz et al./Ice Templating of MicromonolithsFig. 4. Macroporous YSZ ice templated monoliths (a) macroscopic view (b) SEM micrograph perpendicular to ice solidification direction, showing the macroporous channels (c) mercury porosimetry results (d) SEM micrograph along ice solidification direction (e) SEM micrograph of the monolith washcoated with boehmite (f) close-up view of the washcoat, the arrows indicates the thickness of the coating. Scale bars (b) 50 mm, (d) 20 mm, (e) 2 mm, and (f) 250 nm.