Silica thin films with a two-dimensional (2D) hexagonal structure were produced from TEOS and the F127 triblock copolymer PEO106PPO70PEO106. The structure of the films was deduced from transmission electron microscopy (TEM) performed on microtomed sections and from a 2D X-ray scattering technique adapted for film characterization. Both methods are complementary and allow for a detailed characterization of the film structure. The pore channels within the coatings are organized in domains, which spin and curve inside the film, but align with the surface plan at the air/film and film/substrate interfaces. The formation of the film was monitored by in situ time-resolved SAXS experiments to follow the structural evolution during the first minutes after deposition. Cylindrical micelles, which gives rise to a wormlike structure, form first at the air/film interface and extend toward the film/substrate interface via solvent evaporation. When most of the liquid phase is evaporated, the well-aligned domains located at both interfaces are obtained by a self-arrangement of the micelles parallel to the interfaces. This rearrangement occurs when the film is considered to be dry. The atom content profiles in the as-prepared films were obtained by Rutherford backscattering (RBS) and show homogeneous distribution of atoms throughout the film thickness. To stiffen the network and remove the surfactant, various postsynthesis treatments were applied to the coatings, that is, thermal treatment, base-catalyzed condensation, and solvent extraction. Each method induces shrinkage, leading to 2D-centered rectangular films through a contraction of the initial 2D hexagonal structure. As-prepared and treated films exhibit excellent optical transparency and high degree of organization. Ellipsometry measurements and N2 adsorption/desorption isotherms were thus used to estimate the refractive index and the porosity of the films. Refractive index down to 1.2 was obtained in the film that was pretreated under a NH3 atmosphere before solvent extraction of the surfactant. This shows the efficiency of this treatment to minimize the network shrinkage. N2 adsorption-desorption measurement performed on films calcined at 350 °C gives a surface area of 800 m2 g-1 and a porosity of 63%.@en

Since mesoporous materials can be prepared by combining the sol-gel chemistry and the structuring effect of surfactants, they have attracted attention for application in various high technology fields. The present work deals with the analyses of the mechanisms involved in the formation of SiO2 and TiO2 highly organised 2D-hexagonal meso-structured films using Brij 58 as surfactant. The preparation of such films by dip-coating involves rapid evaporation which makes the different steps difficult to control. Simultaneous in-situ SAXS (synchrotron) and interferometry analyses have been performed to get a first understanding of the self-assembly process. SiO2 and TiO2 materials have a different chemical reactivity (kinetics and coordination aspects). However, we show that the mechanisms involved during dip-coating are quite similar : The self-assembly leading to the organised phase takes place at a final stage of the drying process, involves the formation of a disorganised intermediate phase and depends also on the presence of micellar interfaces in addition to film/air and film/substrate interfaces.@en

The synthesis and characterisation of hybrid organic-inorganic mesoporous thin films made from organosiloxane precursors are presented. Three-dimensional mesostructures (P63/mmc, Pm3n) have been obtained and their formation is related to dip coating conditions and sol compositions. Calcination at moderate temperatures allows the removal of the templating surfactant without destroying the organic functions covalently bonded to the porous network.@en

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 networks - 3D 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 very fast self-assembly process ( <30 s), high-flux synchrotron radiation was used, which allows to record good quality X-ray patterns in 100 ms. For the first time, interferometry measurements were also combined with the SAXS experiments to correlate the organization steps detected during dip coating with the thickness profiles. A model has thus been proposed for the film formation: organization at the mesoscale (i) takes place at the final stage of liquid-phase evaporation; (ii) involves the formation of micelles at the film/air interface in the early stage of deposition and, in some cases, the formation of intermediate phases; and (iii) is influenced by the condensation degree of inorganic intermediates, the surfactant concentration, and the deposition external conditions.@en

Highly oriented 3D-hexagonal silica thin films have been produced on silicon substrates by dip-coating technique, using cetyltrimethylammonium (CTAB) bromide as structuring agent. For the first time, time-resolved in situ X-ray diffraction experiments have been used to investigate the formation of such mesostructured films. Interestingly, the data shows that an intermediate mesophase appears just after film deposition (t<500 ms), characterized by one diffraction peak centered at a d spacing of 65 Å. Then after 20 s, another mesophase appears with a shorter d spacing (44 Å), which corresponds to the 3D-hexagonal structure found for the final dried film.@en