In this paper, we report the complete synthesis and characterization procedures to generate highly organized and oriented mesoporous titania thin films, using poly(ethylene oxide) (PEO)-based templates. Controlled conditions in the deposition, postsynthesis, and thermal treatment steps allow one to tailor the final mesostructure (2D hexagonal, p6m, or 3D cubic, Im3m). Various techniques were used to determine the time evolution of the mesostructure. Spectroscopic techniques (UV/vis, (17)O NMR) and EXAFS/XANES have been used to follow the chemical changes in the Ti(IV) environment. Crossing these techniques spanning all ranges permits a complete description of the chemistry all the way from solution to the mesostructured metal oxide. A critical discussion on all important chemical and processing parameters is provided; the understanding of these features is essential for a rational design and the reproducible construction of mesoporous materials.

This article gives an overall view of the mechanisms involved in the mesostructuring that takes place during the formation of surfactant‐templated inorganic materials by evaporation. Since such a method of preparation is well suited to fabricating thin films by dip coating, spin coating, casting, or spraying, it is of paramount interest to draw a general description of the processes occurring during the formation of self‐assembled hybrid organic/inorganic materials, taking into account all critical parameters. The following study is based on very recent works on the meso‐organization of thin silica films using tetraethylorthosilicate (TEOS) as the inorganic source and cetyltrimethylammonium bromide (CTAB) as the structuring agent, but we will show that the method can also be extended to other systems based on non‐silica oxides and block copolymer surfactants. We demonstrate that the organization depends mainly on the chemical composition of the film when it reaches the modulable steady state (MSS), where the inorganic framework is still flexible and the composition is stable after reaching an equilibrium in the diffusion of volatile species. This MSS state is generally attained seconds after the drying line, and the film's composition depends on various parameters: the relative vapor pressures in the environment, the evaporation conditions, and the chemical conditions in the initial solution. Diagrams of textures, in which the stabilized structures are controlled by local minima, are proposed to explain the complex phenomena associated with mesostructuring induced by evaporation.

TiO 2 optical thin films stable to 700 °C, exhibiting 35% volume porosity, more than 100 m 2 ‚g -1 in surface area, fully nanocrystalline anatase framework, and organized mesostructure (cubic Im3m derived), have been stabilized by careful delayed rapid crystallization (DRC) thermal treatments. In-situ time-resolved SAXS and WAXS investigations were simultaneously performed during such treatments. They revealed that a slow and progressive heating to a temperature just below that of the formation of anatase (T c ≈ 400 °C), followed by a long pretreatment at this temperature, stabilizes the amorphous network. A following rapid increase of temperature up to temperatures as high as typically 700 °C, followed by a short residence time at this high temperature, provokes the homogeneous formation of crystalline small nanoparticles and the total elimination of organic residues. The crystallization is accompanied by matter migration through diffusing sintering and pore merging along the [111] directions of the cubic structure, leading to a novel grid-like mesostructure with open porosity. This DRC treatment allows the preparation of highly porous and crystalline anatase films, with thermal stability 200 °C higher than previously reported, that are ideal for energy transfer applications. This emphasizes the role of the treatment method to stabilize transition metal oxide mesoporous materials over extended crystallization at high temperatures. These films exhibit excellent long time stability below 500 °C.

A study is presented of the self-assembly process that takes place during CTAB-templated silica film formation through in situ SAXS, interferometry and water titration investigations during evaporation associated with dip coating under various conditions. This work shows that the quantity of water present in the film when the mesostructuration takes place depends on the relative humidity (RH) during deposition. Indeed, the system contains considerable quantities of water at high RH, while it loses water at low RH. The water content is demonstrated to be a critical parameter, as poorly ordered, 2D-hexagonal or 3D-cubic final structures are obtained, depending on the RH, in agreement with the general physico-chemical laws of CTAB mesophases. Furthermore, changing the RH or the solvent vapour pressure just after evaporation induces a film composition change and a potential mesostructure modification, evidencing a modulable steady state, during which the mesostructure can be modified by external influences. The present study pinpoints the role of processing conditions that are often considered secondary to chemical conditions. The conclusions of this study into the CTAB-TEOS system are also relevant to other surfactant-templated systems which undergo evaporation-controlled self-assembly.

We report the remarkable surface behavior of class II hydrophobin proteins HFBI and HFBII from Trichoderma reesei and the resulting effect that these proteins have on the stability of air bubbles to the process of disproportionation. The surface properties were studied using surface tensiometry and surface shear rheology. Surface tensiometry data show that hydrophobins are very surface active proteins, reducing the surface tension to approximately 30 mN m-1. The rate at which the hydrophobins adsorb at the surface may also be related to the self-assembly behavior in aqueous solution. We further show that hydrophobins form air/water surfaces with high elasticity, the magnitude of which is well in excess of that of surface layers formed by other common proteins used as foam or emulsion stabilizers. The measured surface properties translate to the stability of bubbles with adsorbed hydrophobin, and in this study, we demonstrate the ability of hydrophobin to have a dramatic effect on the rate of disproportionation in some simple bubble dissolution studies.

Various organic moieties are homogeneously introduced in high quantities into mesostructured porous silica films through a general co-condensation process, which influences the self-assembly mechanism, depending on the physico-chemical properties of each function.

No abstract

Supramolecular systems obtained by assembling molecular subunits through noncovalent interactions have been the focus of recent intense investigations. [1] In the last decade there has been a blossoming in the preparation of inorganic and organometallic macrocycles which have shown particular promise in the supramolecular chemistry of host ± guest interactions. [2] Cryptands, which are the most fascinating macrobicyclic systems, possess intramolecular cavities that are available for the encapsulation of ionic guests. [3] In a spectacular demonstration by Lehn and co-workers a bis-(tren) chelate receptor was used to encapsulate fluoride anions. [4] Recently Bowman-James and co-workers have elegantly shown that a bicyclic polyammonium receptor can encapsulate two nitrate anions. [5] Although the chemistry of organic cryptands is steadily expanding, less is known about metallocryptands. [6] Herein we report a rational high-yield (70 ± 85 %) strategy for preparing organometallic cryptands that is based on iridium coordination chemistry (Scheme 1) Scheme 1. General synthetic strategy for metallocryptands. and demonstrate their properties as anion hosts. Although the coordination chemistry of cations is well developed, the chemistry of anion encapsulation is still in its infancy: [7] only one example of a metallo-helicate encapsulating a PF 6 À ion has been described by Steel and co-workers and two supramolecular tetrahedron complexes encapsulating a BF 4 À ion have been reported by the groups of Huttner, and Ward and McCleverty. [8] To our knowledge no metallo-cryptate that encapsulates a polyfluoroanion has so far been reported.The novelty of our work is the use of [Cp*M(Solv) 3 ][BF 4 ] 2 (Cp* C 5 (CH 3 ) 5 , M Rh, Ir, Solv acetone) (1 a, b) complexes [9] as ªtripod connectorsº. These compounds possess piano-stool structures in which the h 5 -Cp* ligand remains firmly attached, whereas three weakly bound acetone molecules occupy the three legs of the tripod. In this work we have used diamines that were designed to coordinate to two different tripod connectors rather than to chelate to a single metal center. We sought the spontaneous and cooperative self-assembly of metallocryptands by combining two metal fragments and three diamines (Scheme 1).To demonstrate the viability of our strategy we prepared the bidentate ligand 1,3-bis(aminomethyl)-2,5-dimethoxy-4,6dimethylbenzene (2 a). Significantly, treatment of three equivalents of the diamine 2 a with two equivalents of tripod connectors 1 a or 1 b, prepared in situ, affords in one-pot reactions the rhodium and iridium cryptands [(Cp*M) 2 (2 a) 3 ][BF 4 ] 4 (3 a and 3 b), respectively, in 77 ± 85 % yield. The 1 H and 13 C NMR data recorded in CD 3 CN are consistent with the proposed formulas. Most remarkably, the resonances ascribed to the protons of the amino groups appear at very different fields: at d 5.12 (td, J 11.5, 4.4 Hz, 1 H) and at d 1.41 (br t, 1 H) for 3 a and at d 5.91 (td, J