Silica films mesostructured

Grosso, D. Babonneau, F. Albouy, P. A. Amenitsch, H. Balkenende, A. R. Brunet-Bruneau, A. Rivory, J. 2002. An in situ study of mesostructured CTAB-silica film formation during dip coating using time-resolved SAXS and interferometry measurements. Chem. Mater. 14 931-939. 

Supplit, R Husing, N. Gross, S. Bernstorff, S. Puchberger, M. 2007. Hafnium oxide doped mesostructured silica films. Eur. J. Inorg. Chem. 2797-2802. 

The immobilization of photoactive species into the silica-surfactant mesostructured materials is worth investigating toward future photofunctional materials. Photochemistry on solid surfaces is a growing new field which yields a wide variety of useful application such as sensitive optical media, reaction paths for controlled photochemical reactions, molecular devices for optics, etc. [17] Along this line, the incorporation of organic dyes into silica-surfactant mesostructured materials [17-20] as well as nanoporous silica films[3] have been reported so far. 

The thin film of silica-surfactant mesostructured material was prepared by the reactions of TMOS and C18TAC, as reported previously[3]. The film was calcined in air to prepare nanoporous silica films. The adsorption of the dye onto the nanoporous silica film was conducted either by immersing the calcined film into an ethanol solution of the dye or casting the solution onto the film. 

By spin coating the mixture containing the prehydrolyzed TMOS and a 0.2 M aqueous solution of C18TAC (pH=2, at the molar ratio of TMOS C18TAC=9.2.T), a transparent thin film formed on the substrate. The X-ray diffraction pattern of the film (Figure 1a) showed a sharp diffraction peak with the d value of 4.6 nm, which accompanied the 2nd order reflection. In order to remove the surfactants from the substrate to obtain porous silica films, the as coated film of the silica-surfactant mesostructured material was calcined in air at 450 °C. Sharp diffraction peak was observed in the XRD pattern of the calcined film... 

Figure 1b), showing that the ordered microstructure was retained even after the removal of surfactants. The d value of the calcined film was 4.1 nm. The SEM image of the film surface (data not shown) also indicates that the film is continuous and crack free. These observations are well consistent with those reported in the previous paper[2], showing the formation of silica-surfactant mesostructured material and the successful transformation of the as coated film into a nanoporous silica film. 

Coating substrates with mesostructured silica film... 

The synthesis of mesoporous silica films typically begins with the preparation of precursor solutions. These solutions contain a silica source (typically an alkoxide, although chloride and colloidal precursors can be used), a surfactant molecule used to template the mesostructure, an acid or base catalyst, and solvents. The nanoscale structure is then formed by a cooperative self-assembly of monomeric or partially... 

To determine the success of synthesis efforts and to provide feedback on quality control, the mesoporous silica films are characterized by several techniques. The ability to determine the continuity and quality of the films must be quick and accurate. Owing to this fact, x-ray diffraction has proven the easiest way to resolve the film structure. However, phase identification by x-ray diffraction alone is not always conclusive (e.g., when only one peak is observed). Other techniques must be employed to fully determine the phase of the mesostructure. 

Ogawa, M. Kikuchi, T. Preparation of self-standing transparent films of silica-surfactant mesostructured materials and the conversion to porous silica films. Adv. Mater. 1998,10 (14), 1077. 

TEM micrographs of bimetallic catalysts revealed the presence of randomly accessible ordered domains as well as the partly disordered mesostructure of silica films (Figure 4). The nanoparticles of Ru-Pt have a mean size of 1.4 nm with a narrow particle size distribution (Figure 5). However, the TEM image also shows the small agglomeration of nanoparticles due to the absence of a local mesostructure. 

Mesostructured thin silica films can be prepared as freestanding films or supported by a variety of different substrates. In the following, a short description of the different synthesis methods is given the synthesis and the formation mechanism of mesoporous silica films has been reviewed in detail elsewhere. " ... 

Electrodeposition or pulsed-laser deposition techniques are additional possibilities for forming thin mesostructured films. These techniques have mainly been applied to non-silica mesostructured films such as niobia or platinum, but also hexagonally oriented mesoporous silica films were prepared by pulsed-laser deposition. ... 

The application of a 11-ferrocenylundecyl-ammonium bromide/hexa-decylammonium bromide surfactant mixture as structure-directing agent resulted in a lamellar mesostructured silica film, which showed electronic conductivity due to electron transport in the ferrocenyl chains. Lyotropic lithium triflate-silicate liquid crystals have been utilized as supramolecular templates in the synthesis of ionically conducting nanocomposite films. ... 

Figure 2.2 Schematic of a cross-section along the pore of a mesostructured film showing the functionalisation of surfactant templated silica in different locations using functional alkoxysdanes. White boxes show pairs of molecules incorporated simultaneously into silica films by Minoofar et al. Reprinted with permission from Minoofar, P.N. Hernandez, R. Chia, S. Dunn, B. Zink, J.I. Franville, A.-C., Placement and Characterization of Pairs of Luminescent Molecules in Spatially Separated Regions of Nanostructured Thin Films, J. Am. Chem. Soc., 124, 14388-14396. Copyright 2002 American Chemical Society...

Summary Well-defined amphiphilic block copolymers containing a poly(dimethyl siloxane) (PDMS) and a poly(ethylene oxide) (PEO) block were synthesized by ringopening polymerization of hexamethylcyclotrisiloxane, followed by chain extension with a PEO block of a defined length. These amphiphilic molecules were used as structure-directing agents in a solvent evaporation-driven synthesis approach to self-assembled mesostructured silica films. In addition, a general theoretical approach for an understanding and ultimately a prediction of the phase behaviour of block copolymers is presented. 

For the PDMS-b-PEO diblock copolymer surfactant, mesostructured silica films were successfully synthesized. Figure 1 shows examples of the X-ray diffraction patterns of a film prepared with E08-f>-DMSi8 a) prior to and b) after calcination at 450 °C/3 h. The reflections at a d-spacing of about 48 nm clearly indicate the presence of ordered domains in the film. 

Figure 24-2. ID X-ray diffraction patterns of different as-synthesized (bottom) and calcined (top) silica films approximately 200-500 nm in thickness with (a) lameUar, (b) hexagonal, and (c) cubic mesostructural ordering. The diffraction patterns are indexed according to the different symmetries (lamellar, 2D hexagonal p6mm, and body-centered-cubic ImSm). The absence of, e.g., the (1 1 0) reflection in the hexagonal film is due to preferential orientational ordering of the cylindrical mesostructures parallel to the substrate. (Reprinted with permission from Alberius (2002) 2002 American Chemical Society)...

P ure 24-7. The mesostructures of the products prepared at various TMOS CTAC ratios and pH-values Letters denote the observed mesophases L lamellar, H hexagonal, C cubic, and C cubic or hexagonal. (Reprinted from Microporous Mesoporous Mater., 38, M. Ogawa and N. Masukawa, Preparation of transparent thin films of lamellar, hexagonal and cubic silica-surfactant mesostructured materials by rapid solvent evaporation methods, 35-41 > 2000 with permission from Elsevier Science)... 

Structural contraction during calcination of evaporation induced films is frequently observed due to the low degree of silica condensation in as-prepared films that are deposited at ambient temperatures. A uniaxial distortion of the film mesostructures in the direction perpendicular to the substrate is common both during solvent evaporation and during calcination for aU observed mesostmctures (Grosso, 2000). This can cause an initially 2D... 

Some discrimination between different alcohols is evident (Innocenzi, 2001b). Spin coated silica films with a cubic structure have also been incorporated into a surface photovoltage gas sensor (Yamada, 2002). Dip coated mesoporous thin films on a macroporous or mesoporous support have been prepared for separation membrane applications (Kim, 2002, 2003). Spin coating has also been used to deposit CieTABr templated films where the silicate walls were composed of nanosized zeolite MFI crystals co-deposited with the TEOS solution (Petkov, 2003).The continuous film contained a wormlike mesostructure and zeolite nanocrystals aligned with the a-axis perpendicular to the substrate, however the surface roughness of the film was increased. 

Bard M.H., Scott B.J., Huang H.C., Wirnsberger G., Popitsch, A., Chmelka B.F., Stucky G.D. Synthesis and luminescence properties of mesostructured thin films activated by in-situ formed trivalent rare earth ion complexes. Chem. Commun. 2002 2474-2475 Baskaran S., Liu J., Domansky K., Kohler N., LiX., Coyle C., Fryxell G.E., Thevuthasan S., Williford R.E. Low dielectric constant mesoporous silica films through molecularly tenqilated synthesis. Adv. Mater. 2000 12 291-294... 

Edler K.J., Goldar A., Brennan T., Roser S.J. Spontaneous mesostructured film growth in polyelectrolyte-surfactant solutions. Chem. Comm. 2003b 1724-1725 Edler K.J., Goldar A., Hughes A.V., Roser S.J., Mann S. Structural studies on surfactant-templated silica films grown at the air/water interface. Microporous Mesoporous Mata-. 2001 44/45 661-670... 

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