Silica-surfactant mesostructured

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. 

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. 

Muto, S. Oaki, Y. Imai, H. Incorporation of dyes into silica-surfactant mesostructured nanoparticles as a nanoscale host material for organic molecules. Chem. Lett. 2006,35, 880-881. 

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)... 

Ogawa M. Incorporation of pyrene into an oriented transparent films of layered silica-hexadecyltrimethylammonium bromide nanocomposite. Langmuir 1995 11 4639 641 Ogawa M. A simple sol-gel route for the preparation of silica-surfactant mesostructured materials. Chem. Commun. 1996 1149-1150... 

Ogawa M. Preparation of transparent thin films of silica-surfactant mesostructured materials. Supramol. Sci. 1998a 5 247-251... 

S.H. Tolbert, C.C. Landry, G.D. Stucky, B.F. Chmelka, P. Norby, J.C. Hanson, and A. Monnier, Phase Transitions in Mesostructured Silica/Surfactant Composites Surfactant Packing and the Role of Charge Density Matching. Chem. Mater., 2001, 13, 2247-2256. 

The type of mesostructure obtained depends strongly on the surfactant to inorganic ratio. In fact, there is a close correlation between the surfactant to solvent ratio in the phase diagram of a surfactant and the surfactant to inorganic ratio in the mesostructured materials obtained. Alberius et al. demonstrated this correlation by the so-called general predictive synthesis approach. They used the phase diagrams of the water-surfactant system to guide the synthesis of mesoporous silica and titania films. There was a very close correlation between the values of the volume fraction of the surfactant over which different phases are obtained in the water-surfactant system and in the silica-surfactant and titania-surfactant systems. 

Dye-containing mesostructured silica and zeolitic materials are interesting for their potential application in optical devices and as chemical sensors. Congo Red and Curcumin, two pH indicators, have been incorporated in MCM-41. precursors, which have been characterised by means of X-ray diffraction, UV-Visible and FTIR spectroscopy. Dyes are located in the micellar phase of the silica-surfactant mesophase and their spectroscopic properties confirm that they are in a solvated state, where both surfactant and silica wall may act as a solvent. Dyes maintain their pH indicator properties and are accessible to gases such as HCl and NH3. 

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 24-14. Off-specular X-ray reflectivity patterns showing the time-dependent growth of the first order diffraction peak for mesophase silica-surfactant films grown at the surface of a dilute acidic solution with a TMOS/CuTABr molar ratio of (a) 10.87 and (b) 7.25. At the higher TMOS/CuTABr ratio the film grows at the surface by addition of silica-coated surfactant micelles so the diffraction peak becomes narrower as the domains grow into solution, and more intense as the interface is covered. At the intermediate TMOS/Cu TABr ratio the film grows by packing at the interface of mesostructured particles formed in the bulk solution so the peak widtii does not change, but the intensity increases as the interface is covered.

Patterning. Patterned mesostructured silicate surfactant films have been grown from solution onto gold surfaces that had been modified with self-assembled monolayers (SAMs) of hexadecanethiolate stamped onto the surface (Coombs, 1997 Yang, 1997b). At 80°C deposition of mesostructured silica-surfactant composite from an acidic TEOS/CieTACl... 

Feng J., Huo Q., Petroff P.M., Stucky G.D. Morphology definition by disclinations and dislocations in a mesostructured silicate crystal. Appl. Phys. Lett. 1997 71 1887-1889 Ferrer M., Lianos P. Study of silica-surfactant composite films with fluorescent probes. Langmuir... 

Nishiyama N., Tanaka S., Egashira Y., Oku Y., Ueyama K. Vapor-phase s)mthesis of mesoporous silica thin films. Chem. Mate. 2003 15 1006-1011 Noma T., Takada K., Miyata H., lida A. X-ray micro diffraction study on mesostructured silica thin films. Nucl. Instrum. Methods Phys. Res. A 2001 467 1021-1025 Ogawa M. Formation of novel oriented transparent films of layered silica-surfactant nanocomposites. J. Am. Chem. Soc. 1994 116 7941-7942... 

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