Ömer Dag

A New Lyotropic Liquid Crystalline System: Oligo(ethylene oxide) Surfactants with [M(H2O)n]Xm Transition Metal Complexes

Coordinated water molecules induce the aggregation and self-assembly of the lyotropic liquid crystalline phase formed from non-ionic surfactants Cn H2n+1 (CH2 CH2 O)m OH and transition metal aqua complexes ([Ni(H2 O)6 ](NO3 )2 , [Co(H2 O)6 ](NO3 )2 , [Zn(H2 O)6 ](NO3 )2 , [Cd(H2 O)4 ](NO3 )2 , and [Co(H2 O)6 ]Cl2 ) into hexagonal and/or cubic structures. While the NiII and CoII complexes undergo recrystallization and phase separation at high complex concentrations, the ZnII and CdII complexes form cubic phases above metal/surfactant molar ratios of 3.2/1 at room temperature.

Oriented Periodic Mesoporous Organosilica (PMO) Film with Organic Functionality Inside the Channel Walls

The first examples of an oriented periodic mesoporous organosilica (PMO) film, containing a variety of organic groups (ethane, ethene, benzene, thiophene) inside the channel walls, are reported. The mesostructure of the PMO film appears oriented with respect to the surface of the underlying glass substrate. Liquid-crystal topological defects in the precursor gels are replicated in the resulting PMO film and are evident in polarized optical microscopy images, recorded between crossed-polarizers, which show fan-type optical birefringence texture characteristic of the mesostructure.

Free-standing mesoporous silica films; morphogenesis of channel and surface patterns

Extraordinary channel patterns have been observed in an oriented mesoporous silica film that is synthesized at the boundary between air and water. The basic channel designs comprise concentric circles, herringbones, fingerprints and hairpins. It is suggested that these patterns are spatio-temporal silicified recordings of the polymerization and growth of a silicate liquid-crystal seed emerging in two spatial dimensions at the air/water interface. The origin of the channel patterns may be from defects, such as disclinations and dislocations, that spontaneously form in a surface confined precursor silicate liquid-crystal film to give a liquid-crystalline texture to the resulting mesoporous silica film. The reaction–diffusion processes and defects that are believed to contribute to the curved three-dimensional morphologies and channel patterns of mesoporous silica free to grow in solution, may also occur in the surface version, except that the isotropy of solution is replaced by the anisotropy of the air/water interface together with proximity effects from neighboring growth centers. Polymerization induced radial stresses produced in the as-synthesized mesoporous silica film before drying, are relieved through warping of the film into micrometer-scale hillock-shaped protuberances. These mounds are arranged into patterns that appear to reflect the channel designs within the film. A linear radial stress model is found to successfully account for the warp patterns. A possible connection between the two-dimensional channel patterns in mesoporous silica films and the two-dimensional stripe domain patterns found in modulated phases is discussed.

The synthesis of mesostructured silica films and monoliths functionalised by noble metal nanoparticles

A lyotropic AgNO3, HAuCl4 and H2PtCl6–silica liquid crystalline (LC) phase is used as a supramolecular template for a one-pot synthesis of novel noble metal or complex ion containing nanocomposite materials in the form of a film and monolith. In these structures, Ag+, AuCl4− and PtCl62− ions interact with the head group of an oligo(ethylene oxide) type non-ionic surfactant (C12H25(CH2CH2O)10OH, denoted as C12EO10) assembly that are embedded within the channels of hexagonal mesostructured silica materials. A chemical and/or thermal reduction of the metal or complex ions produces nanoparticles of these metals in the mesoporous channels and the void spaces of the silica. The LC mesophase of H2O∶X∶HNO3∶C12EO10, (where X is AgNO3, HAuCl4 and H2PtCl6), and nanocomposite silica materials of meso-SiO2–C12EO10–X and meso-SiO2–C12EO10–M (M is the Ag, Au and Pt nanoparticles) have been investigated using polarised optical microscopy (POM), powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), Fourier transform infrared (FTIR), Fourier transform (FT) Raman and UV-Vis absorption spectroscopy. Collectively the results indicate that the LC phase of a 50 w/w% H2O∶C12EO10 is stable upon mixing with AgNO3, HAuCl4 and H2PtCl6 salts and/or acids. The metal ions or complex ions are distributed inside the channels of the mesoporous silica materials at low concentrations and may be converted into metal nanoparticles within the channels by a chemical and/or thermal reduction process. The metal nanoparticles have a broad size distribution where the platinum and silver particles are very small (typically 2–6 nm) and the gold particles are much larger (typically 5–30 nm).

Assembling Photoluminescent Silicon Nanocrystals into Periodic Mesoporous Organosilica

A contemporary question in the intensely active field of periodic mesoporous organosilica (PMO) materials is how large a silsesquioxane precursor can be self-assembled under template direction into the pore walls of an ordered mesostructure. An answer to this question is beginning to emerge with the ability to synthesize dendrimer, buckyball, and polyhedral oligomeric silsesquioxane PMOs. In this paper, we further expand the library of large-scale silsesquioxane precursors by demonstrating that photoluminescent nanocrystalline silicon that has been surface-capped with oligo(triethoxysilylethylene), denoted as ncSi:(CH(2)CH(2)Si(OEt)(3))(n)H, can be self-assembled into a photoluminescent nanocrystalline silicon periodic mesoporous organosilica (ncSi-PMO). A comprehensive multianalytical characterization of the structural and optical properties of ncSi-PMO demonstrates that the material gainfully combines the photoluminescent properties of nanocrystalline silicon with the porous structure of the PMO. This integration of two functional components makes ncSi-PMO a promising multifunctional material for optoelectronic and biomedical applications.

Origin of Lyotropic Liquid Crystalline Mesophase Formation and Liquid Crystalline to Mesostructured Solid Transformation in the Metal Nitrate Salt—Surfactant Systems

The zinc nitrate salt acts as a solvent in the ZnX-C(12)EO(10) (ZnX is [Zn(H(2)O)(6)](NO(3))(2) and C(12)EO(10) is C(12)H(25)(OCH(2)CH(2))(10)OH) lyotropic liquid crystalline (LLC) mesophase with a drastic dropping on the melting point of ZnX. The salt-surfactant LLC mesophase is stable down to -52 °C and undergoes a phase change into a solid mesostructured salt upon cooling below -52 °C; no phase separation is observed down to -190 °C. The ZnX-C(12)EO(10) mesophase displays a usual phase behavior with an increasing concentration of the solvent (ZnX) in the media with an order of bicontinuous cubic(V(1))-2D hexagonal(H(1))--a mixture of 2D hexagonal and micelle cubic(H(1) + I)-micelle cubic(I)-micelle(L(1)) phases. The phase behaviors, specifically at low temperatures, and the first phase diagram of the ZnX-C(12)EO(10) system was investigated using polarized optical microscopy (POM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infrared (FTIR), and Raman techniques and conductivity measurements.

A New, Highly Conductive, Lithium Salt/Nonionic Surfactant, Lyotropic Liquid‐Crystalline Mesophase and Its Application

Highly conductive electrolyte materials are an essential part of many electrochemical systems, such as fuel cells, solar cells, batteries, electrochromic devices, and next-generation renewable-energy sources. The growing diversity in batteries and electrochemical cells increases the demand for novel electrolyte materials. For instance, in solar-cell applications, an electrolyte material with high viscosity and low volatility is desirable, together with high ionic conductivity. Electrolytes can be solids, gels, or liquids depending on the application. Gel electrolytes are advantageous when the conductivity in the solid form is not sufficient or the leakage or vaporization of the liquid electrolyte is a problem. Gel electrolytes can be aqueous or non-aqueous depending on the application type. While in some battery systems aqueous gel electrolytes have no use—for example, in Li ion batteries—they can be used in many rechargeable batteries, electrochemical capacitors, solar cells, and so on. Liquid-crystal gel electrolytes have also been investigated and are considered to be an important class of ordered materials for the above applications. A lyotropic liquid-crystalline (LLC) mesophase is formed by two main constituents: an amphiphile and a solvent. Common solvents are water, organic liquids, or ionic liquids. LLC-based electrolytes offer many advantages, like rigidity and high ionic mobility and can be an alternative to polymer electrolytes. Solvent-free LC systems (thermotropic LC) usually have low ionic conductivities at room temperature, typically around 10 6 Scm , whereas solvent-containing LLC systems have room-temperature ionic conductivities around 10 3 Scm . Usually high ionic conductivity in solvent-free LC electrolyte systems is achieved at high temperatures, that is, 150 8C and above. Recently we have shown that transition-metal aqua complex salts ([M ACHTUNGTRENNUNG(H2O)6]X2; in which M is a transition-metal cation and X is a suitable counterion), which have melting points close to room temperature, can also be used as solvents in the self-assembly process of some surfactants. The LLC mesophases of molten transition-metal-salt aqua complexes have important physical properties, such as high thermal stability (between 83 and 383 K), high ionic conductivity (room-temperature conductivities close to 2.0 10 4 Scm ), and nonvolatility. A highly concentrated aqueous electrolyte solution of an alkali metal salt can also act as a solvent in the assembly process of oligo(ethylene oxide) type surfactants, in which the highly concentrated electrolyte solution can be considered as an analogue of a molten salt. Their similarities arise due to strong ion–dipole (salt–water) interactions at high salt concentrations (highly concentrated refers to water/salt mole ratios of less than 8 in the case of lithium salts) and as a consequence, the heat of vaporization of water sharply increases. In this contribution, we have investigated the phase behavior and ionic conductivity of a new class of hydrated-salt/ surfactant mesophase, namely; LiNO3–H2O–C12EO10, LiCl– H2O–C12EO10, and LiClO4–H2O–C12EO10 systems, in which C12EO10 is C12H25 ACHTUNGTRENNUNG(OCH2CH2)10OH. The mesophase is a collaborative assembly of a hydrated salt species in the liquid phase and surfactant molecules. Earlier studies on salt– water–surfactant mesophases focus on the effect of salts on the phase behavior of surfactants in dilute aqueous solutions (18–1, water/salt mole ratio). Here, we demonstrate that as little as two water molecules per molecule of lithium salt is sufficient to form a LLC mesophase. At such a low water and high salt concentrations, the bulk properties of water are altered by the salt–water interactions and the salt– water couple collaboratively acts as the solvent in the LLC mesophase. An important outcome of the salt–water interaction is that the LLC mesophase is stable under ambient atmospheric conditions for years (see Supporting Information) and displays high ionic conductivity over a broad temperature range. The LLC samples were prepared by adding each ingredient: salt (LiNO3, LiCl, or LiClO4), surfactant (C12EO10), and water in the required amounts and the resulting mixture was then homogenized by constant shaking in a shaking water bath at 60–110 8C for 24 h. Under ambient conditions, the amount of water in the samples depends on the temperature, relative humidity, and the amount of salt in the mesophase, but always enough water remains in the samples to [a] C. Albayrak, Prof. . Dag Department of Chemistry, Bilkent University 06800, Ankara (Turkey) Fax: (+90)312-266-4068 E-mail : dag@fen.bilkent.edu.tr [b] Prof. A. Cihaner Department of Chemical Engineering and Applied Chemistry Atilim University 06836, Ankara (Turkey) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201103705.

Spatially Confined Redox Chemistry in Periodic Mesoporous Hydridosilica–Nanosilver Grown in Reducing Nanopores

Periodic mesoporous hydridosilica, PMHS, is shown for the first time to function as both a host and a mild reducing agent toward noble metal ions. In this archetypical study, PMHS microspheres react with aqueous Ag(I) solutions to form Ag(0) nanoparticles housed in different pore locations of the mesostructure. The dominant reductive nucleation and growth process involves SiH groups located within the pore walls and yields molecular scale Ag(0) nanoclusters trapped and stabilized in the pore walls of the PMHS microspheres that emit orange-red photoluminescence. Lesser processes initiated with pore surface SiH groups produce some larger spherical and worm-shaped Ag(0) nanoparticles within the pore voids and on the outer surfaces of the PMHS microspheres. The intrinsic reducing power demonstrated in this work for the pore walls of PMHS speaks well for a new genre of chemistry that benefits from the mesoscopic confinement of Si-H groups.

Salted mesostructures : salt-liquid crystal templating of lithium triflate-oligo (ethylene oxide) surfactant-mesoporous silica nanocomposite films and monoliths

A lyotropic lithium triflate-silicate liquid crystal is utilized as a supramolecular template for a ‘one-pot’ synthesis of a novel ionically conducting nanocomposite material, denoted meso-SiO 2 -C 12 (EO) 10 OH-LiCF 3 SO 3 , in the form of a film or monolith. In this structure Li + ions interact, in a crown ether-like fashion, with oligo(ethylene oxide) head groups of a non-ionic surfactant assembly that is imbibed within the channels of hexagonal mesoporous silica. Details of the acid catalyzed polymerization of the silicate oligo(ethylene oxide) surfactant co-assembly in the presence of lithium triflate have been investigated using polarized optical microscopy (POM), powder X-ray diffraction (PXRD), multinuclear nuclear magnetic resonance (NMR) spectroscopy and impedance spectroscopy. Insight into the incorporation of Li + and CF 3 SO 3 – ions into meso-SiO 2 -C 12 (EO) 10 OH-LiCF 3 SO 3 was obtained using NMR and Fourier transform (FT) Raman spectroscopy. Collectively the results indicate that lithium ions coordinate to oxygens of the oligo(ethylene oxide) head group, maintain the structural integrity of both the silicate liquid crystal and templated mesoporous silica, and are essentially completely dissociated with respect to the triflate counteranion. ac Impedance spectroscopy, which bodes well for their use in the fields of polymer electrolytes and battery technology for meso-SiO 2 -C 12 (EO) 10 OH-LiCF 3 SO 3 have demonstrated high ionic conductivities at room temperature measurements. Salt-liquid crystal templating may offer a general approach for synthesizing diverse kinds of salted mesostructures including redox active transition metal complexes, which may be reductively-agglomerated to form metal cluster-based meso-SiO 2 -C 12 (EO) 10 OH-M n or sulfided with H 2 S to produce semiconductor cluster-based meso-SiO 2 -C 12 (EO) 10 OH-(MS) n nanocomposites.

Synthesis of stable mesostructured coupled semiconductor thin films: meso-CdS-TiO(2) and meso-CdSe-TiO(2).

Cd(II) ions can be incorporated into the channels of mesostructured titania films, using the evaporation-induced self-assembly (EISA) approach, up to a record high Cd/Ti mole ratio of 25%. The film samples were obtained by spin or dip coating from a mixture of 1-butanol, [Cd(H(2)O)(4)](NO(3))(2), HNO(3), and Ti(OC(4)H(9))(4) and then aging the samples under 50% humidity at 30 degrees C (denoted as meso-xCd(II)-yTiO(2)). The nitrate ions, from nitric acid and cadmium nitrate, play important roles in the assembly process by coordinating as bidentate and bridged ligands to Cd(II) and Ti(IV) sites, respectively, in the mesostructured titania films. The film samples can be reacted under a H(2)S (or H(2)Se) gas atmosphere to produce CdS (or CdSe) on the channel surface and/or pore walls. However, the presence of such a large number of nitrate ions in the film samples also yields an extensive amount of nitric acid upon H(2)S (or H(2)Se) reaction, where the nanoparticles are not stable (they undergo decomposition back to metal ion and H(2)S or H(2)Se gas). However, this problem can be overcome by further aging the samples at 130 degrees C for a few hours before H(2)S (or H(2)Se) reaction. This step removes about 90% of the nitrate ions, eliminates the nitric acid production step, and stabilizes the CdS nanoparticles on the surface and/or walls of the pores of the coupled semiconductor films, denoted as meso-xCdS-yTiO(2). However, the H(2)Se reaction, additionally, needs to be carried at lower H(2)Se pressures in an N(2) atmosphere to produce stable CdSe nanoparticles on the surface and/or walls of the pores of the films, denoted as meso-xCdSe-yTiO(2). Otherwise, an excessive number of Se(8) particles form in the film samples.