Browsing by Subject "Mesophases"

Now showing 1 - 7 of 7

Open Access
Effects of some transition metal salts on the synthesis of mesoporous silica
(2005) Demirörs, Ahmet Faik
Open Access
Investigation of lithium salt-nonionic surfactant mesophases and their applications in solar cells as gel electrolyte
(2013) Barım, Gözde
Some salts and some nonionic surfactants self-assemble together into lyotropic liquid crystalline (LLC) mesophases. The salt can be either in aqueous solution phase or in its molten phase in the self-assembly process. Concentrated aqueous solutions of lithium salts (LiCl, LiBr, or LiI) and pluronics (triblock copolymers, such as P65, P85, P103, or P123) or 10-lauryl ether (C12H25(CH2CH2O)10OH, denoted as C12EO10) type nonionic surfactant mesophases were investigated in this thesis work. The LLC mesophases are well ordered between 5.0 and 25.0 salt/pluronics and 2.0 and 10.0 salt/C12EO10 mole ratios, and remain stable for months under the ambient conditions. The water molecules remain as the hydrates under open atmosphere in the LLC mesophases of lithium salts-nonionic surfactants. The lithium salt-pluronic LLC mesophases are birefringent and have a hexagonal mesophase in a broad range of salt concentrations. The unit cell of the mesophases increases and a transition from the hexagonal to a cubic mesophases occurs upon increasing the salt content of the media. Moreover the LLC mesophases are ordered and stable up to 25.0 salt to pluronic mole ratio. At higher salt content, one can observe either a disordered phase or co-existence of salt crystals and mesophase. There is a big demand on the gel electrolytes for dye sensitized solar cells (DSSC) in order to overcome solvent problems caused by liquid electrolytes. The LLC mesophases of LiI, LiCl and LiBr salts with 10-lauryl ether (C12EO10) has been considered as gel-electrolyte for the DSSC. We demonstrate that the LiI/I2 couple can be incorporated into above LLC mesophases of various lithium salt-nonionic surfactant systems. Those LLC phases, with LiI/I2 couple have been characterized by means of diffraction, microscopy, spectroscopy and conductivity measurements. The LLC mesophases diffract at small angles and do not show any phase segregation upon incorporating the LiI/I2 redox couple. The LLC mesophases of these systems are 2D hexagonal, and they remain stable under ambient conditions for months. In the LLC media, the iodide ion and iodine molecule react to produce triodide ion in the media. The iodide/triodide (I- /I3 - ) redox couples containing gel electrolytes were formed and their solar performance was investigated by using a solar simulator and a cell consisting of a dye sensitized anode (FTO-dye modified TiO2), gel-electrolyte, and a cathode (FTO-Pt nanoparticles). The LLC mesophases of various lithium saltnonionic surfactant systems with the I- /I3 - redox couple were characterized using POM (Polarized Optical Microscope), XRD (X-ray Diffraction), FT-IR (Fourier Transform Infrared Spectroscopy) and Raman techniques. These new LLC mesophases can be used as gel electrolytes in solar cells after incorporation of redox couple into the media and display responses as good as commonly used liquid electrolytes.
Open Access
Lyotropic liquid crystal to soft mesocrystal transformation in hydrated salt-surfactant mixtures
(Wiley, 2013) Albayrak, C.; Barım, G.; Dag, Ö.
Hydrated CaCl2, LiI, and MgCl2 salts induce self-assembly in nonionic surfactants (such as C12H 25(OCH2CH2)10OH) to form lyotropic liquid-crystalline (LLC) mesophases that undergo a phase transition to a new type of soft mesocrystal (SMC) under ambient conditions. The SMC samples can be obtained by aging the LLC samples, which were prepared as thin films by spin-coating, dip-coating, or drop-casting of a clear homogenized solution of water, salt, and surfactant over a substrate surface. The LLC mesophase exists up to a salt/surfactant mole ratio of 8, 10, and 4 (corresponding to 59, 68, and 40wt % salt/surfactant) in the CaCl2, LiI, and MgCl2 mesophases, respectively. The SMC phase can transform back to a LLC mesophase at a higher relative humidity. The phase transformations have been monitored using powder X-ray diffraction (PXRD), polarized optical microscopy (POM), and FTIR techniques. The LLC mesophases only diffract at small angles, but the SMCs diffract at both small and wide angles. The broad surfactant features in the FTIR spectra of the LLC mesophases become sharp and well resolved upon SMC formation. The unit cell of the mesophases expands upon SMC transformation, in which the expansion is largest in the MgCl2 and smallest in the CaCl2 systems. The POM images of the SMCs display birefringent textures with well-defined edges, similar to crystals. However, the surface of the crystals is highly patterned, like buckling patterns, which indicates that these crystals are quite soft. This unusual phase behavior could be beneficial in designing new soft materials in the fields of phase-changing materials and mesostructured materials, and it demonstrates the richness of the phase behavior in the salt-surfactant mesophases.
Open Access
Lyotropic liquid crystalline (LLC) phosphoric acid-10-lauryl ether: mesophases, proton conductivity and synthesis of transparent mesoporous hydroxyapatite thin films
(2014-06) Tunkara, Ebrima
Many salts, acids, and bases with low deliquescence relative humidity (DRH) can organize non-ionic surfactants into lyotropic liquid crystalline (LLC) mesophases that form a ready platform for the synthesis of mesoporous materials. In this study, we show that phosphoric acid (H3PO4, PA) with low DRH value can also be used as a solvent in assembling non-ionic surfactant (C12H25(OCH2CH2)10OH, C12EO10) into stable LLC mesophases within a broad range of composition (the concentration can be as high as 20 PA/C12EO10 mole ratio). The PA/C12EO10 mesophase is bi-continuous cubic phase (V1) in extremely low concentrations (2 PA/C12EO10 mole ratio), 2D/3D hexagonal phases (H1) at moderate compositions (3 to 5 PA/C12EO10 mole ratio) and micelle cubic (I1) at high, (more than 5) H3PO4/C12EO10 mole ratios, with a typical unit cell parameter of 127, 55, and 116 Å, respectively. The mesophases of the lower concentrated samples (less than 15 mole ratio) have high thermal stability, with melting points greater than 120 oC. However the melting point drops to less than 50 oC for extremely high concentrations (more than 17 PA/C12EO10 mole ratio). The LLC mesophases were also found to exhibit high proton conductivities (~10-3 S/cm) at room temperature. The proton conductivities were even higher (10-2 S/cm) at some elevated temperatures and reduced to (10-4 S/cm) at temperatures less than 0oC. The conductivity in the cubic phase is slightly higher. Both the temperature and composition-dependent conductivity obey the most accepted proton conductivity mechanisms: Grotthuss and Vehicle. We went further to show that the combination of H3PO4 and another low DRH species, such as Ca(NO3)2·4H2O also form stable mesophases; without precipitating salts, under a wide range of concentration, from 5.3/1 to 13.3/1 precursor to surfactant ratio. High acidity stabilizes both the aqueous solution as well as the LLC phases. The clear solutions obtained from the precursor-surfactant mixtures were spin coated on glass substrates (as thin as a few hundred nanometers) and calcined to form transparent nano-size mesoporous hydroxyapatite (HAp) thin films. The formation of semi-crystalline HAp in our synthetic approach is not a straight forward process; it involves the formation of some intermediate products and also requires a calcination temperature of at least 300 oC. The formation, which starts at 300 oC, is preceded by the evaporation of nitric acid and excess water molecules to the surrounding. The crystallization continues at 400 oC and completes at 500 oC, keeping the uniformity, porosity, and transparency of the films. Films of the 5.3/1 ratio, calcined at 300 oC have high surface area of up to 96 m2/g, which dropped down to 20 m2/g at 500 oC. The mesopores start collapsing at around 600 oC. The pore size, pore walls, and the pore volumes were obtained from the N2 sorption measurements and the values are 22.4 nm, 10 nm, and 0.58 cm3/g, respectively. We also investigated the effect of precursor concentration on both the pore sizes, as well as the thicknesses of the pore walls. The results showed a reduction of surface area, and also narrower pore size distribution with increasing concentration. Temperature was also observed to have the same effect on crystallinity in all the compositions studied. All the investigations on these two systems were carried out using XRD (X-ray diffraction), FT-IR (Fourrier Transform Infrared Spectroscopy), Raman spectroscopy, POM (Polarized Light Optical Microscope), N2-sorption measurements, PEIS (Potentiostatic Electrochemical Impedance Spectroscopy), TEM (Transition Electron Microscopy), SEM (Scanning Electron Microscopy) etc.
Open Access
Lyotropic liquid-crystalline mesophases of [Zn(H2O)6](NO3)2-C12EO10-CTAB-H2O and [Zn(H2O)6](NO3)2-C12EO10-SDS-H2O systems
(2008) Albayrak, C.; Soylu, A. M.; Dag, Ö.
The mixture of two surfactants (C12EO10-CTAB and C 12EO10-SDS) forms lyotropic liquid-crystalline (LLC) mesophases with [Zn(H2O)6](NO3)2 in the presence of a minimum concentration of 1.75 H2O per C 12EO10. The metal ion/C12EO10 mole ratio can be increased up to 8.0, which is a record high metal ion density in an LLC mesophase. The metal ion concentration can be increased in the medium by increasing the CTAB/C12EO10 or SDS/C12EO 10 mole ratio at the expense of the stability of the LLC mesophase. The structure and some thermal properties of the new mesophase have been investigated using XRD, POM, FTIR, and Raman techniques. © 2008 American Chemical Society.
Open Access
A new lyotropic liquid crystalline system: oligo(ethylene oxide) surfactants with [M(H2O)n]Xm transition metal complexes
(Wiley, 2001) Çelik, Ö.; Dag, Ö.
Coordinated water molecules induce the aggregation and self-assembly of the lyotropic liquid crystalline phase formed from non-ionic surfactants CnH2n+1(CH2CH2O)mOH and transition metal aqua complexes ([Ni(H2O)6](NO3)2, [Co(H2O)6](NO3)2, [Cd(H2O)4](NO3)2, and [Co(H2O)6]Cl2) into hexagonal (see schematic representation) 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.
Open Access
Synthesis of mesostructured metal sulfide films using [M(H2O)n](NO3)2:P85 (M = Cd(II) and Zn(II)) liquid crystalline mesophases
(2008) Türker, Y.; Dag, Ö.
Transition metal salt-pluronic liquid crystalline (TMS-PLC) mesophases of A-P85, B-P85 and ((1 - x)A + xB)-P85 (where A is [Cd(H2O) 4](NO3)2, B is [Zn(H2O) 6](NO3)2 and P85 is a triblock copolymer, HO(CH2CH2O)26(CH2(CH 3)CHO)40(CH2CH2O)26H) have been used to produce mesostructured metal sulfide films. The TMS-PLC mesophases of A-P85, B-P85 and (A + B)-P85 are well ordered with a salt/P85 mole ratio between 3.0 and 11.0 with a 3D hexagonal structure. The reaction between the mesophases of A-P85, B-P85 and ((1 - x)A + xB)-P85 and H2S gas at room temperature produces mesostructured CdS, ZnS and Cd1-xZn xS films, respectively. The initial salt concentrations in the TMS-PLC phase determine the final Cd(ii) and Zn(ii) ions in the Cd 1-xZnxS crystal structure, where x can be controlled between 0.0 and 1.0. Fresh samples of the mesophase reacted under an H 2S atmosphere are continues films that slowly leach out excess P85 producing P85 rich dendrite domains and aggregates of 50 to 100 nm particles of mesostructured CdS, ZnS or Cd1-xZnxS. However, well homogenized TMS-PLC mesophases produce stable film samples upon H2S reaction.