Browsing by Subject "Lyotropic liquid crystal"

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Open Access
Highly proton conductive phosphoric acid-nonionic surfactant lyotropic liquid crystalline mesophases and application in graphene optical modulators
(American Chemical Society, 2014) Tunkara, E.; Albayrak, C.; Polat, E. O.; Kocabas, C.; Dag, Ö.
Proton conducting gel electrolytes are very important components of clean energy devices. Phosphoric acid (PA, H3PO4 3 H2O) is one of the best proton conductors, but needs to be incorporated into some matrix for real device applications, such as into lyotropic liquid crystalline mesophases (LLCMs). Herein, we show that PA and nonionic surfactant (NS, C12H25(OCH2CH2)10OH, C12E10) molecules self-assemble into PANS LLCMs and display high proton conductivity. The content of the PANS LLCM can be as high 75% H3PO4 3 H2O and 25% 10-lauryl ether (C12H25(OCH2CH2)10OH, C12E10), and the mesophase follows the usual LLC trend, bicontinuous cubic (V1) normal hexagonal (H1) micelle cubic (I1), by increasing the PA concentration in the media. The PANS LLCMs are stable under ambient conditions, as well as at high (up to 130 C) and low ( 100 C) temperatures with a high proton conductivity, in the range of 10 2 to 10 6 S/cm. The mesophase becomes a mesostructured solid with decent proton conductivity below 100 C. The mesophase can be used in many applications as a proton-conducting media as well as a phosphate source for the synthesis of various metal phosphates. As an application, we demonstrate a graphene-based optical modulator using supercapacitor structure formed by graphene electrodes and a PANS electrolyte. A PANS LLC electrolyte-based supercapacitor enables efficient optical modulation of graphene electrodes over a range of wavelengths, from 500 nm to 2 μm, under ambient conditions.
Open Access
Investigation of lithium salts-nonionic surfactant lyotropic liquid crystalline mesophases in a dye sensitized solar cell as gel electrolyte
(2015-09) Yılmaz, Ezgi
Liquid crystals are one of the most widely studied and used materials in chemistry. The properties of liquid crystals make them interesting to research also for various electrochemical applications. In this context, lithium salts such as LiI, LiCl, LiBr, and LiNO3 can be assembled using non-ionic surfactants into lyotropic liquid crystalline (LLC) mesophases[1], [2] and used as gel electrolytes in various applications. In this work, the LLC mesophases of LiI with and without other lithium salts (such as LiCl, LiBr, and LiNO3) were prepared using 10-lauryl ether (C12H25(CH2CH2O)10OH, denoted as C12EO10) and characterized using the FT-IR (Fourier Transform Infrared Spectroscopy), Raman spectroscopy, XRD (X-Ray Diffraction), POM (Polarized Optical Microscopy), and AC conductivity measurements. Beside from single salt-surfactant mesophases, we also prepared LiI/I2 redox couple in an LLC phase with the help of a non-ionic surfactant and they were also characterized using the same techniques. We found out that the mesophases can be prepared as gels by directly mixing salt and surfactant with certain amounts of water or as solutions using excess solvent (such as water, ethanol, or acetonitrile) that can be evaporated to form the LLC mesophases. The water content of both sets of samples is the same upon exposing to the atmosphere for a certain time and it only depends on the salt amount and humidity under the ambient conditions (around room temperature and 20-25 % RH). The required water/salt ratio for a stable mesophase is around 3.0 which, it is much lower than the water needed to dissolve those salts in an aqueous media. The water/salt mole ratio closely follows the Hofmeister series of anions, where the water amount order is as follows; LiCl>LiBr>LiI>LiNO3, however, the AC ionic conductivity follows a different order; LiNO3>LiCl>LiBr>LiI. Adding I2 by 1/10 mole ratio of the LiI into the media does not change the properties of the mesophases. The AC conductivity increases with increasing salt and water content of the mesophases with a typical conductivity of around 0.1 to 1.0 mS/cm-1. The mesophases are also stable in a very broad temperature (below 0 °C to 60-130 °C) and salt concentration (2-10 salt/surfactant mole ratio) ranges. Finally, the LiI/I2 mesophases were used as gel-electrolytes in dye sensitized solar cells (DSSCs) as gel-electrolytes and redox couples. A set of samples were prepared with different ratios of the LiI:I2 redox couple (such as, 1:0.1, 1:0.2, 2:0.2, 2:0.3, 3:0.2, 3:0.3, 4:0.4, and 5:0.5) and the solar performances were tested in a DSSC, which contains N719 dye sensitized TiO2 anode and Pt cathode using a solar simulator. However, the LLC phases have gel like structure and it is hard to infiltrate the gel into the pores of dye modified nano-TiO2 films. To overcome the diffusion problem, the gel-electrolytes were also prepared as a solution in excess water, ethanol or acetonitrile that evaporates upon infiltration over time. In addition to this, by changing the procedure of preparing the TiO2 paste, improvement on results was also obtained. The DSSC provides 0.2 % efficiencies with 0.50 fill factors when gel-electrolytes are used. Since water is used for preparing the LLC phases, we had always lower Voc values. However, when it is prepared as a solution with excess ethanol, it provides up to 3.33 % efficiencies with 9.58 mA/cm2 short circuit current and 0.6 V open circuit voltage. Also, new procedure for preparing the TiO2 paste provides us even higher Voc values such as 0.76 V, which is unusual for the water based LLC electrolytes in this area.
Open Access
A new lyotropic liquid crystalline system: Oligo (ethylene oxide) surfactants with transition metal complexes and the synthesis of mesoporous metal sulfides
(2001) Çelik, Özgür
In this study a new templating method, which can be used to synthesise mesporous materials, has been developed. The main objective of this work is to form organic mesophase in the presence of inorganic salts. This is an organic-inorganic hybrid mesophase, which can be used to template the growth of inorganic materials. Here for the first time, a new lyotropic liquid crystalline (LLC) system has been presented from oligo (ethylene oxide) type surfactant and transition metal aqua complexes. The temperature and the metal aqua complex concentration range of the complex/surfactant mixtures have been determined, where the mixtures have a liquid crystalline (LC) phase. Here, the complex refers to Ni(NO3)2·6H2O, Co(NO3)2·6H2O, Zn(NO3)2·6H2O, Cd(NO3)2·4H2O, and CoCl2·6H2O and the surfactant is C12H25(CH2CH2O)10OH, (C12EO10). The addition of the metal aqua complexes directly to the surfactant produces a LC phase. The LC phase obtained from the mixture of these two is more stable than the LC phase obtained from a mixture of free water and surfactant. The FT-IR and UV-Vis absorption, Polarised Optical Microscopy (POM) and Powder X-ray Diffraction measurements show that the coordinated water molecules mediate the formation of the LC phase. Our observations also show that the coordinated water molecules make a stronger interaction with ethylene oxide (EO) chains than free water molecules. The LC templating approach, which is demonstrated as a new system has been used for synthesis of meso-structured metal oxides, metal sulphides and even metal mesh. From all these studies, it is well known that in order to maintain LC phase the metal ion concentration should correspond to metal ion to surfactant mole ratio below 0.8. However, this work shows that the amount of metal aqua complex concentration can be increased up to a 6.5 complex to surfactant mole ratio by maintaining the integrity of the hexagonal and/or cubic structure of the LC phase. This may open a new area for the realisation of new mesostructured materials with better qualities and much higher yields. In the first part of the thesis, the thermal and structural properties of the new LLC phase has been established by using polarized optical microscopy (POM) with an attached hot plate, PXRD, FT-IR and UV-Vis absorption methods. In the second part, the new phase has been used as a template to synthesise mesoporus metal sulfides. The second part of the thesis deals mainly with the structure and synthesis of mesostructured CdS and ZnS. It has been demonstrated that the LC phase of Zn(NO3)2·6H2O, and Cd(NO3)2·4H2O in oligo(ethylene oxide) surfactant survive partially during the reaction with H2S to produce the corresponding metal sulfides.
Open Access
Role of silica in the self-assembly of salt-surfactant mesophases and synthesis of mesoporous metal oxides
(2023-07) Ullah, Najeeb
In recent years, mesoporous metal oxides have attracted great attraction due to their unique optical, electrochemical, and catalytic properties. Mesoporous nickel oxide (m-NiO) is a p-type semiconductor, versatile in its application due to its high surface area, and has been investigated towards electrochromic devices, electrodes, supercapacitors, and catalysts. The electrochemical properties of NiO depend on its morphology, surface area, and particle size. In this thesis, mesoporous nickel oxide has been synthesized by combining soft templating (molten salt-assisted self-assembly method) and hard templating methods to attain a high surface area. Homogeneous aqueous solutions of nickel(II) nitrate hexahydrate ([Ni(H2O)6](NO3)2), TMOS (as silica source), and two surfactants, CTAB (charged surfactant) and C12E10 (nonionic surfactant) are stable only if a concentrated nitric acid is added before the TMOS addition. In the absence of nitric acid, TMOS hydrolyzes and condenses quickly, resulting in silica precipitation. The silica precipitation also occurs by using other salts, such as nickel(II) chloride hexahydrate, nickel(II) sulfate hexahydrate, cobalt(II) nitrate hexahydrate, and manganese(II) nitrate tetrahydrate. The silica precipitate is characterized by ATR-FTIR, small-angle, and wide-angle XRD and N2 adsorption-desorption measurements. The diffraction lines at 1.7 and 23o, 2θ, indicate the formation of mesostructured amorphous silica, in which the surfactant species fill the pores. . The silica precipitate is calcined at 450 oC for two hours to remove the surfactant completely, and characterized by ATR-FTIR, small-angle and wide-angle XRD measurements, N2- adsorption-desorption analysis and SEM-EDX techniques. The maximum surface area (1395 m2/g) is obtained from the cobalt(II) nitrate hexahydrate salt, and the EDX analysis confirms that there is no element other than silicon and oxygen in its elemental detection limit. The homogeneous, stable aqueous solutions of the nickel(II) nitrate hexahydrate ([Ni(H2O)6](NO3)2), HNO3, TMOS (as silica source), and two surfactants, CTAB (charged surfactant) and C12E10 (nonionic surfactant) solution is drop-casted on a glass slide to form a mesophase and analyzed by small-angle XRD, ATR-FTIR and POM techniques. The diffraction lines at 1.5 and 1.6o, 2θ, show the formation of ordered lyotropic liquid crystalline mesophases. The mesophases are then calcined at different temperatures (from 250 to 500 °C), to obtain m-NiO/SiO2 powders and characterized by ATR-FTIR, XRD measurements, N2- adsorption-desorption analysis, and SEM-EDX techniques. The XRD patterns show broad lines at small- and wide-angles, indicating the formation of m-NiO/SiO2 at 300 °C, where the pore-walls are made up 2.6 nm crystalline NiO coated amorphous silica . The NiO particle size (on the pore wall) grows with increasing annealing temperature, and at 500 °C, the particle size reaches 7.9 nm. This is also supported by the BET surface area that decreases at higher temperatures. At 300 °C, the BET surface area is 305 m2/g, which drops to 174 m2/g at 500 °C. However, the pore size of m-NiO/SiO2 does not responds to annealing temperature. It means that the pore walls grow in 2D space rather than 3D due to the presence of silica as a hard template. Therefore, combining the hard- and soft-templating methods can efficiently synthesize the crystalline materials with a high surface area. The m-NiO/SiO2 films can be coated over the FTO glass and calcined at different temperatures to fabricate the electrodes for oxygen evolution reaction (OER). During CV measurement, the NiO pore-walls get oxidized to NiOOH and reduced to Ni(OH)2 in the back cycle. Moreover, overpotential that is determined for the OER improves with the usage of the electrode, independent of the electrode thickness.
Open Access
Swollen liquid crystals (SLCs): A versatile template for the synthesis of nano structured materials
(Royal Society of Chemistry, 2017) Dutt, S.; Siril, P. F.; Remita, S.
Liquid crystal (LCs) is the state of matter that exhibits properties between a conventional liquid and solid crystals. Liquid crystals mainly can be classified into two types: thermotropic and lyotropic liquid crystals. A thermotropic liquid crystal shows properties that are dependent on temperature conditions. On the other hand in lyotropic liquid crystals (LLCs), the amphiphiles are dissolved in a solvent and exhibit liquid crystalline properties in certain concentration ranges. In the literature, lot of reviews have been presented on thermotropic and lyotropic liquid crystals (LLCs). But nowadays, swollen liquid crystals (SLCs) have become a much more important area of research because of their easily tunable properties, their stability and versatility of the system. Swollen liquid crystals (SLCs) consist of infinite liquid crystalline non polar cylinders organized on a hexagonal lattice in a polar medium and are prepared with the proper ratios of salted water and non polar solvents with cationic or anionic or non ionic surfactants and co surfactants i.e. water:oil:surfactant:cosurfactant. In this review article, we will briefly discuss the synthesis of swollen liquid crystals (SLCs), factors affecting their stability, different kinds of nanomaterials such as metallic, bimetallic, polymeric nanostructures synthesized inside swollen liquid crystals (SLCs) using different methods and the effect of swollen liquid crystal (SLC) confinement on the final morphology of nanomaterials with their potential applications.
Open Access
Synthesis and characteization of mesoporous nickel oxide and nickel cobaltite thin films
(2019-09) Amirzhanova, Assel
In this thesis work, molten-salt assisted self-assembly (MASA) approach was adopted to synthesize mesoporous nickel oxide (m-NiO) and nickel cobaltite (m-NiCo2O4) thin films. The m-NiO and m-NiCo2O4 films were obtained by coating clear ethanol solutions of nickel salt and two surfactants (charged, CTAB and neutral, 10-lauryl ether), and nickel and cobalt salts with the same surfactants, respectively, followed by calcination at different temperatures (between 250 and 500 oC). The method has been established in a very broad range of salt concentrations in the lyotropic liquid crystalline (LLC) mesophase that can be calcined to produce mesoporous thin films. Both Ni(II) and Ni(II)/Co(II) systems form stable and oriented LLC mesophases in a broad range of salt concentrations (salt surfactant mole ratio of 2-8) upon evaporation of ethanol from the media. This can be achieved by either spin coating of the clear solutions (this ensure immediate evaporation of ethanol, leaving the LLC gel phase as thin film) or drop casting and evaporation of ethanol (the gelation process takes more time). At higher salt concentrations (10-30 salt/surfactant mole ratios), the mesophase is disordered and leach out salt crystals. However, those compositions can still be used for the synthesis of mesoporous metal oxides, if the samples are calcined immediately after the gelation step. The mesophase is 2D hexagonal at low salt concentrations and disordered or cubic at higher salt concentrations. The calcined films were characterized by recording x-ray diffraction (XRD), N2-adsorption desorption measurements, imaging (SEM, TEM, and POM) and spectroscopic (UV-Vis, XPS, EDX, and ATR-FTIR) techniques. The N2 adsorption-desorption isotherms are type IV and characteristic for mesoporous materials. The XRD data show that the crystalline m-NiO and m-NiCo2O4 form at around 300 and 250 oC, respectively, with a pore-wall thickness of around 3-4 nm. The pore-walls grow with increasing the calcination/annealing temperature up to 20 nm at around 500 oC. It accords well with the BET surface area that decreases with increasing calcinations temperature; it is 223 m2/g at 300 oC and drops to 20 m2/g at 500oC in mesoporous nickel oxide, and 223 m2/g at 250 oC and drops to 31 m2/g at 500 oC in mesoporous nickel cobaltite. The observed diffraction patterns can be indexed to rock salt cubic structure of NiO and cubic spinel structure of NiCo2O4. The diffraction lines gradually become sharper indicating crystallization and growth of the pore-walls that accord well with the reduction on the surface area. The m-NiO and m-NiCo2O4 films can be coated over FTO glass to use as an electrochromic electrode (oxidation dark-reduction clear) and electrode for water oxidation reactions (WOR) and WOR, respectively. In nickel oxide case, during cyclic voltammograms cycling, water oxidation process, and electrochromic switching, a few atomic layer of nanocrystalline NiO pore-wall is converted to NiOOH in oxidation and Ni(OH)2 upon reduction processes; initially formed nanocrystalline NiO (after calcination) pore-walls become NiO coated Ni(OH)2 (core-shell structure) upon electrochemical treatments. Both NiO and NiCo2O4 having high surface area and electrochemical stability show promising capacitive properties and can be used as electrocatalysts. From the Tafel slope analysis, it has been shown that nickel cobaltite can oxidize water at low overpotentials and therefore can be used as a promising water splitting catalyst.