Browsing by Author "Albayrak, C."

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Open Access
Assembly of molten transition metal salt surfactant in a confined space for the synthesis of mesoporous metal oxide-rich metal oxide silica thin films
(2011) Karakaya, C.; Türker, Y.; Albayrak, C.; Dag, Ö.
Uniform and homogeneous coating of mesoporous materials with an active (catalytically, photonic, electrical) nanostructure can be very useful for a number of applications. Understanding chemical reactions in a confined space is important in order to design new advanced materials. In this work, we demonstrate that an extensive amount (as high as 53 mol percent) of transition metal salts can be confined between silica walls and two surfactant domains (cetyltrimethylammonium bromide, CTAB, and lauryl ether, C12H25(OCH2CH2)10OH, C12EO10) as molten salts and then converted into sponge-like mesoporous silica–metal oxides by thermal annealing. This investigation has been carried out using two different salts, namely, zinc nitrate hexahydrate, [Zn(H2O)6](NO3)2, and cadmium nitrate tetrahydrate, [Cd(H2O)4](NO3)2, in a broad range of salt concentrations. The ZnO (or CdO) layers are as thin as about ∼1.6 nm and are homogenously coated as crystalline nano-islands over the silica pore walls.
Open Access
The effect of cationic surfactant and some organic/inorganic additives on the morphology of mesostructured silica templated by pluronics
(Elsevier, 2008-11-01) Poyraz, A. S.; Albayrak, C.; Dag, Ö.
Tri-block copolymers (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), represented as EOxPOyEOx), pluronics (F127=EO106PO70EO106, P65=EO20PO30EO20, P85=EO27PO39EO27, P103= EO17PO55EO17, and P123 = EO20PO70EO20) and cationic surfactants (cethyltrimethylammonium bromide (CTAB)), two surfactant systems, form complex micelles that self-assemble into mesostructured particles with distinct morphology depending on the pluronic type, the concentration of the cationic surfactant and the organic-inorganic ingredients in a siliceous reaction media under acidic conditions. The CTAB-P65 and CTAB-P85 systems form spheres, CTAB-P103 and CTAB-P123 systems form wormlike particles, and CTAB-F127 system form single crystals of mesostructured silica particles under very similar conditions. However addition of various salts (such as KCI and NaNO3) into a CTAB-P103 or CTAB-P123 solution system and cyclohexane and KCI into a CTAB-P85 solution system produces the mesostructured silica spheres and wormlike particles, respectively. By controlling the hydrophilic-hydrophobic character of the pluronics, core-corona interface, by means of additives, such as small organic molecules or salts, one could obtain the desired morphology that is dictated by the shape of the micelles of the pluronic-cationic surfactant complex. The effects of the additives and the formation mechanism of those morphologies have been discussed using spectroscopy (FT-IR and Raman), diffraction (XRD) and microscopy (POM and SEM) data. (c) 2008 Elsevier Inc. All rights reserved.
Open Access
Effect of hygroscopicity of the metal salts on the formation and air stability of lyotropic liquid crystalline mesophases in hydrated salt-surfactant systems
(Elsevier, 2014-11-01) Albayrak, C.; Barım, G.; Dag, Ö.
It is known that alkali, transition metal and lanthanide salts can form lyotropic liquid crystalline (LLC) mesophases with non-ionic surfactants (such as CiH2i+1(OCH2CH2)jOH, denoted as CiEj). Here we combine several salt systems and show that the percent deliquescence relative humidity (%DRH) value of a salt is the determining parameter in the formation and stability of the mesophases and that the other parameters are secondary and less significant. Accordingly, salts can be divided into 3 categories: Type I salts (such as LiCl, LiBr, LiI, LiNO3, LiClO4, CaCl2, Ca(NO3)2, MgCl2, and some transition metal nitrates) have low %DRH and form stable salt–surfactant LLC mesophases in the presence of a small amount of water, type II salts (such as some sodium and potassium salts) that are moderately hygroscopic form disordered stable mesophases, and type III salts that have high %DRH values, do not form stable LLC mesophases and leach out salt crystals. To illustrate this effect, a large group of salts from alkali and alkaline earth metals were investigated using XRD, POM, FTIR, and Raman techniques. Among the different salts investigated in this study, the LiX (where X is Cl, Br, I, NO3 , and ClO4 ) and CaX2 (X is Cl, and NO3 ) salts were more prone to establish LLC mesophases because of their lower %DRH values. The phase behavior with respect to concentration, stability, and thermal behavior of Li(I) systems were investigated further. It is seen that the phase transitions among different anions in the Li(I) systems follow the Hofmeister series.
Open Access
Highly conducting lyotropic liquid crystalline mesophases of pluronics (P65, P85, P103, and P123) and hydrated lithium salts (LiCl and LiNO3)
(American Chemical Society, 2014) Barım, G.; Albayrak, C.; Yilmaz, E.; Dag, Ö.
Demand for ionically conducting materials, as membranes and electrodes, is one of the driving forces of current research in chemistry, physics, and engineering. The lithium ion is a key element of these materials, and its assembly into nanostructures and mesophases is important for the membrane and electrode technologies. In this investigation, we show that hydrated lithium salts (such as LiCl·xH2O and LiNO3· xH2O, x is as low as 1.5 and 3.0, respectively) and pluronics (triblock copolymer such as PX where X is 65, 85, 103, and 123) form lyotropic liquid crystalline mesophases (LLCM), denoted as LiY·xH2O-PX-n (Y is Cl− or NO3 −, and n is the salt/PX mole ratio). The structure of the mesophase is hexagonal over a broad salt concentration and transforms to a cubic mesophase and then to disordered gel phase with an increasing salt content of the mixtures. The mesophases are unstable at low salt contents and undergo a phase separation into pure pluronics and salt-rich LLCMs. The salt content of the ordered mesophase can be as high as 30 mole ratio for each pluronic, which is a record high for any known salted phases. The mesophases also display high ac ionic conductivities, reaching up to 21 mS/cm at room temperature (RT), and are sensitive to the water content. These mesophases can be useful as ion-conducting membranes and can be used as media for the synthesis of lithium-containing nanoporous materials.
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
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 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, highly conductive, lithium salt/nonionic surfactant, lyotropic liquid-crystalline mesophase and its application
(Wiley-VCH Verlag, 2012) Albayrak, C.; Cihaner, A.; Dag, Ö.
Salty water! Lithium salts (LiCl, LiNO3, and LiClO4) at very high concentrations in water form lyotropic liquid crystalline (LLC) mesophases with a nonionic surfactant (10-lauryl ether) and display high ionic conductivities (10−2–10−4 S cm−1) over a broad temperature range (−10 to 80 °C) with excellent behavior as gel electrolytes in electrochemical applications.
Open Access
Origin of lyotropic liquid crystalline mesophase formation and liquid crystalline to mesostructured solid transformation in the metal nitrate salt-surfactant systems
(American Chemical Society, 2011) Albayrak, C.; Özkan, N.; Dag, Ö.
The zinc nitrate salt acts as a solvent in the ZnX-C12EO10 (ZnX is [Zn(H2O)6](NO3)2 and C12EO10 is C12H25- (OCH2CH2)10OH) 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-C12EO10 mesophase displays a usual phase behavior with an increasing concentration of the solvent (ZnX) in the media with an order of bicontinuous cubic(V1)-2D hexagonal(H1) - a mixture of 2D hexagonal and micelle cubic(H1 þ I)- micelle cubic(I)-micelle(L1) phases. The phase behaviors, specifically at low temperatures, and the first phase diagram of the ZnX-C12EO10 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.
Open Access
Phase separation in liquid crystalline mesophases of [Co(H 2O)6]X2: P65 Systems (X = NO3-, Cl-, or ClO4-)
(2007) Albayrak, C.; Gülten, G.; Dag, Ö.
Transition-metal aqua complex salts [M(H2O)6]X 2 (where M is Mn(II), Co(II), Ni(II), Zn(II), or Cd(II) and X is NO3-, Cl-, or ClO4-) can be dissolved in triblock poly(ethylene oxide) - poly(propylene oxide) - poly(ethylene oxide) copolymers (Pluronics, such as P65) to form homogeneous liquid crystalline (LC) mesophases. However, the [Co-(H2O) 6]X2:P65 LC mesophases slowly undergo phase separation into a disordered ion-free phase and an ordered ion-rich LC mesophase. The phase separation also takes place in the two-salt systems [Co(H2O) 6](NO3):[Co(H2O)6]-(ClO 4)2:P65 in which the ion-free disordered domains separate out from the initially ordered homogeneous mesophase. The phase separation results in a physical mixture of a hexagonal nitrate-rich and cubic perchlorate-rich LC and disordered ion-free domains in the mixed salt systems. The driving force in the phase separation in the [Co(H2O) 6]-X2:P65 system is Co(II)-catalyzed aerobic oxidation of P65 into ester and/or other oxidation products. The separation of ions in the [Co(H2O)6](NO3)2:[Co(H 2O)6](ClO4)2:P65 system is related to the mesostructures of the two-salt systems that are different, hexagonal in the [Co(H2O)6](NO3)2:P65 system and cubic in the [Co(H2O)6](ClO4)2:P65 system. There is no visible phase separation in the other transition-metal salt:P65 systems. The phase separation in the [Co-(H2O) 6]X2:P65 systems can also be eliminated by keeping the mesophase under a N2 atmosphere. © 2007 American Chemical Society.
Open Access
The role of charged surfactants in the thermal and structural properties of lyotropic liquid crystalline mesophases of [Zn(H2O)6](NO3)2-CnEOm-H2O
(2010) Albayrak, C.; Soylu, A. M.; Dag, Ö.
The mixtures of [Zn(H2O)6](NO3)2 salt, 10-lauryl ether (C12H25(OCH2CH2)10OH, represented as C12EO10), a charged surfactant (cetyltrimethylammonium bromide, C16H33N(CH3)3Br, represented as CTAB or sodium dodecylsulfate, C12H25OSO3Na, SDS) and water form lyotropic liquid crystalline mesophases (LLCM). This assembly accommodates up to 8.0 Zn(II) ions (corresponds to about 80% w/w salt/(salt + C12EO10)) for each C12EO10 in the presence of a 1.0 CTAB (or 0.5 SDS) and 3.5 H2O in its LC phase. The salt concentration can be increased by increasing charged surfactant concentration of the media. Addition of charged surfactant to the [Zn(H2O)6](NO3)2–C12EO10 mesophase not only increases the salt content, it can also increase the water content of the media. The charged surfactant-C12EO10 (hydrophobic tail groups) and the surfactant (head groups)-salt ion (ion-pair, hydrogen-bonding) interactions stabilize the mesophases at such salt high and water concentrations. The presence of both Br and NO 3 ions influences the thermal and structural properties of the [Zn(H2O)6](NO3)2–C12EO10–CTAB(or SDS)–H2O LLCM, which have been investigated using XRD, POM (with a hot stage), FT-IR and Raman techniques.