Browsing by Subject "Surfactants"

Filter results by typing the first few letters
Now showing 1 - 6 of 6
  • Thumbnail Image
    ItemOpen 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.
  • Thumbnail Image
    ItemOpen 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.
  • Thumbnail Image
    ItemOpen Access
  • Thumbnail Image
    ItemOpen 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.
  • Thumbnail Image
    ItemOpen Access
    Non-covalent interactions between carbon nanotubes and conjugated polymers
    (Royal Society of Chemistry, 2011) Tuncel, D.
    Carbon nanotubes (CNTs) are interest to many different disciplines including chemistry, physics, biology, material science and engineering because of their unique properties and potential applications in various areas spanning from optoelectronics to biotechnology. However, one of the drawbacks associated with these materials is their insolubility which limits their wide accessibility for many applications. Various approaches have been adopted to circumvent this problem including modification of carbon nanotube surfaces by non-covalent and covalent attachments of solubilizing groups. Covalent approach modification may alter the intrinsic properties of carbon nanotubes and, in turn make them undesirable for many applications. On the other hand, a non-covalent approach helps to improve the solubility of CNTs while preserving their intrinsic properties. Among many noncovalent modifiers of CNTs, conjugated polymers are receiving increasing attention and highly appealing because of a number of reasons. To this end, the aim of this feature article is to review the recent results on the conjugated polymer-based non-covalent functionalization of CNTs with an emphasis on the effect of conjugated polymers in the dispersibility/solubility, optical, thermal and mechanical properties of carbon nanotubes as well as their usage in the purification and isolation of a specific single-walled nanotube from the mixture of the various tubes.
  • Thumbnail Image
    ItemOpen Access
    Salt-acid-surfactant lyotropic liquid crystalline mesophases: synthesis of highly transparent mesoporous calcium hydroxyapatite thin films
    (Wiley-VCH Verlag, 2016) Tunkara, E.; Dag, Ö.
    Even though calcium hydroxyapatite [Ca10(PO4)6(OH)2, HAp] is one of the most investigated materials in the literature, the synthesis of mesoporous transparent thin film of HAp has not yet been reported. We show herein that mixtures of phosphoric acid (H3PO4·H2O, PA), calcium nitrate tetrahydrate [Ca(NO3)2·4H2O, CaN] and non‐ionic surfactant [C12H25(OCH2CH2)10OH, C12E10] can self‐assemble into stable lyotropic liquid crystalline (LLC) mesophases. The clear aqueous solutions of the mixtures can be spin‐coated over any substrate and then calcined to form highly transparent mesoporous HAp (mHAp) thin films. From among the compositions studied, three molar ratios of CaN/PA/C12E10 [3.3:2:1 (low), 5.8:3.5:1 (intermediate) and 8.4:5:1 (high)] were chosen for large‐scale preparation to investigate their structural and thermal properties. The mHAp films form at around 300 °C and fully crystalize at 500 °C, retaining their transparency, uniformity and porosity in all compositions with few differences. The surface area and pore volume decrease, and the pore size and pore size distribution increase with increasing annealing temperature for all compositions.