Using a magnetic Frederiks transition technique, we measure the temperature and concentration dependences of splay K1, twist K2, and bend K3 elastic constants for the lyotropic chromonic liquid crystal sunset yellow formed through noncovalent reversible aggregation of organic molecules in water. K1 and K3 are comparable to each other and are an order of magnitude higher than K2. At higher concentrations and lower temperatures, K1 and the ratios K1/K3 and K1/K2 increase, which is attributed to elongation of self-assembled lyotropic chromonic liquid crystal aggregates, a feature not found in conventional thermotropic and lyotropic liquid crystals formed by covalently bound units of a fixed length.

The surface alignment of lyotropic chromonic liquid crystals (LCLCs) can be not only planar (tangential) but also homeotropic, with self-assembled aggregates perpendicular to the substrate, as demonstrated by mapping optical retardation and by three-dimensional imaging of the director field. With time, the homeotropic nematic undergoes a transition into a tangential state. The anchoring transition is discontinuous and can be described by a double-well anchoring potential with two minima corresponding to tangential and homeotropic orientation.PACS numbers: 42.70.Df Spatial bounding of a liquid crystal (LC) lifts degeneracy of molecular orientation specified by the director n and sets an "easy axis" n 0 at the surface. Deviation of n from n 0 requires some work thus establishing a phenomenon of "surface anchoring" that has been explored extensively for thermotropic LCs [1][2][3][4][5][6][7][8][9][10][11]. For lyotropic LCs, such as water solutions of polyelectrolytes, surfactants, dyes, etc., the studies of anchoring are scarce. The view is that the surface alignment of lyotropic LCs is determined by an excluded volume effect, which favors the longest dimension of building units to be parallel to a substrate [12][13][14][15]. We study surface phenomena in nematic lyotropic chromonic LCs (LCLCs), a distinct class of self-assembled LCs formed by water solutions of planklike molecules with polyaromatic cores and ionic peripheral groups [16]. Reversible chromonic assembly and mesomorphism are displayed broadly by dyes, drugs and nucleotides [16]. In water, the LCLC molecules stack face-to-face, forming elongated aggregates. The aggregates are not fixed by covalent bonds, being polydisperse with an average length l ∝ √ φ ln (E/k B T ) that depends on temperature T , volume fraction φ, and stacking energy E ∼ (4 − 10) k B T [17]. We demonstrate that in LCLCs, n 0 can be either parallel to a substrate (planar or tangential alignment, denoted "P") or perpendicular (homeotropic, or H alignment), with discontinuous transitions between the two, thus suggesting that both entropy and anisotropic molecular interactions control the surface phenomena.We study disodium cromoglycate (DSCG) [16], C 23 H 14 O 11 N a 2 (Spectrum Inc, purity 98%), dissolved in water at 15 wt % (mixture A) and 12.5wt% doped with 1.5wt% of Na 2 SO 4 (mixture B). The H alignment was achieved by treating glass plates with 1% water solution of N,N-dimethyl-N-octadecyl-3-aminopropyl trimethoxysilyl chloride (DMOAP) [2]. The two plates are separated by Mylar strips; the cell thickness d was measured by light interference technique. The cells were filled at T N I + 10 K, sealed with a UV-cured Norland epoxy glue, and cooled down to T = 298 K with a rate 5 K/ min in a thermal stage HS-1 (Instec, Inc.). We used an LC PolScope for in-plane mapping of opticale sin 2 θ −1/2 , θ is the angle between n and the normal z to the cell, n o and n e are the ordinary and extraordinary refractive indices, respectively. At 546 nm and T = 298 K, we determined n o = 1.37 ± ...

Zinc oxide nanoparticles codoped with Co2+ and Mn2+ ions (Zn(1−x−y)MnxCoyO NPs) were obtained for the first time by microwave solvothermal synthesis. The nominal content of Co2+ and Mn2+ in Zn(1−x−y)MnxCoyO NPs was x = y = 0, 1, 5, 10 and 15 mol % (the amount of both ions was equal). The precursors were obtained by dissolving zinc acetate dihydrate, manganese (II) acetate tetrahydrate and cobalt (II) acetate tetrahydrate in ethylene glycol. The morphology, phase purity, lattice parameters, dopants content, skeleton density, specific surface area, average particle size, average crystallite size, crystallite size distribution and magnetic properties of NPs were determined. The real content of dopants was up to 25.0% for Mn2+ and 80.5% for Co2+ of the nominal content. The colour of the samples changed from white to dark olive green in line with the increasing doping level. Uniform spherical NPs with wurtzite structure were obtained. The average size of NPs decreased from 29 nm to 21 nm in line with the increase in the dopant content. Brillouin type paramagnetism and an antiferromagnetic interaction between the magnetic ions was found for all samples, except for that with 15 mol % doping level, where a small ferromagnetic contribution was found. A review of the preparation methods of Co2+ and Mn2+ codoped ZnO is presented.

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A newly synthesized four-ring bent-core liquid crystal (BCLC) has been studied using experimental and quantum chemical approach. Differential scanning calorimetry (DSC), polarised optical microscopy (POM), and X-ray investigations were carried out to identify the phase transitions and associated phases.DSC along with POM revealed four phase transitions i.e. Cr -SmX -SmC -N cybC -Iso in the temperature range from 30 1C to 180 1C. The existence of smectic C like fluctuations also known as cybotactic groups in the broad temperature range of the nematic phase was confirmed by small angle X-ray diffraction. Conformational and vibrational analyses have been performed using density functional theory (DFT), to identify the most stable conformer having a bent shape. Analysis of the potential energy surface (PES) for different torsional angles revealed the most probable conformational states for the BCLC. Temperature dependent Fourier transform infrared (TD-FTIR) spectroscopy is used to study phase transitions and revealed marked changes in the spectral line shape especially the vibrations of OH, CH 2 , CH 3 , CQO, and HCQN groups during the SmC -N cybC phase transition above B95 1C. A good agreement between the calculated and observed infrared spectra validates the structure of this conformer that has been used for further studies.