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Sample records for nematic lyotropic liquid

  1. Surface alignment and anchoring transitions in nematic lyotropic chromonic liquid crystal.

    PubMed

    Nazarenko, V G; Boiko, O P; Park, H-S; Brodyn, O M; Omelchenko, M M; Tortora, L; Nastishin, Yu A; Lavrentovich, O D

    2010-07-01

    The surface alignment of lyotropic chromonic liquid crystals can not only be 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. PMID:20867479

  2. Polar Switching in a Lyotropic Columnar Nematic Liquid Crystal Made of Bowl-Shaped Molecules.

    PubMed

    Guilleme, Julia; Cavero, Emma; Sierra, Teresa; Ortega, Josu; Folcia, César L; Etxebarria, Jesus; Torres, Tomás; González-Rodríguez, David

    2015-08-01

    A polar response in a lyotropic columnar nematic material is reported. The material accommodates bowl-shaped molecules with strong axial dipole moments in column segments without head-to-tail invariance. Optical second-harmonic-generation methods confirm that the nematic columns align unidirectionally under an applied electric field and the material develops remnant macroscopic polarization observable for hours. The switching takes place by a flip of the columns. PMID:26078047

  3. Annihilation dynamics of stringlike topological defects in a nematic lyotropic liquid crystal.

    PubMed

    Guimarães, R R; Mendes, R S; Fernandes, P R G; Mukai, H

    2013-10-01

    Topological defects can appear whenever there is some type of ordering. Its ubiquity in nature has been the subject of several studies, from early Universe to condensed matter. In this work, we investigated the annihilation dynamics of defects and antidefects in a lyotropic nematic liquid crystal (ternary mixture of potassium laurate, decanol and deionized-destillated water) using the polarized optical light microscopy technique. We analyzed Schlieren textures with topological defects produced due to a symmetry breaking in the transition of the isotropic to nematic calamitic phase after a temperature quench. As result, we obtained for the distance D between two annihilating defects (defect-antidefect pair), as a function of time t remaining for the annihilation, the scaling law D ∝ t(α), with α = 0.390 and standard deviation σ = 0.085. Our findings go in the direction to extend experimental results related to dynamics of defects in liquid crystals since only thermotropic and polymerics ones had been investigated. In addition, our results are in good quantitative agreement with previous investigations on the subject. PMID:24025970

  4. Anomalous behavior in the crossover between the negative and positive biaxial nematic mesophases in a lyotropic liquid crystal.

    PubMed

    Akpinar, Erol; Reis, Dennys; Figueiredo Neto, Antonio M

    2014-05-19

    A novel quaternary lyotropic liquid-crystalline mixture of dodecyltrimethylammonium bromide (DDTMABr)/sodium bromide/1-dodecanol/water, presenting the biaxial nematic phase (NB ) in addition to two uniaxial discotic (ND) and calamitic (NC) nematic ones, was synthesized. The partial phase diagram of this new mixture was constructed as a function of the DDTMABr molar-fraction concentration. The phase transitions from uniaxial to biaxial nematic phases were studied by means of the temperature dependence of the optical birefringence. In a particular region of the phase diagram, anomalous behavior was observed in the crossover from N-B to N+b: the contrast of the conoscopic fringes, which allows the birefringence measurements, almost vanishes, and the sample loses its alignment. This behavior, which was not observed before in lyotropics, was interpreted as a decrease in the mean diamagnetic susceptibility anisotropy (Δχ) of the sample, which was related to the shape anisotropy of the micelles. Small-angle X-ray scattering measurements were performed to evaluate the micellar shape anisotropy; these revealed that this mixture presented a smaller shape anisotropy than those of other lyotropic micellar systems presenting the NB phase. PMID:24692308

  5. Stereochemical control of nonamphiphilic lyotropic liquid crystals: chiral nematic phase of assemblies separated by six nanometers of aqueous solvents.

    PubMed

    Yang, Sijie; Wang, Bing; Cui, Dawei; Kerwood, Deborah; Wilkens, Stephan; Han, Junjie; Luk, Yan-Yeung

    2013-06-13

    Unlike conventional thermotropic and lyotropic liquid crystals, nonamphiphilic lyotropic liquid crystals consist of hydrated assemblies of nonamphiphilic molecules that are aligned with a separation of about 6 nm between assemblies in an aqueous environment. This separation raises the question of how chirality, either from chiral mesogens or chiral dopants, would impact the phase as the assemblies that need to interact with each other are about 6 nm apart. Here, we report the synthesis of three stereoisomers of disodium chromonyl carboxylate, 5'DSCG-diviol, and the correlation between the molecular structure, bulk assembly, and liquid crystal formation. We observed that the chiral isomers (enantiomers 5'DSCG-(R,R)-diviol and 5'DSCG-(S,S)-diviol) formed liquid crystals while the achiral isomer 5'DSCG-meso-diviol did not. Circular dichroism indicated a chiral conformation with bisignate cotton effect. The nuclear Overhauser effect in proton NMR spectroscopy revealed conformations that are responsible for liquid crystal formation. Cryogenic transmission electron microscopy showed that chiral 5'DSCG-diviols form assemblies with crossings. Interestingly, only planar alignment of the chiral nematic phase was observed in liquid crystal cells with thin spacers. The homeotropic alignment that permitted a fingerprint texture was obtained only when the thickness of the liquid crystal cell was increase to above ~500 μm. These studies suggest that hydrated assemblies of chiral 5'DSCG-diviol can interact with each other across a 6 nm separation in an aqueous environment by having a twist angle of about 0.22° throughout the sample between the neighboring assemblies. PMID:23688325

  6. Electrolyte effects on the chiral induction and on its temperature dependence in a chiral nematic lyotropic liquid crystal.

    PubMed

    Dawin, Ute C; Osipov, Mikhail A; Giesselmann, Frank

    2010-08-19

    We present a study on the effect of added CsCl and of temperature variation on the chiral induction in a chiral nematic lyotropic liquid crystal (LC) composed of the surfactant cesium perfluorooctanoate (CsPFO), water, and the chiral dopant d-Leucine (d-Leu). The chiral induction was measured as the helical pitch P. The role of the additives CsCl and d-Leu on the phase behavior is investigated and discussed. The thermal stabilization effect of CsCl is shown to lead to an apparent salt effect on the pitch when the pitch is compared at a constant temperature. This apparent effect is removed by comparing the pitch measured for different salt concentrations at a temperature relative to the phase-transition temperatures; thus, the real salt effect on the pitch is described. High salt concentrations are shown to increase the pitch, that is, hinder the chiral induction. The effect is discussed in terms of a decreased solubilization of the amphiphilic chiral solute d-Leu in the micelles due to the salt-induced screening of the surfactant head groups and the consequential denser packing of the surfactants. The temperature variation of the pitch is investigated for all CsCl concentrations and is found to be essentially independent of the salt concentration. The temperature variation is analyzed and discussed in the context of a theoretical model taking into account specific properties of lyotropic liquid crystals. A hyperbolic decrease of the pitch is found with increasing temperature, which is known, from thermotropic liquid crystals, to stem from pretransitional critical fluctuations close to the lamellar phase. However, the experimental data confirmed the theoretical prediction that, at high temperature, that is, far away from the transition into the lamellar phase, the pitch is characterized by a linear temperature dependence which is determined by a combination of steric and dispersion chiral interactions. The parameters of the theoretical expression for the pitch have

  7. Brownian Dynamics of Colloidal Particles in Lyotropic Chromonic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Martinez, Angel; Collings, Peter J.; Yodh, Arjun G.

    We employ video microscopy to study the Brownian dynamics of colloidal particles in the nematic phase of lyotropic chromonic liquid crystals (LCLCs). These LCLCs (in this case, DSCG) are water soluble, and their nematic phases are characterized by an unusually large elastic anisotropy. Our preliminary measurements of particle mean-square displacement for polystyrene colloidal particles (~5 micron-diameter) show diffusive and sub-diffusive behaviors moving parallel and perpendicular to the nematic director, respectively. In order to understand these motions, we are developing models that incorporate the relaxation of elastic distortions of the surrounding nematic field. Further experiments to confirm these preliminary results and to determine the origin of these deviations compared to simple diffusion theory are ongoing; our results will also be compared to previous diffusion experiments in nematic liquid crystals. We gratefully acknowledge financial support through NSF DMR12-05463, MRSEC DMR11-20901, and NASA NNX08AO0G.

  8. Optical characterization of lyotropic chromonic liquid crystals

    NASA Astrophysics Data System (ADS)

    Liu, Hui

    Lyotropic chromonic liquid crystals (LCLCs) represent a special class of lyotropic mesophases markedly different from conventional amphiphilic mesogens. Materials forming LCLCs are composed of plank-like molecules with a polyaromatic central core and hydrophilic ionic groups at the periphery. The individual molecules tend to assemble into rodlike aggregates that form the N phase once the concentration exceeds about 0.1M. The LCLC materials show a tremendous potential for applications in optics as self-assembling polarizing and compensating films and in the area of real-time biological sensing. The emerging applications require an understanding of basic properties of LCLC. This work addresses these needs by providing the optical characterization of LCLC. We studied in detail the optical anisotropic properties of three different nematic LCLCs: disodium cromoglycate (DSCG), Blue 27, and Violet 20. We determined the birefringence of these three materials as the function of the temperature T and wavelength lambda and the corresponding dependencies of the absorption coefficients for Blue 27 and Violet 20. The birefringence is negative and significantly lower in the absolute value as compared to the birefringence of typical thermotropic N materials. We determined the scalar order parameter of the nematic phase of Blue 27 and its temperature dependence. The scalar order parameter is close to the one predicted by the classic Onsager theory for solutions of rigid rods. However, this similarity is not complete, as the measured scalar order parameter depends on temperature. The I-N pretransitional fluctuations in an aqueous solution of DSCG were studied by light scattering. We obtained the correlation length of the orientational order-parameter fluctuations of isotropic DSCG solution. The pretransitional behavior of light scattering does not completely follow the classic Landau-de Gennes model. This feature is explained by the variable length of DSCG aggregates as a function

  9. Homeotropic alignment of lyotropic chromonic liquid crystals using noncovalent interactions.

    PubMed

    Jeong, Joonwoo; Han, Ganghee; Johnson, A T Charlie; Collings, Peter J; Lubensky, Tom C; Yodh, Arjun G

    2014-03-18

    We report on the homeotropic alignment of lyotropic chromonic liquid crystals (LCLCs). Homeotropic anchoring of LCLCs is difficult to achieve, and this challenge has limited development of applications for LCLCs. In this work, homeotropic alignment is achieved using noncovalent interactions between the LCLC molecules and various alignment layers including graphene, parylene films, poly(methyl methacrylate) films, and fluoropolymer films. The LCLC molecules are unique in that they self-assemble via noncovalent interactions in water into elongated aggregates which, in turn, form nematic and columnar liquid crystal (LC) phases. Here we exploit these same noncovalent interactions to induce homeotropic anchoring of the nematic LCLC. Homeotropic alignment is confirmed by polarized optical microscopy and conoscopy. We also report on novel transient stripe textures that occur when an initial flow-induced planar alignment transforms into the equilibrium homeotropic alignment required by boundary conditions. An understanding of this behavior could be important for switching applications. PMID:24559290

  10. Liquid crystalline thermotropic and lyotropic nanohybrids

    NASA Astrophysics Data System (ADS)

    Saliba, Sarmenio; Mingotaud, Christophe; Kahn, Myrtil L.; Marty, Jean-Daniel

    2013-07-01

    This review is meant to give the reader an insight into hybrids incorporating different types of nanoparticles, e.g. metallic or metal oxides, within different types of lyotropic and thermotropic liquid crystals, from relatively small calamitic molecules to the larger discotics and polymers. In particular, this review highlights the importance of nanoparticle-liquid crystal interactions in accessing hybrid materials that exhibit synergetic properties.

  11. Nematic liquid crystal bridges

    NASA Astrophysics Data System (ADS)

    Doss, Susannah; Ellis, Perry; Vallamkondu, Jayalakshmi; Danemiller, Edward; Vernon, Mark; Fernandez-Nieves, Alberto

    We study the effects of confining a nematic liquid crystal between two parallel glass plates with homeotropic boundary conditions for the director at all bounding surfaces. We find that the free surface of the nematic bridge is a surface of constant mean curvature. In addition, by changing the distance between the plates and the contact angle with the glass plates, we transition between loops and hedgehogs that can be either radial or hyperbolic.

  12. Organized composites of Carbon Nanotubes and Lyotropic Liquid Crystals at very low Surfactant Concentration

    NASA Astrophysics Data System (ADS)

    Scalia, Giusy; Jo, Hyeran; Park, Ji Hyun; Lagerwall, Jan

    The difficulties in dispersing and organizing carbon nanotubes (CNTs) can be efficiently tackled using surfactant-based lyotropic liquid crystals, combining high nanotube loading with long-range order. A problem with surfactants is, however, that their residues negatively affect CNT device performance. Here we show aligned CNT-lyotropic composites at reduced surfactant concentration. By combining cat- and anionic surfactants a lyotropic nematic phase forms at just 8% surfactant concentration, and CNTs can be well dispersed and aligned in it. The CNTs themselves were first dispersed below the Krafft temperature of the surfactant used for their stabilization, minimizing also its concentration. The composites exhibit very interesting properties with strong sensitivity to the surfactant ratios. They were investigated by Polarized Optical Microscopy and Polarized Raman spectroscopy, and also the electrical properties were studied

  13. Uniaxial-to-biaxial cholesteric and nematic phase transitions on a lyotropic alcohol-free mixture

    SciTech Connect

    de Sant'Ana, Z.A.; Figueiredo Neto, A.M. )

    1992-12-15

    Interferometric measurements of the chirality-induced biaxiality in the vicinity of the uniaxial-to-biaxial cholesteric transition of the lyotropic system potassium laurate, decylammonium chloride, H[sub 2]O, and brucine sulfate are reported. The mean-field approach to describe the cholesteric-to-cholesteric transition allows an estimate of the ratio between coefficients of the Landau expansion. The values of the bare correlation length, [xi][sub 0][similar to]1000 A, calculated are larger than in lyotropic systems with alcohol. The chirality-induced biaxiality measurements in the limit of zero elastic field ([ital q][sup 2]=0) and the birefringence measurements in the nematic phase confirm critical properties of the uniaxial-to-biaxial nematic transition. The critical exponents for the order parameter ([beta]) and the susceptibility ([gamma]) are in good agreement with the values calculated for the [ital XY] model.

  14. Kerr response of nematic liquids.

    NASA Technical Reports Server (NTRS)

    Johnston, A. R.

    1973-01-01

    Description of the results of recent observations of the Kerr effect in nematic liquid crystals in a temperature range just above their nematic-isotropic transition. These results indicate that the intermolecular ordering forces in a nematic substance can enhance the Kerr effect just above the nematic transition in their isotropic state. It is felt that existing theory provides a useful approximation for relating molecular size to response time.

  15. Adding Mono- and Multivalent Ions to Lyotropic Chromonic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Tortora, Luana; Park, Heung-Shik; Antion, Kelly; Woolwerton, Chris; Finotello, Daniele; Lavrentovich, Oleg

    2006-03-01

    Lyotropic Chromonic Liquid Crystals (LCLCs) are a distinct class of liquid crystals formed in aqueous solutions by molecules with rigid polyaromatic cores and ionic groups at the periphery [1-4]. The phase diagrams of these materials should depend on entropic factors (as in the Onsager model) and electrostatic interactions. Using optical polarizing microscopy, we studied the effects of mono- and multivalent ions on the phase diagrams of Blue 27 [3] and Sunset Yellow [2]. The monovalent ions change the temperatures of phase transitions, as described in [4], while the effect of multivalent ions is more dramatic and, in addition to the changed temperatures of phase transitions by tens of degrees, it often involves condensation of LCLC aggregates into domains with birefringence much higher than that in a normal nematic phase. Work supported by OBR B-7844. [1]J. Lydon, Current Opin. Colloid & Interface Sci. 3, 458 (1998);8, 480-489 (2004); [2]V. R. Horowitz, L. A. Janowitz, A. L. Modic, P. J. Heiney, and P. J. Collings, 2005, Phys. Rew. E 72, 041710; [3]Yu. A. Nastishin, H. Liu, T. Schneider, T., V. Nazarenko, R. Vasyuta, S. V. Shiyanovskii, and O. D. Lavrentovich, 2005, Phys. Rev. E 72, 041711; [4]A.F. Kostko, B. H. Cipriano, O. A. Pinchuk, L. Ziserman, M. A. Anisimov, D. Danino, and S. R. Raghavan. J. Phys. Chem. B 109, 19126-19133 (2005)

  16. Phase states and thermomorphologic, thermotropic, and magnetomorphologic properties of lyotropic mesophases: Sodium lauryl sulphate-water-1-decanol liquid-crystalline system

    NASA Astrophysics Data System (ADS)

    Özden, Pınar; Nesrullajev, Arif; Oktik, Şener

    2010-12-01

    Phase states in sodium lauryl sulphate-water-1-decanol lyotropic liquid-crystalline system have been investigated for different temperature ranges. The dependence of triangle phase diagram types, phase boundaries, and sequence of lyotropic mesophases vs temperature has been found. The thermomorphologic, thermotropic, and magnetomorphologic properties of hexagonal E, lamellar D, nematic-calamitic NC , nematic-discotic ND , and biaxial nematic Nbx mesophases have been studied in detail. Dynamics of transformations of magnetically induced textures has been investigated. Peculiarities of typical and magnetically induced textures have been investigated in detail. Triangle phase diagrams of sodium lauryl sulphate-water-1-decanol lyotropic liquid-crystalline system for different temperatures and typical and magnetically induced textures of E, D, NC , ND , and Nbx mesophases are presented.

  17. Orientational Order of a Lyotropic Chromonic Liquid Crystal Measured by Polarized Raman Spectroscopy.

    PubMed

    Yao, Xuxia; Nayani, Karthik; Park, Jung Ok; Srinivasarao, Mohan

    2016-05-19

    Lyotropic chromonic liquid crystals are distinct from thermotropic nematics from a fundamental standpoint as the structure of the aggregating columns is a function of both the temperature and concentration. We report on the thermal evolution of orientational order parameters, both the second (=scalar) (⟨P200⟩ (=S)) and fourth (⟨P400⟩) order, of sunset yellow FCF aqueous solutions, measured using polarized Raman spectroscopy for different concentrations. The order parameter increases with the concentration, and their values are high in comparison with those of thermotropic liquid crystals. On the basis of Raman spectroscopy, we provide the strongest evidence yet that the hydrozone tautomer of SSY is the predominant form in aqueous solutions in the isotropic, nematic, and columnar phases, as well as what we believe to be the first measurements of (⟨P400⟩) for this system. PMID:27074395

  18. Thermotropic and lyotropic behaviour of new liquid-crystalline materials with different hydrophilic groups: synthesis and mesomorphic properties

    PubMed Central

    Kašpar, Miroslav; Hamplová, Věra; Dawin, Ute; Giesselmann, Frank

    2013-01-01

    Summary Several new calamitic liquid-crystalline (LC) materials with flexible hydrophilic chains, namely either hydroxy groups or ethylene glycol units, or both types together, have been synthesized in order to look for new functional LC materials exhibiting both, thermotropic and lyotropic behaviour. Such materials are of high potential interest for challenging issues such as the self-organization of carbon nanotubes or various nanoparticles. Thermotropic mesomorphic properties have been studied by using polarizing optical microscopy, differential scanning calorimetry and X-ray scattering. Four of these nonchiral and chiral materials exhibit nematic and chiral nematic phases, respectively. For some molecular structures, smectic phases have also been detected. A contact sample of one of the prepared compounds with diethylene glycol clearly shows the lyotropic behaviour; namely a lamellar phase was observed. The relationship between the molecular structure and mesomorphic properties of these new LCs with hydrophilic chains is discussed. PMID:23504455

  19. Phase and Topological Behavior of Lyotropic Chromonic Liquid Crystals in Double Emulsions

    NASA Astrophysics Data System (ADS)

    Davidson, Zoey S.; Jeong, Joonwoo; Tu, Fuquan; Lohr, Matt; Lee, Daeyeon; Collings, Peter J.; Lubensky, Tom C.; Yodh, A. G.

    2013-03-01

    Lyotropic chromonic liquid crystals, assembled by non-covalent interactions, have fascinating temperature- and concentration-dependent phase behavior. Using water-oil-water double emulsions, we are able control the inner droplet chromonic phase concentration by osmosis through the oil phase. We then study the configurations of the chromonic liquid crystal phases in droplets by varying the oil types, oil soluble surfactants, and inner droplet diameter. We employ polarization microscopy to observe resulting nematic and columnar phases of Sunset Yellow FCF, and we deduce the liquid crystal configuration of both phases within the droplets. Simulations based on Jones matrices confirm droplet appearance, and preliminary observations of chromonic liquid crystal shells in oil-water-oil double emulsions are reported. Supported by UPenn MRSEC DMR 11-20901 and NSF DMR 12-05463

  20. Boundary Stability of a Nematic Liquid Bridge

    NASA Astrophysics Data System (ADS)

    Barnes, William; Santangelo, Chris

    2014-03-01

    We consider a nematic liquid crystal droplet in air confined between two parallel plates with homeotropic boundary conditions. The boundary conditions at the nematic-plate and nematic-air interfaces induce either a hedgehog or planar ring disclination within the nematic bridge, depending on the plate separation and bridge radius. We study the stability of the liquid crystal-air boundary of a nearly cylindrical nematic bridge by minimizing the Frank elastic energy.

  1. Escaped-radial configuration with a twist: lyotropic chromonic liquid crystals confined to cylindrical cavities

    NASA Astrophysics Data System (ADS)

    Jeong, Joonwoo; Kang, Louis; Davidson, Zoey S.; Lohr, Matthew; Beller, Daniel A.; Kamien, Randall D.; Lubensky, Tom C.; Yodh, A. G.; Collings, Peter J.

    2014-03-01

    We report new chiral-symmetry-broken configurations of nematic liquid crystals (LCs) confined to cylindrical cavities with a homeotropic boundary condition. In order to relieve high splay deformation in the center of the cylinder with the homeotropic boundary condition, many nematic LCs adopt an escaped-radial configuration where LC directors are radial near the cavity wall but parallel to the cylindrical axis near the center. Interestingly, we find that achiral lyotropic chromonic liquid crystals (LCLCs) having an unusually small twist modulus can have a configuration that is both escaped and twisted radially. Sunset Yellow FCF, a nematic LCLC, is introduced into capillaries coated with a homeotropic alignment layer, and its configurations are investigated by polarized optical microscopy and numerical calculations. Additionally, we discuss other newly observed structures: 1) domain-wall-like defects separating regions of opposite handedness in the twisted- and escaped-radial configuration and 2) another chiral configuration having a double helix of disclination lines along the cylindrical axis. We acknowledge support from the National Science Foundation: DGE-1321851, DMR-1104707, DMR-1205463, and MRSEC DMR-1120901.

  2. Spontaneous emergence of chirality in achiral lyotropic chromonic liquid crystals confined to cylinders

    PubMed Central

    Nayani, Karthik; Chang, Rui; Fu, Jinxin; Ellis, Perry W.; Fernandez-Nieves, Alberto; Park, Jung Ok; Srinivasarao, Mohan

    2015-01-01

    The presumed ground state of a nematic fluid confined in a cylindrical geometry with planar anchoring corresponds to that of an axial configuration, wherein the director, free of deformations, is along the long axis of the cylinder. However, upon confinement of lyotropic chromonic liquid crystals in cylindrical geometries, here we uncover a surprising ground state corresponding to a doubly twisted director configuration. The stability of this ground state, which involves significant director deformations, can be rationalized by the saddle-splay contribution to the free energy. We show that sufficient anisotropy in the elastic constants drives the transition from a deformation-free ground state to a doubly twisted structure, and results in spontaneous symmetry breaking with equal probability for either handedness. Enabled by the twist angle measurements of the spontaneous twist, we determine the saddle-splay elastic constant for chromonic liquid crystals for the first time. PMID:26287517

  3. Spontaneous emergence of chirality in achiral lyotropic chromonic liquid crystals confined to cylinders.

    PubMed

    Nayani, Karthik; Chang, Rui; Fu, Jinxin; Ellis, Perry W; Fernandez-Nieves, Alberto; Park, Jung Ok; Srinivasarao, Mohan

    2015-01-01

    The presumed ground state of a nematic fluid confined in a cylindrical geometry with planar anchoring corresponds to that of an axial configuration, wherein the director, free of deformations, is along the long axis of the cylinder. However, upon confinement of lyotropic chromonic liquid crystals in cylindrical geometries, here we uncover a surprising ground state corresponding to a doubly twisted director configuration. The stability of this ground state, which involves significant director deformations, can be rationalized by the saddle-splay contribution to the free energy. We show that sufficient anisotropy in the elastic constants drives the transition from a deformation-free ground state to a doubly twisted structure, and results in spontaneous symmetry breaking with equal probability for either handedness. Enabled by the twist angle measurements of the spontaneous twist, we determine the saddle-splay elastic constant for chromonic liquid crystals for the first time. PMID:26287517

  4. Ionic-content dependence of viscoelasticity of the lyotropic chromonic liquid crystal sunset yellow

    NASA Astrophysics Data System (ADS)

    Zhou, Shuang; Cervenka, Adam J.; Lavrentovich, Oleg D.

    2014-10-01

    A lyotropic chromonic liquid crystal (LCLC) is an orientationally ordered system made by self-assembled aggregates of charged organic molecules in water, bound by weak noncovalent attractive forces and stabilized by electrostatic repulsions. We determine how the ionic content of the LCLC, namely, the presence of mono- and divalent salts and p H enhancing agent, alter the viscoelastic properties of the LCLC. Aqueous solutions of the dye sunset yellow with a uniaxial nematic order are used as an example. By applying a magnetic field to impose orientational deformations, we measure the splay K1, twist K2, and bend K3 elastic constants and rotation viscosity γ1 as a function of concentration of additives. The data indicate that the viscoelastic parameters are influenced by ionic content in dramatic and versatile ways. For example, the monovalent salt NaCl decreases K3 and K2 and increases γ1, while an elevated p H decreases all the parameters. We attribute these features to the ion-induced changes in length and flexibility of building units of LCLC, the chromonic aggregates, a property not found in conventional thermotropic and lyotropic liquid crystals formed by covalently bound units of fixed length.

  5. Lyotropic chromonic liquid crystals: From viscoelastic properties to living liquid crystals

    NASA Astrophysics Data System (ADS)

    Zhou, Shuang

    Lyotropic chromonic liquid crystal (LCLC) represents a broad range of molecules, from organic dyes and drugs to DNA, that self-assemble into linear aggregates in water through face-to-face stacking. These linear aggregates of high aspect ratio are capable of orientational order, forming, for example nematic phase. Since the microscopic properties (such as length) of the chromonic aggregates are results of subtle balance between energy and entropy, the macroscopic viscoelastic properties of the nematic media are sensitive to change of external factors. In the first part of this thesis, by using dynamic light scattering and magnetic Frederiks transition techniques, we study the Frank elastic moduli and viscosity coefficients of LCLC disodium cromoglycate (DSCG) and sunset yellow (SSY) as functions of concentration c , temperature T and ionic contents. The elastic moduli of splay (K1) and bend (K3) are in the order of 10pN, about 10 times larger than the twist modulus (K2). The splay modulus K1 and the ratio K1/K3 both increase substantially as T decreases or c increases, which we attribute to the elongation of linear aggregates at lower T or higher c . The bend viscosity is comparable to that of thermotropic liquid crystals, while the splay and twist viscosities are several orders of magnitude larger, changing exponentially with T . Additional ionic additives into the system influence the viscoelastic properties of these systems in a dramatic and versatile way. For example, monovalent salt NaCl decreases bend modulus K3 and increases twist viscosity, while an elevated pH decreases all the parameters. We attribute these features to the ion-induced changes in length and flexibility of building units of LCLC, the chromonic aggregates, a property not found in conventional thermotropic and lyotropic liquid crystals form by covalently bound units of fixed length. The second part of the thesis studies a new active bio-mechanical hybrid system called living liquid crystal

  6. Chirality Amplification in Tactoids of Lyotropic Chromonic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Peng, Chenhui; Lavrentovich, Oleg

    2014-03-01

    We demonstrate an effective chirality amplification based on the long-range forces, extending over the scales of tens of micrometers, much larger than the single molecule (nanometer) scale. The mechanism is rooted in the long-range elastic nature of orientational order in lyotropic chromonic liquid crystals (LCLCs) that represent water solutions of achiral disc-like molecules. Minute quantities of chiral molecules such as amino acid L-alanine and limonene added to the droplets of LCLC lead to chiral amplification characterized by an increase of optical activity by a factor of 103 - 104. This effect allows one to discriminate and detect the absolute configuration of chiral molecules in an aqueous system, thus opening new possibilities in biosensing and other biological applications.

  7. Interaction between lyotropic chromonic liquid crystals and polymers

    NASA Astrophysics Data System (ADS)

    Yao, Xuxia; Park, Jung; Srinivasarao, Mohan

    2010-03-01

    Lyotropic chromonic liquid crystals (LCLCs) consist of various dyes, drugs, etc., so their importance is self-evident. The interaction of chromonic molecules and polymers is involved in their real applications, such as the dyeing process of fibers, textiles and food, and the functionalization of drugs in vivo. In our research, polymer dispersed LCLC droplets and polymer coated LCLC cells have been fabricated. Effect of interaction was observed by optical texture of LCLCs, as the different polymers induce different director configuration of LCLCs. A textile dye-Benzopurpurine 4B, food dye-Sunset Yellow FCF, and drug-Disodium Cromoglycate mixed with water soluble polymers, proteins and textile polymers have been all studied and compared.

  8. Electro-osmosis in nematic liquid crystals.

    PubMed

    Tovkach, O M; Calderer, M Carme; Golovaty, Dmitry; Lavrentovich, Oleg; Walkington, Noel J

    2016-07-01

    We derive a mathematical model of a nematic electrolyte based on a variational formulation of nematodynamics. We verify the model by comparing its predictions to the results of the experiments on the substrate-controlled liquid-crystal-enabled electrokinetics. In the experiments, a nematic liquid crystal confined to a thin planar cell with surface-patterned anchoring conditions exhibits electro-osmotic flows along the "guiding rails" imposed by the spatially varying director. Extending our previous work, we consider a general setup which incorporates dielectric anisotropy of the liquid-crystalline matrix and the full set of nematic viscosities. PMID:27575193

  9. Electro-osmosis in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Tovkach, O. M.; Calderer, M. Carme; Golovaty, Dmitry; Lavrentovich, Oleg; Walkington, Noel J.

    2016-07-01

    We derive a mathematical model of a nematic electrolyte based on a variational formulation of nematodynamics. We verify the model by comparing its predictions to the results of the experiments on the substrate-controlled liquid-crystal-enabled electrokinetics. In the experiments, a nematic liquid crystal confined to a thin planar cell with surface-patterned anchoring conditions exhibits electro-osmotic flows along the "guiding rails" imposed by the spatially varying director. Extending our previous work, we consider a general setup which incorporates dielectric anisotropy of the liquid-crystalline matrix and the full set of nematic viscosities.

  10. Macroscopic dynamics of polar nematic liquid crystals.

    PubMed

    Brand, Helmut R; Pleiner, Harald; Ziebert, Falko

    2006-08-01

    We present the macroscopic equations for polar nematic liquid crystals. We consider the case where one has both, the usual nematic director, n[over ] , characterizing quadrupolar order as well as the macroscopic polarization, P , representing polar order, but where their directions coincide and are rigidly coupled. In this case one has to choose P as the independent macroscopic variable. Such equations are expected to be relevant in connection with nematic phases with unusual properties found recently in compounds composed of banana-shaped molecules. Among the effects predicted, which are absent in conventional nematic liquid crystals showing only quadrupolar order, are pyro-electricity and its analogs for density and for concentration in mixtures as well as a flow alignment behavior, which is more complex than in usual low molecular weight nematics. We also discuss the formation of defect structures expected in such systems. PMID:17025458

  11. Fine structure of the topological defect core: Disclination in lyotropic chromonic liquid crystal

    NASA Astrophysics Data System (ADS)

    Zhou, Shuang; Shiyanovskii, Sergij; Park, Heung-Shik; Kim, Young-Ki; Hearn, Tristan; Reichel, Lothar; Lavrentovich, Oleg

    Topological defects represent an important concept in many branches of modern physics ranging from cosmology and optics to hard and soft matter. One of the most difficult problems is the fine structure of the so-called core region of defects, where the deformations of the order parameter are so strong that the phenomenological description valid in the far field becomes invalid. Experimental exploration of the fine core structure is usually hindered by the small size (atomic/molecular level) of the core, where optical or even electron microscopy techniques are invalid. In this work, we take advantage of the peculiar nature of the so-called lyotropic chromonic liquid crystals (LCLC) of a nematic type that carry disclinations with a core extending over macroscopic distances (tens of micrometers), large enough to explore their spatial variation by optical and electron microscopy. We demonstrate that the director and the scalar order parameter (associated with the degree of orientational order) show a profound change in the core region. In particular, as one approaches the center of the defect, the azimuthal dependency of the director field changes dramatically and the scalar order parameter shows a strong dependence on the strength of splay and bend deformations. This work is supported by NSF Grant DMS-1434185.

  12. Lyotropic chromonic liquid crystals as materials for optical and biosensing applications

    NASA Astrophysics Data System (ADS)

    Tortora, L.; Park, H.-S.; Antion, K.; Finotello, D.; Lavrentovich, O. D.

    2007-02-01

    Lyotropic chromonic liquid crystals (LCLCs) are formed by molecules with rigid polyaromatic cores and ionic groups at the periphery that form aggregates while in water. Most of the LCLCs are not toxic to the biological cells and can be used as an amplifying medium in real-time biosensors. The detector is based on the principle that the immune aggregates growing in the LCLC bulk trigger the director distortions. Self-assembly of LCLC molecules into oriented structures allows one to use them in various structured films. For example, layer-by-layer electrostatic deposition produces monomolecular layers and stacks of layers of LCLC with long-range in-plane orientational order which sets them apart from the standard Langmuir-Blodgett films. We demonstrate that divalent and multivalent salts as well as acidic and basic materials that alter pH of the LCLC water solutions, are drastically modifying the phase diagrams of LCLC, from shifting the phase transition temperatures by tens of degrees, to causing condensation of the LCLC aggregates into more compact structures, such as birefringent bundles or formation of a columnar hexagonal phase from the nematic phase.

  13. Chirality amplification and detection by tactoids of lyotropic chromonic liquid crystals.

    PubMed

    Peng, Chenhui; Lavrentovich, Oleg D

    2015-10-01

    Detection of chiral molecules requires amplification of chirality to measurable levels. Typically, amplification mechanisms are considered at the microscopic scales of individual molecules and their aggregates. Here we demonstrate chirality amplification and visualization of structural handedness in water solutions of organic molecules that extends over the scale of many micrometers. The mechanism is rooted in the long-range elastic nature of orientational order in lyotropic chromonic liquid crystals (LCLCs) formed in water solutions of achiral disc-like molecules. The nematic LCLC coexists with its isotropic counterpart, forming elongated tactoids; the spatial confinement causes a structural twist even when the material is nonchiral. Minute quantities of chiral molecules such as the amino acid l-alanine and limonene transform the racemic array of left- and right-twisted tactoids into a homochiral set. The left and right chiral enantiomers are readily distinguished from each other as the induced structural handedness is visualized through a simple polarizing microscope observation. The effect is important for developing our understanding of chirality amplification mechanisms; it also might open up new possibilities in biosensing. PMID:26238525

  14. Self-assembly, Condensation, and Order in Aqueous Lyotropic Chromonic Liquid Crystals Crowded with Additives

    SciTech Connect

    Tortora, L.; Park, H; Kang, S; Savaryn, V; Hong, S; Kaznatcheev, K; Finotello, D; Sprunt, S; Kumar, S; Lavrentovich, O

    2010-01-01

    Dense multicomponent systems with macromolecules and small solutes attract a broad research interest as they mimic the molecularly crowded cellular interiors. The additives can condense and align the macromolecules, but they do not change the degree of covalent polymerization. We chose a lyotropic chromonic liquid crystal with reversibly and non-covalently assembled aggregates as a much softer system, reminiscent of 'living polymers', to demonstrate that small neutral and charged additives cause condensation of aggregates with ensuing orientational and positional ordering and nontrivial morphologies of phase separation, such as tactoids and toroids of the nematic and hexagonal columnar phase coexisting with the isotropic melt. Scanning transmission X-ray microscopy (STXM) with near edge X-ray absorption fine structure (NEXAFS) analysis as well as fluorescent microscopy demonstrates segregation of the components. The observations suggest that self-assembly of chromonic aggregates in the presence of additives is controlled by both entropy effects and by specific molecular interactions and provide a new route to the regulated reversible assembly of soft materials formed by low-molecular weight components.

  15. Self-assembly, condensation, and order in aqueous lyotropic chromonic liquid crystals crowded with additives

    SciTech Connect

    Tortora, Luana; Park, Heung-Shik; Kang, Shin-Woong; Savaryn, Victoria; Hong, Seung-Ho; Kaznatcheev, Konstantine; Finotello, Daniele; Sprunt, Samuel; Kumar, Satyendra; Lavrentovich, Oleg D.

    2012-09-06

    Dense multicomponent systems with macromolecules and small solutes attract a broad research interest as they mimic the molecularly crowded cellular interiors. The additives can condense and align the macromolecules, but they do not change the degree of covalent polymerization. We chose a lyotropic chromonic liquid crystal with reversibly and non-covalently assembled aggregates as a much softer system, reminiscent of 'living polymers', to demonstrate that small neutral and charged additives cause condensation of aggregates with ensuing orientational and positional ordering and nontrivial morphologies of phase separation, such as tactoids and toroids of the nematic and hexagonal columnar phase coexisting with the isotropic melt. Scanning transmission X-ray microscopy (STXM) with near edge X-ray absorption fine structure (NEXAFS) analysis as well as fluorescent microscopy demonstrates segregation of the components. The observations suggest that self-assembly of chromonic aggregates in the presence of additives is controlled by both entropy effects and by specific molecular interactions and provide a new route to the regulated reversible assembly of soft materials formed by low-molecular weight components.

  16. Hexagonal Lyotropic Liquid Crystal from Simple “Abiotic” Foldamers

    PubMed Central

    Chen, Yu; Zhao, Zhiqiang; Jin, Rizhe; Kang, Chuanqing; Qiu, Xuepeng; Guo, Haiquan; Du, Zhijun; Gao, Lianxun

    2016-01-01

    Abstract The motivation of foldamer chemistry is to identify novel building blocks that have the potential to imitate natural species. Peptides and peptide mimetics can form stable helical conformations and further self‐assemble into diverse aggregates in water, where it is difficult to isolate a single helix. In contrast, most “abiotic” foldamers may fold into helical structures in solution, but are difficult to assemble into tertiary ones. It remains a challenge to obtain “abiotic” species similar to peptides. In this paper, a novel foldamer scaffold, in which p‐phenyleneethynylene units are linked by chiral carbon atoms, was designed and prepared. In very dilute solutions, these oligomers were random coils. The hexamer and octamers could form a hexagonal lyotropic liquid crystal (LC) in CH2Cl2 when the concentrations reached the critical values. The microscopic observations indicated that they could assemble into the nanofibers in the LC. Interestingly, after some LC phases were diluted at room temperature, the nanofibers could be preserved. The good stabilities of the assemblies are possibly attributed to a more compact backbone and more rigid side chains. PMID:27547649

  17. Hexagonal Lyotropic Liquid Crystal from Simple "Abiotic" Foldamers.

    PubMed

    Chen, Yu; Zhao, Zhiqiang; Bian, Zheng; Jin, Rizhe; Kang, Chuanqing; Qiu, Xuepeng; Guo, Haiquan; Du, Zhijun; Gao, Lianxun

    2016-08-01

    The motivation of foldamer chemistry is to identify novel building blocks that have the potential to imitate natural species. Peptides and peptide mimetics can form stable helical conformations and further self-assemble into diverse aggregates in water, where it is difficult to isolate a single helix. In contrast, most "abiotic" foldamers may fold into helical structures in solution, but are difficult to assemble into tertiary ones. It remains a challenge to obtain "abiotic" species similar to peptides. In this paper, a novel foldamer scaffold, in which p-phenyleneethynylene units are linked by chiral carbon atoms, was designed and prepared. In very dilute solutions, these oligomers were random coils. The hexamer and octamers could form a hexagonal lyotropic liquid crystal (LC) in CH2Cl2 when the concentrations reached the critical values. The microscopic observations indicated that they could assemble into the nanofibers in the LC. Interestingly, after some LC phases were diluted at room temperature, the nanofibers could be preserved. The good stabilities of the assemblies are possibly attributed to a more compact backbone and more rigid side chains. PMID:27547649

  18. Polycontinuous Lyotropic Liquid Crystalline Network Phases from Gemini Dicarboxylate Surfactants

    NASA Astrophysics Data System (ADS)

    Mahanthappa, Mahesh; Sorenson, Gregory; Schmitt, Adam

    2015-03-01

    Arising from the water concentration-dependent self-assembly of amphiphilic molecules, lyotropic liquid crystals (LLCs) form a wide variety of structurally periodic nanoscale morphologies including discontinuous micellar phases (I), hexagonally-packed cylinders (C), and lamellar (L) phases. In intermediate amphiphile concentration windows between the L and C phases, one typically observes three bicontinuous cubic network phases: gyroid (G), diamond (D), and primitive (P). Recent theoretical work has suggested the possible stability of a variety of non-cubic network phase LLCs, yet none of these phases have been previously observed. In this presentation, we describe the experimental discovery of the first triply periodic network phase LLC with 3D-hexagonal symmetry (space group #193) in binary mixtures of water with a simple gemini dicarboxylate surfactant based on dodecanoic acid. Using a combination of SAXS and rheological methods, we structurally characterize this new phase and show that it is comprised of three interpenetrating lipidic networks of 3-fold connectors in a matrix of water. This finding highlights the unusual aqueous phase behavior of gemini surfactants and suggests new methods for discovering and stabilizing new network phase LLCs beyond the gyroid.

  19. Micellar structures in lyotropic liquid crystals and phase transitions

    NASA Astrophysics Data System (ADS)

    Saupe, A.; Xu, S. Y.; Plumley, Sulakshana; Zhu, Y. K.; Photinos, P.

    1991-05-01

    The formation of micellar nematics is discussed with emphasis on the transitions between nematic phases and nematic-smectic transitions. Phase diagrams for MTAB/l-decanol/D,O systems show a direct transition between uniaxial nematics. Electrical conductivity and birefringence measurements on a mixture of sodium decylsulfate. 1-decanol, D,O demonstrate, on the other hand, the existence of a biaxial nemantic range that separates the Uniaxial nematics. On a mixture of cesium perflouroctanoate and H 2O the electrical conductivity and rotational viscosity are used to discuss the relevant features of nematic-lamellar-smectic transitions. The formation of elongated ribbon-like micelles at the nematic-smectic transition is suggested. Transitions between different nematic phases in the MTAB system may be connected with a structural change from long micelles with a fairly circular cross section to similar micelles with a more elliptical cross section.

  20. Homeotropic alignment of the lyotropic chromonic liquid crystal Sunset Yellow FCF using pi-pi stacking chemical interactions

    NASA Astrophysics Data System (ADS)

    Jeong, Joonwoo; Han, Ganghee; Johnson, A. T. Charlie; Lubensky, Tom C.; Collings, Peter J.; Yodh, A. G.

    2013-03-01

    We report on the homeotropic alignment of the lyotropic chromonic liquid crystal, Sunset Yellow FCF (SSY), using pi-pi stacking interactions between the SSY molecules and (1) thin parylene films or (2) a graphene monolayer. The nematic and columnar phases of SSY molecules arise via self-assembly in water into stacks through non-covalent attractions between the SSY molecules. Interestingly, we find that the same non-covalent interactions between SSY molecules and a parylene or graphene alignment layer lead to homeotropic anchoring of these stacks. The nematic phase of SSY is introduced between two glass substrates coated with parylene films or graphene monolayers, and homeotropic alignment of SSY is confirmed by polarized optical microscopy and conoscopy. Additionally, we observe and can explain the stripe domains that occur during cooling of the sample in this cell, and we consider possible novel applications for homeotropically aligned chromonic liquid crystals. We gratefully acknowledge financial support from the National Science Foundation through NSF DMR-1205463 and UPENN MRSEC DMR-1120901

  1. Simulation of electrically controlled nematic liquid crystal Rochon prism

    NASA Astrophysics Data System (ADS)

    Buczkowska, M.; Derfel, G.

    2016-09-01

    Operation of an electrically controlled beam steering device based on Rochon prism made by use of nematic liquid crystal is modelled numerically. Deflection angles and angular distribution of light intensity in the deflected beam are calculated. Dynamics of the device is studied. Advantage of application of dual frequency nematic liquid crystal is demonstrated. Role of flexoelectric properties of the nematic is analyzed.

  2. Pattern formation from consistent dynamical closures of uniaxial nematic liquid crystals.

    PubMed

    Híjar, Humberto; de Hoyos, Diego Marquina; Santamaría-Holek, Iván

    2012-03-21

    Pattern formation in uniaxial polymeric liquid crystals is studied for different dynamic closure approximations. Using the principles of mesoscopic non-equilibrium thermodynamics in a mean-field approach, we derive a Fokker-Planck equation for the single-particle non-homogeneous distribution function of particle orientations and the evolution equations for the second and fourth order orientational tensor parameters. Afterwards, two dynamic closure approximations are discussed, one of them considering the relaxation of the fourth order orientational parameter and leading to a novel expression for the free-energy like function in terms of the scalar order parameter. Considering the evolution equation of the density of the system and values of the interaction parameter for which isotropic and nematic phases coexist, our analysis predicts that patterns and traveling waves can be produced in lyotropic uniaxial nematics even in the absence of external driving. PMID:22443750

  3. Triply Periodic Multiply Continuous Lyotropic Liquid Crystals Derived from Gemini Dicarboxylate Surfactants

    NASA Astrophysics Data System (ADS)

    Sorenson, Gregory; Mahanthappa, Mahesh

    2013-03-01

    A delicate balance of non-covalent interactions drives the supramolecular assembly of hydrated small molecule amphiphiles into aqueous lyotropic liquid crystals (LLCs). High symmetry multiply continuous phases, exemplified by the gyroid phase, are particularly desirable for many applications due to their interpenetrating hydrophilic and hydrophobic domains with well-defined chemical functionality decorating the interface between the two domains. However, these high symmetry assemblies are often difficult to obtain due to limited levels of hydration and temperature ranges over which they are accessible. Recent work suggests that small molecule amphiphiles known as ``gemini'' surfactants readily form these lyotropic network phases. Herein we report the lyotropic phase behaviors of a new class of dicarboxylate gemini surfactants that form stable, multiply continuous, high symmetry network structures over broad hydration and temperature ranges.

  4. Stochastic rotation dynamics for nematic liquid crystals

    SciTech Connect

    Lee, Kuang-Wu Mazza, Marco G.

    2015-04-28

    We introduce a new mesoscopic model for nematic liquid crystals (LCs). We extend the particle-based stochastic rotation dynamics method, which reproduces the Navier-Stokes equation, to anisotropic fluids by including a simplified Ericksen-Leslie formulation of nematodynamics. We verify the applicability of this hybrid model by studying the equilibrium isotropic-nematic phase transition and nonequilibrium problems, such as the dynamics of topological defects and the rheology of sheared LCs. Our simulation results show that this hybrid model captures many essential aspects of LC physics at the mesoscopic scale, while preserving microscopic thermal fluctuations.

  5. Electric heating effects in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Yin, Y.; Shiyanovskii, S. V.; Lavrentovich, O. D.

    2006-07-01

    Electric heating effects in the nematic liquid crystal change the liquid crystal physical properties and dynamics. We propose a model to quantitatively describe the heating effects caused by dielectric dispersion and ionic conductivity in the nematic liquid crystals upon the application of an ac electric field. The temperature increase of the liquid crystal cell is related to the properties of the liquid crystal such as the imaginary part of the dielectric permittivity, thermal properties of the bounding plates, and the surrounding medium as well as frequency and amplitude of the electric field. To study the temperature dynamics experimentally, we use a small thermocouple inserted directly into the nematic bulk; we assure that the thermocouple does not alter the thermal behavior of the system by comparing the results to those obtained by a noncontact birefringent probing technique recently proposed by Wen and Wu [Appl. Phys. Lett. 86, 231104 (2005)]. We determine how the temperature dynamics and the stationary value of the temperature increase depend on the parameters of the materials and the applied field. We used different surrounding media, from extremely good heat conductors such as aluminum cooling device to extremely poor conductor, Styrofoam; these two provide two limiting cases as compared to typical conditions of nematic cell exploitation in a laboratory or in commercial devices. The experiments confirm the theoretical predictions, namely, that the temperature rise is controlled not only by the heat transfer coefficient of the surrounding medium (as in the previous model) but also by the thickness and the thermal conductivity coefficient of the bounding plates enclosing the nematic layer. The temperature increase strongly depends on the director orientation and can change nonmonotonously with the frequency of the applied field.

  6. Molecular reorientation of a nematic liquid crystal by thermal expansion

    PubMed Central

    Kim, Young-Ki; Senyuk, Bohdan; Lavrentovich, Oleg D.

    2012-01-01

    A unique feature of nematic liquid crystals is orientational order of molecules that can be controlled by electromagnetic fields, surface modifications and pressure gradients. Here we demonstrate a new effect in which the orientation of nematic liquid crystal molecules is altered by thermal expansion. Thermal expansion (or contraction) causes the nematic liquid crystal to flow; the flow imposes a realigning torque on the nematic liquid crystal molecules and the optic axis. The optical and mechanical responses activated by a simple temperature change can be used in sensing, photonics, microfluidic, optofluidic and lab-on-a-chip applications as they do not require externally imposed gradients of temperature, pressure, surface realignment, nor electromagnetic fields. The effect has important ramifications for the current search of the biaxial nematic phase as the optical features of thermally induced structural changes in the uniaxial nematic liquid crystal mimic the features expected of the biaxial nematic liquid crystal. PMID:23072803

  7. Lyotropic liquid crystalline L3 phase silicated nanoporous monolithic composites and their production

    DOEpatents

    McGrath, Kathryn M.; Dabbs, Daniel M.; Aksay, Ilhan A.; Gruner, Sol M.

    2003-10-28

    A mesoporous ceramic material is provided having a pore size diameter in the range of about 10-100 nanometers produced by templating with a ceramic precursor a lyotropic liquid crystalline L.sub.3 phase consisting of a three-dimensional, random, nonperiodic network packing of a multiple connected continuous membrane. A preferred process for producing the inesoporous ceramic material includes producing a template of a lyotropic liquid crystalline L.sub.3 phase by mixing a surfactant, a co-surfactant and hydrochloric acid, coating the template with an inorganic ceramic precursor by adding to the L.sub.3 phase tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS) and then converting the coated template to a ceramic by removing any remaining liquids.

  8. Continuous Rotation of Achiral Nematic Liquid Crystal Droplets Driven by Heat Flux

    NASA Astrophysics Data System (ADS)

    Ignés-Mullol, Jordi; Poy, Guilhem; Oswald, Patrick

    2016-07-01

    Suspended droplets of cholesteric (chiral nematic) liquid crystals spontaneously rotate in the presence of a heat flux due to a temperature gradient, a phenomenon known as the Lehmann effect. So far, it is not clear whether this effect is due to the chirality of the phase and the molecules or only to the chirality of the director field. Here, we report the continuous rotation in a temperature gradient of nematic droplets of a lyotropic chromonic liquid crystal featuring a twisted bipolar configuration. The achiral nature of the molecular components leads to a random handedness of the spontaneous twist, resulting in the coexistence of droplets rotating in the two senses, with speeds proportional to the temperature gradient and inversely proportional to the droplet radius. This result shows that a macroscopic twist of the director field is sufficient to induce a rotation of the droplets, and that the phase and the molecules do not need to be chiral. This suggests that one can also explain the Lehmann rotation in cholesteric liquid crystals without introducing the Leslie thermomechanical coupling—only present in chiral mesophases. An explanation based on the Akopyan and Zeldovich theory of thermomechanical effects in nematics is proposed and discussed.

  9. Continuous Rotation of Achiral Nematic Liquid Crystal Droplets Driven by Heat Flux.

    PubMed

    Ignés-Mullol, Jordi; Poy, Guilhem; Oswald, Patrick

    2016-07-29

    Suspended droplets of cholesteric (chiral nematic) liquid crystals spontaneously rotate in the presence of a heat flux due to a temperature gradient, a phenomenon known as the Lehmann effect. So far, it is not clear whether this effect is due to the chirality of the phase and the molecules or only to the chirality of the director field. Here, we report the continuous rotation in a temperature gradient of nematic droplets of a lyotropic chromonic liquid crystal featuring a twisted bipolar configuration. The achiral nature of the molecular components leads to a random handedness of the spontaneous twist, resulting in the coexistence of droplets rotating in the two senses, with speeds proportional to the temperature gradient and inversely proportional to the droplet radius. This result shows that a macroscopic twist of the director field is sufficient to induce a rotation of the droplets, and that the phase and the molecules do not need to be chiral. This suggests that one can also explain the Lehmann rotation in cholesteric liquid crystals without introducing the Leslie thermomechanical coupling-only present in chiral mesophases. An explanation based on the Akopyan and Zeldovich theory of thermomechanical effects in nematics is proposed and discussed. PMID:27517793

  10. Selective Sequence for the Peptide-Triggered Phase Transition of Lyotropic Liquid-Crystalline Structures.

    PubMed

    Liu, Qingtao; Dong, Yao-Da; Boyd, Ben J

    2016-05-24

    A novel concept of using mixed lipids to construct selective peptide-sequence-sensing lyotropic liquid-crystalline (LLC) dispersion systems was investigated. The LLC systems were constructed using a mixture of phytantriol, a lipid that forms lyotropic liquid-crystalline phases, and a novel synthesized peptide-lipid (peplipid) for sensing a target peptide with the RARAR sequence. The internal structure of the dispersed LLC particles was converted from the lamellar structure (liposomes) to the inverse bicontinuous cubic phase (cubosomes) in the presence of the target peptide. The addition of common human proteins did not induce any structural change, indicating a high selectivity of interaction with the target peptide. The concept has potential for the design of targeted controlled release drug delivery agents. PMID:27148806

  11. Lyotropic liquid crystal engineering-ordered nanostructured small molecule amphiphile self-assembly materials by design.

    PubMed

    Fong, Celesta; Le, Tu; Drummond, Calum J

    2012-02-01

    Future nanoscale soft matter design will be guided to a large extent by the teachings of amphiphile (lipid or surfactant) self-assembly. Ordered nanostructured lyotropic liquid crystalline mesophases may form in select mixtures of amphiphile and solvent. To reproducibly engineer the low energy amphiphile self-assembly of materials for the future, we must first learn the design principles. In this critical review we discuss the evolution of these design rules and in particular discuss recent key findings regarding (i) what drives amphiphile self-assembly, (ii) what governs the self-assembly structures that are formed, and (iii) how can amphiphile self-assembly materials be used to enhance product formulations, including drug delivery vehicles, medical imaging contrast agents, and integral membrane protein crystallisation media. We focus upon the generation of 'dilutable' lyotropic liquid crystal phases with two- and three-dimensional geometries from amphiphilic small molecules (225 references). PMID:21975366

  12. Free surface dynamics of nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Cummings, Linda; Kondic, Lou; Lam, Michael; Lin, Te-Sheng

    2014-11-01

    Spreading thin films of nematic liquid crystal (NLC) are known to behave very differently to those of isotropic fluids. The polar interactions of the rod-like molecules with each other, and the interactions with the underlying substrate, can lead to intricate patterns and instabilities that are not yet fully understood. The physics of a system even as simple as a film of NLC spreading slowly over a surface (inclined or horizontal) are remarkably complex: the outcome depends strongly on the details of the NLC's behavior at both the substrate and the free surface (so-called ``anchoring'' effects). We will present a dynamic flow model that takes careful account of such nematic-substrate and nematic-free surface interactions. We will present model simulations for several different flow scenarios that indicate the variety of behavior that can emerge. Spreading over a horizontal substrate may exhibit a range of unstable behavior. Flow down an incline also exhibits intriguing instabilities: in addition to the usual transverse fingering, instabilities can be manifested behind the flowing front in a manner reminiscent of Newtonian flow down an inverted substrate. NSF DMS-1211713.

  13. pH-responsive lyotropic liquid crystals for the preparation of pure cubic zirconia nanoparticles

    NASA Astrophysics Data System (ADS)

    He, Wei Yan; Liu, Jin Rong; He, Zhang; Cao, Zhen Zhu; Li, Cai Hong; Gao, Yan Fang

    2016-07-01

    We present a lyotropic liquid crystal system consisting of SDS/Triton X-100/water at 25 °C. This system is respond to pH variations with a phase switch. When pH is altered from alkaline (pH 13) to acidic (pH 2) conditions, phase change occurs from a bicontinuous hexagonal phase to a partially hexagonal phase until it disappears. The hexagonal phase under alkaline conditions is stable. Thus, this system is an ideal candidate for the preparation of pure cubic ZrO2 nanoparticles. XRD results confirm that the as-synthesized powder is composed of pure cubic ZrO2. These nanoparticles also exhibit a thermal stability of up to 800 °C. The size and morphological characteristics of the nanoparticles are greatly affected by ZrOCl2 concentration. The mechanism of zirconia nanoparticle synthesis in a lyotropic hexagonal phase was proposed.

  14. Thermal diode made by nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Melo, Djair; Fernandes, Ivna; Moraes, Fernando; Fumeron, Sébastien; Pereira, Erms

    2016-09-01

    This work investigates how a thermal diode can be designed from a nematic liquid crystal confined inside a cylindrical capillary. In the case of homeotropic anchoring, a defect structure called escaped radial disclination arises. The asymmetry of such structure causes thermal rectification rates up to 3.5% at room temperature, comparable to thermal diodes made from carbon nanotubes. Sensitivity of the system with respect to the heat power supply, the geometry of the capillary tube and the molecular anchoring angle is also discussed.

  15. Isotropization of nematic liquid crystals by TMDSC

    SciTech Connect

    Chen, Wei; Dadmun, M.; Zhang, Ge; Boller, A.; Wunderlich, B. |

    1997-12-01

    Temperature-modulated differential scanning calorimetry (TMDSC) and traditional DSC are used to study the transition between the nematic liquid crystalline state and the isotropic liquid for two small molecules [4,4{prime}-azoxyanisole and N,N`-bis(4-n-octyloxybenzal)-1,4-phenylenediamine] and one macromolecule (4,4{prime}-dihydroxy-{alpha}-methylstilbene copolymerized with a 1:1 molar mixture of 1,7-dibromoheptane and 1,9-dibromononane). The DSC measurements with 4,4{prime}-azoxyanisole were used for temperature calibration with varying heating and cooling rates. Quasi-isothermal TMDSC with small temperature amplitude and standard TMDSC with underlying heating and cooling rates were utilized to analyze the breadth of the transitions. It could be verified that the isotropization transition of a nematic liquid crystal is, indeed, reversible for all three molecules. The nature of the transition changes, however, from relatively sharp, for small, rigid molecules, to about three kelvins wide for the small molecule with flexible ends, to as broad as 20 K for the macromolecule. It was also demonstrated that quantitative heats of fusion of sharp transitions can be extracted from TMDSC, but only from the time-domain heat-flow signal.

  16. Particles and curvatures in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Serra, Francesca; Luo, Yimin; Yang, Shu; Kamien, Randall D.; Stebe, Kathleen J.

    Elastic interactions in anisotropic fluids can be harnessed to direct particle interactions. A strategy to smoothly manipulate the director field in nematic liquid crystals is to vary the topography of the bounding surfaces. A rugged landscape with peaks and valleys create local deformations of the director field which can interact with particles in solution. We study this complex interaction in two different settings. The first consists of an array of shallow pores in a poly-dimethyl-siloxane (PDMS) membrane, whose curvature can be tuned either by swelling the PDMS membrane or by mechanical stretching. The second is a set of grooves with wavy walls, fabricated by photolithography, with various parameters of curvature and shapes. In this contexts we study how the motion of colloidal particles in nematic liquid crystals can be influenced by their interaction with the peaks and valleys of the bottom substrate or of the side walls. Particles with different associated topological defects (hedgehogs or Saturn rings) behave differently as they interact with the topographical features, favoring the docking on peaks or valleys. These experimental systems are also ideal to study the ``lock and key'' mechanism of particles in holes and to investigate a possible route for particle sorting.

  17. Role of Molecular Structure on X-ray Diffraction in Thermotropic Uniaxial and Biaxial Nematic Liquid Crystal Phases

    SciTech Connect

    Acharya, Bharat R.; Kang, Shin-Woong; Prasad, Veena; Kumar, Satyendra

    2009-08-27

    X-ray diffraction is one of the most definitive methods to determine the structure of condensed matter phases, and it has been applied to unequivocally infer the structures of conventional calamitic and lyotropic liquid crystals. With the advent of bent-core and tetrapodic mesogens and the discovery of the biaxial nematic phase in them, the experimental results require more careful interpretation and analysis. Here, we present ab-initio calculations of X-ray diffraction patterns in the isotropic, uniaxial nematic, and biaxial nematic phases of bent-core mesogens. A simple Meier-Saupe-like molecular distribution function is employed to describe both aligned and unaligned mesophases. The distribution function is decomposed into two, polar and azimuthal, distribution functions to calculate the effect of the evolution of uniaxial and biaxial nematic orientational order. The calculations provide satisfactory semiquantitative interpretations of experimental results. The calculations presented here should provide a pathway to more refined and quantitative analysis of X-ray diffraction data from the biaxial nematic phase.

  18. Chromonic liquid crystalline nematic phase exhibited in binary mixture of two liquid crystals

    SciTech Connect

    Govindaiah, T. N. Sreepad, H. R.; Sridhar, K. N.; Sridhara, G. R.; Nagaraja, N.

    2015-06-24

    A binary mixture of abietic acid and orthophosphoric acid (H{sub 3}PO{sub 4}) exhibits co-existence of biphasic region of Nematic+Isotropic (N+I), lyotropic Nematic (ND) and Smectic-G (SmG) phases. The mixture exhibits N+I, N and SmG phases at different concentrations and at different temperatures. Mixtures with all concentrations of abietic acid exhibit I→N+I→N→SmG phases sequentially when the specimen is cooled from its isotropic melt. These phases have been characterized by using differential scanning calorimetric, X-ray diffraction, and optical texture studies.

  19. Lattice model for biaxial and uniaxial nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Sauerwein, Ricardo A.; de Oliveira, Mário J.

    2016-05-01

    We use a lattice gas model to describe the phase transitions in nematic liquid crystals. The phase diagram displays, in addition to the isotropic phase, the two uniaxial nematics, the rod-like and discotic nematics, and the biaxial nematic. Each site of the lattice has a constituent unit that takes only six orientations and is understood as being a parallelepiped brick with the three axes distinct. The possible orientations of a brick are those in which its axes are parallel to the axes of a Cartesian reference frame. The analysis of the model is performed by the use of a mean-field approximation and a Landau expansion of the free energy.

  20. Light-scattering study of a polymer nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Taratuta, Victor G.; Hurd, Alan J.; Meyer, Robert B.

    1985-07-01

    We study the relaxation of thermally excited orientation fluctuations in a polymer nematic liquid crystal using photon correlation spectroscopy. The material studied is poly-γ-benzyl glutamate at a concentration just above the isotropic to nematic transition point. The relaxation rates of elastic deformation modes exhibit large anisotropies. Quantitative measurements of ratios of Frank elastic constants and Leslie viscosities are described.

  1. Simulated Textures of Toroidal Nematic Liquid Crystal Droplets

    NASA Astrophysics Data System (ADS)

    Ellis, Perry; Fernandez-Nieves, Alberto

    2014-03-01

    Nematic liquid crystals under confinement by curved surfaces can produce complex hierarchical structures whose design principles and properties have yet to be unraveled. Here we focus on toroidal geometries and perform computer simulations of the nematic textures seen between crossed-polarizers. We find agreement with experiments using director fields that exhibit pronounced twist deformations with contributions from bend and splay.

  2. Nonionic diethanolamide amphiphiles with isoprenoid-type hydrocarbon chains: thermotropic and lyotropic liquid crystalline phase behaviour

    SciTech Connect

    Sagnella, Sharon M.; Conn, Charlotte E.; Krodkiewska, Irena; Drummond, Calum J.

    2014-09-24

    The thermotropic and lyotropic liquid crystalline phase behaviour of a series of diethanolamide amphiphiles with isoprenoid-type hydrocarbon chains (geranoyl, H-farnesoyl, and phytanoyl) has been investigated. When neat, both H-farnesoyl and phytanoyl diethanolamide form a smectic liquid crystalline structure at sub-zero temperatures. In addition, all three diethanolamides exhibit a glass transition temperature at around -73 C. Geranoyl diethanolamide forms a lamellar crystalline phase with a lattice parameter of 17.4 {angstrom} following long term storage accompanied by the loss of the glass transition. In the presence of water, H-farnesoyl and phytanoyl diethanolamide form lyotropic liquid crystalline phases, whilst geranoyl diethanolamide forms an L{sub 2} phase. H-farnesoyl diethanolamide forms a fluid lamellar phase (L{sub {alpha}}) at room temperature and up to {approx} 40 C. Phytanoyl diethanolamide displays a rich mesomorphism forming the inverse diamond (Q{sub II}{sup D}) and gyroid (Q{sub II}{sup G}) bicontinuous cubic phases in addition to an L{sub {alpha}} phase.

  3. Carbon Nanotube Liquid Crystals: Nematic Droplets and Coarsening Dynamics

    NASA Astrophysics Data System (ADS)

    Behabtu, Natnael; Senyuk, Bohdan; Smalyukh, Ivan; Pasquali, Matteo

    2012-02-01

    On a fundamental basis, carbon nanotubes (CNTs) offer a new model molecule to explore the dynamics and phases of rigid rods and test theories. Their large aspect ratio (100 to 100,000) and persistence length (˜ 100 microns) allow exploring the physics of nematic phases with high Frank elastic constant. Moreover, understanding of CNT liquid crystals is key to their rational processing into ordered materials such as fibers. Here we report the formation of elongated nematic droplets of CNTs in chlorosulfonic acid. In nematic droplets, a continuous transition from a homogeneous to bipolar nematic director field is expected theoretically, as a function of droplet volume; yet, experimental determination of such transition has been elusive. We show that CNT nematic droplets display such transition. We study the coarsening dynamics of positive and negative nematic droplets and observe that two or more droplets merge by matching their nematic director. Merging scenarios that lead to defect formation are not observed. Negative tactoids (isotropic phase in liquid crystalline continuum) merge through attractive forces induced by the nematic director distortion with quadrupolar symmetry.

  4. Light diffraction by acoustically induced domains in nematic liquid crystals

    SciTech Connect

    Kapustina, O. A.

    2006-05-15

    The phenomenon of light diffraction by a system of linear domains formed in planar layers of nematic liquid crystals in an oscillating Couette flow, acoustically induced at sound frequencies, is investigated.

  5. Nematic liquid crystals for optical shutters: A concept

    NASA Technical Reports Server (NTRS)

    Imus, R. E.

    1972-01-01

    Nonmechanical shutter utilizes nematic crystals to attenuate illumination, thus protecting light-sensitive devices such as vidicon or image orthicon tubes and phototubes. Opacity of liquid crystals is controlled by photosensor.

  6. Oriental transitions in nematic liquid crystals on grooved substrates

    SciTech Connect

    Krekhov, A.P.; Khasimullin, M.V.; Lebedev, Y.A.

    1995-12-31

    An expression for the surface energy of a nematic liquid crystal (NLC) on a fine-grooved substrate is obtained with the phenomenological approach. Temperature-induced orientational transitions in nematic liquid crystals are analyzed as functions of the surface-profile parameters. A planar{yields}tilted{yields}homeotropic alignment transition was observed near the clearing point of an MBBA layer sandwiched between two grooved glass substrates, with a microrelief obtained by oblique evaporation of silicon monoxide. 15 refs., 1 fig.

  7. Laser damage resistant nematic liquid crystal cell

    NASA Astrophysics Data System (ADS)

    Raszewski, Z.; Piecek, W.; Jaroszewicz, L.; Soms, L.; Marczak, J.; Nowinowski-Kruszelnicki, E.; Perkowski, P.; Kedzierski, J.; Miszczyk, E.; Olifierczuk, M.; Morawiak, P.; Mazur, R.

    2013-08-01

    There exists a problem in diagnostics of a dense plasma (so-called Thomson diagnostics). For this purpose, the plasma is illuminated by series of high energy laser pulses. Such pulses are generated by several independent lasers operating sequentially, and these pulses are to be directed along an exactly the same optical path. In this case, the energy of each separate pulse is as large as 3 J, so it is impossible to generate a burst of such pulses by a single laser. In this situation, several independent lasers have to be used. To form optical path with λ = 1.064 μm and absolute value of the energy of laser pulse through of 3 J, a special refractive index matched twisted Nematic Liquid Crystal Cell (NLCC) of type LCNP2 with switching on time τON smaller than 5 μs might be applied. High laser damage resistance of NLCC and short τON can be fulfilled by preparation of liquid crystal cells with Liquid Crystal Mixture (LCM), well tuned to twisted nematic electro-optical effect, and well tuned all optical interfaces (Air - Antireflection - Quartz Plate - Electrode - Blocking Film - Aligning Layer - LCM - Aligning Layer - Blocking Film - Electrode - Quartz Plate - Antireflection - Air). In such LCNP2 cell, the transmission is higher than 97% at λ = 1.064 μm, as it is presented by Gooch and Tarry [J. Phys. D: Appl. Phys. 8, 1575 (1975)]. The safe laser density energy is about 0.6 J/cm2 for a train of laser pulses (λ = 1.064 μm, pulse duration 10 ns FWHM, pulse repetition rate 100 pps, train duration 10 s), so the area of liquid crystal cell tolerating 3 J through it shall be as large as 5 cm2. Due to the presence of two blocking film layers between electrodes, LCNP2 can be driven by high voltages. Switching on time smaller than τON = 5 μs was obtained under 200 V switching voltage.

  8. Transmission characteristics of a twisted nematic liquid-crystal layer

    NASA Technical Reports Server (NTRS)

    Grinberg, J.; Jacobson, A. D.

    1976-01-01

    An approximate analytical expression is calculated for the transmission of thin twisted nematic layers situated between a polarizer/analyzer pair. The approximation assumes that the twist angle of the nematic liquid crystal is smaller than the maximum retardation of the cell. The direction of the incident light is assumed to be parallel to the normal of the electrode. This configuration is analyzed for a general arrangement of polarizer and analyzer; the general result is evaluated for the case of the polarizer parallel and analyzer perpendicular to the liquid-crystal optical axis on the input and output electrodes, respectively. The results show that in the case of a thin twisted nematic layer the transmission depends on the thickness of the layer, on the birefringence of the liquid crystal, and on the wavelength of the light. This is a departure from the well-known independence of the transmission on these parameters for a thick twisted nematic layer.

  9. Tuning Lyotropic Liquid Crystalline Phase Behavior of Gemini Surfactants by Linker Parity

    NASA Astrophysics Data System (ADS)

    Perroni, Dominic; Baez-Cotto, Carlos; Mantha, Sriteja; Sorenson, Gregory; Yethiraj, Arun; Mahanthappa, Mahesh

    2015-03-01

    Aqueous bicontinuous lyotropic liquid crystals (LLCs) derived from small molecule surfactants are useful nanostructured materials with myriad applications, in fields ranging from structural biology to membrane science. However, access to these coveted phases is limited by the fact that few surfactant platforms readily stabilize these network phases over the wide amphiphile concentration and temperature phase windows necessary for their widespread applications. We have recently shown that gemini (``twin tail'') dicarboxylate surfactants, comprising two single tail amphiphiles covalently linked near the headgroup by a hydrophobic bridge, exhibit a greatly increased propensity to form stable double gyroid LLC phases. In this presentation, we will demonstrate the unusual sensitivity of gemini dicarboxylate surfactant lyotropic self-assembly to the length of the hydrophobic bridge: odd-carbon linkers produce stable double gyroid phases over amphiphile composition windows as wide as 40 wt% that are stable between T = 22-100 °C. We rationalize these results in terms of the detailed molecular conformations of the surfactants that stem from the length of the bridging moiety, which suggests that this molecular design strategy may generally extend to other surfactant classes.

  10. Alignment and Graphene-Assisted Decoration of Lyotropic Chromonic Liquid Crystals Containing DNA Origami Nanostructures.

    PubMed

    Martens, Kevin; Funck, Timon; Kempter, Susanne; Roller, Eva-Maria; Liedl, Tim; Blaschke, Benno M; Knecht, Peter; Garrido, José Antonio; Zhang, Bingru; Kitzerow, Heinz

    2016-03-01

    Composites of DNA origami nanostructures dispersed in a lyotropic chromonic liquid crystal are studied by polarizing optical microscopy. The homogeneous aqueous dispersions can be uniformly aligned by confinement between two glass substrates, either parallel to the substrates owing to uniaxial rubbing or perpendicular to the substrates using ozonized graphene layers. These opportunities of uniform alignment may pave the way for tailored anisometric plasmonic DNA nanostructures to photonic materials. In addition, a decorated texture with nonuniform orientation is observed on substrates coated with pristine graphene. When the water is allowed to evaporate slowly, microscopic crystal needles appear, which are aligned along the local orientation of the director. This decoration method can be used for studying the local orientational order and the defects in chromonic liquid crystals. PMID:26849188

  11. Domain Structures in Nematic Liquid Crystals on a Polycarbonate Surface

    PubMed Central

    Parshin, Alexander M.; Gunyakov, Vladimir A.; Zyryanov, Victor Y.; Shabanov, Vasily F.

    2013-01-01

    Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It is established by optical methods that the domains are stable formations visualizing the polymer surface structures. In nematic droplets, the temperature-induced transition from the domain structure with two extinction bands to the structure with four bands is observed. This transition is shown to be caused by reorientation of the nematic director in the liquid crystal volume from the planar alignment to the homeotropic state with the pronounced radial configuration of nematic molecules on the surface. The observed textures are compared with different combinations of the volume LC orientations and the radial distribution of the director field and the disclination lines at the polycarbonate surface. PMID:23965955

  12. Domain structures in nematic liquid crystals on a polycarbonate surface.

    PubMed

    Parshin, Alexander M; Gunyakov, Vladimir A; Zyryanov, Victor Y; Shabanov, Vasily F

    2013-01-01

    Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It is established by optical methods that the domains are stable formations visualizing the polymer surface structures. In nematic droplets, the temperature-induced transition from the domain structure with two extinction bands to the structure with four bands is observed. This transition is shown to be caused by reorientation of the nematic director in the liquid crystal volume from the planar alignment to the homeotropic state with the pronounced radial configuration of nematic molecules on the surface. The observed textures are compared with different combinations of the volume LC orientations and the radial distribution of the director field and the disclination lines at the polycarbonate surface. PMID:23965955

  13. Nematic liquid crystals exhibiting high birefringence

    NASA Astrophysics Data System (ADS)

    Thingujam, Kiranmala; Bhattacharjee, Ayon; Choudhury, Basana; Dabrowski, Roman

    2016-06-01

    Two fluorinated isothiocyanato nematic liquid crystalline compounds, 4'-butylcyclohexyl-3, 5-difluoro-4-isothiocyanatobiphenyl and 4'-pentylcyclohexyl-3, 5-difluoro-4-isothiocynatobiphenyl are studied in detail to obtain their different physical parameters. Optical polarizing microscopy, differential scanning calorimetry, density and dielectric studies have been carried out for the two samples. Both the samples were found to have high clearing temperature (>100 °C) and exhibit small enthalpy of transition. The two samples exhibit high optical birefringence (Δ n > 0.2). The values of order parameters for the two samples were obtained using different approaches, namely, Vuks', Neugebauer's, modified Vuks' and direct extrapolation method from birefringence data. Experimentally obtained values of order parameters have also been compared with theoretical Maier-Saupe values. The parallel and perpendicular components of dielectric permittivity values of the two compounds were also calculated and their anisotropy values were found to be small. The effect of temperature on the molecular dipole moment μ and the angle of inclination β of the dipole axis with the director have also been investigated in this work.

  14. Characterization of the phase behaviour of a novel polymerizable lyotropic ionic liquid crystal.

    PubMed

    Goujon, Nicolas; Forsyth, Maria; Dumée, Ludovic F; Bryant, Gary; Byrne, Nolene

    2015-09-21

    The development of new polymerizable lyotropic liquid crystals (LLCs) utilizing charged amphiphilic molecules such as those based on long chain imidazolium compounds, is a relatively new design direction for producing robust membranes with controllable nano-structures. Here we have developed a novel polymerizable ionic liquid based LLC, 1-hexadecyl-3-methylimidazolium acrylate (C16mimAcr), where the acrylate anion acts as the polymerizable moiety. The phase behaviour of the C16mimAcr upon the addition of water was characterized using small and wide angle X-ray scatterings, differential scanning calorimetry and polarized optical microscopy. We compare the phase behaviour of this new polymerizable LLC to that of the well known LLC chloride analogue, 1-hexadecyl-3-methylimidazolium chloride (C16mimCl). We find that the C16mimAcr system has a more complex phase behaviour compared to the C16mimCl system. Additional lyotropic liquid crystalline mesophases such as hexagonal phase (H1) and discontinuous cubic phase (I1) are observed at 20 °C for the acrylate system at 50 and 65 wt% water respectively. The appearance of the hexagonal phase (H1) and discontinuous cubic phase (I1) for the acrylate system is likely due to the strong hydrating nature of the acrylate anion, which increases the head group area. The formation of these additional mesophases seen for the acrylate system, especially the hexagonal phase (H1), coupled with the polymerization functionality offers great potential in the design of advanced membrane materials with selective and anisotropic transport properties. PMID:26271610

  15. Thin liquid crystal films on liquids in the nematic range of temperatures.

    PubMed

    Delabre, Ulysse; Richard, Céline; Sang, Yann Yip Cheung; Cazabat, Anne-Marie

    2010-08-17

    Hybrid nematic films deposited on liquid substrates reveal a complex behavior, which is not fully understood. Here, the behavior of the n-cyanobiphenyl series on water and glycerol has been studied in a wide temperature range, including the vicinity of the nematic-isotropic (NI) transition. Wettability, allowed film thicknesses, and line tension of nematic domains have been investigated. The study provides a coherent picture of hybrid nematic films, allowing us to account for lower thickness threshold, structure of the film edge, and line tension of domains in the whole nematic range of temperatures. PMID:20695580

  16. Lyotropic Liquid Crystalline Cubic Phases as Versatile Host Matrices for Membrane-Bound Enzymes.

    PubMed

    Sun, Wenjie; Vallooran, Jijo J; Fong, Wye-Khay; Mezzenga, Raffaele

    2016-04-21

    Lyotropic liquid crystalline cubic mesophases can function as host matrices for enzymes because of their biomimetic structural characteristics, optical transparency, and capability to coexist with water. This study demonstrates that the in meso immobilized membrane-bound enzyme d-fructose dehydrogenase (FDH) preserves its full activity, follows ideal Michaelis-Menten kinetics, and shows improved stability compared to its behavior in solution. Even after 5 days, the immobilized FDH retained its full activity in meso, whereas a model hydrophilic enzyme, horseradish peroxidase, maintained only 21% of its original activity. We reason that the lipidic bilayers in the three-dimensional structures of cubic mesophases provide an ideal environment for the reconstitution of a membrane-bound enzyme. The preserved activity, long-term stability, and reusability demonstrate that these hybrid nanomaterials are ideal matrices for biosensing and biocatalytic fuel cell applications. PMID:27050734

  17. Positron lifetime measurements in chiral nematic liquid crystals

    NASA Technical Reports Server (NTRS)

    Singh, Jag J.; Eftekhari, Abe; Parmar, Devendra S.

    1991-01-01

    Positron lifetimes in the isotropic phases of chiral nematic liquid crystal formulations and their mixtures up to the racemic level were measured. The lifetime spectra for all liquid crystal systems were analyzed into three components. Although the individual spectra in the left- and right-handed components are identical, their racemic mixtures exhibit much larger orthopositronium lifetimes; these larger lifetimes indicate the presence of larger microvoids. This result is consistent with the reportedly higher thermodynamic stability and color play range in the racemic mixtures of chiral nematic liquid crystals.

  18. The Nematic Phases of Bent-Core Liquid Crystals

    PubMed Central

    Gleeson, Helen F; Kaur, Sarabjot; Görtz, Verena; Belaissaoui, Abdel; Cowling, Stephen; Goodby, John W

    2014-01-01

    Over the last ten years, the nematic phases of liquid crystals formed from bent-core structures have provoked considerable research because of their remarkable properties. This Minireview summarises some recent measurements of the physical properties of these systems, as well as describing some new data. We concentrate on oxadiazole-based materials as exemplars of this class of nematogens, but also describe some other bent-core systems. The influence of molecular structure on the stability of the nematic phase is described, together with progress in reducing the nematic transition temperatures by modifications to the molecular structure. The physical properties of bent-core nematic materials have proven difficult to study, but patterns are emerging regarding their optical and dielectric properties. Recent breakthroughs in understanding the elastic and flexoelectric behaviour are summarised. Finally, some exemplars of unusual electric field behaviour are described. PMID:24700653

  19. Lattice model for biaxial and uniaxial nematic liquid crystals.

    PubMed

    Sauerwein, Ricardo A; de Oliveira, Mário J

    2016-05-21

    We use a lattice gas model to describe the phase transitions in nematic liquid crystals. The phase diagram displays, in addition to the isotropic phase, the two uniaxial nematics, the rod-like and discotic nematics, and the biaxial nematic. Each site of the lattice has a constituent unit that takes only six orientations and is understood as being a parallelepiped brick with the three axes distinct. The possible orientations of a brick are those in which its axes are parallel to the axes of a Cartesian reference frame. The analysis of the model is performed by the use of a mean-field approximation and a Landau expansion of the free energy. PMID:27208971

  20. Flexoelectric polarization studies in bent-core nematic liquid crystals.

    PubMed

    Sreenilayam, S P; Panarin, Yu P; Vij, J K; Torgova, S I; Lehmann, A; Tschierske, C

    2015-08-01

    The flexoelectric polarization (Pf) of four bent-core nematic liquid crystals (LCs) has been measured using the pyroelectric effect. Hybrid aligned nematic cells are fabricated for measuring the pyroelectric response over the entire range of the nematic phase. It is found that the magnitude of flexoelectric polarization Pf and the sum of the flexoelectric coefficients |e1+e3| for the bent-core LCs studied here are three to six times higher than for the calamitics. Pf is found to depend on the transverse dipole moment of LC molecules. However, |e1+e3| values are by no means giant as |e3| alone had been reported for a bent-core nematic system previously. The dependence of the sum of "splay and bend flexoelectric coefficients" is discussed in terms of the shape of the molecule and of the dipole moment directed normal to the molecular axis. PMID:26382418

  1. Statistical mechanics of the flexoelectric effect in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Dhakal, Subas; Selinger, Jonathan V.

    2009-03-01

    Flexoelectricity is the phenomenon in which polarization is induced by imposed deformations of the director field in nematic liquid crystals. Recent experiments [1,2] have found that the flexoelectric effect is three orders of magnitude greater for bent-core liquid crystals than for conventional rod-like liquid crystals. To understand this experimental result, we develop a lattice model for the statistical mechanics of the flexoelectric effect. We perform Monte Carlo simulations and mean-field calculations to find the behavior as a function of interaction parameters, temperature, and applied electric field. The resulting phase diagram has four phases: isotropic, uniaxial nematic, biaxial nematic, and polar. In the uniaxial and biaxial nematic phases, there is a large splay or bend flexoelectric effect, which diverges as the system approaches the nematic-polar transition. This model may explain the large bend flexoelectric coefficient observed in bent-core liquid crystals, which have a tendency toward polar order. [1] J. Harden, B. Mbanga, N. Eber, K. Fodor-Csorba, S. Sprunt, J. T. Gleeson, and A. Jakli, Phys. Rev. Lett. 97,157802 (2006). [2] J. Harden, R. Teeling, J. T. Gleeson, S. Sprunt, and A.Jakli, Phys. Rev. E 78, 031702 (2008).

  2. Dynamics of a disc in a nematic liquid crystal.

    PubMed

    Antipova, Alena; Denniston, Colin

    2016-01-28

    We use lattice Boltzmann simulations to study the dynamics of a disc immersed in a nematic liquid crystal. In the absence of external torques, discs with homeotropic anchoring align with their surface normal parallel to the director of the nematic liquid crystal. In the presence of a weak magnetic field a ferromagnetic disc will rotate to equilibrate the elastic torque due to the distortion of the nematic director and the magnetic torque. When the magnetic field rotates the disc so that the angle θ between normal to the surface of the disc â and director of the liquid crystal n[combining circumflex] becomes greater than π/2, the disc flips around the axis perpendicular to the rotation axis so that â sweeps through π radians. An analysis of this behaviour was performed. In particular, we look at the impact of the disc thickness and edges on defect creation and the flipping transition. We also analyse the importance of backflow. PMID:26575160

  3. Colloidal spirals in nematic liquid crystals.

    PubMed

    Senyuk, Bohdan; Pandey, Manoj B; Liu, Qingkun; Tasinkevych, Mykola; Smalyukh, Ivan I

    2015-12-01

    One of the central experimental efforts in nematic colloids research aims to explore how the interplay between the geometry of particles along with the accompanying nematic director deformations and defects around them can provide a means of guiding particle self-assembly and controlling the structure of particle-induced defects. In this work, we design, fabricate, and disperse low-symmetry colloidal particles with shapes of spirals, double spirals, and triple spirals in a nematic fluid. These spiral-shaped particles, which are controlled by varying their surface functionalization to provide tangential or perpendicular boundary conditions of the nematic molecular alignment, are found inducing director distortions and defect configurations with non-chiral or chiral symmetry. Colloidal particles also exhibit both stable and metastable multiple orientational states in the nematic host, with a large number of director configurations featuring both singular and solitonic nonsingular topological defects accompanying them, which can result in unusual forms of colloidal self-assembly. Our findings directly demonstrate how the symmetry of particle-generated director configurations can be further lowered, or not, as compared to the low point group symmetry of solid micro-inclusions, depending on the nature of induced defects while satisfying topological constraints. We show that achiral colloidal particles can cause chiral symmetry breaking of elastic distortions, which is driven by complex three-dimensional winding of induced topological line defects and solitons. PMID:26358649

  4. Reverse lyotropic liquid crystals from europium nitrate and P123 with enhanced luminescence efficiency.

    PubMed

    Yi, Sijing; Li, Qintang; Liu, Hongguo; Chen, Xiao

    2014-10-01

    Fabrication of lyotropic aggregates containing the lanthanide ions is becoming a preferable way to prepare novel functional materials. Here, the lyotropic liquid crystals (LLCs) of reverse hexagonal, reverse bicontinuous cubic, and lamellar phases have been constructed in sequence directly from the mixtures of Eu(NO3)3·6H2O and Pluronic P123 amphiphilc block copolymer with increasing the salt proportion. Their phase types and structural characteristics were analyzed using polarized optical microscopy (POM) and small-angle X-ray scattering (SAXS) measurements. The driving forces of reverse LLC phase formation were investigated using Fourier-transformed infrared spectroscopy (FTIR) and rheological measurements. The hydrated europium salt was found to act not only as a solvent here, but also as the bridge to form hydrogen bonding between coordinated water molecules and PEO blocks, which played a key role in the reverse LLCs formation. Compared to those in aqueous solutions and solid state, the enhanced luminescence quantum yields and prolonged excited state lifetimes were observed in two europium containing reverse mesophases. The luminescence quenching effect of lanthanide ions was efficiently suppressed, probably due to the substitution of coordinated water molecules by oxyethyl groups of P123 and ordered phase structures of LLCs, where the coordinated europium ions were confined and isolated by PEO blocks. The optimum luminescence performance was then found to exist in the reverse hexagonal phase. The obtained results on such lanthanide-induced reverse LLCs should be referable for designing new luminescent soft materials construction to expand their application fields. PMID:25215923

  5. In situ synthesis of mesoporous CdS nanoparticles in ternary cubic phase lyotropic liquid crystal

    NASA Astrophysics Data System (ADS)

    Huang, N. M.; Kan, C. S.; Radiman, S.

    An in situ technique for the synthesis of CdS nanoparticles in a ternary lyotropic cubic phase liquid crystal has been carried out. The extremely viscous cubic phase liquid-crystal system consists of poly(oxyethylene)10 nonyl phenol ether as non-ionic surfactant, octane as oil phase and an aqueous phase containing reactant ions (Cd2+ and S2-). Thioacetamide (TAA) has been utilized as a source for slow release of sulfur in the in situ synthesis of CdS. Rheological results show that CdS nanoparticle growth did not disrupt the structure of the cubic phase liquid-crystal system. This indicates that homogenous synthesis of CdS in the liquid crystal had been achieved. The final products were characterized using X-ray photoelectron spectroscopy, thermal gravimetric analysis, transmission electron microscopy and UV-visible spectroscopy. It was found that the CdS nanoparticles formed have a mesoporous structure with a size dependent on the TAA decomposition aging time.

  6. Templated synthesis of ZnSe nanostructures using lyotropic liquid crystals.

    PubMed

    Karanikolos, Georgios N; Alexandridis, Paschalis; Mallory, Robert; Petrou, Athos; Mountziaris, T J

    2005-10-01

    We report a technique for controlled synthesis of zero-, one-, and two-dimensional compound semiconductor nanostructures by using cubic, hexagonal, and lamellar lyotropic liquid crystals as templates, respectively. The liquid crystals were formed by self-assembly in a ternary system consisting of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) amphiphilic block copolymer as the surfactant, heptane as the non-polar dispersed phase, and formamide as the polar continuous phase. ZnSe quantum dots and nanowires with diameters smaller than 10 nm, as well as free-standing, disc-like quantum wells, were grown inside the spherical, cylindrical, and planar nanodomains, respectively, by reacting diethylzinc that was dissolved in the heptane domains with hydrogen selenide gas that was brought into contact with the liquid crystal in a sealed chamber at room temperature and atmospheric pressure. The shape and size of the resulting nanostructures can be manipulated by selecting the templating phase of the liquid crystal, the size of the dispersed nanodomains that is controlled by the composition of the template, and the concentration of diethylzinc in them. PMID:20818020

  7. Templated synthesis of ZnSe nanostructures using lyotropic liquid crystals

    NASA Astrophysics Data System (ADS)

    Karanikolos, Georgios N.; Alexandridis, Paschalis; Mallory, Robert; Petrou, Athos; Mountziaris, T. J.

    2005-10-01

    We report a technique for controlled synthesis of zero-, one-, and two-dimensional compound semiconductor nanostructures by using cubic, hexagonal, and lamellar lyotropic liquid crystals as templates, respectively. The liquid crystals were formed by self-assembly in a ternary system consisting of a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) amphiphilic block copolymer as the surfactant, heptane as the non-polar dispersed phase, and formamide as the polar continuous phase. ZnSe quantum dots and nanowires with diameters smaller than 10 nm, as well as free-standing, disc-like quantum wells, were grown inside the spherical, cylindrical, and planar nanodomains, respectively, by reacting diethylzinc that was dissolved in the heptane domains with hydrogen selenide gas that was brought into contact with the liquid crystal in a sealed chamber at room temperature and atmospheric pressure. The shape and size of the resulting nanostructures can be manipulated by selecting the templating phase of the liquid crystal, the size of the dispersed nanodomains that is controlled by the composition of the template, and the concentration of diethylzinc in them.

  8. Lyotropic Phase Behavior of Polybutadiene-Poly(ethylene oxide) Diblock Copolymers in Ionic Liquids

    SciTech Connect

    Simone, Peter M.; Lodge, Timothy P.

    2008-08-26

    The lyotropic phase behavior of three poly(1,2-butadiene-b-ethylene oxide) diblock copolymers (PB-PEO) with different monomer volume fractions has been studied in two different ionic liquids, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]) and 1-butyl-3-methylimidazolium hexafluorophosphate ([BMI][PF{sub 6}]), across the complete concentration range. The ordered microstructures present in the solutions were characterized via small-angle X-ray scattering (SAXS). The phase diagrams for the PB-PEO/ionic liquid solutions include regions corresponding to the classical copolymer microstructures: body-centered-cubic lattices of spheres, hexagonally ordered cylinders, and lamellae. Additionally, the phase diagrams also include wide regions of coexisting microstructures and regions apparently corresponding to a disordered network microstructure. The phase behavior of the PB-PEO copolymers in both ionic liquids was comparable to their previously reported aqueous solution behavior. The temperature dependence of the phase diagrams was very modest, indicative of a highly segregated system. The level of solvent selectivity was also investigated via cryogenic transmission electron microscopy (cryo-TEM) on dilute solutions. On the basis of the morphology of the dilute solution copolymer aggregate structures in the ionic liquid solvents, and on the structural length scales of the concentrated solutions, it was concluded that for PB-PEO [BMI][PF{sub 6}] behaves as a more selective solvent than [EMI][TFSI].

  9. Simulation of weak anchoring effects on nematic liquid crystal hemispheres

    NASA Astrophysics Data System (ADS)

    Gillen, Sean; Somers, David A. T.; Munday, Jeremy N.

    The free energy of a nematic liquid crystal droplet depends on an interplay between elastic and surface interactions. When the two contributions are of similar magnitude, there exists a transition of the nematic structure of the droplet. Because the two contributions scale differently with length scales, this transition is visible as a function of the size of the droplet. We carry out numerical simulations to explore the use of this transition in measuring surface anchoring energies. This technique could help elucidate alignment forces on liquid crystals, such as those caused by rubbed surfaces, electric fields, or even the Casimir torque. Electrical and Computer Engineering.

  10. Bonded boojum-colloids in nematic liquid crystals.

    PubMed

    Eskandari, Zahra; Silvestre, Nuno M; Telo da Gama, Margarida M

    2013-08-20

    We investigate bonded boojum-colloids in nematic liquid crystals, configurations where two colloids with planar degenerate anchoring are double-bonded through line defects connecting their surfaces. This bonded structure promotes the formation of linear chains aligned with the nematic director. We show that the bonded configuration is the global minimum in systems that favor twist deformations. In addition, we investigate the influence of confinement on the stability of bonded boojum-colloids. Although the unbonded colloid configuration, where the colloids bundle at oblique angles, is favored by confinement, the bonded configuration is again the global minimum for liquid crystals with sufficiently small twist elastic constants. PMID:23859624

  11. Controlling materials architecture on the nanometer-scale: PPV nanocomposites via polymerizable lyotropic liquid crystals[Poly(p-phenylenevinylene)

    SciTech Connect

    Smith, R.C.; Deng, H.; Fischer, W.M.; Gin, D.L.

    1998-07-01

    The authors have developed a general strategy for the construction of ordered nanocomposites with hexagonal symmetry, using polymerizable lyotropic (i.e., amphiphilic) liquid crystals. In this approach, self-organizing lyotropic liquid-crystalline monomers are used to form an ordered template matrix in the presence of a reactive hydrophilic solution. Subsequent photopolymerization to lock-in the matrix architecture, followed by initiation of chemistry within the ordered hydrophilic domains to afford solid-state fillers, yields the anisotropic nanocomposites. Composites have been synthesized that have a regular hexagonal arrangement of extended poly(p-phenylenevinylene) (PPV) domains, with a regular interchannel spacing of 4 nm. The photoluminescence of these materials is significantly altered from that of bulk PPV. The dimensions of these nanocomposites can be tuned by varying the size of the hydrophobic tails and/or the nature of the counterion associated with the hydrophilic headgroup of the monomer.

  12. Dynamic arrest of nematic liquid-crystal colloid networks

    NASA Astrophysics Data System (ADS)

    Zou, Lu; Hwang, Jeoung-Yeon; Kim, Chanjoong

    2013-10-01

    We report interesting self-assembly structures of nematic liquid-crystal colloid (NLCC) networks, which are arrested during cooling from the isotropic temperature to room temperature. The NLCC is composed of sterically stabilized colloidal particles and a nematic liquid crystal (NLC) with nematic-isotropic transition temperature (TNI) that is much higher than those of previously studied 4-Cyano-4'-pentylbiphenyl and N-(4-Methoxybenzylidene)-4-butylaniline. We find that the structure of NLCCs depends on TNI, cooling rates, and boundary conditions, varying from cellular network to hierarchical fern structures in different length scales. Our time-lapse study shows that the transition from the cellular network to the fern structure directly corresponds to the transition from a spinodal demixing to a nucleation-and-growth mechanism.

  13. Dielectrophoretic manipulation of the mixture of isotropic and nematic liquid

    NASA Astrophysics Data System (ADS)

    Kim, Soo-Dong; Lee, Bomi; Kang, Shin-Woong; Song, Jang-Kun

    2015-08-01

    In various applications involving liquid crystals, the manipulation of the nanoscale molecular assembly and microscale director alignment is highly useful. Here we show that a nematic-isotropic mixture, a unique bi-liquid system, has potential for the fabrication of microstructures having an ordered phase within a disordered phase, or vice versa. The volume expansion and shrinkage, migration, splitting, mergence and elongation of one phase within the other are easily accomplished via thermal treatment and dielectrophoretic manipulation. This is particularly achievable when one phase is suspended in the middle. In that case, a highly biased ordered-phase preference of surfaces, that is, the nematic-philic nature of a polyimide layer and the nematic-phobic nature of a self-assembled monolayer of chlorosilane derivatives, is used. Further, by combining this approach with photopolymerization, the patterned microstructure is solidified as a patterned polymer film having both isotropic and anisotropic molecular arrangements simultaneously, or as a template with a morphological variation.

  14. Brownian motion of particles in nematic fluids

    NASA Astrophysics Data System (ADS)

    Yao, Xuxia; Nayani, Karthik; Park, Jung; Srinivasarao, Mohan

    2011-03-01

    We studied the brownian motion of both charged and neutral polystyrene particles in two nematic fluids, a thermotropic liquid crystal, E7, and a lyotropic chromonic liquid crystal, Sunset Yellow FCF (SSY). Homogeneous planar alignment of E7 was easliy achieved by using rubbed polyimide film coated on the glass. For SSY planar mondomain, we used the capillary method recently developed in our lab. By tracking a single particle, the direction dependent diffussion coefficients and Stokes drag were measured in the nematic phase and isotropic phase for both systems.

  15. Metric approach for sound propagation in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Pereira, E.; Fumeron, S.; Moraes, F.

    2013-02-01

    In the eikonal approach, we describe sound propagation near topological defects of nematic liquid crystals as geodesics of a non-Euclidian manifold endowed with an effective metric tensor. The relation between the acoustics of the medium and this geometrical description is given by Fermat's principle. We calculate the ray trajectories and propose a diffraction experiment to retrieve information about the elastic constants.

  16. A Liquid Crystalline Oligomer Exhibiting Nematic and Twist-Bend Nematic Mesophases.

    PubMed

    Mandle, Richard J; Goodby, John W

    2016-04-01

    The twist-bend nematic phase (NTB ) has been described as the structural link between the untilted uniaxial nematic phase (N) and the helical chiral nematic phase (N*). The NTB phase exhibits phenomena of fundamental importance to science, that is, 1) the spontaneous formation of a helical pitch on the nanometer scale in a fluid and 2) the spontaneous breaking of mirror symmetry, leading to the emergence of chiral domains in an achiral system. In this Communication, we present a study on T49 [bis(4-(9-(4-((4-cyanobenzoyl)oxy)phenyl)nonyl)phenyl) 4,4'-(nonane-1,9-diyl)dibenzoate], a liquid-crystalline oligomer exhibiting the twist-bend nematic phase, which has a molecular length that is of comparable dimensions to the sub-10 nm pitch determined for CB9CB, and provide new insights into the differentiation between the nano- and macro-science for self-assembling supermolecular systems. PMID:26777310

  17. Rayleigh Light Scattering from Nematic Liquid Crystals at Oblique Incidence.

    NASA Astrophysics Data System (ADS)

    da, Xiao-Yi.

    Ryuichi Akiyama 1980 and his co-workers first showed the possibility that light scattering experiments on nematic liquid crystals could be carried out preferably by using oblique incidence rather than the conventional normal incidence. Miraldi, et al 1980 strongly recommended the application of oblique incidence, and gave a discussion in detail. The present work starts from an attempt to obtain the three Frank elastic constants and viscosity coefficients of nematic liquid crystals by Rayleigh light scattering. A suitable scattering geometry has been chosen; a systematic method of measuring these constants and coefficients has been developed by measuring the linewidths of the scattered light from a single sample at various incidence angles and fitting the measured linewidths with appropriate theoretical expressions. It is shown in the present work that the light scattering experiments on nematic liquid crystals at oblique incidence have many advantages over the same kind of experiments at normal incidence so far widely employed, and show a promising future. After a brief introduction to the general theory of the dynamic light scattering, nematic liquid crystals and light scattering from nematic liquid crystals in Chapters 1, 2, and 3, and a brief review of the measurements of elastic constants and viscosity coefficients of nematic liquid crystals by light scattering in Chapter 4, a straightforward method concerning the calculation of variations of the wave vectors upon scattering is developed in Chapter 5. This method assumes that a nematic liquid crystal behaves optically like a uniaxial crystal. In doing so, all we have to know is the ordinary and extraordinary refractive indices n(,o) and n(,e) of the sample under consideration. The linewidth and intensity distributions of the scattered light can then be determined by inserting the variations in wave vectors into appropriate equations for a known material for which the knowledge of the elastic constants as well

  18. Global defect topology in nematic liquid crystals

    PubMed Central

    Machon, Thomas

    2016-01-01

    We give the global homotopy classification of nematic textures for a general domain with weak anchoring boundary conditions and arbitrary defect set in terms of twisted cohomology, and give an explicit computation for the case of knotted and linked defects in R3, showing that the distinct homotopy classes have a 1–1 correspondence with the first homology group of the branched double cover, branched over the disclination loops. We show further that the subset of those classes corresponding to elements of order 2 in this group has representatives that are planar and characterize the obstruction for other classes in terms of merons. The planar textures are a feature of the global defect topology that is not reflected in any local characterization. Finally, we describe how the global classification relates to recent experiments on nematic droplets and how elements of order 4 relate to the presence of τ lines in cholesterics. PMID:27493576

  19. Hybrid graphene nematic liquid crystal light scattering device.

    PubMed

    Qasim, M M; Khan, A A; Kostanyan, A; Kidambi, P R; Cabrero-Vilatela, A; Braeuninger-Weimer, P; Gardiner, D J; Hofmann, S; Wilkinson, T D

    2015-09-01

    A hybrid graphene nematic liquid crystal (LC) light scattering device is presented. This device exploits the inherent poly-crystallinity of chemical vapour deposited (CVD) graphene films to induce directional anchoring and formation of LC multi-domains. This thereby enables efficient light scattering without the need for crossed polarisers or separate alignment layers/additives. The hybrid LC device exhibits switching thresholds at very low electric fields (< 1 V μm(-1)) and repeatable, hysteresis free characteristics. This exploitation of LC alignment effects on CVD graphene films enables a new generation of highly efficient nematic LC scattering displays as well as many other possible applications. PMID:26243047

  20. Propagating director bend fluctuations in nematic liquid crystals.

    PubMed

    Humpert, Anja; Allen, Michael P

    2015-01-16

    We show, by molecular simulation, that for a range of standard, coarse-grained, nematic liquid crystal models, the director bend fluctuation is a propagating mode. This is in contrast to the generally accepted picture of nematic hydrodynamics, in which all the director modes (splay, twist, bend, and combinations thereof) are overdamped. By considering the various physical parameters that enter the equations of nematodynamics, we propose an explanation of this effect and conclude that propagating bend fluctuations may be observable in some experimental systems. PMID:25635566

  1. Anomalous light transmission by nematic liquid crystal cells

    NASA Astrophysics Data System (ADS)

    Konshina, E. A.; Fedorov, M. A.; Ivanova, N. L.; Amosova, L. P.

    2008-01-01

    Light transmission through nematic liquid crystal (NLC) cells with a planar alignment and various boundary conditions has been studied as a function of the bias voltage in the regimes of maximum transmittance and complete extinction. The phenomenon of anomalous light leakage in the regime of complete extinction has been observed in the NLC sells with alignment layers of amorphous hydrogenated carbon (a-C:H) and poly(vinyl alcohol) (PVA), in which an anisotropy was induced by rubbing the electrode surface (for a-C:H) and the alignment layer (for PVA). The anomalous transmission is caused by the deformation of nematic molecules, which are situated near the surface, in the direction perpendicular to the direction of rubbing. The magnitude of anomalous transmission increases with the bias voltage. This behavior is explained by the anisotropy of the surface anchoring energy of nematic molecules at the interface.

  2. Dispersions of ellipsoidal particles in a nematic liquid crystal.

    PubMed

    Tasinkevych, Mykola; Mondiot, Frédéric; Mondain-Monval, Olivier; Loudet, Jean-Christophe

    2014-03-28

    Colloidal particles dispersed in a partially ordered medium, such as a liquid crystal (LC) phase, disturb its alignment and are subject to elastic forces. These forces are long-ranged, anisotropic and tunable through temperature or external fields, making them a valuable asset to control colloidal assembly. The latter is very sensitive to the particle geometry since it alters the interactions between the colloids. We here present a detailed numerical analysis of the energetics of elongated objects, namely prolate ellipsoids, immersed in a nematic host. The results, complemented with qualitative experiments, reveal novel LC configurations with peculiar topological properties around the ellipsoids, depending on their aspect ratio and the boundary conditions imposed on the nematic order parameter. The latter also determine the preferred orientation of ellipsoids in the nematic field, because of elastic torques, as well as the morphology of particle aggregates. PMID:24651907

  3. Structure of nematic liquid crystalline elastomers under uniaxial deformation

    SciTech Connect

    Zhang Fan; Heiney, Paul A.; Srinivasan, Amritha; Naciri, Jawad; Ratna, Banahalli

    2006-02-15

    We have used in situ x-ray diffraction and calorimetry to study liquid crystalline elastomers prepared using a one-step photopolymerization method. We used suspended weights to stretch free-standing crystalline elastomer films. With the mechanical stress parallel to the initial director, we observed a gradual nematic to isotropic transition with increasing temperature. The thermal evolution of the nematic order parameter on cooling, together with the observation of isotropic-nematic coexistence over a broad temperature range, suggests that the heterogeneity in the samples introduces a distribution of transition temperatures. With the mechanical stress perpendicular to the initial director, we observed both uniform director rotation and stripe formation, depending on the details of sample preparation.

  4. Fluctuation Modes of a Twist-Bend Nematic Liquid Crystal

    NASA Astrophysics Data System (ADS)

    Parsouzi, Z.; Shamid, S. M.; Borshch, V.; Challa, P. K.; Baldwin, A. R.; Tamba, M. G.; Welch, C.; Mehl, G. H.; Gleeson, J. T.; Jakli, A.; Lavrentovich, O. D.; Allender, D. W.; Selinger, J. V.; Sprunt, S.

    2016-04-01

    We report a dynamic light-scattering study of the fluctuation modes in a thermotropic liquid crystalline mixture of monomer and dimer compounds that exhibits the twist-bend nematic (NTB ) phase. The results reveal a spectrum of overdamped fluctuations that includes two nonhydrodynamic modes and one hydrodynamic mode in the NTB phase, and a single nonhydrodynamic mode plus two hydrodynamic modes (the usual nematic optic axis or director fluctuations) in the higher temperature, uniaxial nematic phase. The properties of these fluctuations and the conditions for their observation are comprehensively explained by a Landau-de Gennes expansion of the free-energy density in terms of heliconical director and helical polarization fields that characterize the NTB structure, with the latter serving as the primary order parameter. A "coarse-graining" approximation simplifies the theoretical analysis and enables us to demonstrate quantitative agreement between the calculated and experimentally determined temperature dependence of the mode relaxation rates.

  5. Dynamic-Mechanical Analysis of Monodomain Nematic Liquid Crystalline Elastomers

    NASA Astrophysics Data System (ADS)

    Hotta, Atsushi; Terentjev, Eugene

    2003-03-01

    Dynamic-mechanical analysis was performed in the glassy, nematic and isotropic states of several monodomain nematic liquid crystalline elastomers (LCE) which differ in their degrees of anisotropy and internal microstructure. It was found that the type of network crosslinker makes a significant difference in the equilibrium properties of these elastomers, in particular, in their effective anisotropy. In spite of these differences, the observed dynamic-mechanical behaviour was very similar. The fact that there is a consistently high and wide loss over the whole nematic region, where storage modulus G' behaves non-monotonically, is most likely an indicator of the fact that the dynamic-mechanical response is not linear. Master curves have been built between the glassy state and the nematic-isotropic phase transition, where the modulus reaches a low-level soft plateau. Above the nematic-isotropic transition temperature Tni, the modulus rises substantially, since internal relaxation is no longer able to reduce the elastic response - and further time-temperature superposition fails. The dynamics of these elastomers are dominated by power laws, which was confirmed by the successful procedure of the master curve inversion (time-frequency inversion) to describe the static stress relaxation. Interestingly, it was found that mechanical properties characterized by power laws (in time) of stress relaxation match very well with the dynamic properties, where power laws (in frequency) were also observed in the dynamic modulus in the appropriate range of temperatures. The work demonstrates the potential for the use of nematic liquid crystalline elastomers in many acoustic and vibration damping applications.

  6. Structural characterization of lyotropic liquid crystals containing a dendrimer for solubilization and release of gallic acid.

    PubMed

    Bitan-Cherbakovsky, Liron; Aserin, Abraham; Garti, Nissim

    2013-12-01

    The role of 2nd generation polypropyleneimine (PPIG2) dendrimer in controlling the release of gallic acid (GA) as a model drug from lyotropic liquid crystal was explored. GA (0.2wt%) was solubilized in three types of mesophases: lamellar (Lα), cubic (space group of Ia3d, Q(G)), and reverse hexagonal (HII), composed of GMO and water (and d-α-tocopherol, or tricaprylin in the case of HII mesophases). Small angle X-ray scattering (SAXS) and attenuated total reflectance Fourier transform infrared (ATR-FTIR) along with UV spectrophotometry were utilized to elucidate the structure modifications and release resulting from the cosolubilization of GA and PPIG2. Solubilization of PPIG2 into Lα and Q(G) phases caused transformation of both structures to HII. The diffusion of GA out of the mesophases was found to be dependent on water content and PPIG2 concentration. Rapid release from Lα+PPIG2 and Q(G)+PPIG2 mesophases was recorded. The release from both HII mixtures (with d-α-tocopherol and tricaprylin) was shown to be dependent on the type of oil. Release studies conducted for 72h showed that GA release can be modulated and sustained by the presence of PPIG2, supposedly due to the electrostatic interactions between the dendrimer and the drug molecule. PMID:23973908

  7. Spiral textures in lyotropic liquid crystals : first order transition between normal hexagonal and lamellar gel phases

    NASA Astrophysics Data System (ADS)

    McGrath, K. M.; Kékicheff, P.; Kléman, M.

    1993-06-01

    The first order transition between the normal hexagonal phase (H{α}) and lamellar gel phase (L{β}, L{β'}, L{δ}, ... type) in lyotropic liquid crystals of binary surfactant/water systems is investigated. Structural transformations and epitaxial relations are investigated by small-angle X-ray scattering on powdered and oriented samples. By slow evaporation of water, growth of the gel layered structure from the two-dimensional packing of surfactant cylinders of the hexagonal mesophase in the presence of a solid wall reveals a spectacular new texture composed of interwoven spirals. It is demonstrated that the layers grow from the rods of the hexagonal phase, in planes coplanar with the hexagonal packing and perpendicular to the wall. The configuration is such that line wedge disclinations of strength s= + 1/2 of the hexagonal phase are preserved through the phase transition. Estimates of the radii for the developable domain and cores, and also for the bending elastic constant are obtained. A mechanism for the phase transformation is discussed in view of topological structural transformations and a modification of the short-range order associated to the disorder order transition of the configuration of the paraffinic chains.

  8. Oil and drug control the release rate from lyotropic liquid crystals.

    PubMed

    Martiel, Isabelle; Baumann, Nicole; Vallooran, Jijo J; Bergfreund, Jotam; Sagalowicz, Laurent; Mezzenga, Raffaele

    2015-04-28

    The control of the diffusion coefficient by the dimensionality d of the structure appears as a most promising lever to efficiently tune the release rate from lyotropic liquid crystalline (LLC) phases and dispersed particles towards sustained, controlled and targeted release. By using phosphatidylcholine (PC)- and monolinoleine (MLO)-based mesophases with various apolar structural modifiers and water-soluble drugs, we present a comprehensive study of the dimensional structural control of hydrophilic drug release, including 3-d bicontinuous cubic, 2-d lamellar, 1-d hexagonal and 0-d micellar cubic phases in excess water. We investigate how the surfactant, the oil properties and the drug hydrophilicity mitigate or even cancel the effect of structure variation on the drug release rate. Unexpectedly, the observed behavior cannot be fully explained by the thermodynamic partition of the drug into the lipid matrix, which points out to previously overlooked kinetic effects. We therefore interpret our results by discussing the mechanism of structural control of the diffusion rate in terms of drug permeation through the lipid membrane, which includes exchange kinetics. A wide range of implications follow regarding formulation and future developments, both for dispersed LLC delivery systems and topical applications in bulk phase. PMID:25744826

  9. Photorefractivity in polymer-stabilized nematic liquid crystals

    SciTech Connect

    Wiederrecht, G.P.; Wasielewski, M.R. |

    1998-07-01

    Polymer-stabilized liquid crystals, consisting of low concentrations of a polymeric electron acceptor, are shown to exhibit significantly enhanced photorefractive properties. The charge generation and transport properties of these composite systems are strongly modified from nematic liquid crystals doped with electron donors and acceptors. The new composites are produced by polymerizing a small quantity of a 1,4:5,8-naphthalenediimide electron acceptor functionalized with an acrylate group in an aligned nematic liquid crystal. Photopolymerization creates an anisotropic gel-like medium in which the liquid crystal is free to reorient in the presence of a space charge field, while maintaining charge trapping sites in the polymerized regions of the material. The presence of these trapping sites results in the observation of longer lived, higher resolution holographic gratings in the polymer-stabilized liquid crystals than observed in nematic liquid crystals alone. These gratings display Bragg regime diffraction. Asymmetric beam coupling, photo-conductivity, and four-wave mixing experiments are performed to characterize the photophysics of these novel materials.

  10. Photorefractivity in polymer-stabilized nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Wiederrecht, Gary P.; Wasielewski, Michael R.

    1998-10-01

    Polymer-stabilized liquid crystals, consisting of low concentrations of a polymeric electron acceptor, are shown to exhibit significantly enhanced photorefractive properties. The charge generation and transport properties of these composite systems are strongly modified from nematic liquid crystals doped with electron donors and acceptors. The new composites are produced by polymerizing a small quantity of a 1,4:5,8-naphthalenediimide electron acceptor functionalized with an acrylate group in an aligned nematic liquid crystal. Photopolymerization creates an anisotropic gel-like medium in which the liquid crystal is free to reorient in the presence of a space charge field, while maintaining charge trapping sites in the polymerized regions of the material. The presence of these trapping sites results in the observation of longer lived, higher resolution holographic gratings in the polymer-stabilized liquid crystals than observed in nematic liquid crystals alone. These gratings display Bragg regime diffraction. Asymmetric beam coupling, photo-conductivity, and four-wave mixing experiments are performed to characterize the photophysics of these novel materials.

  11. Photoalignment of a Nematic Liquid Crystal Fluid and Glassy-Nematic Oligofluorenes on Coumarin-Containing Polymer Films

    SciTech Connect

    Trajkovska, A.; Kim, C.; Marshall, K.L.; Mourey, T.H.; Chen, S.H.

    2007-03-19

    The orientations of both a nematic liquid crystal fluid and a series of monodisperse glassy-nematic oligofluorenes were investigated on photoalignment films comprising a polymethacrylate backbone with 7-benzoyloxycoumarin pendants. Both classes of liquid crystalline material were found to undergo a transition from a parallel to a perpindicular orientation with reference to the polarization axis of UV-irradiation at a sufficiently high extent of dimerization.

  12. Two-Dimensional NMR Study of a Liquid-Crystal Solution under Magic-Angle Spinning. Conformation of Carboxylic Ionophore Lasalocid A Dissolved in a Lyotropic Liquid Crystal

    NASA Astrophysics Data System (ADS)

    Kimura, Atsuomi; Kano, Tetsushi; Fujiwara, Hideaki

    1996-07-01

    The conformation of a carboxylic ionophore, lasalocid A, has been determined in a lyotropic liquid crystal by means of magic-angle spinning (MAS) and two-dimensional NMR experiments. The information extracted from ROESY spectra measured under MAS was analyzed according to the distance-geometry algorithm. The liquid crystal used for the solvent is cesium perfluorooctanoate dissolved in D2O, and the resulting structure of lasalocid A is a cyclic one, indicating cation complexation within a hydrophobic region of the liquid crystal. In this way, the two-dimensional MAS NMR experiment is proved to be a useful technique in conformational studies of complex molecules dissolved in lyotropic liquid crystal which may be regarded as offering a membrane-like environment.

  13. Orientational dynamics of nematic liquid crystals under shear flow

    NASA Astrophysics Data System (ADS)

    Rienäcker, G.; Hess, S.

    The orientational dynamics of low molecular weight and polymeric nematic liquid crystals in a flow field is investigated, based on a nonlinear relaxation equation for the second rank alignment tensor. Various approximations are discussed: Assuming uniaxial alignment with a constant order parameter, the results of the Ericksen-Leslie theory are recovered. The detailed analysis to be presented here for plane Couette flow concerns (i) uniaxial alignment with a variable degree of order and (ii) the tensorial analysis involving the three symmetry-adapted components of the five components of the alignment tensor. The transitions between tumbling, wagging and aligning behavior observed in polymeric liquid crystals and described by the Doi theory of rod-like nematic polymers are recovered. Consequences for the rheological behavior are indicated.

  14. Simulation and visualization of topological defects in nematic liquid crystals.

    PubMed

    Callan-Jones, A C; Pelcovits, Robert A; Slavin, V A; Zhang, S; Laidlaw, D H; Loriot, G B

    2006-12-01

    We present a method of visualizing topological defects arising in numerical simulations of liquid crystals. The method is based on scientific visualization techniques developed to visualize second-rank tensor fields, yielding information not only on the local structure of the field but also on the continuity of these structures. We show how these techniques can be used to first locate topological defects in fluid simulations of nematic liquid crystals where the locations are not known a priori and then study the properties of these defects including the core structure. We apply these techniques to simulation data obtained by previous authors who studied a rapid quench and subsequent equilibration of a Gay-Berne nematic. The quench produces a large number of disclination loops which we locate and track with the visualization methods. We show that the cores of the disclination lines have a biaxial region and the loops themselves are of a hybrid wedge-twist variety. PMID:17280078

  15. Simulation and visualization of topological defects in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Callan-Jones, A. C.; Pelcovits, Robert A.; Slavin, V. A.; Zhang, S.; Laidlaw, D. H.; Loriot, G. B.

    2006-12-01

    We present a method of visualizing topological defects arising in numerical simulations of liquid crystals. The method is based on scientific visualization techniques developed to visualize second-rank tensor fields, yielding information not only on the local structure of the field but also on the continuity of these structures. We show how these techniques can be used to first locate topological defects in fluid simulations of nematic liquid crystals where the locations are not known a priori and then study the properties of these defects including the core structure. We apply these techniques to simulation data obtained by previous authors who studied a rapid quench and subsequent equilibration of a Gay-Berne nematic. The quench produces a large number of disclination loops which we locate and track with the visualization methods. We show that the cores of the disclination lines have a biaxial region and the loops themselves are of a hybrid wedge-twist variety.

  16. Optical Fluctuation of Texture in Nematic Liquid Crystal Droplets

    NASA Astrophysics Data System (ADS)

    Kim, Sung-Jo; Back, Sang-In; Lev, Bohdan; Kim, Jong-Hyun

    2016-07-01

    We report the observation of texture of a nematic liquid crystal droplet using a high-speed camera mounted on a polarizing optical microscope. The dark crossed texture obtained by the polarizing optical microscope of a nematic liquid crystal droplet has texture wobbles, which are related to the director field fluctuation excited by thermal energy. We confirm relaxation and oscillation modes. An exact solution of the director fluctuation modes with one-constant approximation and an external electric field is proposed. The theoretical predictions of the relaxation time match with our experimental results when varying the temperature, droplet size, and electric field. Relaxation time was insensitive to the temperature, increased with radius of droplet and slightly decreased with electric field. Several oscillation modes, which have no specific trend, were also found. The external electric field freezes the oscillation modes.

  17. Spinodal dewetting of a nematic liquid crystal film

    PubMed

    Braun; Yokoyama

    2000-08-01

    We discuss spinodal dewetting of a nematic film destabilized by Van der Waals forces, focusing on the case of non-antagonistic anchoring conditions. Using physical parameters pertinent to low-molecular-weight thermotropic liquid crystals, we predict a small damping effect. In the presence of an antagonistic applied magnetic field, the anchoring conditions become more significant, and can influence the shape and dynamics of the unstable modes. PMID:11088786

  18. Metric approach for sound propagation in nematic liquid crystals.

    PubMed

    Pereira, E; Fumeron, S; Moraes, F

    2013-02-01

    In the eikonal approach, we describe sound propagation near topological defects of nematic liquid crystals as geodesics of a non-Euclidian manifold endowed with an effective metric tensor. The relation between the acoustics of the medium and this geometrical description is given by Fermat's principle. We calculate the ray trajectories and propose a diffraction experiment to retrieve information about the elastic constants. PMID:23496534

  19. Orientational behaviour of thermotropic and lyotropic liquid crystal polymer systems under shear flow

    NASA Astrophysics Data System (ADS)

    Andresen, E. M.; Mitchell, G. R.

    1998-08-01

    A comparison is made of the development of global orientation during shearing of lyotropic solutions of hydroxypropylcellulose with that observed for the thermotropic phase of hydroxypropylcellulose. At shear rates > 10 s-1 the behaviour of the two systems is similar, both during steady-state shear, and in terms of relaxation following cessation of shear flow. At low shear rates, the levels of orientation observed for the thermotropic system are substantially greater than observed for the lyotropic solutions. The relationship of these differences to variations in molecular parameters, viscous stress and to director tumbling is discussed.

  20. Controlled polymer nanostructure and properties through photopolymerization in lyotropic liquid crystal templates

    NASA Astrophysics Data System (ADS)

    Forney, Bradley Steven

    Incorporating nanotechnology into polymers has tremendous potential to improve the functionality and performance of polymer materials for use in a wide range of biomedical and industrial applications. This research uses lyotropic liquid crystals (LLCs) to control polymer structure on the nanometer scale in order to improve material properties. The overall goal of this research is to establish fundamental methods of synthesizing polymers with controlled nanostructured architectures in order to understand and utilize useful property relationships that result from the organized polymer morphologies. This work aims to establish a fundamental understanding of the reaction conditions needed to control polymer nanostructure and determine the benefits of organized polymer network structures on mechanical and transport properties. The synthesis of nanostructured polymers for improved material performance has utilized LLCs and photopolymerization kinetics to direct polymer structure. Self-assembled LLC phases provide a useful template that may be used as a photopolymerization platform to control polymer morphology on the nanometer size scale. Photopolymerization kinetics were used as a tool to examine the thermodynamics and phase structure evolution that occurs during the polymerization reaction. Additionally, several methods were developed to control polymer morphology and prevent loss of LLC order that can occur during polymerization. LLCs were also used to generate nanocomposite polymers with two distinct polymer networks to impart improvements in material properties. Other useful property relationships including increases in mechanical integrity, greater diffusive transport, and larger water uptake were established in this research. Finally, the LLC templating process was applied to solve performance problems associated with stimuli-sensitive polymer materials. Dramatic improvements in the response rate, dynamic range, and mechanical properties were achieved using LLCs

  1. Polypeptide-Coated Silica Particles Dispersed in Lyotropic Liquid Crystals of the Same Polypeptide.

    PubMed

    Rosu, Cornelia; Balamurugan, Sreelatha; Cueto, Rafael; Roy, Amitava; Russo, Paul S

    2016-07-28

    When a particle is introduced into a liquid crystal (LC), it distorts the LC director field, leading to new arrangements of the particles. This phenomenon is ordinarily studied using >100 nm particles and ∼2 nm mesogens. Usually the particle surface and mesogens are chemically distinct, which adds an enthalpic effect, even though the more interesting interactions are entropic. To raise the structures to the visible regime, while minimizing chemical differences between the particle surface and mesogen, silica particles coated with an α-helical polypeptide have been prepared and dispersed in lyotropic polypeptide LCs. The polypeptide is poly(γ-stearyl-α,l-glutamate) or PSLG. To make the particles easy to manipulate and easy to find, the silica core included superparamagnetic magnetite (Fe3O4) and covalently attached dye. Two methods were used to place polypeptides on these magnetic, fluorescent particles: a multistep grafting-to approach in which whole polypeptides were attached and a one-pot grafting-from approach in which the polymerization of the monomers was initiated from the particle surface. These approaches resulted in sparse and dense surface coverages, respectively. The influence of surface curvature and polypeptide molecular weight on the design of sparsely covered particles was investigated using the grafting-to approach. The aggregated grafting-from particles when freshly dispersed in a PSLG/solvent matrix disrupted the orientation of the characteristic cholesteric LC (ChLC) phase directors. In time, the hybrid particles were expelled from some domains, enabling the return of the familiar helical twist of the cholesteric mesophase. The sparsely coated grafting-to hybrid particles when inserted in the PSLG/solvent matrix assembled into stable islet-like formations that could not be disrupted even by an external magnetic field. The bulk particles aligned in chains that were easily manipulated by a magnetic field. These results indicate that

  2. Photoluminescence analysis of self induced planer alignment in azo dye dispersed nematic liquid crystal complex

    SciTech Connect

    Kumar, Rishi Sood, Srishti Raina, K. K.

    2014-04-24

    We have developed azo dye doped nematic liquid crystal complex for advanced photonic liquid crystal display technology aspects. Disperse orange azo dye self introduced planer alignment in the nematic liquid crystal without any surface anchoring treatment. Planer alignment was characterized by optical polarizing microscopy. The electro-optical switching response of dye disperse planer aligned nematic cell was investigated as a function of applied voltage with the help of photoluminescence spectrophotometer for the tuning of photoluminescence contrast.

  3. Enhanced energy transfer efficiency and stability of europium β-diketonate complex in ionic liquid-based lyotropic liquid crystals.

    PubMed

    Yi, Sijing; Wang, Jiao; Chen, Xiao

    2015-08-21

    Luminescent materials from europium β-diketonate complex in ionic liquids (ILs) could achieve enhanced luminescence efficiencies and photostabilities. However, the question of how to provide a feasible and environmentally-friendly way to distribute these lanthanide complexes uniformly and stably within IL-based matrix remains a significant challenge. Here, a soft luminescent material from IL-mediated lyotropic liquid crystals (LLCs) doped with [Bmim][Eu(TTA)4] (Bmim = 1-butyl-3-methyl imidazolium, TTA = 2-thenoyltrifluoroacetone) has been constructed by a convenient self-assembling method. The hexagonal or lamellar LLC phases could be identified by small-angle X-ray scattering (SAXS) measurements. All LLC samples exhibited intense red luminescence upon exposure to ultraviolet radiation. The good dispersibility of the complexes in LLC matrices and their good photostability (as in ILs) was verified by steady-state luminescence spectroscopy. The isolated and unique characteristics of the microenvironment within the LLCs were noteworthy to decrease the nonradiative deactivation of the excited states, thereby allowing more efficient energy transfer and longer lifetimes than those in pure complex or IL solutions. Both the luminescent property and the stability of the LLC materials were different in different phase structures, the complexes behaving better in the lamellar phase than in the hexagonal one. The findings reported herein will not only present an easy way to design novel luminescent lanthanide β-diketonate soft materials, but also provide a useful reference to better understand the LLC phase structure effects on the luminescence properties. PMID:26190789

  4. Propylammonium nitrate as a solvent for amphiphile self-assembly into micelles, lyotropic liquid crystals, and microemulsions.

    PubMed

    Atkin, Rob; Bobillier, Sophie M C; Warr, Gregory G

    2010-01-28

    The phase behavior and self-assembled microstructures of a range of oligo(oxyethylene)-n-alkyl ether (C(i)E(j)) surfactants has been investigated in propylammonium nitrate (PAN), a room temperature ionic liquid. Micelles and single-phase microemulsions were all found to form at alkyl chain lengths from dodecyl to octadecyl, and lyotropic liquid crystals formed with hexadecyl chains or longer. Small-angle neutron scattering (SANS) shows that self-assembly occurs by solvophobic interactions driving the aggregation of the alkyl chains, but several results indicate that these are weaker in PAN than in water or ethylammonium nitrate, due chiefly to the hydrophobicity of PAN. Longer alkyl chains are needed for lyotropic liquid crystals to form, and higher surfactant concentrations are needed to form a single phase microemulsion. Conductivity shows these microemulsions to be weakly structured, and relatively insensitive to oil or surfactant molecular structure, unlike water-based systems. However, SANS contrast variation reveals a nanosegregation of oil from the alkyl tails of surfactants within the microemulsion, and may suggest a cosurfactant-like role for the propylammonium cation. Molecular areas within microemulsions and lamellar phases are larger than corresponding water- or ethylammonium nitrate-based systems due to the large molecular volume of the solvating PANs. PMID:20039680

  5. Thermal Characterization of Thermotropic Nematic Liquid-Crystalline Elastomers

    NASA Astrophysics Data System (ADS)

    Thomas, David; Cardarelli, Matt; Sanchez-Ferrer, Antoni; Mbanga, Badel L.; Atherton, Timothy J.; Cebe, Peggy

    Nematic Liquid-Crystallline Elastomers (LCEs) are weakly crosslinked polymeric networks that exhibit rubber elasticity and liquid-crystalline orientational order due to the presence of mesogenic groups. Three end-on side-chain nematic LCEs were investigated using real-time synchrotron wide-angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), and thermogravimetry (TG) to correlate thermal behavior with structural and chemical differences among them. The elastomers differed in crosslinking density and mesogen composition. Thermally reversible glass transition temperature, Tg, and nematic-to-isotropic transition temperature, Tni, were observed upon heating and cooling for all samples. By varying the heating rate, Tg0 and Tni0 were determined at zero heating rate. The temperature dependence of the orientational order parameter was determined from the anisotropic azimuthal angular distribution of the equatorial reflection seen during real-time WAXS experiments. Our results show that the choice of crosslinking unit, its shape, density, as well as the structure of co-monomers, all influence the temperature range over which the thermal transitions take place.

  6. Dielectrophoretic manipulation of the mixture of isotropic and nematic liquid.

    PubMed

    Kim, Soo-Dong; Lee, Bomi; Kang, Shin-Woong; Song, Jang-Kun

    2015-01-01

    In various applications involving liquid crystals, the manipulation of the nanoscale molecular assembly and microscale director alignment is highly useful. Here we show that a nematic-isotropic mixture, a unique bi-liquid system, has potential for the fabrication of microstructures having an ordered phase within a disordered phase, or vice versa. The volume expansion and shrinkage, migration, splitting, mergence and elongation of one phase within the other are easily accomplished via thermal treatment and dielectrophoretic manipulation. This is particularly achievable when one phase is suspended in the middle. In that case, a highly biased ordered-phase preference of surfaces, that is, the nematic-philic nature of a polyimide layer and the nematic-phobic nature of a self-assembled monolayer of chlorosilane derivatives, is used. Further, by combining this approach with photopolymerization, the patterned microstructure is solidified as a patterned polymer film having both isotropic and anisotropic molecular arrangements simultaneously, or as a template with a morphological variation. PMID:26242251

  7. Dynamics of an overdamped active nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Putzig, Elias; Baskaran, Aparna

    2015-03-01

    A continuum model for the dynamics of an overdamped (often termed ``dry'') active nematic liquid crystal will be presented here. This talk will focus on how such a model can be used to describe the formation and self-propulsion of defects which has been seen in active liquid crystals in experiments and simulations. We will start with a general model which shows phase-separations and structure formation near the critical density (for the isotropic-nematic phase transition), and show how this model can be extended to describe extensile active nematics which are deeper within the ordered phase. The spontaneous formation of defects occurs when the contribution of the extensile stresses, to the dynamics of the order parameter, gives rise to a bend instability. This leads to a steady state of defect formation and annihilation, and the self-propulsion of defects, as is seen in experiments and simulation. This work was supported through the NSF (NSF-DMR-1149266), Brandeis-MRSEC through the NSF (DMR-0820492), and the HPC cluster at Brandeis which provided computing time. EFP also acknowledges support through (NIH-5T32EB009419) and IGERT (DGE-1068620).

  8. Rheology of a Twist-bend Nematic Liquid Crystal

    NASA Astrophysics Data System (ADS)

    Salili, Seyyed Muhammad; Kim, Chanjoong; Sprunt, Samuel; Gleeson, James; Parri, Owain; Jakli, Antal; Kim Lab Team; Merck Lab Team

    2015-03-01

    First detailed flow shear alignment studies and rheological measurements in the twist-bend nematic (Ntb) liquid crystalline phase of odd numbered flexible dimer molecules is presented. It is found that the Ntb phase is strongly shear-thinning. At shear stresses below 1 Pa the apparent viscosity of the Ntb phase is 1000 times larger than in the nematic phase. At stresses above 10 Pa the Ntb viscosity drops by two orders of magnitude and the material exhibits Newtonian fluid behavior. The results are consistent with the behavior of a system with pseudo-layer structure with layer spacing determined by the heliconical pitch. From the measurements of dynamic modulus we estimate the compression modulus of the pseudo-layers to be B ~ 2 kPa this value is discussed within the context of a simple theoretical model based upon a coarse-grained elastic free energy. www.jakligroup.com.

  9. Geometry of nematic liquid crystals under shearing flow

    NASA Astrophysics Data System (ADS)

    Simões, M.; Alves, F. S.; Palangana, A. J.

    2009-09-01

    In this work, an extended version of the Hess-Baalss conformal approach is used to propose a relation connecting the viscosity coefficients of the nematic liquid crystals. Starting from the well-known fact that, in its usual form, the conformal transformation leads to results which are not observed experimentally, it is shown that, when the director field of an ordered nematic phase under sheared motion is taken as a three-dimensional surface with torsion, the resulting theory describes the observed experimental data efficiently. Moreover, this model predicts that the five viscosity coefficients of the Leslie ah hoc model are not independent, but connected. A comparison of the deduced relationship with experimental data is performed and an excellent agreement is obtained.

  10. Isotropic and nematic liquid crystalline phases of adaptive rotaxanes

    NASA Astrophysics Data System (ADS)

    He, Hao; Sevick, Edith M.; Williams, David R. M.

    2016-03-01

    We describe the thermodynamics of a solution of rotaxanes which can change their length from a short state of length L to a long state of length qL in response to their surrounding environment. We call these rotaxanes "adaptive." We show that such a system can exhibit both isotropic and nematic liquid crystalline phases. The system shows several interesting kinds of behaviour. First we predict that the fraction of short-length rotaxanes increases linearly with concentration and is a maximum at the critical concentration that marks the isotropic to nematic transition. Second, the critical concentration shows a minimum at a certain value of q. Our model suggests that the effect of adaptive length changes is most dramatic at small q and where the long state is slightly favoured.

  11. Compatibility of lyotropic liquid crystals with viruses and mammalian cells that support the replication of viruses.

    PubMed

    Cheng, Li-Lin; Luk, Yan-Yeung; Murphy, Christopher J; Israel, Barbara A; Abbott, Nicholas L

    2005-12-01

    We report a study that investigates the biocompatibility of materials that form lyotropic liquid crystals (LCs) with viruses and mammalian cells that support the replication of viruses. This study is focused on aqueous solutions of tetradecyldimethyl-amineoxide (C(14)AO) and decanol (D), or disodium cromoglycate (DSCG; C(23)H(14)O(11)Na(2)), which can form optically birefringent, liquid crystalline phases. The influence of these materials on the ability of vesicular stomatitis virus (VSV) to infect human epitheloid cervical carcinoma (HeLa) cells was examined by two approaches. First, VSV was dispersed in aqueous C(14)AO+ D or DSCG, and then HeLa cells were inoculated by contacting the cells with the aqueous C(14)AO + D or DSCG containing VSV. The infectivity of VSV to the HeLa cells was subsequently determined. Second, VSV was incubated in LC phases of either C(14)AO + D or DSCG for 4 h, and the concentration (titer) of infectious virus in the LC was determined by dilution into cell culture medium and subsequent inoculation of HeLa cells. Using these approaches, we found that the LC containing C(14)AO + D caused inactivation of virus as well as cell death. In contrast, we determined that VSV retained its infectivity in the presence of aqueous DSCG, and that greater than 74-82% of the HeLa cells survived contact with aqueous DSCG (depending on concentration of DSCG). Because VSV maintained its function (and we infer structure) in LCs formed from DSCG, we further explored the influence of the virus on the ordering of the LC. Whereas the LC formed from DSCG was uniformly aligned on surfaces prepared from self-assembled monolayers (SAMs) of HS(CH(2))(11)(OCH(2)CH(2))(4)OH on obliquely deposited films of gold in the absence of VSV, the introduction of 10(7)-10(8) infectious virus particles per milliliter caused the LC to assume a non-uniform orientation and a colorful appearance that was readily distinguished from the uniformly aligned LCs. Control experiments using

  12. Material Flows in an Active Nematic Liquid Crystal

    NASA Astrophysics Data System (ADS)

    Decamp, Stephen; Redner, Gabriel; Baskaran, Aparna; Hagan, Michael; Dogic, Zvonimir

    Active matter systems are composed of energy consuming constituent components which drive far-from-equilibrium dynamics. As such, active materials exhibit energetic states which would be unfavorable in passive, equilibrium materials. We study one such material; an active nematic liquid crystal which exists in a dynamical steady state where +/-1/2 defects are continuously generated and annihilated at a constant rate. The active nematic is composed of micron-sized microtubule filaments which are highly concentrated into a quasi-2D film that resides on an oil-water interface. Kinesin motor proteins drive inter-filament sliding which results in net extensile motion of the microtubule film. Notably, we find a mesophase in which motile +1/2 defects, acquire system-spanning orientational order. Currently, we are tracking material flows generated by the active stresses in the system to measure length scales at which energy is dissipated, and to measure the relation between internally generated flows and bend in the nematic field.

  13. Twisted quasiperiodic textures of biaxial nematic liquid crystals.

    PubMed

    Golo, V L; Kats, E I; Sevenyuk, A A; Sinitsyn, D O

    2013-10-01

    Textures (i.e., smooth space nonuniform distributions of the order parameter) in biaxial nematics turned out to be much more complex and interesting than expected. Scanning the literature we find only a very few publications on this topic. Thus, the immediate motivation of the present paper is to develop a systematic procedure to study, classify, and visualize possible textures in biaxial nematics. Based on the elastic energy of a biaxial nematic (written in the most simple form that involves the least number of phenomenological parameters) we derive and solve numerically the Lagrange equations of the first kind. It allows one to visualize the solutions and offers a deep insight into their geometrical and topological features. Performing Fourier analysis we find some particular textures possessing two or more characteristic space periods (we term such solutions quasiperiodic ones because the periods are not necessarily commensurate). The problem is not only of intellectual interest but also of relevance to optical characteristics of the liquid-crystalline textures. PMID:24229198

  14. Topological transitions in unidirectional flow of nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Cummings, Linda; Anderson, Thomas; Mema, Ensela; Kondic, Lou

    2015-11-01

    Recent experiments by Sengupta et al. (Phys. Rev. Lett. 2013) revealed interesting transitions that can occur in flow of nematic liquid crystal under carefully controlled conditions within a long microfluidic channel of rectangular cross-section, with homeotropic anchoring at the walls. At low flow rates the director field of the nematic adopts a configuration that is dominated by the surface anchoring, being nearly parallel to the channel height direction over most of the cross-section; but at high flow rates there is a transition to a flow-dominated state, where the director configuration at the channel centerline is aligned with the flow (perpendicular to the channel height direction). We analyze simple channel-flow solutions to the Leslie-Ericksen model for nematics. We demonstrate that two solutions exist, at all flow rates, but that there is a transition between the elastic free energies of these solutions: the anchoring-dominated solution has the lowest energy at low flow rates, and the flow-dominated solution has lowest energy at high flow rates. NSF DMS 1211713.

  15. Nematic quantum liquid crystals of bosons in frustrated lattices

    NASA Astrophysics Data System (ADS)

    Zhu, Guanyu; Koch, Jens; Martin, Ivar

    2016-04-01

    The problem of interacting bosons in frustrated lattices is an intricate one due to the absence of a unique minimum in the single-particle dispersion where macroscopic number of bosons can condense. Here, we consider a family of tight-binding models with macroscopically degenerate lowest energy bands, separated from other bands by a gap. We predict the formation of exotic states that spontaneously break rotational symmetry at relatively low filling. These states belong to three nematic phases: Wigner crystal, supersolid, and superfluid. The Wigner crystal phase is established exactly at low filling. Supersolid and superfluid phases, at larger filling, are obtained by making use of a projection onto the flat band, construction of an appropriate Wannier basis, and subsequent mean-field treatment. The nematic superfluid that we predict is uniform in real space but has an anisotropic momentum distribution, providing a novel scenario for Bose condensation with an additional nematic order. Our findings open up a promising direction of studying microscopic quantum liquid crystalline phases of bosons.

  16. Factors affecting order, photopolymerization behavior, and nanostructure development of reactive lyotropic liquid crystals

    NASA Astrophysics Data System (ADS)

    Sievens Figueroa, Lucas

    2009-10-01

    Polymerization of reactive lyotropic liquid crystals (LLC) provides a facile means for the synthesis of nanostructured organic materials. In this work the photopolymerization kinetics and polymer structure evolution have been investigated. By studying the polymerization behavior and the order retention after polymerization, the contribution of the type of reactive surfactant, cross-linking, pH, and ionic strength on the LLC order preservation has been determined. Polymerization rates are higher in more highly ordered LLC phases compared to isotropic phases. In turn, reactive LLC phases that exhibit higher reaction rates also preserve the order to a greater extent during polymerization. Reactive surfactants with longer aliphatic tails exhibit lower order and lower reaction rates. The polymerization kinetics are highly driven by segregation of the reactive groups. Lower polymerization rates are observed in isotropic discontinuous phases for the surfactant monomer bearing the reactive group near the polar head while the opposite behavior is observed for surfactant monomer bearing the reactive group in the aliphatic tail. The effect of polymerization kinetics on the resulting polymer order has also been determined using small angle X-ray scattering (SAXS). By using high light intensity and a more efficient initiator, the LLC order is more likely to be retained after polymerization. LLC phases that exhibit higher degrees of order are formed at low ionic strength and low pH. Higher polymerization rates are observed as the ionic strength increases due to an increase in the propagation rate. Higher polymerization rates are also observed as the pH increases due to an increase in the propagation rates and decrease in termination rates. The addition of a crosslinker enables the retention of LLC phases after polymerization. Competing effects between crosslinking and order are observed in the polymerization kinetics as a decrease in polymerization rate is observed at high

  17. Triply Periodic Multiply Continuous Lyotropic Liquid Crystals Derived from Gemini Surfactants

    NASA Astrophysics Data System (ADS)

    Sorenson, Gregory P.

    A subtle balance of non-covalent interactions directs the self-assembly of small molecule amphiphiles in aqueous media into supramolecular assemblies known as aqueous lyotropic liquid crystals (LLCs). Aqueous LLCs form many intricate, ordered nanoscale morphologies comprising distinct and structurally periodic hydrophobic and hydrophilic domains. Triply periodic multiply continuous (TPMC) LLC morphologies, which exhibit continuous hydrophobic and aqueous domains that percolate in three-dimensions, are of particular interest by virtue of their potentially wide ranging technological applications including advanced membranes for electrical energy storage and utilization, therapeutic delivery, and templates for new organic and inorganic mesoporous materials. However, robust molecular design criteria for amphiphiles that readily form TMPC morphologies are notably lacking in the literature. Recent reports have described the increased propensity for quaternary ammonium and phosphonium gemini surfactants, derived from dimerization of traditional single-tail surfactants at or near the hydrophilic headgroups through a hydrophobic linker, to stabilize TMPC mesophases. The generality of this surfactant design strategy remains untested in other amphiphiles classes bearing different headgroup chemistries. In this thesis, we describe the unusual aqueous LLC phase behavior of series of gemini dicarboxylate amphiphiles as a function of the alkyl tail length, hydrophobic linker length, and the charge-compensating counterion. These dicarboxylate surfactants unexpectedly exhibit a strong propensity to form TPMC LLCs over amphiphile concentration windows as wide as 20 wt% over a temperature range T = 25--100 °C. Through systematic modifications of the length of the hydrophobic linker and alkyl tails, we use small-angle X-ray scattering to demonstrate that these surfactants adopt new LLC mesophases including the first report of a single-gyroid phase (I4132 symmetry) and a new

  18. Flexoelectricity in an oxadiazole bent-core nematic liquid crystal

    SciTech Connect

    Kaur, S. Panov, V. P.; Gleeson, H. F.; Greco, C.; Ferrarini, A.; Görtz, V.; Goodby, J. W.

    2014-12-01

    We have determined experimentally the magnitude of the difference in the splay and bend flexoelectric coefficients, |e{sub 1} − e{sub 3}|, of an oxadiazole bent-core liquid crystal by measuring the critical voltage for the formation of flexodomains together with their wave number. The coefficient |e{sub 1} − e{sub 3}| is found to be a factor of 2–3 times higher than in most conventional calamitic nematic liquid crystals, varying from 8 pCm{sup −1} to 20 pCm{sup −1} across the ∼60 K—wide nematic regime. We have also calculated the individual flexoelectric coefficients e{sub 1} and e{sub 3}, with the dipolar and quadrupolar contributions of the bent-core liquid crystal by combining density functional theory calculations with a molecular field approach and atomistic modelling. Interestingly, the magnitude of the bend flexoelectric coefficient is found to be rather small, in contrast to common expectations for bent-core molecules. The calculations are in excellent agreement with the experimental values, offering an insight into how molecular parameters contribute to the flexoelectric coefficients and illustrating a huge potential for the prediction of flexoelectric behaviour in bent-core liquid crystals.

  19. Dispersion and Excluded Volume Interactions in Nematic Liquid Crystals.

    NASA Astrophysics Data System (ADS)

    Poliks, Mark David

    1988-12-01

    The effectiveness of the potential of mean torque in accounting for solute orientation is explored. It is described by repulsive (excluded volume) and attractive forces (dispersion) and is tested using rigid, semi-flexible and flexible solutes dissolved in nematic phases. For rigid molecules (benzenes and anthracene) the attractive short range potential gave the best results. For anthracene the results indicated that the potential can discriminate between solute/solvent interactions. For wholly aliphatic solvents the excluded volume forces gave excellent agreement, as did the attractive forces for the aromatic solvents. For the semi-flexible molecule, biphenyl, quadrupole splittings were simulated using the internal torsion angle as a parameter. The values of this angle were predicted to vary systematically with temperature. Using crystallographic and idealized structural data as the starting points for the calculation, the structure of PAA in the nematic phase was estimated. Both the internal angle and the aromatic proton valence angles were determined. Flexible, "siamese-twin" liquid crystals having an internal per-deuterated spacer consisting of ten methylenes were studied. They differed only in the length of the aliphatic tails (5105, 101010). The quadrupole splittings of both twins dissolved in the nematic phase of BCH-S1131 were identical. Quantitative simulations of the splittings using standard RIS geometry and excluded volume forces were successful. In the bulk nematic phase the order parameter of 5105 was greater than 101010. The difference was interpreted as a dilution effect of the mesogenic cores by aliphatic tails. Simulations indicated the conformation of the spacer is highly extended. As parameterized the required strength of the mean field is a strong function of the molecular dimensions, suggesting that the current description still is incomplete.

  20. Numerical bifurcation study of electrohydrodynamic convection in nematic liquid crystals.

    PubMed

    Tavener, S J; Mullin, T; Blake, G I; Cliffe, K A

    2001-01-01

    We present the results of a numerical investigation of the Ericksen-Leslie equations for the problem of electrohydrodynamic convection in a nematic liquid crystal. The combination of a finite element approach and numerical bifurcation techniques allows us to provide details of the basic flow and include the physically relevant effect of nonslip side walls. We are also able to include material properties as parameters and this permits us to draw comparisons with available experimental data. We then compare and contrast the bifurcation structure with that of Rayleigh-Bénard and Taylor-Couette flows and explore the role of symmetries by including a fringing electric field. PMID:11304279

  1. Surface-induced structures in nematic liquid crystal colloids.

    PubMed

    Chernyshuk, S B; Tovkach, O M; Lev, B I

    2014-08-01

    We predict theoretically the existence of a class of colloidal structures in nematic liquid crystal (NLC) cells, which are induced by surface patterns on the plates of the cell (like cells with UV-irradiated polyamide surfaces using micron sized masks in front of the cell). These bulk structures arise from nonuniform boundary conditions for the director distortions at the confining surfaces. In particular, we demonstrate that quadrupole spherical particles (like spheres with boojums or Saturn-ring director configurations) form a square lattice inside a planar NLC cell, which has checkerboard patterns on both its plates. PMID:25215675

  2. Programmable lattices of optical vortices in nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Barboza, R.; Assanto, G.; Bortolozzo, U.; Clerc, M. G.; Residori, S.; Vidal-Henriquez, E.

    2015-09-01

    Using self-induced vortex-like defects in the nematic liquid crystal layer of a light valve with photo-sensible wall, we demonstrate the realization of programable optical vortices lattices with arbitrary configuration in space. On each lattice site, every matter vortex acts as a photonic spin-to-orbital momentum coupler and an array of circularly polarized input beams is converted into an output array of vortex beams with topological charges consistent with the vortex matter lattice. The vortex arrangements are explained the basis of light-induced matter defects and topological rules.

  3. Polarization converters based on axially symmetric twisted nematic liquid crystal.

    PubMed

    Ko, Shih-Wei; Ting, Chi-Lun; Fuh, Andy Y-G; Lin, Tsung-Hsien

    2010-02-15

    An axially symmetric twisted nematic liquid crystal (ASTNLC) device, based on axially symmetric photoalignment, was demonstrated. Such an ASTNLC device can convert axial (azimuthal) to azimuthal (axial) polarization. The optical properties of the ASTNLC device are analyzed and found to agree with simulation results. The ASTNLC device with a specific device can be adopted as an arbitrary axial symmetric polarization converter or waveplate for axially, azimuthally or vertically polarized light. A design for converting linear polarized light to axially symmetric circular polarized light is also demonstrated. PMID:20389369

  4. Surfactant-induced nematic wetting layer at a thermotropic liquid crystal/water interface.

    PubMed

    Bahr, Ch

    2006-03-01

    An ellipsometric study of the interface between a thermotropic liquid crystal and water near the nematic-isotropic phase transition of the liquid crystal is presented. At temperatures above the transition, a nematic wetting layer appears at the interface if the water phase contains a surfactant inducing a homeotropic alignment of the nematic phase. The detailed behavior is significantly influenced by the concentration of the surfactant. The results can be described by a Landau model of nematic wetting in which the surfactant concentration tunes the magnitude of an ordering interface potential. PMID:16605490

  5. Substrate-induced gliding in a nematic liquid crystal layer

    NASA Astrophysics Data System (ADS)

    Mema, E.; Kondic, L.; Cummings, L. J.

    2015-12-01

    We consider the interaction between nematic liquid crystals (NLCs) and polymer substrates. Such substrates can interact with NLCs, exhibiting a phenomenon known as director gliding: the preferred orientation of the NLC molecules at the interface changes on time scales that are slow relative to the elastic relaxation time scale of the NLC. We present two models for gliding, inspired by experiments that investigate the interaction between the NLC and a polymer substrate. These models, though simple, lead to nontrivial results, including loss of bistability under gliding. Perhaps surprisingly, we find that externally imposed switching between the steady states of a bistable system may reverse the effect of gliding, preventing loss of bistability if switching is sufficiently frequent. Our findings may be of relevance to a variety of technological applications involving liquid crystal devices, and particularly to a new generation of flexible liquid crystal displays that implement polymeric substrates.

  6. Substrate-induced gliding in a nematic liquid crystal layer.

    PubMed

    Mema, E; Kondic, L; Cummings, L J

    2015-12-01

    We consider the interaction between nematic liquid crystals (NLCs) and polymer substrates. Such substrates can interact with NLCs, exhibiting a phenomenon known as director gliding: the preferred orientation of the NLC molecules at the interface changes on time scales that are slow relative to the elastic relaxation time scale of the NLC. We present two models for gliding, inspired by experiments that investigate the interaction between the NLC and a polymer substrate. These models, though simple, lead to nontrivial results, including loss of bistability under gliding. Perhaps surprisingly, we find that externally imposed switching between the steady states of a bistable system may reverse the effect of gliding, preventing loss of bistability if switching is sufficiently frequent. Our findings may be of relevance to a variety of technological applications involving liquid crystal devices, and particularly to a new generation of flexible liquid crystal displays that implement polymeric substrates. PMID:26764717

  7. Simulation of coherent backscattering of light in nematic liquid crystals

    SciTech Connect

    Aksenova, E. V. Kokorin, D. I. Romanov, V. P.

    2012-08-15

    Multiple scattering of light by the fluctuations of the director in a nematic liquid crystal (NLC) aligned by a magnetic field is considered. A peak of coherent backscattering is calculated by numerical simulation. Since the indicatrix of single scattering for a liquid crystal (LC) is known exactly, the calculations are carried out without any simplifying assumptions on the parameters of the liquid crystal. Multiple scattering is simulated as a random walk of photons in the medium. A peak of coherent backscattering in such a medium is very narrow; therefore, the so-called semianalytical method is applied. The parameters of the backscattering peak obtained by numerical simulation are compared with the available experimental data and with the results of analytical approximations. It turns out that the experimental data are in good agreement with the results of simulation. The results of numerical simulation adequately describe the anisotropy and the width of the backscattering peak.

  8. The Viscoelastic Properties of Nematic Monodomains Containing Liquid Crystal Polymers.

    NASA Astrophysics Data System (ADS)

    Gu, Dongfeng

    The work presented here investigates the viscoelastic properties of nematic materials containing liquid crystal polymers (LCP). We focus on how the elastic constants and the viscosity coefficients of the mixture systems are influenced by polymer architectures. In dynamic light scattering studies of the relaxation of the director orientation fluctuations for the splay, twist, and bend deformation modes, decrease of the relaxation rates was observed when LCPs were dissolved into low molar mass nematics (LMMN). For the side-chain LCPs, the slowing down in the bend mode is comparable to or larger than those of the splay and twist modes. For main-chain LCPs, the relative changes in the relaxation rates for the twist and splay modes are about one order of magnitude larger than that for the bend mode. The results of light scattering under an electric field show that the decrease in the twist relaxation rate is due to a large increase in the twist viscosity and a minor decrease in the twist elastic constant. These changes were found to increase with decrease of the spacer length, with increase of molecular weight, and with decrease of the backbone flexibility. In Freedericksz transition measurements, the splay and bend elastic constants and the dielectric anisotropies of the nematic mixtures were determined and the values are 5~15% lower than those of the pure solvent. From the analysis of the results of Freedericksz transition and light scattering experiments, a complete set of the elastic constants and viscosity coefficients corresponding to the three director deformation modes were obtained for the LCP mixtures. The changes in the viscosity coefficients due to addition of LCPs were analysed to estimate the anisotropic shapes of the polymer backbone via a hydrodynamic model. The results suggest that an oblate backbone configuration is maintained by the side-chain LCPs and a prolate chain configuration appears for the main-chain LCPs. The rheological behavior of a side

  9. Photoinduced extrinsic electrical conduction of nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Dedov, O. V.; Krivoschekov, V. A.

    1996-05-01

    During recent years the interest in media with strong nonlinear response is growing. These media allow the user to observe different nonlinear optic effects using small intensities of light. It is well known that liquid crystals are rather promising media for this research. This paper is devoted to the experimental research of the photoinduced conduction of a mixture of a nematic liquid crystal and a dye. Dependence of the conduction on the intensity of light was studied for different concentrations of a dye added to the nematic crystal. Also the problem of the optimum type of a dye for observing the photorefractive nonlinearity using Ar+- ion laser was considered. We made the experiments using the following available laser dyes: rhodamine '6G,' rhodamine 'G,' rhodamine 'C' and two ocsasine-type dyes also. The mixture of the nematic crystal 5CB and a dye was placed in a cell of 100 micrometer width, with the plates filmed with the transparent electrodes of SnO2. The dc voltage on the order of magnitude 1 V was applied to decrease the influence of the cell capacity on the conduction measurements of the samples. We used the light of two wavelengths: lambda1 equals 488 nm, lambda2 equals 514.5 nm. The best dyes for these wavelengths were the rhodamine- type dyes. Taking the other two dyes we observed much smaller effect of influence of the laser radiation on conduction of the samples. Maybe the reason was that the pump wavelength of ocsasine dyes is too far way from the wavelength of the radiation used. So the optimum dye must have the wavelength of the pump near to the wavelength used. Using rhodamine 'C' we obtained the dependencies of the induced conduction on laser light intensity for three different concentrations of the dye.

  10. Dendritic Growth in Nematic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Martin, Joshua; Garg, Shila

    2000-03-01

    The experimental study of the onset of electrohydrodynamic convection (EHC) through a dendritic growth is reported. If a magnetic Freedericksz-distorted liquid crystal of negative dielectric anisotropy is subjected to an electric field parallel to the magnetic field, EHC sets in through the nucleation of dendrites [1,2]. Measurements of tip speeds of the dendrites as a function of applied voltage at a fixed magnetic field are made. The goal is to explore the effect of the magnetic and electric fields on the dendritic growth. In addition, pattern dynamics is monitored once the final state of spatio-temporal chaos is reached by the system. [1] J. T. Gleeson, Nature 385, 511 (1997). [2] J. T. Gleeson, Physica A 239, 211 (1997). This research was supported by NSF grants DMR 9704579 and DMR 9619406.

  11. A Numerical Investigation on Configurational Distortions in Nematic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Pandolfi, Anna; Napoli, Gaetano

    2011-10-01

    When subjected to magnetic or electric fields, nematic liquid crystals confined between two parallel glass plates and initially uniformly oriented may undergo homogeneous one-dimensional spatial distortions (Fréedericksz and Zolina, Trans. Faraday Soc. 29:919, 1933) or periodic distortions (Lonberg and Meyer, Phys. Rev. Lett. 55(7):718-721, 1985; and Srajer et al., Phys. Rev. Lett. 67(9):1102-1105, 1991). According to the experimental observations, periodic phases are stable configurations at intermediate intensity of the acting field, while homogeneous phases are stable at higher strengths. We present a fully nonlinear finite element approach able to describe homogeneous and periodic configurational phases in a cell of confined nematic liquid crystal with strong planar anchoring boundary conditions. Stationary configurations are obtained by setting to zero the first variation of the discretized total energy of the system. Unstable configurations are identified by evaluating the behavior of the solution under small numerical perturbations. Numerical calculations are able to describe the evolution of the configurational distortions as a function of the applied field and are able to capture the critical points between homogeneous and periodic phases. The proposed approach has been proved to be an excellent tool to predict the existence of unstable or metastable distortions, characterized by higher energy levels.

  12. Interaction between two spherical particles in a nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Fukuda, Jun-Ichi; Stark, Holger; Yoneya, Makoto; Yokoyama, Hiroshi

    2004-04-01

    We numerically investigate the interaction between two spherical particles in a nematic liquid crystal mediated by elastic distortions in the orientational order. We pay attention to the cases where two particles with equal radii R0 impose rigid normal anchoring on their surfaces and carry a pointlike topological defect referred to as a hyperbolic hedgehog. To describe the geometry of our system, we use bispherical coordinates, which prove useful in the implementation of boundary conditions at the particle surfaces and at infinity. We adopt the Landau de Gennes continuum theory in terms of a second-rank tensor order parameter Qij for the description of the orientational order of a nematic liquid crystal. We also utilize an adaptive mesh refinement scheme that has proven to be an efficient way of dealing with topological defects whose core size is much smaller than the particle size. When the two “dipoles,” composed of a particle and a hyperbolic hedgehog, are in parallel directions, the two-particle interaction potential is attractive for large interparticle distances D and proportional to D-3 as expected from the form of the dipole-dipole interaction, until the well-defined potential minimum at D≃2.46 R0 is reached. For the antiparallel configuration with no hedgehogs between the two particles, the interaction potential is repulsive and behaves as D-2 for D≲10 R0 , which is stronger than the dipole-dipole repulsion ( ˜ D-3 ) expected theoretically as an asymptotic behavior for large D .

  13. Hysteresis upon light-induced hydrodynamic reorientation of the director of a nematic liquid crystal

    SciTech Connect

    Akopyan, R S; Alaverdyan, R B; Vardanyan, A S; Chilingaryan, Yu S

    2000-08-31

    Oscillations and hysteresis in the behaviour of the director of a nematic liquid crystal were observed upon its light-induced hydrodynamic reorientation caused by direct volume expansion. The light propagated through the liquid crystal placed between crossed polarisers provides the feedback. This light falls back on the liquid crystal and is absorbed by producing the volume expansion. A theory is suggested that describes the observed behaviour of the director of the nematic liquid crystal. (laser applications and other topics in quantum electronics)

  14. Retrieving the saddle-splay elastic constant K24 of nematic liquid crystals from an algebraic approach.

    PubMed

    Fumeron, Sébastien; Moraes, Fernando; Pereira, Erms

    2016-09-01

    The physics of light interference experiments is well established for nematic liquid crystals. Using well-known techniques, it is possible to obtain important quantities, such as the differential scattering cross section and the saddl-splay elastic constant K24. However, the usual methods to retrieve the latter involve adjusting of computational parameters through visual comparisons between the experimental light interference pattern or a (2) H-NMR spectral pattern produced by an escaped-radial disclination, and their computational simulation counterparts. To avoid such comparisons, we develop an algebraic method for obtaining of saddle-splay elastic constant K24. Considering an escaped-radial disclination inside a capillary tube with radius R0 of tens of micrometers, we use a metric approach to study the propagation of the light (in the scalar wave approximation), near the surface of the tube and to determine the light interference pattern due to the defect. The latter is responsible for the existence of a well-defined interference peak associated to a unique angle [Formula: see text] . Since this angle depends on factors such as refractive indexes, curvature elastic constants, anchoring regime, surface anchoring strength and radius R0, the measurement of [Formula: see text] from the interference experiments involving two different radii allows us to algebraically retrieve K24. Our method allowed us to give the first reported estimation of K24 for the lyotropic chromonic liquid crystal Sunset Yellow FCF: K 24 = 2.1 pN. PMID:27589980

  15. Electro-optic phenomena in nematic liquid crystals studied experimentally and by Monte-Carlo simulations

    SciTech Connect

    Komorowska, K.; Pawlik, G.; Mitus, A. C.; Miniewicz, A.

    2001-08-15

    In this article we compare results of experiments on light self-diffraction in nematic liquid crystal panels with corresponding results of the Monte-Carlo simulations of a two-dimensional nematic liquid crystal model in the presence of a spatially modulated electric field. In the simulations molecular interactions were described by the Lebwohl--Lasher Hamiltonian. The results obtained on the diffraction efficiency and spatial and temporal behavior of refractive index changes in nematic liquid crystal are satisfactorily reproduced by Monte-Carlo simulations. We discuss the complementarity of both methods in studying and designing systems for optical information processing using liquid crystals. {copyright} 2001 American Institute of Physics.

  16. Chiral power change upon photoisomerization in twisted nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Simoncelli, Sabrina; Aramendía, Pedro F.

    2015-05-01

    In this work, we use the photoisomerization of azobenzenes, a phenanthrospirooxazine, and a fulgide in a twisted nematic liquid crystalline phase to change the chiral twisting power of the system. The changes are probed by the rotatory power of linearly polarized light. Time resolved and steady state experiments are carried out. The chiral change and the photoisomerization process have similar characteristic recovery times and activation energy, thus probing that the change is induced by the modification in the chemical composition of the photochromic dopant system. The amplitude of the light twisting power change correlates with the order change in the liquid crystal (LC) but not with the modification in the absorption characteristics of the system. This indicates that the driving force of the chiral change is the microscopic order modification in the LC phase that affects the helical pitch of the phase.

  17. Chiral power change upon photoisomerization in twisted nematic liquid crystals.

    PubMed

    Simoncelli, Sabrina; Aramendía, Pedro F

    2015-05-01

    In this work, we use the photoisomerization of azobenzenes, a phenanthrospirooxazine, and a fulgide in a twisted nematic liquid crystalline phase to change the chiral twisting power of the system. The changes are probed by the rotatory power of linearly polarized light. Time resolved and steady state experiments are carried out. The chiral change and the photoisomerization process have similar characteristic recovery times and activation energy, thus probing that the change is induced by the modification in the chemical composition of the photochromic dopant system. The amplitude of the light twisting power change correlates with the order change in the liquid crystal (LC) but not with the modification in the absorption characteristics of the system. This indicates that the driving force of the chiral change is the microscopic order modification in the LC phase that affects the helical pitch of the phase. PMID:25699698

  18. Substrate induced gliding for a nematic liquid crystal layer

    NASA Astrophysics Data System (ADS)

    Mema, Ensela; Cummings, Linda; Kondic, Lou

    2015-03-01

    The interaction between nematic liquid crystals (NLC) and polymer substrates is of current industrial interest, due to a desire to manufacture a new generation of flexible Liquid Crystal Displays (LCDs) for use in portable electronic devices. Polymer substrates present challenges because they can interact with the NLC, exhibiting a phenomenon known as gliding: the preferred orientation of the NLC molecules at the interface changes over timescales of minutes to hours. We present two models for gliding, inspired by the physics and chemistry of the interaction between the NLC and polymer substrate. These models, though simple, lead to non-trivial results, including loss of bistability, a finding that may have implications for display devices. Supported by NSF Grant No. DMS-1211713.

  19. Disc-shaped colloids interacting in a nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Antipova, Alena; Denniston, Colin

    2014-11-01

    We studied the behavior of pairs of disc-shaped colloidal particles in a nematic liquid crystal using Lattice Boltzmann algorithm. Without any external forces the position of the disc with respect to the liquid crystal director minimizes the free energy of the system and no distortion of the director field is observed. When the rotating magnetic field is present, the torque on the disc with homeotropic surface anchoring should change with analogy to electrostatic energy, which implies the disc continues turning following the field. However, when the disc reaches some critical position and the director field around it is highly distorted, the disc suddenly flips to minimize the free energy. Position and motion of pairs of such discs under similar conditions can be controlled by the angular velocity of magnetic field, it's magnitude and initial configuration of the system. As a result of analysis of discs' dynamics, a new way to control self-organization of disc particles was produced.

  20. Mesogenic linear azobenzene polymer-stabilized nematic liquid crystals

    SciTech Connect

    Bagramyan, Arutyun; Thibault-Maheu, Olivier; Galstian, Tigran; Bessette, Andre; Zhao, Yue

    2011-03-15

    We describe the detailed study of a polymer stabilized liquid crystal compound, which was created by using a reactive (monofunctional) azobenzene mesogenic guest and a nematic liquid crystal host. The resonant interaction of light with the azobenzene segment of the guest and the mesogenic nature of the latter enable the optical alignment of host molecules and the permanent fixing of that orientation by means of UV polymerization of the guest. We use dynamic spectral, polarimetric, and scattering techniques to study the orientational ordering and interaction of the guest-host system. We show that the uniform UV polymerization of this compound results in a low scattering material system with dielectric and elastic properties that are relatively close to those of the host, while still providing the capacity for optical configuration of its morphology.

  1. Design of Light-Triggered Lyotropic Liquid Crystal Mesophases and Their Application as Molecular Switches in "On Demand" Release.

    PubMed

    Aleandri, Simone; Speziale, Chiara; Mezzenga, Raffaele; Landau, Ehud M

    2015-06-30

    Here, we present the design and assembly of a new light-responsive functional lyotropic liquid crystal system using host-guest lipidic mesophases (LMPs). Light as an external stimulus has many advantages in comparison to other stimuli: it is milder than acids or bases, and variation of intensity and duration can provide a high level of pharmacological control. The LMPs are composed of monoolein (MO) and oleic acid (OA) as host lipids and a small amount of a judiciously synthesized lipid bearing an azobenzene photoactive unit as a guest. While preserving the structure and stability of the host lipidic aggregates, the guest lipids render them specific functionalities. Single-step and sequential light-triggered release and retention of the embedded dye molecules are demonstrated, thereby achieving exquisite temporal, spatial, and dosage control of the release, opening up the possibility of using such lipidic biomaterials as effective matrices in therapy, when a continuous release of active drugs might be toxic. PMID:26039728

  2. Theory of the acoustic realignment of nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Malanoski, A. P.; Greanya, V. A.; Weslowski, B. T.; Spector, M. S.; Selinger, J. V.; Shashidhar, R.

    2004-02-01

    When an ultrasonic wave is applied to a nematic liquid-crystal cell, the molecules change their orientation, leading to a change in the optical intensity transmitted through the cell. Modeling this acousto-optic effect involves three separate theoretical issues: (a) calculating the intensity of sound transmitted through the cell walls into the liquid crystal, (b) determining the consequent realignment of the liquid crystal, and (c) deriving the change in optical transmission through the cell. In this paper, we present a theory that addresses all three of these issues, and thereby reproduces the behavior seen in experiments. The theory shows how the performance depends not only on the liquid-crystal material properties, but also on the geometrical parameters of the system, such as the thickness of the glass walls, thickness of the liquid-crystal layer, angle of the ultrasonic wave, viewing angle, and boundary condition at the glass-liquid crystal interface. The theory predicts that the strong dependence on viewing angle still allows an optical image to be seen for realistic dimensions.

  3. Elastic constants and dynamics in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Humpert, Anja; Allen, Michael P.

    2015-09-01

    In this paper, we present molecular dynamics calculations of the Frank elastic constants, and associated time correlation functions, in nematic liquid crystals. We study two variants of the Gay-Berne potential, and use system sizes of half a million molecules, significantly larger than in previous studies of elastic behaviour. Equilibrium orientational fluctuations in reciprocal (k-) space were calculated, to determine the elastic constants by fitting at low |k|; our results indicate that small system size may be a source of inaccuracy in previous work. Furthermore, the dynamics of the Gay-Berne nematic were studied by calculating time correlation functions of components of the order tensor, together with associated components of the velocity field, for a set of wave vectors k. Confirming our earlier work, we found exponential decay for splay and twist correlations, and oscillatory exponential decay for the bend correlation. In this work, we confirm similar behaviour for the corresponding velocity components. In all cases, the decay rates, and oscillation frequencies, were found to be accurately proportional to k2 for small k, as predicted by the equations of nematodynamics. However, the observation of oscillatory bend fluctuations, and corresponding oscillatory shear flow decay, is in contradiction to the usual assumptions appearing in the literature, and in standard texts. We discuss the advantages and drawbacks of using large systems in these calculations.

  4. Liquid crystal gratings from nematic to blue phase

    NASA Astrophysics Data System (ADS)

    Lu, Yan-qing; Hu, Wei; Lin, Xiao-wen; Srivastava, Abhishek; Chigrinov, Vladimir G.

    2012-10-01

    Some of our recent progress on liquid crystal (LC) gratings, from nematic to blue phase, is reviewed in this invited talk. The first kind of grating is fabricated by periodically adjusting the LC directors to form alternate micro phase retarders and polarization rotators in a cell placed between crossed polarizers. The second one is demonstrated by means of photoalignment technique with alternate orthogonal homogeneously-aligned domains. To improve the response time of the gratings, several approaches are also proposed by using dual-frequency addressed nematic LC, ferroelectric LC and blue phase LC, which shows great performance including high transmittance, polarization independency and submillisecond response. At last, to obtain other controllable LC microstructures rather than simple 1D/2D gratings, we develop a micro-lithography system with a digital micro-mirror device as dynamic mask forms. It may instantly generate arbitrary micro-images on photoalignment layers and further guides the LC molecule orientations. Besides normal phase gratings, more complex patterns such as quasicrystal structures are demonstrated. Some new applications such as tunable multiport optical switching and vector beam generations are expected.

  5. Rheological properties of a reentrant nematic liquid crystal.

    PubMed

    Ananthaiah, J; Rajeswari, M; Sastry, V S S; Dabrowski, R; Dhara, Surajit

    2012-07-01

    We report experimental studies on small angle light scattering (SALS), and rheodielectric and electrorheological properties of a binary mixture of octyloxy cyanobiphenyl and hexyloxy cyanobiphenyl liquid crystals. The mixture exhibits nematic (N) to smectic-A (SmA) phase transitions, and then again to a reentrant nematic (N(R)) phase transition. Rapid shear thinning in the quenched samples in the low shear rate region in the N and SmA phases observed from SALS experiments is attributed to the realignment of the director within the domains. The domains are elongated along the shear direction at higher shear rates. The temperature variation of the effective viscosity and static dielectric constant reveals the changes in the director orientation across N-SmA-N(R) phase transitions. At a steady shear rate the effective viscosity increases with the electric field in all the phases and saturates at much higher fields. It also exhibits two anomalous peaks across N-SmA-N(R) phase transitions beyond a particular field. The shear modulus of the SmA phase in an intermediate field is significantly larger than that measured at both low and high fields. This enhanced viscoelasticity of the SmA phase is argued to originate from the increased dislocation density. PMID:23005440

  6. Rheological properties of a reentrant nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Ananthaiah, J.; Rajeswari, M.; Sastry, V. S. S.; Dabrowski, R.; Dhara, Surajit

    2012-07-01

    We report experimental studies on small angle light scattering (SALS), and rheodielectric and electrorheological properties of a binary mixture of octyloxy cyanobiphenyl and hexyloxy cyanobiphenyl liquid crystals. The mixture exhibits nematic (N) to smectic-A (SmA) phase transitions, and then again to a reentrant nematic (NR) phase transition. Rapid shear thinning in the quenched samples in the low shear rate region in the N and SmA phases observed from SALS experiments is attributed to the realignment of the director within the domains. The domains are elongated along the shear direction at higher shear rates. The temperature variation of the effective viscosity and static dielectric constant reveals the changes in the director orientation across N-SmA-NR phase transitions. At a steady shear rate the effective viscosity increases with the electric field in all the phases and saturates at much higher fields. It also exhibits two anomalous peaks across N-SmA-NR phase transitions beyond a particular field. The shear modulus of the SmA phase in an intermediate field is significantly larger than that measured at both low and high fields. This enhanced viscoelasticity of the SmA phase is argued to originate from the increased dislocation density.

  7. Multi-Scale Characterization of Lyotropic Liquid Crystals Using 2H and Diffusion MRI with Spatial Resolution in Three Dimensions

    PubMed Central

    Bernin, Diana; Koch, Vanessa; Nydén, Magnus; Topgaard, Daniel

    2014-01-01

    The ability of lyotropic liquid crystals to form intricate structures on a range of length scales can be utilized for the synthesis of structurally complex inorganic materials, as well as in devices for controlled drug delivery. Here we employ magnetic resonance imaging (MRI) for non-invasive characterization of nano-, micro-, and millimeter scale structures in liquid crystals. The structure is mirrored in the translational and rotational motion of the water, which we assess by measuring spatially resolved self-diffusion tensors and spectra. Our approach differs from previous works in that the MRI parameters are mapped with spatial resolution in all three dimensions, thus allowing for detailed studies of liquid crystals with complex millimeter-scale morphologies that are stable on the measurement time-scale of 10 hours. The data conveys information on the nanometer-scale structure of the liquid crystalline phase, while the combination of diffusion and data permits an estimate of the orientational distribution of micrometer-scale anisotropic domains. We study lamellar phases consisting of the nonionic surfactant C10E3 in O, and follow their structural equilibration after a temperature jump and the cessation of shear. Our experimental approach may be useful for detailed characterization of liquid crystalline materials with structures on multiple length scales, as well as for studying the mechanisms of phase transitions. PMID:24905818

  8. Shear Alignment Behavior of Nematic Solutions Induced by Ultralong Side-Group Liquid Crystal Polymers

    NASA Astrophysics Data System (ADS)

    Kempe, M. D.; Kornfield, J. A.

    2003-03-01

    Addition of a low concentration of a very long (430 kg/mol) side group liquid crystal polymer is shown to produce dramatic changes in the flow characteristics of a calamitic nematic liquid crystal. This polymer causes a typical flow-aligning nematic liquid crystal to align near the velocity gradient direction rather than near the velocity direction, corresponding to having a tumbling parameter λ<-1, for concentrations greater than 7.5% polymer. Such flow-aligning behavior has not been reported previously in a calamitic nematic. The large molecular weight of the present polymer relative to those examined in the prior literature is responsible for these new phenomena.

  9. Fast switching from isotropic liquids to nematic liquid crystals: rotaxanes as smart fluids.

    PubMed

    He, Hao; Sevick, Edith M; Williams, David R M

    2015-11-28

    We examine a solution of rod-like piston-rotaxanes, which can switch their length by external excitation (for example optically) from a short state of length L to a long state of length qL. We show that this solution can exhibit a number of different behaviours. In particular it can rapidly switch from an isotropic to a nematic liquid crystalline state. There is a minimum ratio q* = 1.13 for which transitions from a pure isotropic state to a pure nematic state are possible. We present a phase-switching diagram, which gives the six possible behaviours for this system. It turns out that a large fraction of the phase switching diagram is occupied by the transition from a pure isotropic to a pure nematic state. PMID:26419821

  10. Chemically induced twist-bend nematic liquid crystals, liquid crystal dimers, and negative elastic constants.

    PubMed

    Adlem, K; Čopič, M; Luckhurst, G R; Mertelj, A; Parri, O; Richardson, R M; Snow, B D; Timimi, B A; Tuffin, R P; Wilkes, D

    2013-08-01

    Here we report the chemical induction of the twist-bend nematic phase in a nematic mixture of ether-linked liquid crystal dimers by the addition of a dimer with methylene links; all dimers have an odd number of groups in the spacer connecting the two mesogenic groups. The twist-bend phase has been identified from its optical texture and x-ray scattering pattern as well as NMR spectroscopy, which demonstrates the phase chirality. Theory predicts that the key macroscopic property required for the stability of this chiral phase formed from achiral molecules is for the bend elastic constant to tend to be negative; in addition the twist elastic constant should be smaller than half the splay elastic constant. To test these important aspects of the prediction we have measured the bend and splay elastic constants in the nematic phase preceding the twist-bend nematic using the classic Frederiks methodology and all three elastic constants employing the dynamic light scattering approach. Our results show that, unlike the splay, the bend elastic constant is small and decreases significantly as the transition to the induced twist-bend nematic phase is approached, but then exhibits unexpected behavior prior to the phase transition. PMID:24032852

  11. Shape-dependent dispersion and alignment of nonaggregating plasmonic gold nanoparticles in lyotropic and thermotropic liquid crystals.

    PubMed

    Liu, Qingkun; Tang, Jianwei; Zhang, Yuan; Martinez, Angel; Wang, Shaowei; He, Sailing; White, Timothy J; Smalyukh, Ivan I

    2014-05-01

    We use both lyotropic liquid crystals composed of prolate micelles and thermotropic liquid crystals made of rod-like molecules to uniformly disperse and unidirectionally align relatively large gold nanorods and other complex-shaped nanoparticles at high concentrations. We show that some of these ensuing self-assembled orientationally ordered soft matter systems exhibit polarization-dependent plasmonic properties with strongly pronounced molar extinction exceeding that previously achieved in self-assembled composites. The long-range unidirectional alignment of gold nanorods is mediated mainly by anisotropic surface anchoring interactions at the surfaces of gold nanoparticles. Polarization-sensitive absorption, scattering, and extinction are used to characterize orientations of nanorods and other nanoparticles. The experimentally measured unique optical properties of these composites, which stem from the collective plasmonic effect of the gold nanorods with long-range order in a liquid crystal matrix, are reproduced in computer simulations. A simple phenomenological model based on anisotropic surface interaction explains the alignment of gold nanorods dispersed in liquid crystals and the physical underpinnings behind our observations. PMID:25353813

  12. Control of the bias tilt angles in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Yablonskii, S. V.; Nakayama, K.; Okazaki, S.; Ozaki, M.; Yoshino, K.; Palto, S. P.; Baranovich, M. Yu.; Michailov, A. S.

    1999-03-01

    The pretilt angle controlled by electric field was studied by the modulation ellipsometry technique. The easy direction of compensated nematic liquid crystals was controlled by surface flexoelectric torque created by the linear coupling of the director deformation and electric field. The weak anchoring energy necessary for the occurrence of flexoelectric distortion was produced by unidirectional rubbing of the clean indium-tin-oxide covered glasses with a cotton cloth. The pretilt angle was measured as a function of electric field. Long relaxation times of the optical response (hundreds of seconds) were observed. The rubbed thin polyvinyl alcohol and polyimide aligning layers were seen to promote strong anchoring energy (>0.5 erg/cm2) preventing any deviation of pretilt angle and, consequently, to suppress the optical response. The probable applications of the obtained results are discussed.

  13. Orientational defects near colloidal particles in a nematic liquid crystal.

    PubMed

    Feng, James J; Zhou, Chixing

    2004-01-01

    We study the interaction between a surface-anchoring colloidal particle and a liquid-crystalline host, and in particular the formation of orientational defects near the particle. A mean-field theory based on the nonlocal Marrucci-Greco nematic potential is used to represent molecular interactions in an inhomogeneous orientational field. An evolution equation for the molecular configuration tensor is solved numerically whose steady state minimizes the total free energy of the system. With strong homeotropic anchoring on the particle surface, three types of solutions may appear depending on initial conditions and particle size: Saturn rings, satellite point defects, and polar rings. The Saturn ring remains stable on micrometer-sized particles, contrary to previous calculations but consistent with experiments. A phase diagram is constructed for the three regimes. Based on the free energy, the most stable state is the Saturn ring for smaller particles and the satellite defect for larger ones. PMID:14651897

  14. Dielectric Anisotropy of Gold Nanoparticle Colloids in Nematic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Visco, Angelo; Foust, Jon; Mahmood, Rizwan

    We present electrical and optical studies of hexanethiol-treated gold nanoparticle (GNPs) colloids in 4-cyano-4 '-pentyl-biphenyl (5CB) liquid crystals. Preliminary data analysis suggests an unusual behavior of sudden drop and then rise in the dielectric anisotropy at a critical concentration of 0.0862% by wt. GNPs and a sudden rise and then drop in the nematic to isotropic transition temperature. Above the critical concentration the data level off to within the uncertainty of the experimental errors. This colloidal system will help us to understand the interaction and the effects of nanoparticles on the self-assembly of LC molecules and the manner in which these particles organize in LC. This study is important for further developments in nanotechnology, sharp and fast display panels, and within the medical field.

  15. Spatiotemporal complexity of electroconvection patterns in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Krekhov, Alexei; Dressel, Bernd; Pesch, Werner; Delev, Vladimir; Batyrshin, Eduard

    2015-12-01

    We investigate a number of complex patterns driven by the electroconvection instability in a planarly aligned layer of a nematic liquid crystal. They are traced back to various secondary instabilities of the ideal roll patterns bifurcating at onset of convection, whereby the basic nematohydrodynamic equations are solved by common Galerkin expansion methods. Alternatively these equations are systematically approximated by a set of coupled amplitude equations. They describe slow modulations of the convection roll amplitudes, which are coupled to a flow field component with finite vorticity perpendicular to the layer and to a quasihomogeneous in-plane rotation of the director. It is demonstrated that the Galerkin stability diagram of the convection rolls is well reproduced by the corresponding one based on the amplitude equations. The main purpose of the paper is, however, to demonstrate that their direct numerical simulations match surprisingly well new experiments, which serves as a convincing test of our theoretical approach.

  16. Nonlinear flow behaviors of nematic liquid crystals in complex geometries

    NASA Astrophysics Data System (ADS)

    Araki, Takeaki

    2013-02-01

    We study nematic liquid crystals flowing in a regular-shaped porous medium by means of lattice Boltzmann simulations. With strong anchoring, the director field cannot align uniformly and topological defects are stably formed with a large number of possible configurations. In a quiescent state, each configuration is arrested since the energy barriers between possible configurations are higher than the thermal energy. If the flow speed is slow enough, the defect pattern is not changed from the initial quiescent configuration. Above a critical flow speed, the defect pattern transforms to a new stable configuration. In a regular-shaped porous matrix, there remain regularly aligned disclination loops. This regular pattern is maintained even after the flow is stopped.

  17. Breakup of partially wetting nanoscale nematic liquid films

    NASA Astrophysics Data System (ADS)

    Lam, Michael; Linda Cummings Collaboration; Lou Kondic Collaboration; Te-Sheng Lin Collaboration

    2015-11-01

    The breakup of nematic liquid crystals (NLCs) films with thicknesses less than a micrometer is studied. Particular attention is paid to the interplay between the bulk elasticity and the anchoring (boundary) conditions at the substrate and free surface. Within the framework of the long wave approximation, a fourth order nonlinear partial differential equation (PDE) is derived for the free surface height. Numerical simulations of a perturbed flat film show that, depending on the initial average thickness of the film, satellite droplets form and persist on time scales much longer than dewetting. Formulating the model in terms of an effective disjoining pressure (elastic response and van der Waals interaction), simulations further suggest that satellite droplets form when the initial average film thickness corresponds to a positive effective disjoining pressure. Our results may shed light on the so-called ''forbidden film thicknesses'' seen in experiments. Supported by NSF grant DMS-1211713.

  18. Phase diagrams of orientational transitions in absorbing nematic liquid crystals

    SciTech Connect

    Zolot’ko, A. S. Ochkin, V. N.; Smayev, M. P.; Shvetsov, S. A.

    2015-05-15

    A theory of orientational transitions in nematic liquid crystals (NLCs), which employs the expansion of optical torques acting on the NLC director with respect to the rotation angle, has been developed for NLCs with additives of conformationally active compounds under the action of optical and low-frequency electric and magnetic fields. Phase diagrams of NLCs are constructed as a function of the intensity and polarization of the light field, the strength of low-frequency electric field, and a parameter that characterizes the feedback between the rotation of the NLC director and optical torque. Conditions for the occurrence of first- and second-order transitions are determined. The proposed theory agrees with available experimental data.

  19. Spatiotemporal complexity of electroconvection patterns in nematic liquid crystals.

    PubMed

    Krekhov, Alexei; Dressel, Bernd; Pesch, Werner; Delev, Vladimir; Batyrshin, Eduard

    2015-12-01

    We investigate a number of complex patterns driven by the electroconvection instability in a planarly aligned layer of a nematic liquid crystal. They are traced back to various secondary instabilities of the ideal roll patterns bifurcating at onset of convection, whereby the basic nematohydrodynamic equations are solved by common Galerkin expansion methods. Alternatively these equations are systematically approximated by a set of coupled amplitude equations. They describe slow modulations of the convection roll amplitudes, which are coupled to a flow field component with finite vorticity perpendicular to the layer and to a quasihomogeneous in-plane rotation of the director. It is demonstrated that the Galerkin stability diagram of the convection rolls is well reproduced by the corresponding one based on the amplitude equations. The main purpose of the paper is, however, to demonstrate that their direct numerical simulations match surprisingly well new experiments, which serves as a convincing test of our theoretical approach. PMID:26764714

  20. Coherent backscattering of light in nematic liquid crystals

    SciTech Connect

    Aksenova, E. V. Kuz'min, V. L.; Romanov, V. P.

    2009-03-15

    Multiple light scattering by director fluctuations in nematic liquid crystals is considered. A uniform director orientation is assumed to be specified by an applied magnetic field. The coherent backscattering effect, which consists in the presence of a sharp light backscattering peak, is studied. The Bethe-Salpeter equation is used to calculate the multiple scattering intensity taking into account the contributions of ladder and cyclic diagrams. An analytical expression for the angular and polarization dependences of the coherent backscattering intensity is obtained in terms of the diffusion approximation. The calculation and experimental results are compared. The developed theory is shown to qualitatively describe the elliptical shape of the backscattering cone, to explain the absence of a coherent contribution for crossed polarizations, and to calculate the relative peak height.

  1. The electrohydrodynamic instability in twisted nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Hertrich, A.; Krekhov, A. P.; Scaldin, O. A.

    1994-02-01

    We present some experiments on electrohydrodynamic convection (EHC) in nematic liquid crystals with a planar, but twisted configuration (MBBA). The threshold voltage is shown to depend only weakly on the twist angle. A theoretical analysis of the onset behaviour agrees well with the experiments. More sensitive is a secondary transition to modulation structures, which are not easily observed in untwisted geometries. A rough estimate of the secondary instability based on the behaviour of the most rapidly growing modulation mode seems to account well for the observations. Additional theoretical investigations for materials with positive dielectric anisotropy concerning the competition between the Fréedericksz transition and EHC are included. We predict the existence of a crossover codimension-2 point, which could easily be tested by variation of the twist angle.

  2. Electric field generation of Skyrmion-like structures in a nematic liquid crystal.

    PubMed

    Cattaneo, Laura; Kos, Žiga; Savoini, Matteo; Kouwer, Paul; Rowan, Alan; Ravnik, Miha; Muševič, Igor; Rasing, Theo

    2016-01-21

    Skyrmions are particle-like topological objects that are increasingly drawing attention in condensed matter physics, where they are connected to inversion symmetry breaking and chirality. Here we report the generation of stable Skyrmion-like structures in a thin nematic liquid crystal film on chemically patterned patchy surfaces. Using the interplay of material elasticity and surface boundary conditions, we use a strong electric field to quench the nematic liquid crystal from a fully aligned phase to vortex-like nematic liquid crystal structures, centered on patterned patches, which carry two different sorts of topological defects. Numerical calculations reveal that these are Skyrmion-like structures, seeded from the surface boojum topological defects and swirling towards the second confining surface. These observations, supported by numerical methods, demonstrate the possibility to generate, manipulate and study Skyrmion-like objects in nematic liquid crystals on patterned surfaces. PMID:26549212

  3. Optical security devices using nonuniform schlieren texture of UV-curable nematic liquid crystal.

    PubMed

    Nakayama, Keizo; Ohtsubo, Junji

    2016-02-10

    We proposed and quantitatively evaluated an optical security device that provides nonuniform or random patterns of schlieren texture in nematic liquid crystal as unique identification information with a design by employing computer image processing and normalized cross correlation. Using the same photomask as the first author's university logo, the written patterns, which were composed of polymerized isotropic areas and polymerized nematic areas, were stable among different cells. Judging from the maximum correlation coefficient of 0.09, the patterns of the schlieren texture were unique in different cells. These results indicate that photocurable nematic liquid crystal materials have the potential to be applied to security devices for anticounterfeiting measures. PMID:26906368

  4. ESR studies of the slow tumbling of vanadyl spin probes in nematic liquid crystals

    NASA Technical Reports Server (NTRS)

    Eastman, M. P.; Bruno, G. V.; Lawson, J. O.

    1977-01-01

    ESR line shapes that are appropriate for slowly tumbling vanadyl spin probes in viscous nematic liquid crystals were calculated by the stochastic Liouville method. Because of the symmetry possessed by vanadyl, the analysis and interpretation of these line shapes was simplified considerably. Spectral line shapes agreed well with experimental spectra of VOAcAc in the nematic liquid crystal Phase V and BEPC. Deviations from Brownian rotational diffusion were noted. A slowly fluctuating torque analysis yielded good agreement with the experimental spectra.

  5. Water-in-water emulsions stabilized by non-amphiphilic interactions: polymer-dispersed lyotropic liquid crystals.

    PubMed

    Simon, Karen A; Sejwal, Preeti; Gerecht, Ryan B; Luk, Yan-Yeung

    2007-01-30

    Emulsion systems involving surfactants are mainly driven by the separation of the hydrophobic interactions of the aliphatic chains from the hydrophilic interactions of amphiphilic molecules in water. In this study, we report an emulsion system that does not include amphiphilic molecules but molecules with functional groups that are completely solvated in water. These functional groups give rise to molecular interactions including hydrogen bonding, pi stacking, and salt bridging and are segregated into a dispersion of droplets forming a water-in-water emulsion. This water-in-water emulsion consists of dispersing droplets of a water-solvated biocompatible liquid crystal--disodium cromoglycate (DSCG)--in a continuous aqueous solution containing specific classes of water-soluble polymers. Whereas aqueous solutions of polyols support the formation of emulsions of spherical droplets consisting of lyotropic liquid crystal DSCG with long-term stability (for at least 30 days), aqueous solutions of polyamides afford droplets of DSCG in the shape of prolate ellipsoids that are stable for only 2 days. The DSCG liquid crystal in spherical droplets assumes a radial configuration in which the optical axis of the liquid crystal aligns perpendicular to the surface of the droplets but assumes a tangential configuration in prolate ellipsoids in which the optical axis of the liquid crystal aligns parallel to the surface of the droplet. Other classes of water-soluble polymers including polyethers, polycations, and polyanions do not afford a stable emulsion of DSCG droplets. Both the occurrence and the stability of this unique emulsion system can be rationalized on the basis of the functional groups of the polymer. The different configurations of the liquid crystal (DSCG) droplets were also found to correlate with the strength of the hydrogen bonding that can be formed by the functional groups on the polymer. PMID:17241072

  6. Elementary statistical models for nematic transitions in liquid-crystalline systems

    NASA Astrophysics Data System (ADS)

    Liarte, Danilo B.; Salinas, Silvio R.

    2014-03-01

    We introduce a simple Maier-Saupe-Zwanzig (MSZ) model to describe the well-known first-order nematic-isotropic transition in liquid-crystalline systems. We then use the MSZ model, with the addition of disorder degrees of freedom, to investigate the stability of a biaxial nematic phase in a mixture of rods and disks. There is a biaxial nematic structure if we consider a fixed distribution of rods and disks. For a thermalized distribution of shapes, however, this biaxial structure becomes thermodynamically unstable. We then resort to a formalism that accounts for two sets of relaxation times, and show that a small departure from complete thermalization is enough to recover a stable biaxial structure. As another application of the MSZ model, we report an investigation of some properties of nematic elastomers. We point out the possibility of continuous nematic transitions, and reproduce a characteristic stress-strain response, with a plateau that indicates a polydomain-monodomain transition.

  7. Chirality Detection Using Nematic Liquid Crystal Droplets on Anisotropic Surfaces.

    PubMed

    Rudquist, Per; Dietrich, Clarissa F; Mark, Andrew G; Giesselmann, Frank

    2016-06-21

    Nematic liquid crystals (NLCs) form helical macroscopic structures through chiral induction when doped with chiral species. We describe a very simple, though highly sensitive method for determination of handedness and pitch of the induced twist in the case of very weak twisting powers of such chiral dopants. A tiny drop-typically less than 10 nL-of the chiral doped NLC is placed on a plate promoting a uniform planar surface anchoring of the liquid crystal director. At the curved NLC-air interface the anchoring is homeotropic and in the sessile droplets we get a locally twisted hybrid director structure with a disclination line extending across the droplet. The configuration of the disclination line (S-like or backwards S-like) reveals the sign of twisting power and extremely large pitch values in the range of 10 mm can easily be measured. We demonstrate the method using the standard NLC 4-cyano-4'-pentylbiphenyl (5CB), weakly doped with the chiral material 2-hydroxy-2-phenylacetic acid (mandelic acid). PMID:27244587

  8. Nematic liquid crystal interfaces for chemical and biological detection

    NASA Astrophysics Data System (ADS)

    Most, Darrin R.; VanTreeck, Heidi J.; Grinwald, Bart A.; Kupcho, Kurt A.; Sen, Avijit; Bonds, Michael D.; Anhalt, Karla; Israel, Barbara A.; Acharya, Bharat R.

    2011-03-01

    Nematic liquid crystals (NLCs) have traditionally been used in displays and other electro-optical applications where the orientation of NLC is manipulated by using an external electric field to display the information. In recent years, there have been significant advances in unconventional applications of NLCs in photonics, sensors, and diagnostics. In this paper, the application of NLCs for detection of vapor phase chemicals and biological entities is presented. When NLCs are in contact with another medium (solid, liquid or air) the delicate interplay between the properties of medium and NLCs determines the nature of the alignment assumed by NLCs at the interface. Interfaces functionalized with select chemical or biological entities promote alignment of NLCs in predetermined orientations (perpendicular or parallel to that interface) that are primarily dictated by local interactions at the interface. When these interfaces are exposed to target analytes, the interactions at the interfaces are perturbed and the NLC films undergo orientational transitions from perpendicular to parallel alignment, or vice versa. The orientational transition can be detected by viewing the film of NLCs between crossed polarizers (optical signal) or by measuring the differential capacitance associated with the change in alignment of NLCs (electrical signal). By engineering surfaces with different interfacial properties, sensors based on this principle have been demonstrated to selectively detect a wide variety of chemical and biological analytes that have relevance in industrial hygiene, environmental monitoring, homeland security, diagnostics, and biomedical applications.

  9. Generation of harmonics and supercontinuum in nematic liquid crystals

    SciTech Connect

    Nyushkov, B N; Trashkeev, S I; Klementyev, Vasilii M; Pivtsov, V S; Kobtsev, Sergey M

    2013-02-28

    Nonlinear optical properties of nematic liquid crystals (NLC) have been investigated. A technique for efficient laser frequency conversion in a microscopic NLC volume deposited on an optical fibre end face is experimentally demonstrated. An efficient design of a compact NLC-based IR frequency converter with a fibre input and achromatic collimator is proposed and implemented. Simultaneous generation of the second and third harmonics is obtained for the first time under pumping NLC by a 1.56-mm femtosecond fibre laser. The second-harmonic generation efficiency is measured to be about 1 %, while the efficiency of third-harmonic generation is several tenths of percent. A strong polarisation dependence of the third-harmonic generation efficiency is revealed. When pumping NLC by a cw laser, generation of spectral supercontinua (covering the visible and near-IR spectral ranges) is observed. The nonlinear effects revealed can be due to the light-induced change in the orientational order in liquid crystals, which breaks the initial symmetry and leads to formation of disclination structures. The NLC optical nonlinearity is believed to be of mixed orientationalelectronic nature as a whole. (laser optics 2012)

  10. Dynamics of water confined in lyotropic liquid crystals: Molecular dynamics simulations of the dynamic structure factor

    NASA Astrophysics Data System (ADS)

    Mantha, Sriteja; Yethiraj, Arun

    2016-02-01

    The properties of water under confinement are of practical and fundamental interest. In this work, we study the properties of water in the self-assembled lyotropic phases of Gemini surfactants with a focus on testing the standard analysis of quasi-elastic neutron scattering (QENS) experiments. In QENS experiments, the dynamic structure factor is measured and fit to models to extract the translational diffusion constant, DT, and rotational relaxation time, τR. We test this procedure by using simulation results for the dynamic structure factor, extracting the dynamic parameters from the fit as is typically done in experiments, and comparing the values to those directly measured in the simulations. We find that the de-coupling approximation, where the intermediate scattering function is assumed to be a product of translational and rotational contributions, is quite accurate. The jump-diffusion and isotropic rotation models, however, are not accurate when the degree of confinement is high. In particular, the exponential approximations for the intermediate scattering function fail for highly confined water and the values of DT and τR can differ from the measured value by as much as a factor of two. Other models have more fit parameters, however, and with the range of energies and wave-vectors accessible to QENS, the typical analysis appears to be the best choice. In the most confined lamellar phase, the dynamics are sufficiently slow that QENS does not access a large enough time scale.

  11. Acoustooptic Effects of Nematic Liquid Crystals Induced by Elastic Wave Propagating in Glass Substrate

    NASA Astrophysics Data System (ADS)

    Moritake, Hiroshi; Seike, Tadaaki; Toda, Kohji

    1999-05-01

    An elastic wave delay line with a glass plate as a propagation medium is investigated in relations to acoustooptic effects of nematic liquid crystals. A nematic liquid crystal cell is mounted on the central region of a glass plate for elastic wave propagation. The elastic wave propagating in the glass plate interacts with the liquid crystal in a wide frequency range. Two types of periodical domain structures are observed in the nematic liquid crystal cell under the existence of the elastic wave. One exists in both homeotropically and homogeneously aligned cells, and depends not on the kind of liquid crystal but on the carrier frequency of the elastic wave. The other is recognized only in homogeneously aligned cells and depends on the layer thickness and the kind of liquid crystal, but not on the carrier frequency of the elastic wave. Both periodical domain structures are induced by the elastic wave propagating in the glass plate.

  12. Chiral symmetry breaking by spatial confinement in tactoidal droplets of lyotropic chromonic liquid crystals

    PubMed Central

    Tortora, Luana; Lavrentovich, Oleg D.

    2011-01-01

    In many colloidal systems, an orientationally ordered nematic (N) phase emerges from the isotropic (I) melt in the form of spindle-like birefringent tactoids. In cases studied so far, the tactoids always reveal a mirror-symmetric nonchiral structure, sometimes even when the building units are chiral. We report on chiral symmetry breaking in the nematic tactoids formed in molecularly nonchiral polymer-crowded aqueous solutions of low-molecular weight disodium cromoglycate. The parity is broken by twisted packing of self-assembled molecular aggregates within the tactoids as manifested by the observed optical activity. Fluorescent confocal microscopy reveals that the chiral N tactoids are located at the boundaries of cells. We explain the chirality induction as a replacement of energetically costly splay packing of the aggregates within the curved bipolar tactoidal shape with twisted packing. The effect represents a simple pathway of macroscopic chirality induction in an organic system with no molecular chirality, as the only requirements are orientational order and curved shape of confinement. PMID:21402929

  13. Influence of shear flow on the Fréedericksz transition in nematic liquid crystals.

    PubMed

    Makarov, D V; Zakhlevnykh, A N

    2006-10-01

    Within the framework of Ericksen-Leslie continuum theory we analyze the influence of shear flow on the magnetic-field-induced Fréedericksz transition in nematic liquid crystal with rodlike molecules. We consider three basic orientational configurations of a nematic planar layer in the uniform magnetic field. Conditions of rigid director coupling on the boundaries of the layer and constant shear flow gradient inside the layer are used. We exhibit some flow aligning effects for nematic liquid crystals with various ratio of rotary viscosities and investigate how unequal elastic constants (elastic anisotropy) alter the magnetic Fréedericksz transition in sheared nematics. Our calculations predict that surface boundary effects in nematic films and magnetic field action lead to existence of stationary flow regimes in the so-called nonflow aligning nematics, otherwise, surface and magnetic forces extend the range of viscous coefficient values corresponding to the flow aligning regimes. We show that imposing of shear flow on the Fréedericksz transition leads to a threshold behavior or to a "smoothing" of the transition. It depends on the orientation of the nematic layer in magnetic field and magnitudes of rotary viscous coefficients. PMID:17155081

  14. Two-point particle tracking microrheology of nematic complex fluids.

    PubMed

    Gómez-González, Manuel; Del Álamo, Juan C

    2016-06-29

    Many biological and technological complex fluids exhibit tight microstructural alignment that confers them nematic mechanical properties. Among these we count liquid crystals and biopolymer networks, which are often available in microscopic amounts. However, current microrheological methods cannot measure the directional viscoelastic coefficients that appear in the constitutive relation of nematic complex fluids. This article presents directional two-point particle-tracking microrheology (D2PTM) - a novel microrheology technique to determine these coefficients. We establish the theoretical foundation for D2PTM by analyzing the motion of a probing microscopic particle embedded in a nematic complex fluid, and the mutual hydrodynamic interactions between pairs of distant particles. From this analysis, we generalize the formulation of two-point particle tracking microrheology for nematic complex fluids, and demonstrate that the new formulation provides sufficient information to fully characterize the anisotropic viscoelastic coefficients of such materials. We test D2PTM by simulating the Brownian motion of particles in nematic viscoelastic fluids with prescribed directional frequency-dependent shear moduli, showing that D2PTM accurately recovers the prescribed shear moduli. Furthermore, we experimentally validate D2PTM by applying it to a lyotropic nematic liquid crystal, and demonstrate that this new microrheology method provides results in agreement with dynamic light scattering measurements. Lastly, we illustrate the experimental application of the new technique to characterize nematic F-actin solutions. These experiments constitute the first microrheological measurement of the directional viscoelastic coefficients of an anisotropic soft material. PMID:27270816

  15. Predicting photoisomerization profile of the highly polymerized nematic azobenzene liquid crystal network: First principle calculation

    NASA Astrophysics Data System (ADS)

    Yun, J.; Li, C.; Chung, H.; Choi, J.; Cho, M.

    2015-05-01

    The cis profile of azobenzene is a key factor in predicting the photodeformation of the nematic azobenzene liquid crystal network (LCN). An ab initio based method for predicting the photoisomerization profile of azobenzene is developed by coupling the stimulated Raman adiabatic passage (STIRAP) method with non-linear Beers law, and compared with experimental data. Using this combined method, we calculate the photoisomerization profile of azobenzene with various light input conditions. We identify the cis profile of the nematic LCN structure evolves into a step-like decaying shape when the direction of polarized light is parallel to the nematic direction.

  16. Electron paramagnetic resonance studies of slowly tumbling vanadyl spin probes in nematic liquid crystals

    NASA Technical Reports Server (NTRS)

    Bruno, G. V.; Harrington, J. K.; Eastman, M. P.

    1978-01-01

    An analysis of EPR line shapes by the method of Polnaszek, Bruno, and Freed is made for slowly tumbling vanadyl spin probes in viscous nematic liquid crystals. The use of typical vanadyl complexes as spin probes for nematic liquid crystals is shown to simplify the theoretical analysis and the subsequent interpretation. Rotational correlation times tau and orientational ordering parameters S sub Z where slow tumbling effects are expected to be observed in vanadyl EPR spectra are indicated in a plot. Analysis of the inertial effects on the probe reorientation, which are induced by slowly fluctuating torque components of the local solvent structure, yield quantitative values for tau and S sub Z. The weakly ordered probe VOAA is in the slow tumbling region and displays these inertial effects throughout the nematic range of BEPC and Phase V. VOAA exhibits different reorientation behavior near the isotropic-nematic transition temperature than that displayed far below this transition temperature.

  17. Direct mapping of local director field of nematic liquid crystals at the nanoscale.

    PubMed

    Xia, Yu; Serra, Francesca; Kamien, Randall D; Stebe, Kathleen J; Yang, Shu

    2015-12-15

    Liquid crystals (LCs), owing to their anisotropy in molecular ordering, are of wide interest in both the display industry and soft matter as a route to more sophisticated optical objects, to direct phase separation, and to facilitate colloidal assemblies. However, it remains challenging to directly probe the molecular-scale organization of nonglassy nematic LC molecules without altering the LC directors. We design and synthesize a new type of nematic liquid crystal monomer (LCM) system with strong dipole-dipole interactions, resulting in a stable nematic phase and strong homeotropic anchoring on silica surfaces. Upon photopolymerization, the director field can be faithfully "locked," allowing for direct visualization of the LC director field and defect structures by scanning electron microscopy (SEM) in real space with 100-nm resolution. Using this technique, we study the nematic textures in more complex LC/colloidal systems and calculate the extrapolation length of the LCM. PMID:26621729

  18. Direct mapping of local director field of nematic liquid crystals at the nanoscale

    PubMed Central

    Xia, Yu; Serra, Francesca; Kamien, Randall D.; Stebe, Kathleen J.; Yang, Shu

    2015-01-01

    Liquid crystals (LCs), owing to their anisotropy in molecular ordering, are of wide interest in both the display industry and soft matter as a route to more sophisticated optical objects, to direct phase separation, and to facilitate colloidal assemblies. However, it remains challenging to directly probe the molecular-scale organization of nonglassy nematic LC molecules without altering the LC directors. We design and synthesize a new type of nematic liquid crystal monomer (LCM) system with strong dipole–dipole interactions, resulting in a stable nematic phase and strong homeotropic anchoring on silica surfaces. Upon photopolymerization, the director field can be faithfully “locked,” allowing for direct visualization of the LC director field and defect structures by scanning electron microscopy (SEM) in real space with 100-nm resolution. Using this technique, we study the nematic textures in more complex LC/colloidal systems and calculate the extrapolation length of the LCM. PMID:26621729

  19. From the microscopic to the mesoscopic properties of lyotropic reverse hexagonal liquid crystals.

    PubMed

    Libster, Dima; Ishai, Paul Ben; Aserin, Abraham; Shoham, Gil; Garti, Nissim

    2008-03-01

    In the present study we aimed to explore a correlation between the microstructural properties of the lyotropic reverse hexagonal phase (HII) of the GMO/tricaprylin/phosphatidylcholine/water system and its mesoscopic structure. The mesoscopic organization of discontinuous and anisotropic domains was examined, in the native state, using environmental scanning electron microscopy. The topography of the HII mesophases was imaged directly in their hydrated state, as a function of aqueous-phase concentration and composition, when a proline amino acid was solubilized into the systems as a kosmotropic (water-structure maker) guest molecule. The domain structures of several dozen micrometers in size, visualized in the environmental scanning electron microscopy, were found to possess fractal characteristics, indicating a discontinuous and disordered alignment of the corresponding internal water rods on the mesoscale. On the microstructural level, SAXS measurements revealed that as water content (Cw) increases the characteristic lattice parameter of the mesophases increases as well. Using the water concentration as the mass measure of the mixtures, a scaling relationship between the lattice parameter and the concentration was found to obey a power law whereby the derived fractal dimension was the relevant exponent, confirming the causal link between the microscopic and mesoscopic organizations. The topography of the HII mesophase was found to be affected by the microstructural parameters and the composition of the samples. Thermal analysis experiments involving these systems further confirmed that the behavior of water underpins both microscopical and mesoscopic features of the systems. It was shown that both the swelling of the lattice parameter and the mesoscopic domains is correlated to the bulk water concentration in the water rods. PMID:18197712

  20. High-Throughput Screening of Saturated Fatty Acid Influence on Nanostructure of Lyotropic Liquid Crystalline Lipid Nanoparticles.

    PubMed

    Tran, Nhiem; Hawley, Adrian M; Zhai, Jiali; Muir, Benjamin W; Fong, Celesta; Drummond, Calum J; Mulet, Xavier

    2016-05-10

    Self-assembled lyotropic liquid crystalline lipid nanoparticles have been developed for a wide range of biomedical applications with an emerging focus for use as delivery vehicles for drugs, genes, and in vivo imaging agents. In this study, we report the generation of lipid nanoparticle libraries with information regarding mesophase and lattice parameter, which can aid the selection of formulation for a particular end-use application. In this study we elucidate the phase composition parameters that influence the internal structure of lipid nanoparticles produced from monoolein, monopalmitolein and phytantriol incorporating a variety of saturated fatty acids (FA) with different chain lengths at varying concentrations and temperatures. The material libraries were established using high throughput formulation and screening techniques, including synchrotron small-angle X-ray scattering. The results demonstrate the rich polymorphism of lipid nanoparticles with nonlamellar mesophases in the presence of saturated FAs. The inclusion of saturated FAs within the lipid nanoparticles promotes a gradual phase transition at all temperatures studied toward structures with higher negative surface curvatures (e.g., from inverse bicontinuous cubic phase to hexagonal phase and then emulsified microemulsion). The three partial phase diagrams produced are discussed in terms of the influence of FA chain length and concentration on nanoparticle internal mesophase structure and lattice parameters. The study also highlights a compositionally dependent coexistence of multiple mesophases, which may indicate the presence of multicompartment nanoparticles containing cubic/cubic and cubic/hexagonal mesophases. PMID:27023315

  1. Dual-Responsive Viscoelastic Lyotropic Liquid Crystal Fluids to Control the Diffusion of Hydrophilic and Hydrophobic Molecules.

    PubMed

    Wang, Dong; Cao, Yueying; Cao, Meiwen; Sun, Yawei; Wang, Jiqian; Hao, Jingcheng

    2016-07-01

    A smart lyotropic liquid crystal (LLC) system was prepared to control the diffusion rate of hydrophilic and hydrophobic molecules. The LLC system is composed of a nonionic surfactant (tetraethylene glycol monododecylether; C12 EO4 ) and an anionic azobenzene surfactant (Azo-surfactant). C12 EO4 was the main component of the LLC system. The Azo-surfactant, which can undergo photo-isomerization, played the role of trigger in this system. LLC gels formed in a solution comprised of Azo-surfactant (10 mm) and C12 EO4 (300 mm). The LLC gels became broken when more Azo-surfactant was added (e.g., up to 15 mm) and the viscoelasticity was lost. Surprisingly, when we used UV light to irradiate the 300 mm C12 EO4 /15 mm Azo-surfactant sample, the gel was recovered and high viscoelasticity was observed. However, under visible-light irradiation, the gel became broken again. The gel formation could also be triggered by heating the sample. On heating the 300 mm C12 EO4 /15 mm Azo-surfactant sample, the system thickened to a point at which typical gel behavior was registered. When the sample was cooled, the gel broke again. The LLC could be used for controlled release of hydrophilic and hydrophobic molecules, and could be considered as a versatile vehicle for the delivery of actives in systems of practical importance. PMID:27028313

  2. Nematic Director Reorientation at Solid and Liquid Interfaces under Flow: SAXS Studies in a Microfluidic Device

    PubMed Central

    2015-01-01

    In this work we investigate the interplay between flow and boundary condition effects on the orientation field of a thermotropic nematic liquid crystal under flow and confinement in a microfluidic device. Two types of experiments were performed using synchrotron small-angle X-ray-scattering (SAXS). In the first, a nematic liquid crystal flows through a square-channel cross section at varying flow rates, while the nematic director orientation projected onto the velocity/velocity gradient plane is measured using a 2D detector. At moderate-to-high flow rates, the nematic director is predominantly aligned in the flow direction, but with a small tilt angle of ∼±11° in the velocity gradient direction. The director tilt angle is constant throughout most of the channel width but switches sign when crossing the center of the channel, in agreement with the Ericksen–Leslie–Parodi (ELP) theory. At low flow rates, boundary conditions begin to dominate, and a flow profile resembling the escaped radial director configuration is observed, where the director is seen to vary more smoothly from the edges (with homeotropic alignment) to the center of the channel. In the second experiment, hydrodynamic focusing is employed to confine the nematic phase into a sheet of liquid sandwiched between two layers of Triton X-100 aqueous solutions. The average nematic director orientation shifts to some extent from the flow direction toward the liquid boundaries, although it remains unclear if one tilt angle is dominant through most of the nematic sheet (with abrupt jumps near the boundaries) or if the tilt angle varies smoothly between two extreme values (∼90 and 0°). The technique presented here could be applied to perform high-throughput measurements for assessing the influence of different surfactants on the orientation of nematic phases and may lead to further improvements in areas such as boundary lubrication and clarifying the nature of defect structures in LC displays. PMID

  3. Nematic director reorientation at solid and liquid interfaces under flow: SAXS studies in a microfluidic device.

    PubMed

    Silva, Bruno F B; Zepeda-Rosales, Miguel; Venkateswaran, Neeraja; Fletcher, Bretton J; Carter, Lester G; Matsui, Tsutomu; Weiss, Thomas M; Han, Jun; Li, Youli; Olsson, Ulf; Safinya, Cyrus R

    2015-04-14

    In this work we investigate the interplay between flow and boundary condition effects on the orientation field of a thermotropic nematic liquid crystal under flow and confinement in a microfluidic device. Two types of experiments were performed using synchrotron small-angle X-ray-scattering (SAXS). In the first, a nematic liquid crystal flows through a square-channel cross section at varying flow rates, while the nematic director orientation projected onto the velocity/velocity gradient plane is measured using a 2D detector. At moderate-to-high flow rates, the nematic director is predominantly aligned in the flow direction, but with a small tilt angle of ∼±11° in the velocity gradient direction. The director tilt angle is constant throughout most of the channel width but switches sign when crossing the center of the channel, in agreement with the Ericksen-Leslie-Parodi (ELP) theory. At low flow rates, boundary conditions begin to dominate, and a flow profile resembling the escaped radial director configuration is observed, where the director is seen to vary more smoothly from the edges (with homeotropic alignment) to the center of the channel. In the second experiment, hydrodynamic focusing is employed to confine the nematic phase into a sheet of liquid sandwiched between two layers of Triton X-100 aqueous solutions. The average nematic director orientation shifts to some extent from the flow direction toward the liquid boundaries, although it remains unclear if one tilt angle is dominant through most of the nematic sheet (with abrupt jumps near the boundaries) or if the tilt angle varies smoothly between two extreme values (∼90 and 0°). The technique presented here could be applied to perform high-throughput measurements for assessing the influence of different surfactants on the orientation of nematic phases and may lead to further improvements in areas such as boundary lubrication and clarifying the nature of defect structures in LC displays. PMID

  4. Electrically controllable Fresnel lens in 90° twisted nematic liquid crystals.

    PubMed

    Kuo, Chie-Tong; Li, Chien-Yu; Lin, Shih-Hung; Yeh, Hui-Chen

    2015-10-01

    This study presents a theoretical analysis and experimental demonstration of an electrically controllable Fresnel lens in a 90° twisted nematic liquid crystal cell. The cell gap was chosen to satisfy the Gooch-Tarry conditions, and therefore, the polarization rotation effect was valid regardless of the incident polarization direction. The polarization sensitivity of the diffraction efficiency of the 90° twisted nematic Fresnel lens was dependent on the applied voltage regime. Theoretical calculations effectively explain the experimental results. PMID:26480119

  5. Stability of the Melting Hedgehog in the Landau-de Gennes Theory of Nematic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Ignat, Radu; Nguyen, Luc; Slastikov, Valeriy; Zarnescu, Arghir

    2014-09-01

    We investigate stability properties of the radially symmetric solution corresponding to the vortex defect (the so called "melting hedgehog") in the framework of the Landau-de Gennes model of nematic liquid crystals. We prove local stability of the melting hedgehog under arbitrary Q-tensor valued perturbations in the temperature regime near the critical supercooling temperature. As a consequence of our method, we also rediscover the loss of stability of the vortex defect in the deep nematic regime.

  6. Stability of the Melting Hedgehog in the Landau-de Gennes Theory of Nematic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Ignat, Radu; Nguyen, Luc; Slastikov, Valeriy; Zarnescu, Arghir

    2015-02-01

    We investigate stability properties of the radially symmetric solution corresponding to the vortex defect (the so called "melting hedgehog") in the framework of the Landau-de Gennes model of nematic liquid crystals. We prove local stability of the melting hedgehog under arbitrary Q-tensor valued perturbations in the temperature regime near the critical supercooling temperature. As a consequence of our method, we also rediscover the loss of stability of the vortex defect in the deep nematic regime.

  7. Polarization converting textures of nematic liquid crystal in glass cavities

    NASA Astrophysics Data System (ADS)

    Wang, Xiahui; Xu, Miao; Ren, Hongwen

    2014-01-01

    When a nematic liquid crystal (LC) is filled in a glass cavity, the LC molecules present azimuthal orientations in the cavity. If the surface of the cavity is coated with a homeotropic polyimide, then the LC molecules exhibit radial orientations. By treating the LC on one side of the cavity with homogeneous alignment, the former orientations change to a twisted-azimuthal texture, while the latter orientations change to a twisted-radial texture. Both textures are verified experimentally, and they can convert a linearly polarization light to an azimuthal and/or radial polarization light, depending on the polarization direction of the incident light. In contrast to previous approaches, various LC textures can be easily formed in a cavity, and the fabrication procedure is simple. Since the LC texture is confined in a cavity, an array pattern of the texture can be obtained, if the employed substrate has multiple cavities. A LC with twisted-azimuthal and/or twisted-radial textures in a cavity array has potential applications in phase modulation, polarization compensating, sharp focus, and material processing.

  8. Amplitude equations for the electrohydrodynamic instability in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Kaiser, M.; Pesch, W.

    1993-12-01

    We study the near-threshold behavior of electrohydrodynamic convection (EHC) in planarly aligned nematic liquid crystals in the (low-frequency) conduction regime. The investigations are based on a rigorous and systematic weakly nonlinear analysis of the standard hydrodynamic equations leading to a reduced description in terms of order-parameter equations. The typical experimental stability regimes in control parameter and wave-number space are identified for normal rolls near threshold. In particular, the decisive role of mean-flow effects in triggering the typical secondary zigzag instability leading to oblique rolls is emphasized. Subsequently, a set of coupled amplitude equations is derived directly from the basic equations that includes the mean-flow effects and higher-order gradient terms important at least in EHC. Simulations of the amplitude equations point to the possible existence of more than one attractor beyond the zigzag destabilization line, which might explain the sometimes conflicting experimental results. The scenario of ``weak turbulence'' (sometimes called ``defect turbulence'') is well accounted for by the theory.

  9. Anomalous swimming behavior of bacteria in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Sokolov, Andrey; Zhou, Shuang; Lavrentovich, Oleg; Aranson, Igor

    2015-03-01

    Flagellated bacteria stop swimming in isotropic media of viscosity higher than 0.06kgm-1s-1. However, Bacillus Subtilis slows down by only about 30% in a nematic chromonic liquid crystal (CLC, 14wt% DSCG in water), where the anisotropic viscosity can be as high as 6kgm-1s-1. The bacteria velocity (Vb) is linear with the flagella rotation frequency. The phase velocity of the flagella Vf ~ 2Vb in LC, as compared to Vf ~ 10Vb in water. The flow generated by the bacteria is localized along the bacterial body axis, decaying slowly over tens of micrometers along, but rapidly over a few micrometers across this axis. The concentrated flow grants the bacteria new ability to carry cargo particles in LC, ability not seen in their habitat isotropic media. We attribute these anomalous features to the anisotropy of viscosity of the CLC, namely, the viscosities of splay and twist is hundreds times higher than that of bend deformation, which provides extra boost of swimming efficiency and enables the bacteria swim at considerable speed in a viscous medium. Our findings can potentially lead to applications such as particle transportation in microfluidic devices. A.S and I.A are supported by the US DOE, Office of Science, BES, Materials Science and Engineering Division. S.Z. and O.D.L are supported by NSF DMR 1104850, DMS-1434185.

  10. A new insight into the isotropic-nematic phase transition in lyotropic solutions of semiflexible polymers: density-functional theory tested by molecular dynamics.

    PubMed

    Egorov, Sergei A; Milchev, Andrey; Virnau, Peter; Binder, Kurt

    2016-06-14

    Semiflexible polymers in solution are studied for a wide range of both contour length L and persistence length lp as a function of monomer concentration under good solvent conditions. Both density-functional theory (DFT) and molecular dynamics (MD) simulation methods are used, and a very good agreement between both techniques is observed for rather stiff polymers. Evidence for a new mechanism of order parameter fluctuations in the nematic phase is presented, namely collective deformations of bundles of wormlike chains twisted around each other, and the typical wavelengths and amplitudes of these modes are estimated. These long wavelength fluctuations cause a reduction of the order parameter in comparison with the DFT prediction. It is also found that DFT becomes unreliable for rather flexible polymers in predicting that the transition from the isotropic (I)-phase to the nematic (N)-phase still exists at very high monomer concentrations (which in reality does not occur). However, under conditions when DFT is accurate, it provides reliable predictions also for the width of the I-N two-phase coexistence region, which are difficult to obtain from MD in spite of the use of very large systems (up to 500 000 monomers) by means of graphics processing units (GPU). For short and not very stiff chains, a pre-transitional chain stretching is found in the isotropic phase near the I-N-transition, not predicted by theories. A comparison with theoretical predictions by Khokhlov-Semenov, Odijk, and Chen reveals that the scaled transition densities are not simply functions of L/lp only, as these theories predict, but depend on d/lp (where d is the chain diameter) as well. Chain properties in the nematically ordered phase are compared to those of chains confined in tubes, and the deflection length concept is tested. Eventually, some consequences for the interpretation of experiments are spelled out. PMID:27249320

  11. Pattern formation in electrohydrodynamic convection of a nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Gheorghiu, Nadina

    2003-10-01

    The first part of this dissertation is a study of the selection mechanism for the dendritic growth pattern of electrohydrodynamic convection (EHC) in a nematic liquid crystal (NLC). The cell gap d, the magnetic field H, and the voltage V are systematically varied. The transition from the non-convective state to the convective state is first order-like, although in this case it occurs in a nonequilibrium one-phase system. In the layer plane, the two-fold dendritic pattern grows about the only anisotropy direction, perpendicular to the homogeneous director alignment. While for crystalline dendrites the tip radius of curvature rho and the growth speed v are sharply selected, these dendrites show partial selection. At fixed d, H, and V, rho or v for different dendrites varies each within a band. There is no systematic dependence of rho on V. Thus, these dendrites represent an entirely new selection problem for pattern formation. The non-convective state is anisotropic in the plane of the pattern within a (magnetic coherence) length xim of each substrate. The degree of anisotropy decays with xim/d and the selection becomes less sharp. In contrast to sharply interfaced solidification patterns, these dendrites are outlined by a diffuse boundary, which width w ˜ 2xim. While anisotropic surface tension stabilizes crystalline growth, the magnetic field stabilizes this dendritic growth. Finding where and what scale convection first starts is important for understanding pattern selection in EHC. In the second part of this dissertation, fluorescence confocal polarizing microscopy (FCPM) is employed to study normal dielectric rolls (NDRs) in a NLC. While polarizing microscopy gives a two-dimensional information of the integrated three-dimensional (3D) pattern of optical birefringence, FCPM can uniquely map 3D orientational patterns in LC. FCPM visualizes the intensity of polarized fluorescence light emitted by the dye molecules aligned by the LC molecules. The fluorescence

  12. Liquid relaxation: A new Parodi-like relation for nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Biscari, Paolo; DiCarlo, Antonio; Turzi, Stefano S.

    2016-05-01

    We put forward a hydrodynamic theory of nematic liquid crystals that includes both anisotropic elasticity and dynamic relaxation. Liquid remodeling is encompassed through a continuous update of the shear-stress free configuration. The low-frequency limit of the dynamical theory reproduces the classical Ericksen-Leslie theory, but it predicts two independent identities between the six Leslie viscosity coefficients. One replicates Parodi's relation, while the other—which involves five Leslie viscosities in a nonlinear way—is new. We discuss its significance, and we test its validity against evidence from physical experiments, independent theoretical predictions, and molecular-dynamics simulations.

  13. Self-assembled monolayers of alkanethiols on gold prepared in a hexagonal lyotropic liquid crystalline phase of Triton X-100/water system.

    PubMed

    Ganesh, V; Lakshminarayanan, V

    2006-02-14

    In this paper, we have reported a new method of preparing self-assembled monolayers (SAMs) of decanethiol and hexadecanethiol on gold surface by using a lyotropic liquid crystalline phase as an adsorbing medium. The stability and blocking ability of these SAMs were characterized using grazing angle Fourier transform infrared (FTIR) spectroscopy and electrochemical techniques such as cyclic voltammetry and electrochemical impedance spectroscopy. The lyotropic liquid crystalline medium possesses a hexagonal structure consisting of a nonionic surfactant Triton X-100, water, and the corresponding thiol, which provides a highly hydrophobic environment to solubilize the alkanethiols and later to facilitate their delivery to the gold surface. We find that the SAMs formed from the hexagonal liquid crystalline phase are highly compact and have excellent electrochemical blocking ability towards the redox probes compared to conventional SAMs prepared from commonly used organic solvents such as ethanol. From the impedance studies, we have determined the capacitance of the monolayer-coated electrodes and the surface coverage of the SAM, which has been found to be >99.98% on gold surface. We have also estimated the extent of ionic permeability through the film and measured the rate constants for the redox reactions on the SAM-modified electrodes. Our results show that the rate constants of [Fe(CN)6](3-/4-) and [Ru(NH3)6](2+/3+) redox couples are very much lower in the case of monolayers prepared in liquid crystalline phase compared to the SAM formed in 1 mM thiol in ethanol solution, suggesting a better blocking ability of the SAMs in the former case. From the grazing angle FTIR spectroscopic studies and capacitance measurements, we have ruled out any coadsorption of surfactant molecules on the Au surface. These results suggest that SAMs of very low defect density and extremely low ionic permeability can be obtained when a hexagonal lyotropic liquid crystalline phase is used as

  14. Disposition and association of the steric stabilizer Pluronic® F127 in lyotropic liquid crystalline nanostructured particle dispersions.

    PubMed

    Tilley, Adam J; Drummond, Calum J; Boyd, Ben J

    2013-02-15

    Liquid crystalline nanostructured particles, such as cubosomes and hexosomes, are most often colloidally stabilised using the tri-block co-polymer Pluronic® F127. Although the effect of F127 on the internal particle nanostructure has been well studied, the associative aspects of F127 with cubosomes and hexosomes are poorly understood. In this study the quantitative association of F127 with phytantriol-based cubosomes and hexosomes was investigated. The amount of free F127 in the dispersions was determined using pressure ultra-filtration. The percentage of F127 associated with the particles plateaued with increasing F127 concentration above the critical aggregation concentration. Hence the free concentration of F127 in the dispersion medium was proposed as a key factor governing association below the CMC, and partitioning of F127 between micelles and particles occurred above the CMC. The association of F127 with the particles was irreversible on dilution. The F127 associated with both the external and internal surfaces of the phytantriol cubosomes. The effects of lipid and F127 concentration, lipid type, dilution of the dispersions and internal nanostructure were also elucidated. A greater amount of F127 was associated with cubosomes comprised of glyceryl monooleate (GMO) than those prepared using phytantriol. Hexosomes prepared using a mixture of phytantriol and vitamin E acetate (vitEA) had a greater amount of F127 associated with them than phytantriol cubosomes. Hexosomes prepared using selachyl alcohol had less F127 associated with them than phytantriol:vitEA-based hexosomes and GMO-based cubosomes. This indicated that both the lipid from which the particles are composed and the particle internal nanostructure have an influence on the association of F127 with lyotropic liquid crystalline nanostructured particles. PMID:23137909

  15. Reversible switching of liquid crystal micro-particles in a nematic liquid crystal.

    PubMed

    Imamura, Koki; Yoshida, Hiroyuki; Ozaki, Masanori

    2016-01-21

    Liquid crystal micro-particles are functional materials possessing optical and dielectric anisotropies originating from the arrangement of rod-like molecules within the particles. Although they can be switched by an electric field, particles dispersed in isotropic hosts usually cannot return to their original state, because there is no restoration force acting on the particles. Here, we describe reversible switching of liquid crystal micro-particles by dispersing them in a nematic liquid crystal host. We fabricate square micro-particles with unidirectional molecular alignment and investigate their static and dynamic electro-optic properties by applying an in-plane electric field. The behavior of the micro-particles is well-described by the theoretical model we construct, making this study potentially useful for the development of liquid crystal-liquid crystal particle composites with engineered properties. PMID:26514389

  16. High Magnetic Field-Induced Birefringence in Lyotropic Chromonic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Ostapenko, T.; Nastishin, Yu.; Gleeson, J. T.; Sprunt, S. N.; Lavrentovich, O. D.; Collings, P. J.

    2009-03-01

    We studied the effect of magnetic-field induced birefringence of a 14% solution of disodium cromoglycate (DSCG) in water at temperatures above the nematic-isotropic coexistence region. According to Landau-deGennes mean field theory, we expect to find a linear relationship between the inverse of the induced birefringence, δn, and the quantity (T-T*), where T* is the stability limit of the isotropic phase. Using the 31 T resistive magnet at the National High Magnetic Field Laboratory, we observed that, as we increase the temperature above the coexistence region, we deviate from this linear dependence. Our data shows that δn goes to zero, whereas Landau-deGennes predicts that δn should decrease asymptotically. This may be due to the lack of isodesmic aggregate formation at a finite temperature above the coexistence region.Supported by NSF (DMR-0710544 and DMR-0606160). Work performed at NHMFL, supported by NSF cooperative agreements DMR-0084173, the State of Florida and the DOE.

  17. Long Range Order of Motile Defects in Active Nematic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Decamp, Stephen; Redner, Gabriel; Hagan, Michael; Dogic, Zvonimir

    2015-03-01

    Active 2D nematic liquid crystals exist in a dynamical steady state in which +1/2 and -1/2 defects are spontaneously generated and annihilated at a constant rate. Active stresses in the material are thought to destroy nematic order through the generation of these defects. We present an active nematic mesophase in which motile defects of charge +1/2 spontaneously acquire long range order. The system is composed of microtubule filaments and kinesin motor protein clusters which are confined to a flat, 2D oil-water interface. The addition of ATP results in microtubule bundles which exhibit kinesin-driven extensile motion. By tuning the density of the nematic material at the 2D interface, we can tune the order parameter of the +1/2 defect ordered mesophase. Additionally, the defect alignment persists over samples at the centimeter scale.

  18. Recent developments of analysis for hydrodynamic flow of nematic liquid crystals

    PubMed Central

    Lin, Fanghua; Wang, Changyou

    2014-01-01

    The study of hydrodynamics of liquid crystals leads to many fascinating mathematical problems, which has prompted various interesting works recently. This article reviews the static Oseen–Frank theory and surveys some recent progress on the existence, regularity, uniqueness and large time asymptotic of the hydrodynamic flow of nematic liquid crystals. We will also propose a few interesting questions for future investigations. PMID:25332384

  19. In situ laser-imprinted surface realignment of a nematic liquid crystal.

    PubMed

    Mirri, Giorgio; Škarabot, Miha; Muševič, Igor

    2015-05-01

    We present a new method for the in-plane realignment of nematic liquid crystals in already fully assembled cells with uni-directionally rubbed polyimide as an aligning layer. We use nematic liquid crystals (NLCs) with a relatively high nematic-isotropic transition temperature and we focus the IR laser beam of the laser tweezers selectively onto one or the other of the inner interfaces. The heat generated by the IR absorption locally melts the liquid crystal and creates an isotropic island with well-defined molecular anchoring at the nematic-isotropic interface. By scanning the laser beam along a pre-defined line, the moving isotropic-nematic interface leaves behind a well oriented LC domain, with LC molecules aligned at 45° to the rubbing direction. If we in addition move the sample with respect to this scanning line, we would be able to selectively realign micro-domains of the liquid crystal with respect to the original alignment induced by the PI rubbing. The realignment can be performed independently on each LC-glass interface, thereby producing predefined domains with customized and controllable alignment within an otherwise uniformly aligned cell. PMID:25790268

  20. Straining soft colloids in aqueous nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Mushenheim, Peter C.; Pendery, Joel S.; Weibel, Douglas B.; Spagnolie, Saverio E.; Abbott, Nicholas L.

    2016-05-01

    Liquid crystals (LCs), because of their long-range molecular ordering, are anisotropic, elastic fluids. Herein, we report that elastic stresses imparted by nematic LCs can dynamically shape soft colloids and tune their physical properties. Specifically, we use giant unilamellar vesicles (GUVs) as soft colloids and explore the interplay of mechanical strain when the GUVs are confined within aqueous chromonic LC phases. Accompanying thermal quenching from isotropic to LC phases, we observe the elasticity of the LC phases to transform initially spherical GUVs (diameters of 2–50 µm) into two distinct populations of GUVs with spindle-like shapes and aspect ratios as large as 10. Large GUVs are strained to a small extent (R/r < 1.54, where R and r are the major and minor radii, respectively), consistent with an LC elasticity-induced expansion of lipid membrane surface area of up to 3% and conservation of the internal GUV volume. Small GUVs, in contrast, form highly elongated spindles (1.54 < R/r < 10) that arise from an efflux of LCs from the GUVs during the shape transformation, consistent with LC-induced straining of the membrane leading to transient membrane pore formation. A thermodynamic analysis of both populations of GUVs reveals that the final shapes adopted by these soft colloids are dominated by a competition between the LC elasticity and an energy (˜0.01 mN/m) associated with the GUV–LC interface. Overall, these results provide insight into the coupling of strain in soft materials and suggest previously unidentified designs of LC-based responsive and reconfigurable materials.

  1. Straining soft colloids in aqueous nematic liquid crystals.

    PubMed

    Mushenheim, Peter C; Pendery, Joel S; Weibel, Douglas B; Spagnolie, Saverio E; Abbott, Nicholas L

    2016-05-17

    Liquid crystals (LCs), because of their long-range molecular ordering, are anisotropic, elastic fluids. Herein, we report that elastic stresses imparted by nematic LCs can dynamically shape soft colloids and tune their physical properties. Specifically, we use giant unilamellar vesicles (GUVs) as soft colloids and explore the interplay of mechanical strain when the GUVs are confined within aqueous chromonic LC phases. Accompanying thermal quenching from isotropic to LC phases, we observe the elasticity of the LC phases to transform initially spherical GUVs (diameters of 2-50 µm) into two distinct populations of GUVs with spindle-like shapes and aspect ratios as large as 10. Large GUVs are strained to a small extent (R/r < 1.54, where R and r are the major and minor radii, respectively), consistent with an LC elasticity-induced expansion of lipid membrane surface area of up to 3% and conservation of the internal GUV volume. Small GUVs, in contrast, form highly elongated spindles (1.54 < R/r < 10) that arise from an efflux of LCs from the GUVs during the shape transformation, consistent with LC-induced straining of the membrane leading to transient membrane pore formation. A thermodynamic analysis of both populations of GUVs reveals that the final shapes adopted by these soft colloids are dominated by a competition between the LC elasticity and an energy (∼0.01 mN/m) associated with the GUV-LC interface. Overall, these results provide insight into the coupling of strain in soft materials and suggest previously unidentified designs of LC-based responsive and reconfigurable materials. PMID:27140607

  2. Colloidal interactions and self-assembly of plasmonic metal pyramids in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Park, Sungoh; Smalyukh, Ivan

    Combining ordered structure of soft matter systems, such as liquid crystals, with the unique optical properties of metal nano- and micro-particles is a promising approach of designing and realizing mesostructured composites with pre-engineered properties. In this work, we disperse nanofabricated pyramid-shaped plasmonic particles in a nematic host fluid and demonstrate that the particles spontaneously align with respect to the uniform far-field liquid crystal director. This alignment is driven by minimization of the surface anchoring and bulk elastic free energies of the nematic host. Interestingly, multiple stable and metastable orientations of these particles can be controllably observed. Using laser tweezers and video microscopy, we explore inter-particle pair interaction forces as well as the ensuing colloidal self-assembly. We analyze this experimentally observed rich physical behavior of our soft matter composite by invoking electrostatic multipole analogy of elastic distortions induced by the particles in a nematic liquid crystal host and discuss potential practical uses.

  3. Instability of a Biaxial Nematic Liquid Crystal Formed by Homeotropic Anchoring on Surface Grooves

    NASA Astrophysics Data System (ADS)

    Zhang, Zhi-Dong; Xuan, Li

    2011-10-01

    A method used to treat the elastic distortion of a uniaxial nematic liquid crystal induced by homogeneous anchoring on the surface grooves is generalized to biaxial nematic liquid crystals under the homeotropic anchoring condition. Employing some approximations for the elastic constants, we obtain an additional term in the elastic energy per unit area which depends on the angle between the minor director at infinity and the direction of the grooves, with a period of π/2. This leads to instability on the surface grooves so that two states with crossed minor directors are energetically indistinguishable. Our theoretical study explains why the homeotropic alignment method developed for uniaxial liquid crystals loses efficacy for biaxial nematics.

  4. Photorefractive Bragg gratings in nematic liquid crystals aligned by a magnetic field

    SciTech Connect

    Wiederrecht, G.P.; Wasielewski, M.R. |

    1999-06-01

    Photorefractive Bragg gratings are observed in low-molar-mass nematic liquid crystals doped with electron donor and acceptor molecules. This is accomplished by alignment of the nematic liquid crystals in a 0.3 T magnetic field, which produces thicker homeotropic aligned samples than traditional surfactant techniques. Grating fringe spacings as low as 3.7 {mu}m are achieved with 176-{mu}m-thick samples, producing grating {ital Q} values of 33. Up to this point, low molar mass nematic liquid crystals have exhibited photorefractive gratings with Q{le}1. Asymmetric two-beam coupling and photoconductivity experiments are performed to verify the photorefractive origin of the gratings. {copyright} {ital 1999 American Institute of Physics.}

  5. Dynamics and Instabilities of an overdamped active nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Putzig, Elias; Baskaran, Aparna

    Active nematics have been studied extensively in the context of suspensions of active particles, with a Stokes equation describing the flow of the surrounding fluid. Here we will present a continuum model of an overdamped (often termed 'dry') active nematic, where activity enters through self-induced flows. These flows represent the ability of the internal forces to convect, shear, or rotate the nematic order. The self-induced shear gives rise to an instability in the homogeneous ordered state which is analogous to that seen in active suspensions. The self-induced rotation gives rise to a new instability. A phase diagram from this model will be presented, and the phenomenology will be compared with what is seen in experimental and simulated active systems. We would like to acknowledge Grant support through NSF (NSF-DMR-1149266), (DMR-0820492), (NIH-5T32EB009419) and IGERT (DGE-1068620).

  6. Orientational optical nonlinearity induced by comb-shaped polymers in a nematic liquid crystal

    SciTech Connect

    Budagovsky, I. A.; Zolot'ko, A. S. Ochkin, V. N.; Smayev, M. P.; Bobrovsky, A. Yu.; Shibaev, V. P.; Barnik, M. I.

    2008-01-15

    The effect of optical orientation in nematic liquid crystals containing small additions of high-molecular compounds, i.e., comb-shaped polymers with light-absorbing azobenzene side fragments, was studied. The effects of light-induced reorientation of the director of nematic liquid crystals caused by light absorption of polymers and a low-molecular compound with a structure similar to side fragments of the polymers were compared in detail. An explanation was proposed for large values of the orientational nonlinearity induced by polymers.

  7. Photoinduced in-plane switching of a photochromic nematic liquid crystal

    SciTech Connect

    Komitov, L.; Yamamoto, J.; Yokoyama, H.

    2001-06-15

    Photoinduced fast in-plane switching of the optic axis of a photochromic nematic liquid crystal is found in a sandwich cell with substrates promoting a twofold degenerate anchoring. The switching process is governed by the modification of the anchoring conditions associated with the photoisomerization of the photochromic nematic liquid crystal. Photoinduced in-plane reorientation of the sample optic axis of about 80{degree} has been found. Together with the model of photoinduced in-plane switching, some implementations of this effect are briefly discussed. {copyright} 2001 American Institute of Physics.

  8. Control on the anomalous interactions of Airy beams in nematic liquid crystals.

    PubMed

    Shen, Ming; Li, Wei; Lee, Ray-Kuang

    2016-04-18

    We reveal a controllable manipulation of anomalous interactions between Airy beams in nonlocal nematic liquid crystals numerically. With the help of an in-phase fundamental Gaussian beam, attraction between in-phase Airy beams can be suppressed or become a repulsive one to each other; whereas the attraction can be strengthened when the Gaussian beam is out-of-phase. In contrast to the repulsive interaction in local media, stationary bound states of breathing Airy soliton pairs are found in nematic liquid crystals. PMID:27137288

  9. Vitrified chiral-nematic liquid crystalline films for selective reflection and circular polarization

    SciTech Connect

    Katsis, D.; Chen, P.H.M.; Mastrangelo, J.C.; Chen, S.H.; Blanton, T.N.

    1999-06-01

    Nematic and left-handed chiral-nematic liquid crystals comprising methoxybiphenylbenzoate and (S)-(-)-1-phenylethylamine pendants to a cyclohexane core were synthesized and characterized. Although pristine samples were found to be polycrystalline, thermal quenching following heating to and annealing at elevated temperatures permitted the molecular orders characteristic of liquid crystalline mesomorphism to be frozen in the glassy state. Left at room temperature for 6 months, the vitrified liquid crystalline films showed no evidence of recrystallization. An orientational order parameter of 0.65 was determined with linear dichroism of a vitrified nematic film doped with Exalite 428 at a mole fraction of 0.0025. Birefringence dispersion of a blank vitrified nematic film was determined using a phase-difference method complemented by Abbe refractometry. A series of vitrified chiral-nematic films were prepared to demonstrate selective reflection and circular polarization with a spectral region tunable from blue to the infrared region by varying the chemical composition. The experimentally measured circular polarization spectra were found to agree with the Good-Karali theory in which all four system parameters were determined a priori: optical birefringence, average refractive index, selective reflection wavelength, and film thickness.

  10. Deuterium NMR investigations of field-induced director alignment in nematic liquid crystals.

    PubMed

    Sugimura, Akihiko; Luckhurst, Geoffrey R

    2016-05-01

    There have been many investigations of the alignment of nematic liquid crystals by either a magnetic and/or an electric field. The basic features of the important hydrodynamic processes for low molar mass nematics have been characterized for the systems in their equilibrium and non-equilibrium states. These have been created using electric and magnetic fields to align the director and deuterium nuclear magnetic resonance ((2)H NMR) spectroscopy has been used to explore this alignment. Theoretical models based on continuum theory have been developed to complement the experiments and found to describe successfully the static and the dynamic phenomena observed. Such macroscopic behaviour has been investigated with (2)H NMR spectroscopy, in which an electric field in addition to the magnetic field of the spectrometer is used to rotate the director and produce a non-equilibrium state. This powerful technique has proved to be especially valuable for the investigation of nematic liquid crystals. Since the quadrupolar splitting for deuterons observed in the liquid crystal phase is determined by the angle between the director and the magnetic field, time-resolved and time-averaged (2)H NMR spectroscopies can be employed to investigate the dynamic director alignment process in a thin nematic film following the application or removal of an electric field. In this article, we describe some seminal studies to illustrate the field-induced static and dynamic director alignment for low molar mass nematics. PMID:27247284

  11. Anisotropic mechanical properties of a polymer nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Taratuta, Victor G.; Lonberg, Franklin; Meyer, Robert B.

    1988-03-01

    A concentration dependence of elastic and viscous properties of nematic poly-γ-benzyl glutamate (PBG) was studied experimentally. The splay and bend constants are similar in magnitude, both linear in concentration. The twist constant is much smaller and constant. Viscosities exhibit large anisotropies. γ1 and ηc are roughly quadratic in concentration, ηa is linear, while ηb is constant. The data are self-consistently interpreted in terms of the theoretical models for nematics of semi flexible chains rather than those of rigid rods.

  12. Edge pinning and transformation of defect lines induced by faceted colloidal rings in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Senyuk, Bohdan; Liu, Qingkun; Yuan, Ye; Smalyukh, Ivan I.

    2016-06-01

    Nematic colloids exhibit a large diversity of topological defects and structures induced by colloidal particles in the orientationally ordered liquid crystal host fluids. These defects and field configurations define elastic interactions and medium-mediated self-assembly, as well as serve as model systems in exploiting the richness of interactions between topologies and geometries of colloidal surfaces, nematic fields, and topological singularities induced by particles in the nematic bulk and at nematic-colloidal interfaces. Here we demonstrate formation of quarter-strength surface-pinned disclinations, as well as a large variety of director field configurations with splitting and reconnections of singular defect lines, prompted by colloidal particles with sharp edges and size large enough to define strong boundary conditions. Using examples of faceted ring-shaped particles of genus g =1 , we explore transformation of defect lines as they migrate between locations in the bulk of the nematic host to edge-pinned locations at the surfaces of particles and vice versa, showing that this behavior is compliant with topological constraints defined by mathematical theorems. We discuss how transformation of bulk and surface defect lines induced by faceted colloids can enrich the diversity of elasticity-mediated colloidal interactions and how these findings may impinge on prospects of their controlled reconfigurable self-assembly in nematic hosts.

  13. Edge pinning and transformation of defect lines induced by faceted colloidal rings in nematic liquid crystals.

    PubMed

    Senyuk, Bohdan; Liu, Qingkun; Yuan, Ye; Smalyukh, Ivan I

    2016-06-01

    Nematic colloids exhibit a large diversity of topological defects and structures induced by colloidal particles in the orientationally ordered liquid crystal host fluids. These defects and field configurations define elastic interactions and medium-mediated self-assembly, as well as serve as model systems in exploiting the richness of interactions between topologies and geometries of colloidal surfaces, nematic fields, and topological singularities induced by particles in the nematic bulk and at nematic-colloidal interfaces. Here we demonstrate formation of quarter-strength surface-pinned disclinations, as well as a large variety of director field configurations with splitting and reconnections of singular defect lines, prompted by colloidal particles with sharp edges and size large enough to define strong boundary conditions. Using examples of faceted ring-shaped particles of genus g=1, we explore transformation of defect lines as they migrate between locations in the bulk of the nematic host to edge-pinned locations at the surfaces of particles and vice versa, showing that this behavior is compliant with topological constraints defined by mathematical theorems. We discuss how transformation of bulk and surface defect lines induced by faceted colloids can enrich the diversity of elasticity-mediated colloidal interactions and how these findings may impinge on prospects of their controlled reconfigurable self-assembly in nematic hosts. PMID:27415331

  14. The inherent dynamics of isotropic- and nematic-phase liquid crystals

    NASA Astrophysics Data System (ADS)

    Frechette, Layne; Stratt, Richard M.

    2016-06-01

    The geodesic (shortest) pathways through the potential energy landscape of a liquid can be thought of as defining what its dynamics would be if thermal noise were removed, revealing what we have called the "inherent dynamics" of the liquid. We show how these inherent paths can be located for a model liquid crystal former, showing, in the process, how the molecular mechanisms of translation and reorientation compare in the isotropic and nematic phases of these systems. These mechanisms turn out to favor the preservation of local orientational order even under macroscopically isotropic conditions (a finding consistent with the experimental observation of pseudonematic domains in these cases), but disfavor the maintenance of macroscopic orientational order, even in the nematic phase. While the most efficient nematic pathways that maintain nematic order are indeed shorter than those that do not, it is apparently difficult for the system to locate these paths, suggesting that molecular motion in liquid-crystal formers is dynamically frustrated, and reinforcing the sense that there are strong analogies between liquid crystals and supercooled liquids.

  15. The inherent dynamics of isotropic- and nematic-phase liquid crystals.

    PubMed

    Frechette, Layne; Stratt, Richard M

    2016-06-21

    The geodesic (shortest) pathways through the potential energy landscape of a liquid can be thought of as defining what its dynamics would be if thermal noise were removed, revealing what we have called the "inherent dynamics" of the liquid. We show how these inherent paths can be located for a model liquid crystal former, showing, in the process, how the molecular mechanisms of translation and reorientation compare in the isotropic and nematic phases of these systems. These mechanisms turn out to favor the preservation of local orientational order even under macroscopically isotropic conditions (a finding consistent with the experimental observation of pseudonematic domains in these cases), but disfavor the maintenance of macroscopic orientational order, even in the nematic phase. While the most efficient nematic pathways that maintain nematic order are indeed shorter than those that do not, it is apparently difficult for the system to locate these paths, suggesting that molecular motion in liquid-crystal formers is dynamically frustrated, and reinforcing the sense that there are strong analogies between liquid crystals and supercooled liquids. PMID:27334177

  16. Nanofabrication of highly ordered, tunable metallic mesostructures via quasi-hard-templating of lyotropic liquid crystals

    PubMed Central

    Zhang, Xinyi; Lu, Wei; Dai, Jiyan; Bourgeois, Laure; Yao, Jianfeng; Wang, Huanting; Friend, James R.; Zhao, Dongyuan; MacFarlane, Douglas R.

    2014-01-01

    The synthesis of metal frameworks perforated with nanotunnels is a challenge because metals have high surface energies that favor low surface area structures; traditional liquid-crystal templating techniques cannot achieve the synthetic control required. We report a synthetic strategy to fabricate metal nanomaterials with highly ordered, tunable mesostructures in confined systems based on a new quasi-hard-templating liquid-crystals mechanism. The resulting platinum nanowires exhibit long range two-dimensional hexagonally ordered mesopore structures. In addition, single crystalline hexagonal mesoporous platinum nanowires with dominant {110} facets have been synthesized. Finally, we demonstrate that the mesostructures of metal nanomaterials can be tuned from hexagonal to lamellar mesostructures. PMID:25502015

  17. Chiral conglomerates observed for a binary mixture of a nematic liquid crystal trimer and 6OCB.

    PubMed

    Yoshizawa, Atsushi; Kato, Yusuke; Sasaki, Haruna; Takanishi, Yoichi; Yamamoto, Jun

    2015-12-01

    Dark conglomerates of domains with opposite handedness, which are designated as dark conglomerate phases (DC phases), have attracted much attention. After designing an achiral liquid crystal trimer, 4,4′-bis{7-[4-(5-octyloxypyrimidin-2-yl)phenyloxy]heptyloxy}biphenyl (1), which exhibits only a nematic phase, we prepared binary mixtures with some typical rod-like nematic liquid crystals, i.e., 4′-hexyloxy-4-cyanobiphenyl (6OCB), 2-(4-hexyloxyphenyl)-5-pentyloxypyrimidine (PPY), or 4-methyloxyphenyl 4-hexyloxycyclohexanecarboxylate (PCA), and investigated their phase transition behaviour. The binary mixtures containing 55–90 mol% of 6OCB were found to exhibit a nematic phase and a DC phase of chiral domains with opposite handedness. However, neither PPY nor PCA induced such a chiral conglomerate phase in the mixture with trimer 1. We discuss how core–core interactions contribute to produce such a chiral conglomerate phase. PMID:26395546

  18. Self-assembly via branching morphologies in nematic liquid-crystal nanocomposites

    NASA Astrophysics Data System (ADS)

    Gurevich, Sebastian; Soule, Ezequiel; Rey, Alejandro; Reven, Linda; Provatas, Nikolas

    2014-08-01

    We demonstrate that the morphological diversity in liquid-crystal hybrid systems is much richer than previously anticipated. More importantly, we reveal the existence of a dual mechanism for self-assembly of nanoparticles via morphological instabilities at phase boundaries. Using numerical simulations, we study the growth of isolated nematic droplets in an isotropic liquid crystal (LC) doped with nanoparticles (NPs) and provide insight into the nature of microstructure evolution in LC hybrids. Our work expands the numerically accessible time and length scales in these systems, capturing morphologies which develop under the competition of nonequilibrium elastic interactions, diffusive instabilities mediated by NP transport, and the anisotropy of the nematic field. By mapping nematic morphologies, we also propose a methodology for estimating various important LC material parameters that are difficult to obtain experimentally.

  19. Shape-controlled orientation and assembly of colloids with sharp edges in nematic liquid crystals.

    PubMed

    Beller, Daniel A; Gharbi, Mohamed A; Liu, Iris B

    2015-02-14

    The assembly of colloids in nematic liquid crystals via topological defects has been extensively studied for spherical particles, and investigations of other colloid shapes have revealed a wide array of new assembly behaviors. We show, using Landau-de Gennes numerical modeling, that nematic defect configurations and colloidal assembly can be strongly influenced by fine details of colloid shape, in particular the presence of sharp edges. For cylinder, microbullet, and cube colloid geometries, we obtain the particles' equilibrium alignment directions and effective pair interaction potentials as a function of simple shape parameters. We find that defects pin at sharp edges, and that the colloid consequently orients at an oblique angle relative to the far-field nematic director that depends on the colloid's shape. This shape-dependent alignment, which we confirm in experimental measurements, raises the possibility of selecting self-assembly outcomes for colloids in liquid crystals by tuning particle geometry. PMID:25523158

  20. Seeing and Sculpting Nematic Liquid Crystal Textures with the Thom construction

    NASA Astrophysics Data System (ADS)

    Chen, Bryan; Alexander, Gareth

    2012-02-01

    Nematic liquid crystals are the foundation for modern display technology and also exhibit topological defects that can readily be seen under a microscope. Recently, experimentalists have been able to create and control several new families of interesting defect textures, including reconfigurably knotted defect lines around colloids (Ljubljana) and the ``toron,'' a pair of hedgehogs bound together with a ring of double-twist between them (CU Boulder). We apply the Thom construction from algebraic topology to visualize 3 dimensional molecular orientation fields as certain colored surfaces in the sample. These surfaces turn out to be a generalization to 3 dimensions of the dark brushes seen in Schlieren textures of two-dimensional samples of nematics. Manipulations of these surfaces correspond to deformations of the nematic orientation fields, giving a hands-on way to classify liquid crystal textures which is also easily computable from data and robust to noise.

  1. Possible enhancement of physical properties of nematic liquid crystals by doping of conducting polymer nanofibres

    NASA Astrophysics Data System (ADS)

    Manda, R.; Dasari, V.; Sathyanarayana, P.; Rasna, M. V.; Paik, P.; Dhara, Surajit

    2013-09-01

    We report on the preparation and physical characterization of the colloidal suspension of conducting polyaniline (PANI) nanofibres and a nematic liquid crystal (5CB). The ac electrical conductivity anisotropy increases significantly and the rotational viscosity decreases with increasing wt. % of PANI nanofibres, while other physical properties such as birefringence, dielectric anisotropy, splay, and bend elastic constants are changed moderately. The high conductivity anisotropy of liquid crystal nano-composites is very useful for magnetically steered liquid crystal-nanofibre switch.

  2. Effects of temperature on the alignment and electrooptical responses of a nematic nanoscale liquid crystalline film.

    PubMed

    Lee, Lay Min; Kwon, Hye J; Nuzzo, Ralph G; Schweizer, Ken S

    2006-08-17

    The surface-induced alignment and electrooptical (EO) dynamics of a 50-nm-thick liquid crystalline (4-n-pentyl-4'-cyanobiphenyl; 5CB) film were studied at three temperatures: 25 and 33 degrees C (near the crystalline-nematic and nematic-isotropic transition temperatures, respectively) and 29 degrees C (a median temperature in the stability region of the nematic phase). The ZnSe surfaces that entrap the liquid crystal (LC) film have been polished unidirectionally to produce a grooved surface presenting nanometer-scale corrugations, a structure that induces a planar and homogeneous orientation in the nematic phase. The present work attempts to understand the influences of temperature on the surface-induced alignment and corresponding EO dynamics of the material. Step-scan time-resolved spectroscopy measurements were made to determine the rate constants for the electric-field-induced orientation and thermal relaxation of the 5CB film. The field-driven orientation rates vary sensitively with temperature across a range that spans the stability limits of the nematic phase; the relaxation rates, however, vary very little across this same temperature range. We propose that these differences in LC behavior arise as consequence of the interplay of the temperature dependence of the elastic constants, viscosity, and degree of orientational order of the LC medium. A simple theoretical model provides some understanding of these behaviors. PMID:16898726

  3. Xanthan Gum-a lyotropic, liquid crystalline polymer and its properties as a suspending agent

    SciTech Connect

    Salamone, J.C.; Clough, S.B.; Jamison, D.E.; Reid, K.I.G.; Salamone, A.B.

    1982-08-01

    Studies a variety of xanthan solutions of various polymer concentrations in the presence and absence of various salts under a polarized light microscope (100X) in order to test xanthan gum for liquid crystalline order. Xanthan gum, a polysaccharide used in drilling fluids and in tertiary recovery, has relatively stable viscosity properties as a function of salt concentration, pH, temperature, and shear degradation. With solutions from 2 to 10% (wt/vol) xanthan gum in distilled water at room temperature, birefringent, ordered domains were observed at 10% concentration, with a decrease in birefringence as the polymer concentration decreased. When the xanthan solution is sheared between a glass slide and a cover slip, the optic axis (chain direction) aligns using the shear direction (as determined by the colors displayed using a first-order red plate). Examines liquid crystalline behavior of other naturally occurring polymers.

  4. Tunable terahertz fishnet metamaterials based on thin nematic liquid crystal layers for fast switching

    PubMed Central

    Zografopoulos, Dimitrios C.; Beccherelli, Romeo

    2015-01-01

    The electrically tunable properties of liquid-crystal fishnet metamaterials are theoretically investigated in the terahertz spectrum. A nematic liquid crystal layer is introduced between two fishnet metallic structures, forming a voltage-controlled metamaterial cavity. Tuning of the nematic molecular orientation is shown to shift the magnetic resonance frequency of the metamaterial and its overall electromagnetic response. A shift higher than 150 GHz is predicted for common dielectric and liquid crystalline materials used in terahertz technology and for low applied voltage values. Owing to the few micron-thick liquid crystal cell, the response speed of the tunable metamaterial is calculated as orders of magnitude faster than in demonstrated liquid-crystal based non-resonant terahertz components. Such tunable metamaterial elements are proposed for the advanced control of electromagnetic wave propagation in terahertz applications. PMID:26272652

  5. Surface charge and interactions of 20-nm nanocolloids in a nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Ryzhkova, A. V.; Škarabot, M.; Muševič, I.

    2015-04-01

    We studied real-time motion of individual 20-nm silica nanoparticles in a thin layer of a nematic liquid crystal using a dark-field optical videomicroscopy. By tracking the positions of individual nanoparticles we observed that particle pair interactions are not only mediated by strong thermal fluctuations of the nematic liquid crystal, but also with a repulsive force of electric origin. We determined the total electric charge of silanated silica particles in the nematic liquid crystal 5CB by observing the electric-force-driven drift. Surprisingly, the surface electric charge density depends on colloidal size and is ˜4.5 ×10-3C/m2 for 20-nm nanocolloids, and two orders of magnitude lower, i.e., ˜2.3 ×10-5C/m2 , for 1 -μ m colloids. We conclude that electrostatic repulsion between like-charged particles prevents the formation of permanent colloidal assemblies of nanometer size. We also observed strong attraction of 20-nm silica nanoparticles to confining polyimide surfaces and larger clusters, which gradually results in complete expulsion of nanoparticles from the nematic liquid crystal to the surfaces of the confining cell.

  6. A new method for solid surface topographical studies using nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Baber, N.; Strugalski, Z.

    1984-03-01

    A new simple method has been developed to investigate the topography of a wide range of solid surfaces using nematic liquid crystals. Polarizing microscopy is employed. The usefulness of the method for detecting weak mechanical effects has been demonstrated. An application in criminology is foreseen.

  7. Nematicons deflection through interaction with disclination lines in chiral nematic liquid crystals

    SciTech Connect

    Laudyn, Urszula A.; Karpierz, Miroslaw A.

    2013-11-25

    In this work, we study experimentally the interaction of spatial optical soliton in chiral nematic liquid crystals with disclination line created in a wedge shaped cell. We show that in most cases the self-confined beam preserves this interaction. We demonstrate that this interaction can be employed for efficient bending of the soliton trajectory, as a result of reflection and refraction.

  8. Surface charge and interactions of 20-nm nanocolloids in a nematic liquid crystal.

    PubMed

    Ryzhkova, A V; Škarabot, M; Muševič, I

    2015-04-01

    We studied real-time motion of individual 20-nm silica nanoparticles in a thin layer of a nematic liquid crystal using a dark-field optical videomicroscopy. By tracking the positions of individual nanoparticles we observed that particle pair interactions are not only mediated by strong thermal fluctuations of the nematic liquid crystal, but also with a repulsive force of electric origin. We determined the total electric charge of silanated silica particles in the nematic liquid crystal 5CB by observing the electric-force-driven drift. Surprisingly, the surface electric charge density depends on colloidal size and is ∼4.5×10(-3)C/m(2) for 20-nm nanocolloids, and two orders of magnitude lower, i.e., ∼2.3×10(-5)C/m(2), for 1-μm colloids. We conclude that electrostatic repulsion between like-charged particles prevents the formation of permanent colloidal assemblies of nanometer size. We also observed strong attraction of 20-nm silica nanoparticles to confining polyimide surfaces and larger clusters, which gradually results in complete expulsion of nanoparticles from the nematic liquid crystal to the surfaces of the confining cell. PMID:25974514

  9. Shear rheology and in-vitro release kinetic study of apigenin from lyotropic liquid crystal.

    PubMed

    Fan, Jun; Liu, Feng; Wang, Zhongni

    2016-01-30

    Apigenin is a flavonoid compound with diverse pharmacological functions which could develop health benefit products, but its formulation is hampered by its poor water solubility and bioavailability. In this paper, in order to overcome these difficulties, apigenin was encapsulated in LLC formed by polyoxyethylene-10-oleyl ether (Brij 97) and sodium deoxycholate (NaDC) mixtures. The hexagonal liquid crystalline phase (H) and the cubic liquid crystalline phase (C) were found in this system. The shear rheology was used to study the structure change with temperature. It was shown that C3 (Brij 97-NaDC/IPM-PEG400/H2O=36:9:55) was C at low temperature. But above 35.6°C, the matrix of C3 completely transformed to polymer solution. The matrix of H3 was H (Brij 97-NaDC:IPM-PEG 400:H2O=50:9:41) below 50°C, but the structural strength change was obvious. Vitro release experiment was used to study drug release kinetics. It was indicated that apigenin encapsulated in LLC conformed to the concentration diffusion model, and cumulative percentage of apigenin released from C3 and H3 had corresponding relationship with the shear rheology at different temperatures. PMID:26657272

  10. Periodic saddle-splay Freedericksz transition in nematic liquid crystals.

    PubMed

    Kralj, S; Rosso, R; Virga, E G

    2005-05-01

    By use of a local stability criterion recently introduced, we predict the existence of a periodic saddle-splay Freedericksz (PSSF) transition that adds to the existing class of classical Freedericksz transitions driven in a nematic cell by an external field. Occurrence of the PSSF transition requires a saddle-splay elastic constant with a large enough magnitude and different anchoring strengths at the plates confining the nematic cell. Otherwise, either the PSSF transition does not occur at all, or it requires a field higher than that associated with the classical aperiodic splay Freedericksz (ASF) transition, in which case it is not observable. Here, we determine the threshold field for which the PSSF precedes the ASF transition, as well as the structure of the destabilizing mode. PMID:15864725

  11. Nematic liquid-crystal alignment on stripe-patterned substrates.

    PubMed

    Anquetil-Deck, C; Cleaver, D J

    2010-09-01

    Here, we use molecular simulation to consider the behavior of a thin nematic film confined between two identical nanopatterned substrates. Using patterns involving alternating stripes of homeotropic-favoring and homogeneous-favoring substrates, we investigate the influence of the relative stripe width and the film thickness. From this, we show that the polar anchoring angle can be varied continuously from planar to homeotropic by appropriate tuning of these parameters. For very thin films with equal stripe widths, we observe orientational bridging, the surface patterning being written in domains which traverse the nematic film. This dual-bridging-domain arrangement breaks down with increase in film thickness, however, being replaced by a single tilted monodomain. Strong azimuthal anchoring in the plane of the stripe boundaries is observed for all systems. PMID:21230093

  12. Novel biaxial nematic phases of side-chain liquid crystalline polymers

    NASA Astrophysics Data System (ADS)

    Matsuyama, Akihiko

    2012-12-01

    We present a mean field theory to describe biaxial nematic phases of side-chain liquid crystalline polymers, in which rigid side-chains (mesogens) and rigid-backbone chains favor mutually perpendicular orientations. Taking into account both excluded volume and attractive interactions between rigid rods, novel biaxial nematic phases are theoretically predicted. We calculate uniaxial and biaxial orientational order parameters as a function of temperature and the length of backbone chains. We find a first-order biaxial-biaxial phase transition and a first (or second)-order uniaxial-biaxial one, depending on the length of mesogens and backbone chains.

  13. Anisotropic Stokes drag and dynamic lift on spheres sedimenting in a nematic liquid crystal.

    PubMed

    Rovner, Joel B; Reich, Daniel H; Leheny, Robert L

    2013-02-19

    The motion of silica spheres with homeotropic anchoring sedimenting within nematic liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) has been studied at low Ericksen number. The magnitude of the spheres' velocity depends on the angle θ between the far-field nematic director and the gravitational force, indicating an anisotropic Stokes drag. When the director is oriented at an oblique angle to the gravitational force, the velocity also acquires a component normal to the force, demonstrating the existence of a lift force generated by the fluid. The magnitude and direction of the velocity as functions of θ quantitatively obey theoretically predicted forms. PMID:23379634

  14. Highly efficient lasing at difference frequencies in a nematic liquid crystal

    SciTech Connect

    Trashkeev, S I; Klementyev, V M; Pozdnyakov, G A

    2008-04-30

    Highly efficient lasing at difference frequencies is obtained in a nematic liquid crystal excited by several visible lines from a cw argon laser with a total power of 0.08-1.5 W. The maximum conversion efficiency was {approx}1% and the quadratic susceptibility was {approx}2x10{sup -6} m V{sup -1}. The field of application of the approximate mechanism of quadratic nonlinearity and frequency conversion considered in the paper requires specification. The nonlinear conversion of radiation in a nematic crystal has specific features compared to lasing at difference frequencies in solid crystals. (nonlinear optical phenomena)

  15. Temperature-tunable lasing in negative dielectric chiral nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Wu, Ri-Na; Wu, Jie; Wu, Xiao-Jiao; Dai, Qin

    2015-05-01

    In this work, negative dielectric nematic liquid crystal SLC12V620-400, chiral dopant S811, and laser dye DCM are used to prepare dye-doped chiral nematic liquid crystal laser sample. In order to investigate temperature-tunable lasing in negative dielectric chiral nematic liquid crystal, we measure the transmission and lasing spectrum of this sample. The photonic band gap (PBG) is observed to red shift with its width reducing from 71.2 nm to 40.2 nm, and its short-wavelength band edge moves 55.3 nm while the long-wavelength band edge only moves 24.9 nm. The wavelength of output laser is found to red shift from 614.4 nm at 20 °C to 662.8 nm at 67 °C, which is very different from the previous experimental phenomena. The refractive indices, parallel and perpendicular to the director in chiral nematic liquid crystal have different dependencies on temperature. The experiment shows that the pitch of this chiral nematic liquid crystal increases with the increase of temperature. The decrease in the PBG width, different shifts of band edges, and the red shift of laser wavelength are the results of refractive indices change and pitch thermal elongation. Project supported by the National Natural Science Foundation of China (Grant No. 61378042), the Outstanding Young Scholars Growth Plans of Colleges and Universities in Liaoning Province, China (Grant No. LJQ2013022), the Science and Technology Research of Liaoning Province, China (Grant No. L2010465), the Open Funds of Liaoning Province Key Laboratory of Laser and Optical Information of Shenyang Ligong University, China.

  16. Crystallization upon thermal annealing of a glass-forming liquid crystal in the nematic regime

    SciTech Connect

    Mastrangelo, J.C. |; Blanton, T.N.; Chen, S.H. |

    1995-04-24

    As an example of a novel class of glass-forming liquid crystals, compound (I) was synthesized and characterized to possess a nematic mesophase between {ital T}{sub {ital g}} and {ital T}{sub {ital c}} as the pristine crystal was heated beyond its {ital T}{sub {ital m}} followed by quenching to below room temperature. Differential scanning calorimetry (DSC) and x-ray diffraction techniques were employed to investigate its morphological stability. It was found that the nematic mesophase persists upon annealing for a period of up to 22 h without the appearance of new phases. However, after annealing in the nematic regime over a longer period of time, thermally activated phase transformations were observed, resulting in a new crystalline phase plus the pristine crystalline phase based on DSC thermal transition data and x-ray diffraction patterns.

  17. Director orientation of nematic liquid crystal using orientated nanofibers obtained by electrospinning

    NASA Astrophysics Data System (ADS)

    Toan, Duong Quoc; Ozaki, Ryotaro; Moritake, Hiroshi

    2014-01-01

    Nanofibers with diameters less than 1000 nm assembled by electrospinning and with a large surface area per unit mass have been attracting considerable attention and are expected to affect the orientation of liquid crystals (LCs). Firstly, to determine the orientated nanofibers on an indium-tin-oxide (ITO) glass surface, the spectral analysis technique of using fast Fourier transform is applied. Optical observation is performed to confirm the orientation of LC molecules in a twisted nematic LC cell. Finally, optical measurement of an LC cell is carried out to estimate the threshold voltage of the LC in two types of twisted nematic LC cell: one with rubbed polyimide and the other with orientated nanofibers as the alignment layer. A twisted nematic LC is oriented in the cell using orientated nanofibers as the alignment layer and the threshold voltage of this cell agrees with that of the conventional polyimide rubbed cell.

  18. Regular and chaotic states in a local map description of sheared nematic liquid crystals.

    PubMed

    Kamil, S M; Sinha, Sudeshna; Menon, Gautam I

    2008-07-01

    We propose and study a local map capable of describing the full variety of dynamical states, ranging from regular to chaotic, obtained when a nematic liquid crystal is subjected to a steady shear flow. The map is formulated in terms of a quaternion parametrization of rotations of the local frame described by the axes of the nematic director, subdirector, and the joint normal to these, with two additional scalars describing the strength of ordering. Our model yields kayaking, wagging, tumbling, aligned, and coexistence states, accommodated in a phase diagram which closely resembles phase diagrams obtained using representations of the dynamics which are based on ordinary differential equations. We also study the behavior of the map under periodic perturbations of the shear rate. Such a map can serve as a building block for the construction of lattice models of the complex spatiotemporal states predicted for sheared nematics. PMID:18763972

  19. Healing of Defects at the Interface of Nematic Liquid Crystals and Structured Langmuir-Blodgett Monolayers

    NASA Astrophysics Data System (ADS)

    Petit-Garrido, Núria; Trivedi, Rahul P.; Ignés-Mullol, Jordi; Claret, Josep; Lapointe, Clayton; Sagués, Francesc; Smalyukh, Ivan I.

    2011-10-01

    We use Langmuir-Blodgett molecular monolayers and nematic liquid crystals as model two- and three-dimensional orientationally ordered systems to study the stability and healing of topological defects at their contact interfaces. Integer-strength defects at the monolayer induce disclinations of similar strength in the nematic that, however, do not propagate deep into the bulk, but rather form single- or double-split arch-shaped loops pinned to the interface. This behavior is qualitatively independent of the far-field director orientation and involves either half-integer singular or twist-escaped unity-strength nonsingular nematic disclinations. These two defect configurations can be selected by varying sample preparation given their comparable free energy, consistently with direct probing by use of laser tweezers.

  20. Anisotropic Stokes Drag and Dynamic Lift on Cylindrical Colloids in a Nematic Liquid Crystal

    NASA Astrophysics Data System (ADS)

    Rovner, Joel; Lapointe, Clayton; Reich, Daniel; Leheny, Robert

    2011-03-01

    Unlike isotropic fluids, nematic liquid crystals exhibit a complex assortment of hydrodynamic properties that can strongly depend on the director field and local boundary conditions set by inclusions. To understand further these characteristics, measurements were taken of the Stokes drag on magnetic nanowires suspended in nematic 4-cyano-4'-pentylbiphenyl (5CB). Effective drag viscosities for wires moving perpendicular and parallel to the nematic director were measured and were found to differ by factors of approximately 0.88 to 2.4, depending on the wire orientation and surface anchoring. Additionally, a lift force was observed when wires were forced at an oblique angle to the director resulting in motion divergent from the line of force. The lift was greater for wires with homeotropic anchoring and smaller for wires with longitudinal anchoring, suggesting that the lift force can act as a mechanism for sorting colloidal particles according to their surface chemistry.

  1. Thermal and optical study of semiconducting CNTs-doped nematic liquid crystalline material

    NASA Astrophysics Data System (ADS)

    Vimal, T.; Singh, D. P.; Gupta, S. K.; Pandey, S.; Agrahari, K.; Manohar, R.

    2016-06-01

    We report the thermal and spectroscopic analysis of the carbon nanotubes (CNTs)-doped nematic liquid crystal (NLC) material. The CNTs have been oriented in the p-ethoxybenzylidene p-butylaniline NLC. The thermal study of the CNTs doped nematic mixtures shows a significant decrease in the isotropic to nematic phase transition temperature. However higher doping concentration of CNTs has led to the further increase in transition temperature. The UV-Visible spectroscopy has been attempted on the CNTs/NLC mixtures at room temperature. The investigated NLC present one absorption band corresponding to π-π* electronic transition. A red shift of λmax with the increasing concentration of CNTs in the mixture has been observed. The band gap of NLC has been found to decrease after the doping of CNTs. The absorbance was measured for the UV light, polarized parallel and perpendicular to the LC director in the planar aligned cell.

  2. Dynamics of ordered colloidal particle monolayers at nematic liquid crystal interfaces.

    PubMed

    Wei, Wei-Shao; Gharbi, Mohamed Amine; Lohr, Matthew A; Still, Tim; Gratale, Matthew D; Lubensky, T C; Stebe, Kathleen J; Yodh, A G

    2016-05-25

    We prepare two-dimensional crystalline packings of colloidal particles on surfaces of the nematic liquid crystal (NLC) 5CB, and we investigate the diffusion and vibrational phonon modes of these particles using video microscopy. Short-time particle diffusion at the air-NLC interface is well described by a Stokes-Einstein model with viscosity similar to that of 5CB. Crystal phonon modes, measured by particle displacement covariance techniques, are demonstrated to depend on the elastic constants of 5CB through interparticle forces produced by LC defects that extend from the interface into the underlying bulk material. The displacement correlations permit characterization of transverse and longitudinal sound velocities of the crystal packings, as well as the particle interactions produced by the LC defects. All behaviors are studied in the nematic phase as a function of increasing temperature up to the nematic-isotropic transition. PMID:27109759

  3. Wrinkling of a thin film on a nematic liquid-crystal elastomer.

    PubMed

    Soni, Harsh; Pelcovits, Robert A; Powers, Thomas R

    2016-07-01

    Wrinkles commonly develop in a thin film deposited on a soft elastomer substrate when the film is subject to compression. Motivated by recent experiments [Agrawal et al., Soft Matter 8, 7138 (2012)]1744-683X10.1039/c2sm25734c that show how wrinkle morphology can be controlled by using a nematic elastomer substrate, we develop the theory of small-amplitude wrinkles of an isotropic film atop a nematic elastomer. The directors of the nematic elastomer are initially uniform. For uniaxial compression of the film along the direction perpendicular to the elastomer directors, the system behaves as a compressed film on an isotropic substrate. When the uniaxial compression is along the direction of nematic order, we find that the soft elasticity characteristic of liquid-crystal elastomers leads to a critical stress for wrinkling which is very small compared to the case of an isotropic substrate. We also determine the wavelength of the wrinkles at the critical stress and show how the critical stress and wavelength depend on substrate depth and the anisotropy of the polymer chains in the nematic elastomer. PMID:27575192

  4. Wrinkling of a thin film on a nematic liquid-crystal elastomer

    NASA Astrophysics Data System (ADS)

    Soni, Harsh; Pelcovits, Robert A.; Powers, Thomas R.

    2016-07-01

    Wrinkles commonly develop in a thin film deposited on a soft elastomer substrate when the film is subject to compression. Motivated by recent experiments [Agrawal et al., Soft Matter 8, 7138 (2012)], 10.1039/c2sm25734c that show how wrinkle morphology can be controlled by using a nematic elastomer substrate, we develop the theory of small-amplitude wrinkles of an isotropic film atop a nematic elastomer. The directors of the nematic elastomer are initially uniform. For uniaxial compression of the film along the direction perpendicular to the elastomer directors, the system behaves as a compressed film on an isotropic substrate. When the uniaxial compression is along the direction of nematic order, we find that the soft elasticity characteristic of liquid-crystal elastomers leads to a critical stress for wrinkling which is very small compared to the case of an isotropic substrate. We also determine the wavelength of the wrinkles at the critical stress and show how the critical stress and wavelength depend on substrate depth and the anisotropy of the polymer chains in the nematic elastomer.

  5. Topological defects around a spherical nanoparticle in nematic liquid crystal: coarse-grained molecular dynamics simulations.

    PubMed

    Ilnytskyi, Jaroslav M; Trokhymchuk, Andrij; Schoen, Martin

    2014-09-21

    We consider the applicability of coarse-grained molecular dynamics for the simulation of defects in a nematic liquid crystal around a colloidal particle. Two types of colloids are considered, a soft colloid resembling a liquid crystal dendrimer or a similar macromolecule. In addition, a decorated colloid is used which could represent a gold nanoparticle with mesogen-modified surface. For both models we consider homeotropic and tangential anchoring. Precise control of the easy axis on the colloid's surface enables us to focus on specific planar arrangements in the case of a decorated colloid. The nematic phase is modelled explicitly via soft spherocylinders interacting through a potential, suggested by Lintuvuori and Wilson [J. Chem. Phys. 128, 044906 (2008)]. Properties of the nematic phase are studied by computing the Frank elastic constants. In addition, estimates for the nematic-isotropic transition and the coherence length allow us to establish a relation between energy and length scales with respect to experimental systems. Both models exhibit similar defect topologies, namely, that of a Saturn ring and a boojum-type of defect for homeotropic and tangential surface anchoring, respectively. In the decorated colloid model we tune the anchoring strength through the density of the mesogenic shell on the surface. We also found the biaxial boojum defect for the special case of longitudinal planar anchoring. The study demonstrates the potential of coarse-grained simulation methods for studying defects in liquid crystals. PMID:25240368

  6. Nanoparticle doping in nematic liquid crystals: distinction between surface and bulk effects by numerical simulations.

    PubMed

    Urbanski, Martin; Mirzaei, Javad; Hegmann, Torsten; Kitzerow, Heinz-S

    2014-05-19

    Doping nematic liquid crystals with small amounts of nanoparticles can significantly alter the electro-optic response of the nematic host. Some of these effects result from nanoparticles influencing the liquid crystal/substrate interface, while other effects are caused by nanoparticles in the bulk. So far, little attention has been paid to the influence of surface interactions on the determination of bulk properties. In the present study, these effects are investigated experimentally and confirmed by numerical simulations. The splay-type Fréedericksz-transition of the nematic liquid crystal 5CB doped with CdSe quantum dots is investigated, as these dispersions are known from earlier studies to affect the initial alignment layers. In comparison, dispersions of chemically and thermally stable silanized gold nanoparticles in the apolar nematic host FELIX-2900-03 are analyzed, which are expected to be bulk-active only. A data fitting routine is presented which allows a distinction between bulk and surface effects of nanoparticle doping. For the quantum dots, an increase of pretilt angle proportional to the doping concentration is found, as well as a slight decrease of the anchoring energy of molecules at the confining substrates. The silanized gold particles show no influence on the boundary conditions up to doping concentrations of 2.5 % (w). For higher concentrations an increase of pretilt angle is reported. PMID:24482304

  7. Solvation Dynamics in Different Phases of the Lyotropic Liquid Crystalline System.

    PubMed

    Roy, Bibhisan; Satpathi, Sagar; Gavvala, Krishna; Koninti, Raj Kumar; Hazra, Partha

    2015-09-01

    Reverse hexagonal (HII) liquid crystalline material based on glycerol monooleate (GMO) is considered as a potential carrier for drugs and other important biomolecules due to its thermotropic phase change and excellent morphology. In this work, the dynamics of encapsulated water, which plays important role in stabilization and formation of reverse hexagonal mesophase, has been investigated by time dependent Stokes shift method using Coumarin-343 as a solvation probe. The formation of the reverse hexagonal mesophase (HII) and transformation to the L2 phase have been monitored using small-angle X-ray scattering and polarized light microscopy experiments. REES studies suggest the existence of different polar regions in both HII and L2 systems. The solvation dynamics study inside the reverse hexagonal (HII) phase reveals the existence of two different types of water molecules exhibiting dynamics on a 120-900 ps time scale. The estimated diffusion coefficients of both types of water molecules obtained from the observed dynamics are in good agreement with the measured diffusion coefficient collected from the NMR study. The calculated activation energy is found to be 2.05 kcal/mol, which is associated with coupled rotational-translational water relaxation dynamics upon the transition from "bound" to "quasi-free" state. The observed ∼2 ns faster dynamics of the L2 phase compared to the HII phase may be associated with both the phase transformation as well as thermotropic effect on the relaxation process. Microviscosities calculated from time-resolved anisotropy studies infer that the interface is almost ∼22 times higher viscous than the central part of the cylinder. Overall, our results reveal the unique dynamical features of water inside the cylinder of reverse hexagonal and inverse micellar phases. PMID:26258397

  8. Nonionic amphiphile nanoarchitectonics: self-assembly into micelles and lyotropic liquid crystals

    NASA Astrophysics Data System (ADS)

    Shrestha, Lok Kumar; Strzelczyk, Karolina Maria; Goswami Shrestha, Rekha; Ichikawa, Kotoko; Aramaki, Kenji; Hill, Jonathan P.; Ariga, Katsuhiko

    2015-05-01

    Amphiphiles, molecules that possess both hydrophilic and hydrophobic moieties, are architecturally simple molecules that can spontaneously self-assemble into complex hierarchical structures from lower to higher dimensions either in the bulk phase or at an interface. Recent developments in multifunctional nanostructure design using the advanced concept of nanoarchitectonics utilize this simple process of assembly. Amphiphilic self-assemblies involving lipids or proteins mimic the structure of biological systems, thus highlighting the necessity of a fundamental physical understanding of amphiphilic self-assembly towards a realization of the complex mechanisms operating in nature. Herein, we describe self-assembled microstructures of biocompatible and biodegradable tetraglycerol lauryl ether (C12G4) nonionic surfactant in an aqueous solvent system. Temperature-composition analyses of equilibrium phases identified by using small-angle x-ray scattering (SAXS) provide strong evidence of various spontaneously self-assembled mesostructures, such as normal micelles (Wm), hexagonal liquid crystal (H1), and reverse micelles (Om). In contrast to conventional poly(oxyethylene) nonionic surfactants, C12G4 did not exhibit the clouding phenomenon at higher temperatures (phase separation was not observed up to 100 °C), demonstrating the greater thermal stability of the self-assembled mesophases. Generalized indirect Fourier transformation (GIFT) evaluation of the SAXS data confirmed the formation of core-shell-type spherical micelles with a maximum dimension ca. 8.7 nm. The shape and size of the C12G4 micelles remained apparently unchanged over a wide range of concentrations (up to 20%), but intermicellar interactions increased and could be described by the Percus-Yevick (PY) theory (after Carnahan and Starling), which provides a very accurate analytical expression for the osmotic pressure of a monodisperse hard sphere.

  9. Nonionic amphiphile nanoarchitectonics: self-assembly into micelles and lyotropic liquid crystals.

    PubMed

    Shrestha, Lok Kumar; Strzelczyk, Karolina Maria; Shrestha, Rekha Goswami; Ichikawa, Kotoko; Aramaki, Kenji; Hill, Jonathan P; Ariga, Katsuhiko

    2015-05-22

    Amphiphiles, molecules that possess both hydrophilic and hydrophobic moieties, are architecturally simple molecules that can spontaneously self-assemble into complex hierarchical structures from lower to higher dimensions either in the bulk phase or at an interface. Recent developments in multifunctional nanostructure design using the advanced concept of nanoarchitectonics utilize this simple process of assembly. Amphiphilic self-assemblies involving lipids or proteins mimic the structure of biological systems, thus highlighting the necessity of a fundamental physical understanding of amphiphilic self-assembly towards a realization of the complex mechanisms operating in nature. Herein, we describe self-assembled microstructures of biocompatible and biodegradable tetraglycerol lauryl ether (C12G4) nonionic surfactant in an aqueous solvent system. Temperature-composition analyses of equilibrium phases identified by using small-angle x-ray scattering (SAXS) provide strong evidence of various spontaneously self-assembled mesostructures, such as normal micelles (Wm), hexagonal liquid crystal (H1), and reverse micelles (Om). In contrast to conventional poly(oxyethylene) nonionic surfactants, C12G4 did not exhibit the clouding phenomenon at higher temperatures (phase separation was not observed up to 100 °C), demonstrating the greater thermal stability of the self-assembled mesophases. Generalized indirect Fourier transformation (GIFT) evaluation of the SAXS data confirmed the formation of core-shell-type spherical micelles with a maximum dimension ca. 8.7 nm. The shape and size of the C12G4 micelles remained apparently unchanged over a wide range of concentrations (up to 20%), but intermicellar interactions increased and could be described by the Percus-Yevick (PY) theory (after Carnahan and Starling), which provides a very accurate analytical expression for the osmotic pressure of a monodisperse hard sphere. PMID:25912881

  10. Nematic quantum phase transition of composite Fermi liquids in half-filled Landau levels and their geometric response

    NASA Astrophysics Data System (ADS)

    You, Yizhi; Cho, Gil Young; Fradkin, Eduardo

    2016-05-01

    We present a theory of the isotropic-nematic quantum phase transition in the composite Fermi liquid arising in half-filled Landau levels. We show that the quantum phase transition between the isotropic and the nematic phase is triggered by an attractive quadrupolar interaction between electrons, as in the case of conventional Fermi liquids. We derive the theory of the nematic state and of the phase transition. This theory is based on the flux attachment procedure, which maps an electron liquid in half-filled Landau levels into the composite Fermi liquid close to a nematic transition. We show that the local fluctuations of the nematic order parameters act as an effective dynamical metric interplaying with the underlying Chern-Simons gauge fields associated with the flux attachment. Both the fluctuations of the Chern-Simons gauge field and the nematic order parameter can destroy the composite fermion quasiparticles and drive the system into a non-Fermi liquid state. The effective-field theory for the isotropic-nematic phase transition is shown to have z =3 dynamical exponent due to the Landau damping of the dense Fermi system. We show that there is a Berry-phase-type term that governs the effective dynamics of the nematic order parameter fluctuations, which can be interpreted as a nonuniversal "Hall viscosity" of the dynamical metric. We also show that the effective-field theory of this compressible fluid has a Wen-Zee-type term. Both terms originate from the time-reversal breaking fluctuation of the Chern-Simons gauge fields. We present a perturbative (one-loop) computation of the Hall viscosity and also show that this term is also obtained by a Ward identity. We show that the topological excitation of the nematic fluid, the disclination, carries an electric charge. We show that a resonance observed in radio-frequency conductivity experiments can be interpreted as a Goldstone nematic mode gapped by lattice effects.

  11. Nematic polymer liquid-crystal wave plate for high-power lasers at 1054 nm

    SciTech Connect

    Kreuzer, F. ); Korenic, E.M.; Jacobs, S.D.; Houghton, J.K.; Schmid, A. )

    1994-04-01

    A nematic polymer liquid crystal is used to construct wave plates for use at 1054 nm. Three methods of wave-plate construction are discussed: double substrate with fiber spacers in homogeneous distribution, double substrate with fiber spacers in annular distribution, and single substrate. The polymer liquid crystal shows high laser-damage resistance, making it particularly useful for high-peak-power laser applications. Alignment techniques and measurement of birefringence for the highly viscous polymer are described.

  12. Switching and intrinsic position bistability of soliton beams in chiral nematic liquid crystals

    SciTech Connect

    Beeckman, Jeroen; Madani, Abbas; Vanbrabant, Pieter J. M.; Henneaux, Pierre; Gorza, Simon-Pierre; Haelterman, Marc

    2011-03-15

    We study theoretically and experimentally the propagation of light beams in chiral nematic liquid crystals. Despite the rather complex refractive index distribution of these crystals, their reorientational nonlinearity can compensate for diffraction, leading to robust solitonlike beams propagating along helical trajectories. We demonstrate that, due to a symmetry-breaking instability of the liquid crystal structure, these beams undergo abrupt switching and bistability, features that are of potential interest for applications to all-optical signal processing.

  13. Unusual temperature dependence of elastic constants of an ambient-temperature discotic nematic liquid crystal.

    PubMed

    Venkata Sai, D; Mirri, G; Kouwer, P H J; Sahoo, R; Musevic, I; Dhara, Surajit

    2016-03-01

    We report the first experimental studies on the temperature dependence of viscoelastic properties of a room temperature discotic nematic liquid crystal. The splay elastic constant is greater than the bend elastic constant and both show unusual temperature and order parameter dependence. The rotational viscosity is remarkably larger than conventional calamitic liquid crystals. We provide a simple physical explanation based on the columnar short-range order to account for the the unusual temperature dependence of the elastic constants. PMID:26883494

  14. Driving voltage properties sensitive to microscale liquid crystal orientation pattern in twisted nematic liquid crystal cells

    NASA Astrophysics Data System (ADS)

    Honma, Michinori; Takahashi, Koki; Yamaguchi, Rumiko; Nose, Toshiaki

    2016-04-01

    We investigated the micropattern-sensitive driving voltage properties of twisted nematic liquid crystal (LC) cells and found that the threshold voltage for inducing the Fréedericksz transition strongly depends on the micropatterned LC molecular orientation state. We discuss the effects of various cell parameters such as the period of the micropattern Λ, the LC layer thickness d, and the twist angle Φ on the threshold voltage. By a computer simulation of the LC molecular orientation, we found that the threshold voltage V th varies in response to the deformation factor Δ (= d 2/Λ2 + Φ2/π2) of the spatially distributed LC molecular orientation. We confirm that V\\text{th}2 is proportional to 1 - Δ from both theoretical and experimental standpoints.

  15. Optical response from dual-frequency hybrid-aligned nematic liquid crystal cells

    NASA Astrophysics Data System (ADS)

    Konshina, E. A.; Vakulin, D. A.; Ivanova, N. L.; Gavrish, E. O.; Vasil'ev, V. N.

    2012-05-01

    Dual-frequency hybrid-aligned nematic liquid crystal cells and the influence of the parameters of a control electric field on their optical response are studied. It is found that the harmonic oscillations of the optical transmission in such cells are observed in the interval between low frequency-to-high frequency voltage switchings unlike in conventional twisted nematic cells. A V-shaped bistable optical response is obtained by successively applying sinusoidal electric fields with frequencies of 1 and 30 kHz to a twisted nematic cell. For a liquid crystal layer 8 μm thick and an applied voltage of 50 V, the response time is 10 ms. In a hybrid-aligned twisted-nematic cell with a large initial tilt angle of the director (about 70°), the V-shaped optical response is observed when the inclined homeotropic state is switched to the twisted state by applying a 30-kHz field. The initial structure of the layer recovers as a result of natural elastic relaxation, and the response time increases roughly fourfold.

  16. Random lasing in dye doped nematic liquid crystals: the role of confinement geometry

    NASA Astrophysics Data System (ADS)

    Strangi, G.; Ferjani, S.; Barna, V.; De Luca, A.; Versace, C.; Scaramuzza, N.; Bartolino, R.

    2007-05-01

    The first experimental evidence of random laser action in a partially ordered, dye doped nematic liquid crystal with long-range dielectric tensor fluctuations is reported. Above a given pump power the fluorescence curve collapses and discrete sharp peaks emerge above the residual spontaneous emission spectrum. The spectral linewidth of these emission peaks is narrow banded, typically around 0.5nm. The unexpected surviving of interference effects in recurrent multiple scattering of the emitted photons provide the required optical feedback for lasing in nematic liquid crystalline materials. Light waves coherent backscattering in orientationally ordered nematics manifests a weak localization, strongly supporting the diffusive laser action phenomenon in the presence of a gain medium. Unlike distributed feedback mirror-less laser, this system can be considered as a cavity-less microlaser where the disorder unexpectedly plays the most important role, behaving as randomly distributed feedback laser. The far field spatial distribution of the emission intensity shows a huge number of bright tiny spots spatially overlapped and the intensity of each pulse strongly fluctuates in time and space. Here, we report the main characteristics of this novel systems for various confinement geometries and under different conditions. A brief presentation of boundary-less systems such as free standing and freely suspended dye doped nematic films and droplets is also introduced, revealing unique emission features because of the complete absence of confining borders.

  17. Electrically Tunable Critically Coupled Terahertz Metamaterial Absorber Based on Nematic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Isić, Goran; Vasić, Borislav; Zografopoulos, Dimitrios C.; Beccherelli, Romeo; Gajić, Radoš

    2015-06-01

    Liquid-crystal devices are a promising cheap alternative for terahertz light modulation, albeit they suffer from problems associated with thick cells. Here we describe a few-micron-thick polarization-independent nematic liquid-crystal metamaterial device displaying terahertz reflectance modulation depths above 23 dB, millisecond response times, low operating voltages, and a spectral tuning of more than 15%. The dramatic performance improvement is based on invoking critical coupling with external fields, which rests on a suitable choice of resonator geometry. We analyze the coupling mechanism to conclude that perfect absorption can be reached with a wide range of parameters and liquid-crystal materials. The proposed device performance, microscopic details, and the nematic molecule switching dynamics are evaluated with the use of a rigorous tensorial formulation of the Landau-de Gennes theory and shown to be robust to small parameter deviations.

  18. Surface-assisted unidirectional orientation of ZnO nanorods hybridized with nematic liquid crystals.

    PubMed

    Kubo, Shoichi; Taguchi, Rei; Hadano, Shingo; Narita, Mamiko; Watanabe, Osamu; Iyoda, Tomokazu; Nakagawa, Masaru

    2014-01-22

    Inorganic semiconductor nanorods are regarded as the primary components of optical and electrical nanoscale devices. In this paper, we demonstrate the unidirectional alignment of monolayered and dispersed ZnO nanorods on a rubbed polyimide alignment layer, which was achieved by a conventional liquid crystal alignment technique. The outermost surfaces of the ZnO nanorods (average diameter 7 nm; length 50 nm) were modified by polymerization initiator moieties, and nematic liquid crystalline (LC) methacrylate polymers were grown by atom transfer radical polymerization. By regulating the densities of the polymerization initiator moieties, we successfully hybridized LC-polymer-grafted ZnO nanorods and small nematic LC molecules. The LC-polymer-modified ZnO nanorods were hierarchically aligned on the substrate via cooperative molecular interactions among the liquid crystal mesogens, which induced molecular orientation on the rubbed polyimide alignment layer. PMID:24299205

  19. Electron paramagnetic resonance studies of slowly tumbling vanadyl spin probes in nematic liquid crystals

    NASA Technical Reports Server (NTRS)

    Bruno, G. V.; Harrington, J. K.; Eastman, M. P.

    1978-01-01

    The purposes of this vanadyl spin probe study are threefold: (1) to establish when the breakdown of motionally narrowed formulas occurs; (2) to analyze the experimental vanadyl EPR line shapes by the stochastic Lioville method as developed by Polnaszek et al. (1973) for slow tumbling in an anisotropic liquid; and (3) to compare the vanadyl probe study results with those of Polnaszek and Freed (1975). Spectral EPR line shapes are simulated for experimental spectra of vanadyl acetylacetonate (VOAA) in nematic liquid crystal butyl p-(p-ethoxyphenoxycarbonyl) phenyl carbonate (BEPC) and Phase V of EM laboratories. It is shown that the use of typical vanadyl complexes as spin probes for nematic liquid crystals simplifies the theoretical analysis and the subsequent interpretation. Guidelines for the breakdown of motionally narrowed formulas are established. Both the slow tumbling aspects and the effects of non-Brownian rotation should be resolved in order to extract quantitative information about molecular ordering and rotational mobility.

  20. Multiple alignment modes for nematic liquid crystals doped with alkylthiol-capped gold nanoparticles.

    PubMed

    Qi, Hao; Hegmann, Torsten

    2009-08-01

    The ability of alkylthiol capped gold nanoparticles (Au NPs) to tune, alter, and reverse the alignment of nematic liquid crystals (LCs) has been investigated in detail. Adjusting the concentration of the suspended Au NPs in the nematic LC host, optimizing the sample preparation protocol, or providing different sample substrates (untreated glass slides, rubbed polyimide-coated LC test cell, or ITO-coated glass slides) results in several LC alignment scenarios (modes) including vertical alignment, planar alignment, and a thermally controlled alignment switch between these two alignment modes. The latter thermal switch between planar and homeotropic alignment was observed particularly for lower concentrations (i.e., around 1 to 2 wt %) of suspended NPs in the size regime of 1.5-2 nm and was found to be concentration-dependent and thermally reversible. Different scenarios are discussed that could explain these induced alignment modes. In one scenario, the NP-induced alignment is related to the temperature-dependent change of the order parameter, S, of the nematic phase (ordering in the bulk). In the second scenario, a change of the ordering of the nematic molecules around the NPs that reside at the interfaces is described. We also started to test spin coating as an alternative way of preparing nematic thin films with well-separated Au NPs on the substrate and found this to be a possible method for manufacturing of future NP-doped LC devices, as this method produced evenly distributed NPs on glass substrates. Together the presented findings continue to pave the way for LC display-related applications of Au NP-doped nematic LCs and provide insights for N-LC sensor applications. PMID:20355789

  1. Analytical description of 2D magnetic Freedericksz transition in a rectangular cell of a nematic liquid crystal.

    PubMed

    Burylov, S V; Zakhlevnykh, A N

    2016-06-01

    We study the Freedericksz transition induced by a magnetic field in a rectangular cell filled with a nematic liquid crystal. In the initial state the director of the nematic liquid crystal is uniformly aligned in the cross section plane of the cell with rigid anchoring of the director at cell walls: planar on the top and bottom walls, and homeotropic on the left and right ones. The magnetic field is directed perpendicular to the cell cross section plane. We consider two-dimensional (2D) orientational deformations of the nematic liquid crystal in the rectangular cell and determine the critical value of the Freedericksz transition field above which these orientational deformations occur. The 2D expression for the director alignment profile above the threshold of Freedericksz transition is analytically found and the profile shapes as functions of cell sizes, values of the Frank elastic constants of the nematic liquid crystal and the magnetic field are studied. PMID:27349554

  2. Twist-bend nematic liquid crystals in high magnetic fields.

    PubMed

    Challa, P K; Borshch, V; Parri, O; Imrie, C T; Sprunt, S N; Gleeson, J T; Lavrentovich, O D; Jákli, A

    2014-06-01

    We present magneto-optic measurements on two materials that form the recently discovered twist-bend nematic (N_{tb}) phase. This intriguing state of matter represents a fluid phase that is orientationally anisotropic in three directions and also exhibits translational order with periodicity several times larger than the molecular size. N_{tb} materials may also spontaneously form a visible, macroscopic stripe texture. We show that the optical stripe texture can be persistently inhibited by a magnetic field, and a 25T external magnetic field depresses the N-N_{tb} phase transition temperature by almost 1{∘}C. We propose a quantitative mechanism to account for this shift and suggest a Helfrich-Hurault-type mechanism for the optical stripe formation. PMID:25019707

  3. Orientation of nematic liquid crystal in open glass microstructures

    NASA Astrophysics Data System (ADS)

    Azarinia, H.; Beeckman, J.; Neyts, K.; Schacht, E.; Gironès, J.; James, R.; Fernandez, F. A.

    2009-09-01

    Liquid crystal materials can have bulk reorientation due to surface interaction and are therefore of interest for biosensing applications. We present a setup, with holes etched in a substrate, filled with liquid crystal and covered by a sample fluid. The influence of the depth of the microcavities and the type of liquid on the liquid crystal orientation is investigated by experiments and simulations.

  4. Effects of added silica nanoparticles on the nematic liquid crystal phase formation in beidellite suspensions.

    PubMed

    Landman, Jasper; Paineau, Erwan; Davidson, Patrick; Bihannic, Isabelle; Michot, Laurent J; Philippe, Adrian-Marie; Petukhov, Andrei V; Lekkerkerker, Henk N W

    2014-05-01

    In this article, we present a study of the liquid crystal phase behavior of mixed suspensions of the natural smectite clay mineral beidellite and nonadsorbing colloidal silica particles. While virtually all smectite clays dispersed in water form gels at very low concentrations, beidellite displays a first order isotropic-nematic phase transition before gel formation (J. Phys. Chem. B, 2009, 113, 15858-15869). The addition of silica nanospheres shifts the concentrations of the coexisting isotropic and nematic phases to slightly higher values while at the same time markedly accelerating the phase separation process. Furthermore, beidellite suspensions at volume fractions above the isotropic-nematic phase separation, trapped in a kinetically arrested gel state, liquefy on the addition of silica nanospheres and proceed to isotropic-nematic phase separation. Using small-angle X-ray scattering (SAXS), we probe the structural changes caused by the addition of the silica nanospheres, and we relate the modification of the phase transition kinetics to the change of the rheological properties. PMID:24758198

  5. Light-scattering measurement of the nematic correlation length in a liquid crystal with quenched disorder

    NASA Astrophysics Data System (ADS)

    Bellini, Tommaso; Clark, Noel A.; Degiorgio, Vittorio; Mantegazza, Francesco; Natale, Giorgio

    1998-03-01

    We have studied a composite system formed by a nematic thermotropic liquid crystal in which small silica particles have been dispersed. The colloids are aggregated and exert a randomizing effect on the nematic structure. The distorted pattern of the optical axis gives rise to a strong optical turbidity τ. We have measured τ as a function of the silica concentration Φ and of the temperature T in both the isotropic and nematic phase. We have found that, at fixed T, τ has a maximum as a function of Φ, and that, upon changing Φ, the whole shape of τ(T) drastically transforms. We have devised a model to describe the scattering of light from a distorted uniaxial system. The model has been developed both in the Born approximation and in the anomalous diffraction approximation, the two regimes which cover the broad range of experimental conditions. The family of τ(T) curves experimentally obtained at different Φ's is remarkably well described by the theoretical model, using as the only fitting parameter the correlation length ζ. We have found that, upon decreasing Φ, the nematic correlation length diverges as a power law of Φ. We compare the exponent of the power law with the prediction of the Imry-Ma theory of phase behavior in disordered systems, and we discuss the connection between ζ and the fractal correlation length of the silica aggregates.

  6. Elastic and hydrodynamic torques on a colloidal disk within a nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Rovner, Joel B.; Borgnia, Dan S.; Reich, Daniel H.; Leheny, Robert L.

    2012-10-01

    The orientationally dependent elastic energy and hydrodynamic behavior of colloidal disks with homeotropic surface anchoring suspended in the nematic liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) have been investigated. In the absence of external torques, the disks align with the normal of the disk face â parallel to the nematic director n̂. When a magnetic field is applied, the disks rotate â by an angle θ so that the magnetic torque and the elastic torque caused by distortion of the nematic director field are balanced. Over a broad range of angles, the elastic torque increases linearly with θ in quantitative agreement with a theoretical prediction based on an electrostatic analogy. When the disks are rotated to angles θ>(π)/(2), the resulting large elastic distortion makes the disk orientation unstable, and the director undergoes a topological transition in which θπ-θ. In the transition, a defect loop is shed from the disk surface, and the disks spin so that â sweeps through π radians as the loop collapses back onto the disk. Additional measurements of the angular relaxation of disks to θ=0 following removal of the external torque show a quasi-exponential time dependence from which an effective drag viscosity for the nematic can be extracted. The scaling of the angular time dependence with disk radius and observations of disks rotating about â indicate that the disk motion affects the director field at surprisingly modest Ericksen numbers.

  7. Microsecond-range optical shutter for unpolarized light with chiral nematic liquid crystal

    SciTech Connect

    Mohammadimasoudi, Mohammad Neyts, Kristiaan; Beeckman, Jeroen; Shin, Jungsoon; Lee, Keechang

    2015-04-15

    A fast electro-optic shutter is fabricated and demonstrated. The device works independently of the polarization state of the incoming light beam. Modulation between 3% transmission and 60% transmission is obtained within a wavelength range of 50 nm with a response time of 20 μs. The device consists of two partly polymerized chiral nematic liquid crystal layers separated by a half wave plate. The transmission modulation is due to a 50 nm wavelength shift of the photonic band gap of the chiral liquid crystal realized by applying an electric field over a mixture of photo-polymerized LC and non-reactive nematic LC containing a chiral dopant. The shutter features high reflectivity in the photonic band gap. We investigate the influence of the amplitude of the applied voltage on the width and the depth of the reflection band.

  8. Photo-stimulated phase and anchoring transitions of chiral azo-dye doped nematic liquid crystals.

    PubMed

    Kundu, Sudarshan; Kang, Shin-Woong

    2013-12-16

    We report concurring phase and anchoring transitions of chiral azo-dye doped nematic liquid crystals. The transitions are induced by photo-stimulation and stable against light and thermal treatments. Photochromic trans- to cis-isomerization of azo-dye induces an augmented dipole moment and strong dipole-dipole interaction of the cis-isomers, resulting in the formation of nano-sized dye-aggregates. Consequent phase separation of the aggregates of a chiral azo-dye induces phase transition from a chiral to nonchiral nematic phase. In addition, the deposition of dye-aggregates at the surfaces brings about anchoring transition of LC molecules. The stability and irreversibility of the transition, together with no need of pretreatments for LC alignment, provide fascinating opportunity for liquid crystal device applications. PMID:24514707

  9. Self-organization processes and topological defects in nanolayers in a nematic liquid crystal

    SciTech Connect

    Chuvyrov, A. N.; Girfanova, F. M. Mal'tsev, I. S.

    2008-05-15

    Atomic force microscopy is used to study the self-organization processes that occur during the formation of topological defects in nanomolecular layers in a nematic liquid crystal with the homeotropic orientation of its molecules with respect to the substrate. In this case, a smectic monolayer with a thickness of one molecule length (about 2.2 nm) forms on the substrate, and a nanomolecular layer of a nematic liquid crystal forms above this monolayer. In such virtually two-dimensional layers, numerous different nanoclusters, namely, hut structures, pyramids, raft structures with symmetry C{sub nm} (where n = 2, 4, 5, 6, 7, ?, {infinity}), cones, and nanopools, form [1]. They have a regular shape close to the geometry of solid crystals. Modulated linear structures and topological point defects appear spontaneously in the nanopools and raft structures.

  10. Simplified Scheme for Deterministic Synthesis of Chiral-Nematic Glassy Liquid Crystals

    SciTech Connect

    Wallace, J.U.; Chen, S.H.

    2006-07-13

    Potentially useful for the fabrication of nonabsorbing polarizers, optical notch filters and reflectors, and polarized light sources, chiral-nematic glassy liquid crystals can be synthesized by a statistical or deterministic approach. A deterministic approach is characterized by the relative ease of product separation and purification and hence is more amenable to process scale-up. Prompted to minimize the effort involving protection adn deprotection of functional groups, the present work has demonstrated the feasibility of reducing the number of synthesis steps from a previous synthesis scheme. The new methodology is widely applicable to the synthesis of a variety of right- and left-handed chiral-nematic glassy liquid crystals with desired phase transition temperatures.

  11. Unusual temperature dependence of the splay elastic constant of a rodlike nematic liquid crystal doped with a highly kinked bent-core molecule

    NASA Astrophysics Data System (ADS)

    Lee, Ji-Hoon; Yoon, Tae-Hoon; Choi, E.-Joon

    2013-12-01

    We report an unusual temperature dependence of the elastic constants of a rodlike nematic liquid crystal (RLC) mixed with a highly kinked bent-core liquid crystal (BLC). On cooling through the nematic phase, the splay elastic constant (K11) of the RLC-BLC mixture increased below the nematic-isotropic phase transition temperature, but started to decrease midway through the nematic phase. The decrease of K11 was more prominent with a greater concentration of BLC. On the other hand, the bend elastic constant (K33) of the RLC-BLC mixture monotonically increased through the nematic phase with decreasing temperature.

  12. Long-range plasmonic directional coupler switches controlled by nematic liquid crystals.

    PubMed

    Zografopoulos, D C; Beccherelli, R

    2013-04-01

    A liquid-crystal tunable plasmonic optical switch based on a long-range metal stripe directional coupler is proposed and theoretically investigated. Extensive electro-optic tuning of the coupler's characteristics is demonstrated by introducing a nematic liquid crystal layer above two coplanar plasmonic waveguides. The switching properties of the proposed plasmonic structure are investigated through rigorous liquid-crystal studies coupled with a finite-element based analysis of light propagation. A directional coupler optical switch is demonstrated, which combines very low power consumption, low operation voltages, adjustable crosstalk and coupling lengths, along with sufficiently reduced insertion losses. PMID:23571914

  13. Pseudo-casimir structural force drives spinodal dewetting in nematic liquid crystals

    PubMed

    Ziherl; Podgornik; Zumer

    2000-02-01

    We analyze theoretically the fluctuation-induced force in thin nematic films subject to competing surface interactions, and we find that the force is attractive at small distances and repulsive otherwise. The results provide a consistent interpretation of a recent study of spinodal dewetting of 5CB on a silicon wafer [F. Vandenbrouck et al., Phys. Rev. Lett. 82, 2693 (1999)], implying that this experiment can be regarded as the first observation of the pseudo-Casimir effect in liquid crystals. PMID:11017485

  14. Nematic liquid crystals: a suitable medium for self-confinement of coherent and incoherent light.

    PubMed

    Peccianti, Marco; Assanto, Gaetano

    2002-03-01

    Nematic liquid crystals exhibit a saturable, non-instantaneous nonlinear response through light-induced reorientation. In such a material, we demonstrate that (2+1)-dimensional spatial solitary waves can be generated at milliwatt power levels not only with a coherent optical beam, but also with incoherent excitations. Self-trapping also allows the efficient guidance of a weak co-polarized probe. PMID:11909157

  15. Study of Memory Alignment of Nematic Liquid Crystals on Polyvinyl Alcohol Coatings

    NASA Astrophysics Data System (ADS)

    Vetter, Peter; Ohmura, Yoshinori; Uchida, Tatsuo

    1993-09-01

    Polymer layers can cause memory alignment of nematic liquid crystals. We describe an experimental method to characterize this effect. We studied the temperature dependence of the memory alignment on polyvinyl alcohol coatings. We also investigated the influence of the time span during which the memory alignment is generated. We propose an adsorption-desorption mechanism by which we can explain our observations in a reasonable way.

  16. A fast anharmonic mode in electrooptical switching of liquid crystal structures based on chiral nematics

    SciTech Connect

    Palto, S. P. Barnik, M. I.; Blinov, L. M.; Umanskii, B. A. Shtykov, N. M.

    2010-09-15

    Polarization, spectral, and relaxation features of a new electrooptical effect in oriented layers of chiral nematic liquid crystals (LCs) are considered. The physics behind this electrooptical effect is the induction of higher order spatial harmonics in the helical distribution of the director field, which ensures the high speed of electrooptical response. It is shown that the spectral properties of the electrooptical response can be effectively controlled by varying the optical anisotropy of the LC and the pitch of the helical structure.

  17. Finite Time Singularity of the Nematic Liquid Crystal Flow in Dimension Three

    NASA Astrophysics Data System (ADS)

    Huang, Tao; Lin, Fanghua; Liu, Chun; Wang, Changyou

    2016-09-01

    In this paper, we consider the initial and boundary value problem of a simplified nematic liquid crystal flow in dimension three and construct two examples of finite time singularity. The first example is constructed within the class of axisymmetric solutions, while the second example is constructed for any generic initial data {(u_0,d_0)} that has sufficiently small energy, and {d_0} has a nontrivial topology.

  18. Nematic order-disorder state transition in a liquid crystal analogue formed by oriented and migrating amoeboid cells

    NASA Astrophysics Data System (ADS)

    Kemkemer, R.; Teichgräber, V.; Schrank-Kaufmann, S.; Kaufmann, D.; Gruler, H.

    2000-10-01

    In cell culture, liquid crystal analogues are formed by elongated, migrating, and interacting amoeboid cells. An apolar nematic liquid crystal analogue is formed by different cell types like human melanocytes (=pigment cells of the skin), human fibroblasts (=connective tissue cells), human osteoblasts (=bone cells), human adipocytes (=fat cells), etc. The nematic analogue is quite well described by i) a stochastic machine equation responsible for cell orientation and ii) a self-organized extracellular guiding signal, E_2, which is proportional to the orientational order parameter as well as to the cell density. The investigations were mainly made with melanocytes. The transition to an isotropic state analogue can be accomplished either by changing the strength of interaction (e.g. variation of the cell density) or by influencing the cellular machinery by an externally applied signal: i) An isotropic gaseous state analogue is observed at low cell density (ρ < 110melanocytes/mm^2) and a nematic liquid crystal state analogue at higher cell density. ii) The nematic state analogue disappears if the bipolar shaped melanocytes are forced to become a star-like shape (induced by colchicine or staurosporine). The analogy between nematic liquid crystal state analogue formed by elongated, migrating and interacting cells and the nematic liquid crystal phase formed by interacting elongated molecules is discussed.

  19. Unconventional non-Fermi liquid state caused by nematic criticality in cuprates

    NASA Astrophysics Data System (ADS)

    Wang, Jing-Rong; Liu, Guo-Zhu; Zhang, Chang-Jin

    2016-07-01

    At the nematic quantum critical point that exists in the {d}{x2-{y}2}-wave superconducting dome of cuprates, the massless nodal fermions interact strongly with the quantum critical fluctuation of nematic order. We study this problem by means of the renormalization group approach and show that, the fermion damping rate | {Im}{{{Σ }}}R(ω )| vanishes more rapidly than the energy ω and the quasiparticle residue {Z}f\\to 0 in the limit ω \\to 0. The nodal fermions thus constitute an unconventional non-Fermi liquid that represents an even weaker violation of Fermi liquid theory than a marginal Fermi liquid. We also investigate the interplay of quantum nematic critical fluctuation and gauge-potential-like disorder, and find that the effective disorder strength flows to the strong coupling regime at low energies. Therefore, even an arbitrarily weak disorder can drive the system to become a disorder controlled diffusive state. Based on these theoretical results, we are able to understand a number of interesting experimental facts observed in curpate superconductors.

  20. Topological binding and elastic interactions of microspheres and fibres in a nematic liquid crystal.

    PubMed

    Nikkhou, M; Škarabot, M; Muševič, I

    2015-03-01

    We present a detailed analysis of topological binding and elastic interactions between a long, and micrometer-diameter fiber, and a microsphere in a homogeneously aligned nematic liquid crystal. Both objects are surface treated to produce strong perpendicular anchoring of the nematic liquid crystal. We use the opto-thermal micro-quench of the laser tweezers to produce topological defects with prescribed topological charge, such as pairs of a Saturn ring and an anti-ring, hyperbolic and radial hedgehogs on a fiber, as well as zero-charge loops. We study the entanglement and topological charge interaction between the topological defects of the fiber and sphere and we observe a huge variety of different entanglement topologies and defect-mediated elastic bindings. We explain all observed phenomena with simple topological rule: like topological charges repel each other and opposite topological charges attract. These binding mechanisms not only demonstrate the fascinating topology of nematic colloids, but also open a novel route to the assembly of very complex topological networks of fibers, spheres and other objects for applications in liquid crystal photonics. PMID:25813607

  1. Hard Spherocylinders of Two Different Lengths as a Model System of a Nematic Liquid Crystal on an Anisotropic Substrate

    NASA Astrophysics Data System (ADS)

    Koda, Tomonori; Hyodo, Yosuke; Momoi, Yuichi; Kwak, Musun; Kang, Dongwoo; Choi, Youngseok; Nishioka, Akihiro; Haba, Osamu; Yonetake, Koichiro

    2016-02-01

    In this article, we describe the effects of an anisotropic substrate on the alignment of a nematic liquid crystal. We examine how the substrate affects the alignment of a nematic liquid crystal by Monte Carlo simulation. The liquid crystal on a substrate was described by the phase separation of liquid crystal molecules and substrate molecules, both of which were modeled by hard particles. We used hard rods to represent both the liquid crystal and the substrate. The length of the hard rods representing the substrate was adjusted to represent the degree of substrate anisotropy. The results show that the nematic alignment could either be reinforced or weakened, depending on the length of the substrate rods. Mean field theory is used to analyze the simulation results. We confirmed that the distance over which the substrate affects the bulk liquid crystal is about 3 nm for the present hard-rod-based model.

  2. Time history of laser pulse polarization transformation as a tool of the isotropic-nematic phase transition in liquid crystals

    NASA Astrophysics Data System (ADS)

    Makarov, Vladimir A.; Il'inova, Tamara M.; Marchenko, Tatiana B.; Shkurinov, Aleksandr P.; Zolot'ko, Alexander S.

    2003-06-01

    We theoretically investigate in the aberrationless approximation the self-action of the elliptically polarized Gaussian pulse during its propagation in a thin dish with a nematic liquid crystal in the isotropic phase. Quadrature formulas are obtained to describe the time history of the intensity, the elliptisity degree and the rotation angle of the polarization ellipse of the output radiation at the different points of the beam cross-section. They are expressed in terms of the parameters describing two, essential near the temperature of the isotropic-nematic phase transition, mechanisms of the spatial nonlocality of the nonlinear medium optical response, and in terms of the other parameters, which describe the nematic liquid crystal and the elliptically polarized incident pulse. The former mechanism is specified by the medium heating due to light absorption; the latter is determined by the fluctuations of the nematic liquid crystal order parameter tensor near the temperature of the isotropic-nematic phase transition. It is shown that for some values of temperature and of the nematic liquid crystal parameters the elliptical polarization of the incident pulse, which is constant at the entry of the thin dish, transforms into the linear or another different elliptical one at the exit and keeps this new state up to the pulse tail. The dependence of the ellipticity degree on time becomes significantly nonmonotonic and changes its sign in some cases. The nonlocality of the nonlinear medium optical response weakens these transformations.

  3. Molecular model of biaxial ordering in nematic liquid crystals composed of flat molecules with four mesogenic groups

    NASA Astrophysics Data System (ADS)

    Gorkunov, M. V.; Osipov, M. A.; Kocot, A.; Vij, J. K.

    2010-06-01

    Relative stability of uniaxial and biaxial nematic phases is analyzed in a model nematic liquid crystal composed of flat molecules of C2h symmetry with four mesogenic groups rigidly linked to the same center. The generalized effective quadrupole mean-field potential is proposed and its constants are evaluated numerically for the pair intermolecular potential based on Gay-Berne interaction between mesogenic groups. The dependencies of the constants on molecular shape parameters are systematically analyzed. Order parameters of the uniaxial and biaxial nematic phases are evaluated by direct minimization of the free energy at different temperatures. The corresponding phase diagrams are obtained enabling one to study the effects of molecular model parameters on the stability regions of uniaxial and biaxial phases. The results are used to clarify the nature of experimentally observed biaxial ordering in nematic liquid crystals composed of tetrapode molecules with the same symmetry.

  4. Molecular model of biaxial ordering in nematic liquid crystals composed of flat molecules with four mesogenic groups.

    PubMed

    Gorkunov, M V; Osipov, M A; Kocot, A; Vij, J K

    2010-06-01

    Relative stability of uniaxial and biaxial nematic phases is analyzed in a model nematic liquid crystal composed of flat molecules of C2h symmetry with four mesogenic groups rigidly linked to the same center. The generalized effective quadrupole mean-field potential is proposed and its constants are evaluated numerically for the pair intermolecular potential based on Gay-Berne interaction between mesogenic groups. The dependencies of the constants on molecular shape parameters are systematically analyzed. Order parameters of the uniaxial and biaxial nematic phases are evaluated by direct minimization of the free energy at different temperatures. The corresponding phase diagrams are obtained enabling one to study the effects of molecular model parameters on the stability regions of uniaxial and biaxial phases. The results are used to clarify the nature of experimentally observed biaxial ordering in nematic liquid crystals composed of tetrapode molecules with the same symmetry. PMID:20866427

  5. Confined nematic liquid crystal between two spherical boundaries with planar anchoring

    NASA Astrophysics Data System (ADS)

    Seyednejad, Seyed Reza; Mozaffari, Mohammad Reza; Ejtehadi, Mohammad Reza

    2013-07-01

    Nematic shells of liquid crystals have been provided in microscales. Defect structures in the shells are very essential in the electro-optical applications of such colloidal objects. We have numerically minimized the free energy of symmetric and asymmetric spherical shells of the nematic liquid crystal. Considering degenerate planar anchoring on the surfaces and isotropic nematic elasticity, a variety of defect structures are observed by controlling or varying the thicknesses of the shell and its degree of asymmetry. In symmetric shells, our calculations show that boojums (bipolar) defects appear in thick shells and tetrahedral (baseball) defects in thin shells. In asymmetric shells, while we are in the bipolar regime, the boojums defects transform to trigonal configurations. Free energy landscape shows that in this regime the inner droplet is not stable in the center and it is trapped in an off-center minimum energy position. For the case of thin shells, there are two degenerate director textures with similar tetrahedral configuration of the disclination lines. The levels are split in asymmetric shells. The stability of the inner droplet in the center position depends on director texture. It is stable for one texture and unstable for the other one. For an unstable pattern there is no minimum energy position for the inner droplet and it moves until it touches the outer boundary.

  6. Detecting, visualizing, and measuring gold nanoparticle chirality using helical pitch measurements in nematic liquid crystal phases.

    PubMed

    Sharma, Anshul; Mori, Taizo; Lee, Huey-Charn; Worden, Matthew; Bidwell, Eric; Hegmann, Torsten

    2014-12-23

    Chirality at the nanoscale, or more precisely, the chirality or chiroptical effects of chiral ligand-capped metal nanoparticles (NPs) is an intriguing and rapidly evolving field in nanomaterial research with promising applications in catalysis, metamaterials, and chiral sensing. The aim of this work was to seek out a system that not only allows the detection and understanding of NP chirality but also permits visualization of the extent of chirality transfer to a surrounding medium. The nematic liquid crystal phase is an ideal candidate, displaying characteristic defect texture changes upon doping with chiral additives. To test this, we synthesized chiral cholesterol-capped gold NPs and prepared well-dispersed mixtures in two nematic liquid crystal hosts. Induced circular dichroism spectropolarimetry and polarized light optical microscopy revealed that all three gold NPs induce chiral nematic phases, and that those synthesized in the presence of a chiral bias (disulfide) are more powerful chiral inducers than those where the NP was formed in the absence of a chiral bias (prepared by conjugation of a chiral silane to preformed NPs). Helical pitch data here visually show a clear dependence on the NP size and the number of chiral ligands bound to the NP surface, thereby supporting earlier experimental and theoretical data that smaller metal NPs made in the presence of a chiral bias are stronger chiral inducers. PMID:25383947

  7. Localised polymer networks in chiral nematic liquid crystals for high speed photonic switching

    NASA Astrophysics Data System (ADS)

    Tartan, Chloe C.; Salter, Patrick S.; Booth, Martin J.; Morris, Stephen M.; Elston, Steve J.

    2016-05-01

    Self-assembled periodic structures based upon chiral liquid crystalline materials have significant potential in the field of photonics ranging from fast-switching optoelectronic devices to low-threshold lasers. The flexoelectro-optic effect, which is observed in chiral nematic liquid crystals (LCs) when an electric field is applied perpendicular to the helical axis, has significant potential as it exhibits analogue switching in 10-100 μs. However, the major technological barrier that prohibits the commercial realisation of this electro-optic effect is the requirement of a uniform, in-plane alignment of the helix axis between glass substrates. Here, it is shown that periodic polymer structures engineered in the nematic phase of a chiral nematic LC device using direct laser writing can result in the spontaneous formation of the necessary uniform lying helix (ULH) state. Specifically, two-photon polymerization is used in conjunction with a spatial light modulator so as to correct for aberrations introduced by the bounding glass substrates enabling the polymer structures to be fabricated directly into the device. The ULH state appears to be stable in the absence of an externally applied electric field, and the optimum contrast between the bright and dark states is obtained using polymer structures that have periodicities of the order of the device thickness.

  8. Co-dispersion of plasmonic nanorods in thermotropic nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Sheetah, Ghadah; Liu, Qinkun; Smalukh, Ivan

    Colloidal dispersions of plasmonic metal nanoparticles in liquid crystals promise the capability of pre-engineering tunable optical properties of mesostructured metal-dielectric composites. Recently, concentrated dispersions of anisotropic gold, silver, and metal alloy nanoparticles in nematic hosts have been achieved and successfully controlled by low-voltage fields. However, to enable versatile designs of material behavior of the composites, simultaneous co-dispersion of anisotropic particles with different shapes, alignment properties, and compositions are often needed. We achieve such co-dispersions and explore their switching characteristics in response to external stimuli like light and electric fields. We demonstrated that spectral characteristics of co-dispersions of multiple types of anisotropic nanoparticles in a common nematic host provides unprecedented variety of electrically- and optically-tunable material behavior, with a host of potential practical applications in electro-optic devices and displays Ghadah acknowledges support from the King Faisal University (KFU) graduate fellowship.

  9. Propagation of optical spatial solitary waves in bias-free nematic-liquid-crystal cells

    SciTech Connect

    Minzoni, Antonmaria A.; Sciberras, Luke W.; Worthy, Annette L.; Smyth, Noel F.

    2011-10-15

    The propagation of a bulk optical solitary wave in a rectangular cell filled with a nematic liquid crystal--a nematicon--is mathematically modelled. In order to overcome the Freedricksz threshold the cell walls are rubbed to pretilt the nematic. A modulation theory, based on a Lagrangian formulation, is developed for the (2+1)-dimensional propagation of the solitary wave beam down the cell. This modulation theory is based on two different formulations of the director distribution. The relative advantages and disadvantages of these two methods are discussed. A previously unexplored method based on images is found to possess significant advantages. Excellent agreement with full numerical solutions of the nematicon equations is found for both methods. Finally, the implications of the results obtained for some widely used approximations to the nematicon equations are discussed, particularly their use in comparisons with experimental results.

  10. Generalized nematohydrodynamic boundary conditions with application to bistable twisted nematic liquid-crystal displays.

    PubMed

    Fang, Angbo; Qian, Tiezheng; Sheng, Ping

    2008-12-01

    Parallel to the highly successful Ericksen-Leslie hydrodynamic theory for the bulk behavior of nematic liquid crystals (NLCs), we derive a set of coupled hydrodynamic boundary conditions to describe the NLC dynamics near NLC-solid interfaces. In our boundary conditions, translational flux (flow slippage) and rotational flux (surface director relaxation) are coupled according to the Onsager variational principle of least energy dissipation. The application of our boundary conditions to the truly bistable pi -twist NLC cell reveals a complete picture of the dynamic switching processes. It is found that the thus far overlooked translation-rotation dissipative coupling at solid surfaces can accelerate surface director relaxation and enhance the flow rate. This can be utilized to improve the performance of electro-optical nematic devices by lowering the required switching voltages and reducing the switching times. PMID:19256854

  11. Dipole-induced ordering in nematic liquid crystals. II. The elusive holy grail

    NASA Astrophysics Data System (ADS)

    Syvitski, Raymond T.; Burnell, E. Elliott

    2000-08-01

    Similar size and shape molecules with different electric multipoles are used to investigate effects of molecular dipole, quadrupole, and polarizability interactions on the average orientational order of solutes in nematic liquid crystals. Solutes are codissolved in the same sample tube so that the orientational ordering among solutes can be directly compared and analyzed using mean-field models. Permanent dipoles have a negligible influence on solute orientational order. Effects from molecular polarizability interactions could not be separated from short-range interactions. However, order parameters predicted from strong, short-range repulsive forces coupled with interactions between the solute quadrupole and the average electric field gradient felt by the solute are consistent with experimental values. For the nematic mixture 55 wt% ZLI 1132 in EBBA [N-(pethoxybenzylidene)-p'-n-butylaniline] the contribution to solute ordering from long-range electrostatic interactions is negligible.

  12. Optical properties of planar nematic liquid crystals samples which are parallel oriented by nanofibers

    NASA Astrophysics Data System (ADS)

    Yusuf, Yusril; Kusumasari, Ervanggis Minggar; Ula, Nur Mufidatul; Jahidah, Khannah; Triyana, Kuwat; Sosiati, Harini; Harsojo

    2016-04-01

    Optical properties of two nematic liquid crystals, i.e., 4-methoxybenzylidene-4-butylaniline (MBBA) and 4-cyano-4'-pentylbiphenyl (5 CB) which are parallel oriented by nanofibers has been successfully performed. Planar samples of liquid crystals were made using polyvinyl alcohol (PVA) nanofiber from electrospinning process. Electrospinning method was modified using copper (Cu) as gap collector. These planar samples area are 15 mm x 25 mm. Optical characteristic of these samples were studied by using optical polarizing microscope. The optical intensity changes by a rotationof crossed polarizers is observed. The sinusoidal intensity change was observedin these samples as such as in the planar sample prepared by the rubbing method.

  13. Multiscale models of colloidal dispersion of particles in nematic liquid crystals.

    PubMed

    Bennett, T P; D'Alessandro, G; Daly, K R

    2014-12-01

    We use homogenization theory to develop a multiscale model of colloidal dispersion of particles in nematic liquid crystals under weak-anchoring conditions. We validate the model by comparing it with simulations by using the Landau-de Gennes free energy and show that the agreement is excellent. We then use the multiscale model to study the effect that particle anisotropy has on the liquid crystal: spherically symmetric particles always reduce the effective elastic constant. Asymmetric particles introduce an effective alignment field that can increase the Fredericks threshold and decrease the switch-off time. PMID:25615117

  14. Refraction of nonlinear beams by localized refractive index changes in nematic liquid crystals

    SciTech Connect

    Assanto, Gaetano; Minzoni, Antonmaria A.; Smyth, Noel F.; Worthy, Annette L.

    2010-11-15

    The propagation of solitary waves in nematic liquid crystals in the presence of localized nonuniformities is studied. These nonuniformities can be caused by external electric fields, other light beams, or any other mechanism which results in a modified director orientation in a localized region of the liquid-crystal cell. The net effect is that the solitary wave undergoes refraction and trajectory bending. A general modulation theory for this refraction is developed, and particular cases of circular, elliptical, and rectangular perturbations are considered. The results are found to be in excellent agreement with numerical solutions.

  15. Spectral properties of BChl c in nematic liquid crystals. II: Aggregated form of dye

    NASA Astrophysics Data System (ADS)

    Dudkowiak, A.; Francke, C.; Amesz, J.; Planner, A.; Frackowiak, D.

    1996-11-01

    The orientation properties of aggregated bacteriochlorophyll c in a nematic liquid crystal matrix have been studied by means of polarized steady-state and time-resolved spectroscopy. The pigment introduced to the model system was predominantly in tetrameric (or hexameric) form with absorption maxima located at about 670 and 710 nm. Two tetramers with long-wavelength maxima at 704 and 722 nm could be distinguished. They exhibited different orientations in liquid crystal and different yields of fluorescence. Both tetramers exhibited delayed luminescence in the μs time region.

  16. Flow-driven transition and associated velocity profiles in a nematic liquid-crystal cell.

    PubMed

    Jewell, S A; Cornford, S L; Yang, F; Cann, P S; Sambles, J R

    2009-10-01

    The alignment properties and distribution of flow speed during Poiseuille flow through a microchannel of a nematic liquid crystal in a cell with homeotropic surface alignment has been measured using a combination of conoscopy, fluorescence confocal polarizing microscopy, and time-lapse imaging. Two topologically distinct director profiles, with associated fluid velocity fields, are found to exist with the preferred state dictated by the volumetric flow rate of the liquid crystal. The results show excellent agreement with model data produced using the Ericksen-Leslie nematodynamics theory. PMID:19905324

  17. Refraction of nonlinear beams by localized refractive index changes in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Assanto, Gaetano; Minzoni, Antonmaria A.; Smyth, Noel F.; Worthy, Annette L.

    2010-11-01

    The propagation of solitary waves in nematic liquid crystals in the presence of localized nonuniformities is studied. These nonuniformities can be caused by external electric fields, other light beams, or any other mechanism which results in a modified director orientation in a localized region of the liquid-crystal cell. The net effect is that the solitary wave undergoes refraction and trajectory bending. A general modulation theory for this refraction is developed, and particular cases of circular, elliptical, and rectangular perturbations are considered. The results are found to be in excellent agreement with numerical solutions.

  18. Carrier transport simulation of anomalous temperature dependence in nematic liquid crystals.

    PubMed

    Goto, Masanao; Takezoe, Hideo; Ishikawa, Ken

    2007-10-01

    We investigated the carrier transport phenomena in model liquid crystalline systems, which were constructed on the basis of the Gay-Berne potential and Monte Carlo calculation. The carrier transport was analyzed under the condition that the molecular arrangement in the system was fixed and thermally activated carriers were transported by hopping in the system. The carrier transport simulation was performed by Monte Carlo method using Miller-Abrahams hopping ratio. By these calculations, we reproduced the experimental results of the electronic conduction in nematic liquid crystals. PMID:17994925

  19. Carrier transport simulation of anomalous temperature dependence in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Goto, Masanao; Takezoe, Hideo; Ishikawa, Ken

    2007-10-01

    We investigated the carrier transport phenomena in model liquid crystalline systems, which were constructed on the basis of the Gay-Berne potential and Monte Carlo calculation. The carrier transport was analyzed under the condition that the molecular arrangement in the system was fixed and thermally activated carriers were transported by hopping in the system. The carrier transport simulation was performed by Monte Carlo method using Miller-Abrahams hopping ratio. By these calculations, we reproduced the experimental results of the electronic conduction in nematic liquid crystals.

  20. Nematic quantum phase transition of composite Fermi liquids in half-filled Landau levels and their geometric response

    NASA Astrophysics Data System (ADS)

    You, Yizhi; Cho, Gil Young; Fradkin, Eduardo

    We present a theory of isotropic-nematic quantum phase transition in the composite Fermi liquid arising in the half-filled Landau levels. We show that the quantum phase transition is triggered by the attractive quadrupolar interaction. By performing flux attachment, system turns into a composite Fermi liquid. The nematic order parameters act as the dynamical metric interplaying with the underlying topology, the Chern-Simons theory. Here both the fluctuations of the gauge field and the nematic order parameter can soften the Fermi surface and thus the fermions form a non-Fermi liquid. The effective field theory for the isotropic-nematic phase transition has z = 3 dynamical exponent due to the Landau damping due to the finite density of the fermions. We show that there is a Berry phase term of the nematic order parameter, which can be interpreted as the ``Hall viscosity'' of the dynamical metric. We also find the Wen-Zee-like term, which effectively dresses the nematic vortex with the electric charge. Both of the terms are originated from the time reversal breaking fluctuation of the Chern-Simons gauge fields. This indicates the fluctuations of the gauge fields modify the Hall viscosity and orbital spin of the compressible half-filled Landau level.

  1. Critical behavior at the isotropic to nematic, nematic to smectic-A and smectic-A to smectic-C phase transitions in a pyrimidine liquid crystal compound

    NASA Astrophysics Data System (ADS)

    Chakraborty, Anish; Chakraborty, Susanta; Kumar Das, Malay

    2015-12-01

    High-resolution optical birefringence (∆n) measurement of a pyrimidine liquid crystal compound having nematic, smectic-A and smectic-C phases are reported. The high-resolution ∆n data are rather successful in assessing the critical anomaly at different phase transitions in the investigated compound with a reasonably good accuracy. The critical exponent β, describing the limiting behavior of the nematic order parameter close to the isotropic-nematic (I-N) phase transition, is found to be in good agreement with the tricritical hypothesis. The critical behavior at the nematic-smectic-A (N-Sm-A) and the smectic-A-smectic-C (Sm-A-Sm-C) phase transitions has been explored with the aid of a differential quotient extracted from the ∆n values. The yielded effective critical exponent α‧ is appeared to be nearly tricritical in nature for the N-Sm-A phase transition. For the Sm-A-Sm-C phase transition, α‧ exhibits a weak dependence on the fit range and assumes tricritical value for large temperature range considered, which again is found to be diminished slightly with reduction in the temperature range. Related critical amplitude quotient and corrections-to-scaling quotient are found to display deviations from the theoretical models. Such behavior signals the appearance of a non-Landau character for the orthogonal to tilted smectic phase transition in the investigated compound.

  2. Spectral properties of bacteriochlorophyll c in nematic liquid crystal. Part 1. Monomeric forms of dye

    NASA Astrophysics Data System (ADS)

    Dudkowiak, A.; Francke, C.; Amesz, J.; Planner, A.; Hanyz, I.; Fraçkowiak, D.

    1996-02-01

    The spectroscopic features of bacteriochlorophyll c and bacteriopheophytin c in a nematic liquid crystal matrix have been investigated. Absorption, circular dichroism, fluorescence and time resolved delayed luminescence spectra have been measured. The pigment is introduced to the liquid crystal from a dry and from a hydrated chloroform solution. In both cases the pigment is in the monomeric form. Hydration of the solvent and the presence or absence of the central Mg atom affect the interaction of the pigment molecules with the liquid crystal matrix, changing the fluorescence anisotropy. A model for the bacteriochlorophyll c orientation in the liquid crystal is proposed and the averaged angles between the transition moments and the liquid crystal orientation axis are determined. A slow process (in the microsecond range) of radiative deactivation of energy absorbed by the pigments is observed. This delayed emission could be due to pigment ionization and delayed charge recombination and/or thermal activation from the triplet to the excited singlet state.

  3. Equivalent retarder-rotator approach to twisted nematic liquid crystal displays

    NASA Astrophysics Data System (ADS)

    Durán, Vicente; Lancis, Jesus; Tajahuerce, Enrique; Jaroszewicz, Zbigniew

    2005-09-01

    The equivalence between a twisted-nematic liquid crystal cell and the combination of a retardation wave-plate and a polarization rotator can be used to calibrate a voltage-addressed liquid crystal display. We present a simple polarimetric procedure to determine the two parameters that define the optical properties of the equivalent retarder-rotator system for each value of the applied voltage. Once the calibration procedure is performed, the optical response of the liquid crystal cell can be predicted and optimized. In particular, we demonstrate the generation of a family of equi-azimuth polarization states with a liquid crystal display sandwiched by a polarizer and a quarter-wave plate, whose optimal orientations are evaluated by a numerical simulation. Laboratory results corresponding to a commercial liquid crystal display are pre-sented.

  4. Necklaces of Liquid Crystal Beads: Nematic Drops Constrained on Thin Cellulosic Fibers

    NASA Astrophysics Data System (ADS)

    Almeida, Pedro; Geng, Yong; Terentjev, Eugene; Godinho, Maria Helena

    2012-02-01

    Liquid crystal droplets dispersed in a continuous matrix have important applications in electro-optical devices. They also produce intriguing topological defect structures due to the confinement of the liquid crystal by closed boundaries that impose alignment at the interface. In this work we use a simple method to generate stable liquid crystal droplets topologically equivalent to a toroid by depositing tiny volumes of a nematic liquid on cellulosic micro-fibers (1 μm diameter) suspended in air. This system can exhibit non-trivial point topological defects which can be energetically unstable against expanding into ring defects, depending on the fibers constraining geometries. By changing temperature, the system remains stable and allows the study of the defects evolution near the nematic-isotropic transition showing qualitatively different behavior on cooling and heating processes. The necklaces of such liquid crystal drops constitute excellent systems for fundamental studies and open new perspectives for applications. This work was sponsored by Air Force Office of Scientific Research, Air Force Material Command, USAF, under grant number FA8655-10-1-3020. The US Government is authorized to reproduce and distribute reprints for Governmental purpose notwithstanding any copyright notation thereon. Other support includes the Portuguese Science and Technology Foundation grant SFRH/BD/63574/2009 and projects PEst-C/CTM/LA0025/2011 (Strategic Project - LA 25 - 2011-2012, PTDC/CTM/099595/2008, PTDC/FIS/110132/2009 and Windsor Treaty grant 2009-10 UR55.

  5. Topological polymer dispersed liquid crystals with bulk nematic defect lines pinned to handlebody surfaces.

    PubMed

    Campbell, Michael G; Tasinkevych, Mykola; Smalyukh, Ivan I

    2014-05-16

    Polymer dispersed liquid crystals are a useful model system for studying the relationship between surface topology and defect structures. They are comprised of a polymer matrix with suspended spherical nematic drops and are topologically constrained to host defects of an elementary hedgehog charge per droplet, such as bulk or surface point defects or closed disclination loops. We control the genus of the closed surfaces confining such micrometer-sized nematic drops with tangential boundary conditions for molecular alignment imposed by the polymer matrix, allowing us to avoid defects or, on the contrary, to generate them in a controlled way. We show, both experimentally and through numerical modeling, that topological constraints in nematic microdrops can be satisfied by hosting topologically stable half-integer bulk defect lines anchored to opposite sides of handlebody surfaces. This enriches the interplay of topologies of closed surfaces and fields with nonpolar symmetry, yielding new unexpected configurations that cannot be realized in vector fields, having potential implications for topologically similar defects in cosmology and other fields. PMID:24877965

  6. Robustness of the periodic and chaotic orientational behavior of tumbling nematic liquid crystals.

    PubMed

    Heidenreich, Sebastian; Ilg, Patrick; Hess, Siegfried

    2006-06-01

    The dynamical behavior of molecular alignment strongly affects physical properties of nematic liquid crystals. A theoretical description can be made by a nonlinear relaxation equation of the order parameter and leads to the prediction that rather complex even chaotic orientational behavior occur. Here the influence of fluctuating shear rates on the orientational dynamics especially on chaotic solutions is discussed. With the help of phase portraits and time evolution diagrams, we investigated the influence of different fluctuation strengths on the flow aligned, isotropic, and periodic solutions. To explore the effect of fluctuations on the chaotic behavior, we calculated the largest Lyapunov exponent for different fluctuation strengths. We found in all cases that small fluctuations of the shear rate do not affect the basic features of the dynamics of tumbling nematics. Furthermore, we present an amended potential modeling the isotropic to nematic transition and discuss the equivalence and difference to the commonly used Landau-de Gennes potential. In contrast to the Landau-de Gennes potential, our potential has the advantage to restrict the order parameter to physically admissible values. In the case of extensional flow, we show that the amended potential leads for increasing extensional rate to a better agreement with experimental results. PMID:16906852

  7. Effects of molecular elongation on liquid crystalline phase behaviour: isotropic-nematic transition

    NASA Astrophysics Data System (ADS)

    Singh, Ram Chandra; Ram, Jokhan

    2003-08-01

    We present the density-functional approach to study the isotropic-nematic transitions and calculate the values of freezing parameters of the Gay-Berne liquid crystal model, concentrating on the effects of varying the molecular elongation, x0. For this, we have solved the Percus-Yevick integral equation theory to calculate the pair-correlation functions of a fluid the molecules of which interact via a Gay-Berne pair potential. These results have been used in the density-functional theory as an input to locate the isotropic-nematic transition and calculate freezing parameters for a range of length-to-width parameters 3.0⩽ x0⩽4.0 at reduced temperatures 0.95 and 1.25. We observed that as x0 is increased, the isotropic-nematic transition is seen to move to lower density at a given temperature. We find that the density-functional theory is good to study the freezing transitions in such fluids. We have also compared our results with computer simulation results wherever they are available.

  8. Robustness of the periodic and chaotic orientational behavior of tumbling nematic liquid crystals

    SciTech Connect

    Heidenreich, Sebastian; Hess, Siegfried; Ilg, Patrick

    2006-06-15

    The dynamical behavior of molecular alignment strongly affects physical properties of nematic liquid crystals. A theoretical description can be made by a nonlinear relaxation equation of the order parameter and leads to the prediction that rather complex even chaotic orientational behavior occur. Here the influence of fluctuating shear rates on the orientational dynamics especially on chaotic solutions is discussed. With the help of phase portraits and time evolution diagrams, we investigated the influence of different fluctuation strengths on the flow aligned, isotropic, and periodic solutions. To explore the effect of fluctuations on the chaotic behavior, we calculated the largest Lyapunov exponent for different fluctuation strengths. We found in all cases that small fluctuations of the shear rate do not affect the basic features of the dynamics of tumbling nematics. Furthermore, we present an amended potential modeling the isotropic to nematic transition and discuss the equivalence and difference to the commonly used Landau-de Gennes potential. In contrast to the Landau-de Gennes potential, our potential has the advantage to restrict the order parameter to physically admissible values. In the case of extensional flow, we show that the amended potential leads for increasing extensional rate to a better agreement with experimental results.

  9. Field-driven dynamics of microcapillaries filled with nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Fu, Fred; Khayyatzadeh, Pouya; Abukhdeir, Nasser M.

    Polymer-dispersed liquid crystal (PDLC) composites have long been a focus of study for their unique electro-optical properties and the feasibility of manufacturing them on a large scale, resulting in applications such as switchable windows. LC domains within PDLCs are typically spheroidal, as opposed to rectangular in LCD technology, and thus exhibit substantially different behaviour in the presence of an external field. In this work, continuum simulations were performed in order to capture the complex formation and electric field-driven switching dynamics of approximations of PDLC domains. A simplified elliptic cylinder (microcapillary) geometry is used and the effects of varying aspect ratio, surface anchoring, and external field strength were studied using the Landau-de Gennes model. The observed nematic formation and reorientation dynamics were found to be governed by the presence and motion of defects within the domain. Aspect ratio was found to strongly influence domain texture by providing regions of high curvature to which defects are attracted. Simulations also predict the presence of a geometry-controlled transition from nematic order enhanced by an external field (low aspect ratio) to nematic order frustrated by an external field (high aspect ratio). This work was made possible by the Natural Sciences and Engineering Research Council of Canada and Compute Ontario.

  10. Symmetry breaking in nematic liquid crystals: analogy with cosmology and magnetism

    NASA Astrophysics Data System (ADS)

    Repnik, R.; Ranjkesh, A.; Simonka, V.; Ambrozic, M.; Bradac, Z.; Kralj, S.

    2013-10-01

    Universal behavior related to continuous symmetry breaking in nematic liquid crystals is studied using Brownian molecular dynamics. A three-dimensional lattice system of rod-like objects interacting via the Lebwohl-Lasher interaction is considered. We test the applicability of predictions originally derived in cosmology and magnetism. In the first part we focus on coarsening dynamics following the temperature driven isotropic-nematic phase transition for different quench rates. The behavior in the early coarsening regime supports predictions made originally by Kibble in cosmology. For fast enough quenches, symmetry breaking and causality give rise to a dense tangle of defects. When the degree of orientational ordering is large enough, well defined protodomains characterized by a single average domain length are formed. With time subcritical domains gradually vanish and supercritical domains grow with time, exhibiting a universal scaling law. In the second part of the paper we study the impact of random-field-type disorder on a range of ordering in the (symmetry broken) nematic phase. We demonstrate that short-range order is observed even for a minute concentration of impurities, giving rise to disorder in line with the Imry-Ma theorem prediction only for the appropriate history of systems.

  11. Topological Polymer Dispersed Liquid Crystals with Bulk Nematic Defect Lines Pinned to Handlebody Surfaces

    NASA Astrophysics Data System (ADS)

    Campbell, Michael G.; Tasinkevych, Mykola; Smalyukh, Ivan I.

    2014-05-01

    Polymer dispersed liquid crystals are a useful model system for studying the relationship between surface topology and defect structures. They are comprised of a polymer matrix with suspended spherical nematic drops and are topologically constrained to host defects of an elementary hedgehog charge per droplet, such as bulk or surface point defects or closed disclination loops. We control the genus of the closed surfaces confining such micrometer-sized nematic drops with tangential boundary conditions for molecular alignment imposed by the polymer matrix, allowing us to avoid defects or, on the contrary, to generate them in a controlled way. We show, both experimentally and through numerical modeling, that topological constraints in nematic microdrops can be satisfied by hosting topologically stable half-integer bulk defect lines anchored to opposite sides of handlebody surfaces. This enriches the interplay of topologies of closed surfaces and fields with nonpolar symmetry, yielding new unexpected configurations that cannot be realized in vector fields, having potential implications for topologically similar defects in cosmology and other fields.

  12. Symmetry breaking in nematic liquid crystals: analogy with cosmology and magnetism.

    PubMed

    Repnik, R; Ranjkesh, A; Simonka, V; Ambrozic, M; Bradac, Z; Kralj, S

    2013-10-01

    Universal behavior related to continuous symmetry breaking in nematic liquid crystals is studied using Brownian molecular dynamics. A three-dimensional lattice system of rod-like objects interacting via the Lebwohl-Lasher interaction is considered. We test the applicability of predictions originally derived in cosmology and magnetism. In the first part we focus on coarsening dynamics following the temperature driven isotropic-nematic phase transition for different quench rates. The behavior in the early coarsening regime supports predictions made originally by Kibble in cosmology. For fast enough quenches, symmetry breaking and causality give rise to a dense tangle of defects. When the degree of orientational ordering is large enough, well defined protodomains characterized by a single average domain length are formed. With time subcritical domains gradually vanish and supercritical domains grow with time, exhibiting a universal scaling law. In the second part of the paper we study the impact of random-field-type disorder on a range of ordering in the (symmetry broken) nematic phase. We demonstrate that short-range order is observed even for a minute concentration of impurities, giving rise to disorder in line with the Imry-Ma theorem prediction only for the appropriate history of systems. PMID:24025777

  13. Molecular dynamics of a binary mixture of twist-bend nematic liquid crystal dimers studied by dielectric spectroscopy

    NASA Astrophysics Data System (ADS)

    Robles-Hernández, Beatriz; Sebastián, Nerea; Salud, Josep; Diez-Berart, Sergio; Dunmur, David A.; Luckhurst, Geoffrey R.; López, David O.; de la Fuente, M. Rosario

    2016-06-01

    We report a comprehensive dielectric characterization of a liquid crystalline binary mixture composed of the symmetric mesogenic dimer CB7CB and the nonsymmetric mesogenic dimer FFO9OCB. In addition to the high-temperature nematic phase, such a binary mixture shows a twist-bend nematic phase at room temperature which readily vitrifies on slow cooling. Changes in the conformational distribution of the dimers are reflected in the dielectric permittivity and successfully analyzed by means of an appropriate theoretical model. It is shown that the dielectric spectra of the mixture reflect the different molecular dipole properties of the components, resembling in the present case the characteristic dielectric spectra of nonsymmetric dimers. Comparison of the nematic and twist-bend nematic phases reveals that molecular dynamics are similar despite the difference in the molecular environment.

  14. Quasielastic Light Scattering Measurements of the Anisotropic Mechanical Properties of a Polymer Nematic Liquid Crystal.

    NASA Astrophysics Data System (ADS)

    Taratuta, Victor Gregory

    An experimental investigation of macroscopic mechanical properties of a polymer nematic liquid crystal was conducted on nematic solutions formed from rigid or semiflexible main chain polymers that are fully extended in a solution. The particular system under investigation is a poly-(gamma) -benzyl glutamate (PBG) which belongs to a class of synthetic polypeptides. Quasielastic Rayleigh light scattering on well aligned nematic single crystals of PBG was used to measure the elastic constants and the anisotropic viscosities as a function of concentration. The elastic constants are measured from the intensity of the scattered light which is determined by the amplitude of thermally excited director fluctuations. That amplitude depends on the energy of the fluctuation which is proportional to the appropriate elastic constant. The viscosities associated with the elastic deformation modes are computed from the characteristic relaxation times of the fluctuations by measuring their temporal autocorrelation function. The splay and bend elastic constants were found to be very similar in magnitude; both showed a linear dependence on concentration. The twist elastic constant was much smaller than either splay or bend and showed only a weak concentration dependence. Four out of five independent Leslie viscosities were measured (except the elongational flow viscosity (alpha)(,1)). The viscosities were found to exhibit very large anisotropies. Different types of viscosities showed distinctly different patterns of concentration dependence. (gamma)(,1) and (eta)(,c) were quadratic in concentration, (eta)(,a) was linear in concentration, and (eta)(,b) did not show any strong concentration dependence. The viscosity data indicate that even at a moderate length to diameter ratio studied (L/D - 30), the PBG approaches a behavior predicted for a system composed of infinitely long molecular chains. The concentration dependence data for the elastic constants and the anisotropic viscosities

  15. Orientational fluctuation study in nematic liquid crystals by high speed micrograph

    NASA Astrophysics Data System (ADS)

    Yoon, Beom-Jin; Park, Min Sang; Park, Jung O.; Srinivasarao, Mohan

    2009-03-01

    The orientational fluctuations in uniaxial and biaxial nematic liquid crystals were investigated with a polarized microscope and a high speed TV camera. Liquid crystals usually have fluctuations with respect to their director, even when the molecular axes tend to be aligned to each other. These fluctuations are sufficiently slow and large, have long wave length and increase with temperature. Herein, we describe our study on fluctuation dynamics by direct observations in real space, while it has been typically done by the photon scattering in reciprocal space. The twinkling of liquid crystals due to orientational fluctuations was observed with a high speed camera up to 500 frames/sec. The time correlation function of the intensity was computed via 2D spatial Fourier transform of each image and then the relaxation frequency was estimated from it. The elastic constant to the viscosity ratio was computed from the relaxation frequency. This approach provides facile route to analyze fluctuation dynamics in liquid crystals.

  16. Substrate-induced order in confined nematic liquid-crystal films

    NASA Astrophysics Data System (ADS)

    Gruhn, Thomas; Schoen, Martin

    1998-06-01

    In orientationally biased grand canonical ensemble Monte Carlo (GCEMC) simulations we investigated the microscopic structure of liquid-crystalline films confined between two plane parallel solid surfaces (i.e., walls) consisting of Ns discrete, rigidly fixed atoms. These wall atoms are distributed across the plane of a wall according to the (100) structure of the face-centered cubic lattice. Parameters of the film-wall interaction potential are chosen such that a homeotropic alignment of film molecules is favored. In the simulations the thermodynamic state of the film is determined by the temperature T, the chemical potential μ, the distance between the walls sz, and the film-wall interfacial area A. Thermodynamic states of the film are chosen such that a corresponding bulk liquid crystal is nematic. To simulate nematic phases in the GCEMC we modified the classic Gay-Berne potential for the interaction between a pair of film molecules so that the isotropic-nematic phase transition in the bulk occurs at sufficiently low densities. Reliability of the GCEMC method under these conditions is illustrated by a self-consistent comparison between Monte Carlo simulations in the canonical and grand canonical ensembles. In the bulk the nematic nature of the modified Gay-Berne fluid is established by computing the Mayer-Saupe order parameter S and suitably defined pair correlation functions which show that the bulk phase is not smectic even though S is fairly large. For a single temperature we investigate the isotropic-nematic phase transition in the modified Gay-Berne fluid which turns out to be a first-order phase transition. In the corresponding confined film variations of the microscopic structure with increasing sz are correlated with the normal component of the stress tensor Tzz(sz). Our results show that molecules in inner portions of the film undergo a reorganization from an originally planar orientation of their symmetry axes to a perpendicular one with respect to the

  17. Imaging in natural light with nematic liquid crystals (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Galstian, Tigran V.

    2015-10-01

    Nametic liquid crystals (NLC) are most commonly used liquid crystal (LC) materials in various light modulators [1], displays [2] and lenses [3]. However those materials have a fundamental limitation: they are polarization sensitive since the refractive index modulation here is achieved by the electric field induced reorientation of their local anisotropy axis. Thus, the standard imaging optical systems (used in consumer electronic products and dealing with natural light sources [4]) have to use double NLC structures in a cross oriented way and in rather requiring geometrical conditions. We describe a simple but very efficient optical device that allows the dynamic focusing of unpolarized light using a single NLC layer. The operation principle of the proposed device is based on the combination of an electrically variable "single layer lens" with two fixed optical elements for light reflection and 90° polarization flip. Such an approach is made possible thanks to the close integration of thin film wave plate and mirror. Preliminary experimental studies of the obtained electrically variable mirror show very promising results. Several standard camera geometries, using the double layer approach, and possible new geometries, using the reflective approach, will be described. References 1. Gordon D. Love, Wave-front correction and production of Zernike modes with a liquid-crystal spatial light modulator, Applied Optics, Vol. 36, Issue 7, pp. 1517-1524 (1997). 2. P. Yeh and C. Gu, Optics of Liquid Crystal Displays, Wiley, 1999. 3. T. Galstian, Smart Mini-Cameras, CRC Press, Taylor and Francis group, 2013. 4. www.lensvector.com

  18. Lensing effects in a nematic liquid crystal with topological defects.

    PubMed

    Sátiro, C; Moraes, F

    2006-06-01

    Light traveling through a liquid crystal with disclinations perceives a geometrical background which causes lensing effects similar to the ones predicted for cosmic objects like global monopoles and cosmic strings. In this paper we explore the effective geometry as perceived by light in such media. The comparison between both systems suggests that experiments can be done in the laboratory to simulate optical properties, like gravitational lensing, of cosmic objects. PMID:16775663

  19. Half-Integer Point Defects in the Q-Tensor Theory of Nematic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Di Fratta, G.; Robbins, J. M.; Slastikov, V.; Zarnescu, A.

    2016-02-01

    We investigate prototypical profiles of point defects in two-dimensional liquid crystals within the framework of Landau-de Gennes theory. Using boundary conditions characteristic of defects of index k/2, we find a critical point of the Landau-de Gennes energy that is characterised by a system of ordinary differential equations. In the deep nematic regime, b^2 small, we prove that this critical point is the unique global minimiser of the Landau-de Gennes energy. For the case b^2=0, we investigate in greater detail the regime of vanishing elastic constant L → 0, where we obtain three explicit point defect profiles, including the global minimiser.

  20. Chaotic orientational behavior of a nematic liquid crystal subjected to a steady shear flow.

    PubMed

    Rienäcker, Götz; Kröger, Martin; Hess, Siegfried

    2002-10-01

    Based on a relaxation equation for the second rank alignment tensor characterizing the molecular orientation in liquid crystals, we report on a number of symmetry-breaking transient states and simple periodic and irregular, chaotic out-of-plane orbits under steady flow. Both an intermittency route and a period-doubling route to chaos are found for this five-dimensional dynamic system in a certain range of parameters (shear rate, tumbling parameter at isotropic-nematic coexistence, and reduced temperature). A link to the corresponding rheochaotic states, present in complex fluids, is made. PMID:12443167

  1. Director fluctuations in nematic liquid crystals induced by an ultrasonic wave

    NASA Astrophysics Data System (ADS)

    Sátiro, Caio; Vitoriano, Carlindo

    2012-07-01

    The director-density coupling theory was formulated with two parameters (u1 and u2) to explain the acousto-optic effect in nematic liquid crystals. The assumption that the director is not able to accompany rapid oscillations of the sound wave, so that it actually couples to the time-averaged interaction, renders it effectively a u1-independent theory. In this paper, we investigate a route in which the time average is postponed to the end of the calculation. This approach allows us to derive measurable quantities that depend on both u1 and u2.

  2. Conoscopic analysis of electric field driven planar aligned nematic liquid crystal.

    PubMed

    Ranjini, Radhakrishnan; Matham, Murukeshan Vadakke; Nguyen, Nam-Trung

    2014-05-01

    This paper illustrates the conoscopic observation of a molecular reconstruction occurring across a nematic liquid crystal (NLC) medium in the presence of an external electric field. Conoscopy is an optical interferometric method, employed to determine the orientation of an optic axis in uniaxial crystals. Here a planar aligned NLC medium is used, and the topological changes with respect to various applied voltages are monitored simultaneously. Homogenous planar alignment is obtained by providing suitable surface treatments to the ITO coated cell walls. The variation in the conoscopic interferometric patterns clearly demonstrates the transition from planar to homeotropic state through various intermediate states. PMID:24921859

  3. Dielectric investigations of induced memory in chiral doped nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Middha, Manju; Kumar, Rishi; Raina, K. K.

    2015-08-01

    When an electric field is applied to thin film of a chiral doped nematic liquid crystal, unwinding of the helix takes place. Due to the competition of elastic forces of the material with the electrical and surface anchoring forces, defect lines are created. Sometimes after the removal of electric field, the system does not relax back to the original state and shows optical and electro-optical hysteresis. The induction of memory as a result of manipulation of the helix director remains an active field of study and can be useful for the development of memory based bistable low power devices.

  4. Homogeneous alignment of nematic liquid crystals by ion beam etched surfaces

    NASA Technical Reports Server (NTRS)

    Wintucky, E. G.; Mahmood, R.; Johnson, D. L.

    1979-01-01

    A wide range of the ion beam etch parameters are capable of producing uniform homogeneous alignment of nematic liquid crystals on SiO2 films. The alignment surfaces were generated by obliquely incident argon ions; a smaller range of ion beam parameters was also investigated with ZrO2 films and found suitable for homogeneous alignment. Extinction ratios were very high, and twist and tilt-bias angles were very small. The SEM results indicate a parallel oriented surface structure on the ion beam etched surfaces which may determine alignment.

  5. Convection in a nematic liquid crystal with homeotropic alignment and heated from below

    SciTech Connect

    Ahlers, G.

    1995-12-31

    Experimental results for convection in a thin horizontal layer of a homeotropically aligned nematic liquid crystal heated from below and in a vertical magnetic field are presented. A subcritical Hopf bifurcation leads to the convecting state. There is quantitative agreement between the measured and the predicted bifurcation line as a function of magnetic field. The nonlinear state near the bifurcation is one of spatio-temporal chaos which seems to be the result of a zig-zag instability of the straight-roll state.

  6. Electrohydrodynamic Pattern Formation in Nematic Liquid Crystals by External Pure Noise

    NASA Astrophysics Data System (ADS)

    Huh, Jong-Hoon

    2010-12-01

    Pure noise-induced electrohydrodynamic convections (EHCs) in nematic liquid crystals are presented in comparison with ac field-induced ones. There exists a characteristic cutoff frequency fc* of noise dividing EHC patterns qualitatively. Sufficiently colored noise with fc < fc* can induce a variety of well-ordered patterns such as Williams domains, fluctuating Williams domains, and grid patterns. The amplitude of the primary pattern (Williams domains) and its wavelength are investigated with varying intensity VN and/or cutoff frequency fc of noise. The present noise-induced EHCs are discussed on the basis of the conventional (ac-based) Carr-Helfrich mechanism.

  7. Sustained spatio-temporal chaotic flow at onset of electroconvection in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Gleeson, J. T.

    1997-02-01

    In the presence of a strong magnetic field parallel to the applied electric field, electrohydrodynamic convection (EHC) in nematic liquid crystals is a pattern forming system with weakly broken rotational symmetry in the plane parallel to the magnetic field. In this system, the first instability observed is to a spatio-temporally chaotic state, in qualitative agreement with recent theoretical results. We report experimental results demonstrating sustained time dependence and spatial disorder immediately above the subcritical transition from the quiescent state in this system.

  8. Difference in Noise-Induced Threshold Shift between Planar and Homeotropic Electroconvections in Nematic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Huh, Jong-Hoon; Kuribayashi, Akiyuki; Kai, Shoichi

    2009-08-01

    We report the threshold shift induced by externally applied noises for electrohydrodynamic convections (EHCs) in both planarly and homeotropically aligned nematic liquid crystals as well as in both the conduction and dielectric regimes. Owing to the difference in timescales among the intrinsic properties of EHCs, externally applied noises, and deterministic fields, the stabilization or destabilization effects induced by noises are observed. In particular, the difference in the threshold shift between both alignments is found, and discussed in terms of the EHC mechanisms for both alignments. Moreover, a noticeable noise-induced threshold shift is observed in the dielectric regime, which is markedly different from that in the conventional conduction regime.

  9. Equilibrium Configuration in a Nematic Liquid Crystal Droplet with Homeotropic Anchoring of Finite Strength

    NASA Astrophysics Data System (ADS)

    Kanke, Masaki; Sasaki, Kazuo

    2013-09-01

    Equilibrium configuration of order parameter in a nematic liquid crystal droplet with homeotropic anchoring of finite strength at the surface is studied numerically by using the Landau--de Gennes approach. It is found that a hedgehog-like configuration with a disclination loop of a small radius is stable for strong anchoring while an axial configuration without defect is stable for weak anchoring. A first-order phase transition from one configuration to the other occurs as the strength of the anchoring is varied. The critical anchoring strength turns out to increase almost linearly with the inverse of the droplet radius.

  10. Adsorption-induced anchoring transitions at nematic-liquid-crystal-crystal interfaces

    NASA Astrophysics Data System (ADS)

    Pieranski, P.; Jérôme, B.

    1989-07-01

    Discontinuous (first-order) anchoring transitions are shown to occur as a function of water adsorption at the nematic-liquid-crystal(E9)-gypsum and E9-mica interfaces. The transitions involve growth of domains with an anchoring a' making a finite angle with the direction a of the parent anchoring. The growth proceeds by motion of walls separating the domains with the new anchoring a' from the matrix with the parental anchoring a. A Landau-type expression for the interfacial energy is proposed and used to classify the anchoring transitions and to explain the behavior of the domains during the first-order anchoring transitions.

  11. Gel formation in a mixture of a block copolymer and a nematic liquid crystal.

    PubMed

    Khazimullin, Maxim; Müller, Thomas; Messlinger, Stephan; Rehberg, Ingo; Schöpf, Wolfgang; Krekhov, Alexei; Pettau, Robin; Kreger, Klaus; Schmidt, Hans-Werner

    2011-08-01

    The viscoelastic properties of a binary mixture of a mesogenic side-chain block copolymer in a low molecular weight nematic liquid crystal are studied for mass concentrations ranging from the diluted regime up to a liquid crystalline gel state at about 3%. In the gel state, the system does not flow, exhibits a polydomain structure on a microscopic level, and strongly scatters light. Below the gelation point, the system is homogeneous and behaves like a usual nematic, so the continuum theory of liquid crystals can be applied for interpreting the experimental data. Using the dynamic Fréedericksz transition technique, the dependence of the splay elastic constant and the rotational viscosity on the polymer concentration have been obtained. Comparing the dynamic behavior of block copolymer solutions with the respective homopolymer solutions reveals that, above a mass concentration of 1%, self-assembling of the block copolymer chain segments in clusters occurred, resulting in a gel state at higher concentrations. The effective cluster size is estimated as a function of the concentration, and a scaling-law behavior near the sol-gel transition is confirmed. This technique may serve as an alternative method for determining the gelation point. PMID:21929007

  12. Gel formation in a mixture of a block copolymer and a nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Khazimullin, Maxim; Müller, Thomas; Messlinger, Stephan; Rehberg, Ingo; Schöpf, Wolfgang; Krekhov, Alexei; Pettau, Robin; Kreger, Klaus; Schmidt, Hans-Werner

    2011-08-01

    The viscoelastic properties of a binary mixture of a mesogenic side-chain block copolymer in a low molecular weight nematic liquid crystal are studied for mass concentrations ranging from the diluted regime up to a liquid crystalline gel state at about 3%. In the gel state, the system does not flow, exhibits a polydomain structure on a microscopic level, and strongly scatters light. Below the gelation point, the system is homogeneous and behaves like a usual nematic, so the continuum theory of liquid crystals can be applied for interpreting the experimental data. Using the dynamic Fréedericksz transition technique, the dependence of the splay elastic constant and the rotational viscosity on the polymer concentration have been obtained. Comparing the dynamic behavior of block copolymer solutions with the respective homopolymer solutions reveals that, above a mass concentration of 1%, self-assembling of the block copolymer chain segments in clusters occurred, resulting in a gel state at higher concentrations. The effective cluster size is estimated as a function of the concentration, and a scaling-law behavior near the sol-gel transition is confirmed. This technique may serve as an alternative method for determining the gelation point.

  13. Calculation of the nematic entropy using digital images.

    PubMed

    Freire, F M C; Kimura, N M; Luders, D D; Palangana, A J; Simões, M

    2013-12-01

    In this work we will use digital images to compute the entropy dependence on temperature of a nematic lyotropic sample. The set of images comprehend the entire temperature range between a reentrant nematic isotropic phase transition, at a low temperature, and a usual nematic isotropic phase transition at a higher temperature. We will show that, inside the nematic phase, the image entropy profile agrees accurately with the entropy given by the Maier-Saupe model. As far as we know, this is the first time that the entropy of a lyotropic nematic phase is evaluated by this method, which introduces a way to measure their macroscopic variables. Namely, being that the entropy is a thermodynamical potential, this result implies that digital images can be used to compute mean values of nematic random variables. PMID:24483590

  14. Fabrication of twisted nematic structure and vector grating cells by one-step exposure on photocrosslinkable polymer liquid crystals.

    PubMed

    Kuzuwata, Mitsuru; Sasaki, Tomoyuki; Kawatsuki, Nobuhiro; Ono, Hiroshi

    2012-03-15

    We present a simple yet efficient method to automatically fabricate the twisted nematic structure by one-step exposure on an empty glass cell coated with photocrosslinkable polymer liquid crystal (PCLC) films. The resultant photoalignment directions of two substrates can be orthogonal to each other by controlling the difference between the exposure energy for upper and lower PCLC films and the twisted nematic (TN) structure can be automatically fabricated. The vector grating liquid crystalline cell with TN structure was also fabricated by means of a developed method, and the diffraction properties were well explained by the theoretical calculation on the basis of Jones calculus. PMID:22446243

  15. Simulation of three-dimensional director structures in twisted nematic liquid crystal displays

    NASA Astrophysics Data System (ADS)

    Lien, A.

    1993-03-01

    The three-dimensional simulation of the liquid crystal director deformation profile and the electric field distribution for the twisted nematic liquid crystal display has been carried out for the first time. The result gives us a complete understanding about liquid crystal deformation profile inside a pixel and the locus of the disclination line pair across the entire pixel area. This would not be possible in the case of the two-dimensional (2D) simulation [A. Lien, Proceedings of the 10th International Display Research Conference (vde-verlag gmbh, Berlin und Offenbach, 1990), p. 248; G. Haas, H. Wohler, M. W. Fritsch, and D. A. Mlynski, ibid., p. 252; A. Lien and R. A. John, IBM J. Res. Devel. 36, 51 (1992)], since the 2D simulation result is accurate only for the region which is far away from the corner area of a pixel.

  16. Nanosecond electro-optics of a nematic liquid crystal with negative dielectric anisotropy.

    PubMed

    Borshch, Volodymyr; Shiyanovskii, Sergij V; Li, Bing-Xiang; Lavrentovich, Oleg D

    2014-12-01

    We study a nanosecond electro-optic response of a nematic liquid crystal in a geometry where an applied electric field E modifies the tensor order parameter but does not change the orientation of the optic axis (director N ̂). We use a nematic with negative dielectric anisotropy with the electric field applied perpendicularly to N ̂. The field changes the dielectric tensor at optical frequencies (optic tensor) due to the following mechanisms: (a) nanosecond creation of the biaxial orientational order, (b) uniaxial modification of the orientational order that occurs over time scales of tens of nanoseconds, and (c) the quenching of director fluctuations with a wide range of characteristic times up to milliseconds. We develop a model to describe the dynamics of all three mechanisms. We design the experimental conditions to selectively suppress the contributions from the quenching of director fluctuations (c) and from the biaxial order effect (a) and thus, separate the contributions of the three mechanisms in the electro-optic response. As a result, the experimental data can be well fitted with the model parameters. The analysis provides a rather detailed physical picture of how the liquid crystal responds to a strong electric field on a time scale of nanoseconds. The paper provides a useful guidance in the current search for the biaxial nematic phase. Namely, the temperature dependence of the biaxial susceptibility allows one to estimate the temperature of the potential uniaxial-to-biaxial phase transition. An analysis of the quenching of director fluctuations indicates that on a time scale of nanoseconds, the classic model with constant viscoelastic material parameters might reach its limit of validity. The effect of nanosecond electric modification of the order parameter can be used in applications in which one needs to achieve ultrafast (nanosecond) changes in optical characteristics, such as birefringence. PMID:25615116

  17. Monitoring defects on monolayer graphene using nematic liquid crystals.

    PubMed

    Lim, Young Jin; Lee, Byung Hoon; Kwon, You Ri; Choi, Young Eun; Murali, G; Lee, Joong Hee; Nguyen, Van Luan; Lee, Young Hee; Lee, Seung Hee

    2015-06-01

    Defects in graphene governs electrical and optical properties. Although grain boundaries in graphene inevitably formed during large area synthesis process, which act as scattering centers for charge carriers to degrade mobility, have been studied extensively, point defects have been rarely investigated mainly due to the absence of facile observation tools. Here, we report polarized optical microscopy to observe defect distributions in monolayer graphene. This was realized by aligning liquid crystal s (LC) on graphene where the defect population was modulated by irradiating ultraviolet (UV) light directly on graphene surface under moisture condition. Aromatic rings in LC molecules are oriented with hexagonal rings in graphene to have preferred orientation, providing a way to identify relative orientations of graphene domains and point defects. Our studies show that point defects generated by prolonged UV irradiation time give rise to irregular LC alignment with disclination lines on the graphene surface and a large-size LC domain associated with graphene single domain eventually disappeared. This indicates that defects associated with oxygen-containing functional groups cause to reduce the strong stacking interaction between graphene and LC molecules. PMID:26072784

  18. Enhanced magnetic-field-induced optical properties of nanostructured magnetic fluids by doping nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Wang, Xiang; Pu, Shengli; Ji, Hongzhu; Yu, Guojun

    2012-05-01

    Ferronematic materials composed of 4-cyano-4'-pentylbiphenyl nematic liquid crystal and oil-based Fe3O4 magnetic fluid were prepared using ultrasonic agitation. The birefringence (Δ n) and figure of merit of optical properties ( Q = Δ n/α, where α is the extinction coefficient) of pure magnetic fluids and the as-prepared ferronematic materials were examined and compared. The figure of merit of optical properties weighs the birefringence and extinction of the materials and is more appropriate to evaluate their optical properties. Similar magnetic-field- and magnetic-particle-concentration-dependent properties of birefringence and figure of merit of optical properties were obtained for the pure magnetic fluids and the ferronematic materials. For the ferronematic materials, the values of Q increase with the volume fractions of nematic liquid crystal under certain fixed field strength and are larger than those of their corresponding pure magnetic fluids at high field region. In addition, the enhancement of Q value increases monotonously with the magnetic field and becomes remarkable when the applied magnetic field is beyond 50 mT. The maximum relative enhanced value of Q R exceeds 6.8% in our experiments. The results of this work may conduce to extend the pragmatic applications of nanostructured magnetic fluids in optical field.

  19. Enhanced magnetic-field-induced optical properties of nanostructured magnetic fluids by doping nematic liquid crystals.

    PubMed

    Wang, Xiang; Pu, Shengli; Ji, Hongzhu; Yu, Guojun

    2012-01-01

    Ferronematic materials composed of 4-cyano-4'-pentylbiphenyl nematic liquid crystal and oil-based Fe3O4 magnetic fluid were prepared using ultrasonic agitation. The birefringence (Δn) and figure of merit of optical properties (Q = Δn/α, where α is the extinction coefficient) of pure magnetic fluids and the as-prepared ferronematic materials were examined and compared. The figure of merit of optical properties weighs the birefringence and extinction of the materials and is more appropriate to evaluate their optical properties. Similar magnetic-field- and magnetic-particle-concentration-dependent properties of birefringence and figure of merit of optical properties were obtained for the pure magnetic fluids and the ferronematic materials. For the ferronematic materials, the values of Q increase with the volume fractions of nematic liquid crystal under certain fixed field strength and are larger than those of their corresponding pure magnetic fluids at high field region. In addition, the enhancement of Q value increases monotonously with the magnetic field and becomes remarkable when the applied magnetic field is beyond 50 mT. The maximum relative enhanced value of QR exceeds 6.8% in our experiments. The results of this work may conduce to extend the pragmatic applications of nanostructured magnetic fluids in optical field. PMID:22587542

  20. Alignment structures and diffraction properties of chiral nematic liquid crystal cells with periodically patterned photoalignment films

    NASA Astrophysics Data System (ADS)

    Sasaki, Tomoyuki; Shimura, Rei; Kawai, Kotaro; Noda, Kohei; Sakamoto, Moritsugu; Kawatsuki, Nobuhiro; Ono, Hiroshi

    2016-01-01

    Liquid crystal (LC) cells with periodic alignment distributions were fabricated using chiral nematic LCs (N*LCs), which were prepared using mixtures of a nematic LC and a chiral dopant, along with photoreactive liquid crystalline polymer (PLCP) films. Periodic structures were formed by polarization holographic recording in the PLCP films. The director distribution in each cell depended on the ratio of chiral dopant present, i.e., the inherent helical pitch of the N*LCs. These periodic alignment structures with line defects in the LC grating cells were well explained on the basis of the elastic continuum theory of the N*LCs and the photoalignment effect of the PLCP films. The diffraction properties of the grating LC cells were also investigated using a polarized visible laser. The observed intensity and polarization states of the diffracted beams were consistent with theoretical ones calculated using the director distribution models. Our results clarify that the diffraction properties of the grating LC cells can be controlled by the helical pitch of the N*LCs.

  1. Director alignment relative to the temperature gradient in nematic liquid crystals studied by molecular dynamics simulation.

    PubMed

    Sarman, Sten; Laaksonen, Aatto

    2014-07-28

    The director alignment relative to the temperature gradient in nematic liquid crystal model systems consisting of soft oblate or prolate ellipsoids of revolution has been studied by molecular dynamics simulation. The temperature gradient is maintained by thermostating different parts of the system at different temperatures by using a Gaussian thermostat. It is found that the director of the prolate ellipsoids aligns perpendicularly to the temperature gradient whereas the director of the oblate ellipsoids aligns parallel to this gradient. When the director is oriented in between the parallel and perpendicular orientations a torque is exerted forcing the director to the parallel or perpendicular orientation. Because of symmetry restrictions there is no linear dependence of the torque being a pseudovector on the temperature gradient being a polar vector in an axially symmetric system such as a nematic liquid crystal. The lowest possible order of this dependence is quadratic. Thus the torque is very weak when the temperature gradient is small, which may explain why this orientation phenomenon is hard to observe experimentally. In both cases the director attains the orientation that minimises the irreversible entropy production. PMID:24919847

  2. Circular flow formation triggered by Marangoni convection in nematic liquid crystal films with a free surface.

    PubMed

    Choi, Hyunhee; Takezoe, Hideo

    2016-01-14

    We demonstrate circular flow formation at a surface in homeotropically oriented nematic liquid crystals with a free surface using focused laser beam irradiation. Under a weak laser power, a pit together with an associated circular bulge is formed: the Marangoni effect. Here a diverging molecular flow from the pit (thermocapillary flow) also induces director tilt in the radial direction. Upon increasing the laser power, the pit becomes deeper, and eventually evolves into a circular flow associated with a deeper pit and a subsidiary circular bulge or valley structure. This phenomenon is induced by escaping from excess deformation energy due to a bend deformation of the director. Actually, we confirmed that the circular flow is never formed in the isotropic phase. The handedness of the vortex cannot be controlled by circular polarisation, but is controllable by doping with chiral molecules. This rotational motion (a nematic micro-rotor) is a unique phenomenon only exhibited by anisotropic liquids, and is expected to be applied for novel devices. PMID:26482229

  3. Elastic Torque on a Ferromagnetic Disk within a Nematic Liquid Crystal

    NASA Astrophysics Data System (ADS)

    Rovner, Joel B.; Borgnia, Dan S.; Lapointe, Clayton P.; Reich, Daniel H.; Leheny, Robert L.

    2012-02-01

    An aspherical particle suspended in a nematic liquid crystal will impose an orientationally dependent energy due to coupling to the nematic elasticity. This energy depends strongly on the anchoring conditions on the surface of the inclusion, its shape, as well as the proximity of other boundary conditions on the fluid such as those set by the container. To study these properties, ferromagnetic nickel disks with homeotropic surface anchoring were suspended in the liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) in a planar cell. The disks, 300 nm in thickness and 10 μm in diameter, possess a permanent magnetic moment confined to the disk's plane. In the absence of any external torque the disks align with the normal to their faces parallel to the director. Rotating of the disks from this preferred orientation creates an elastic deformation that is manifested by an opposing torque. Balancing this torque with the torque from an external magnetic field for various angles of rotation, we have mapped out the orientationally dependent energy. Over a large range of angles the torque shows a linear dependence as predicted by an electrostatic analogy.

  4. Lattice Boltzmann simulation of asymmetric flow in nematic liquid crystals with finite anchoring

    NASA Astrophysics Data System (ADS)

    Zhang, Rui; Roberts, Tyler; Aranson, Igor S.; de Pablo, Juan J.

    2016-02-01

    Liquid crystals (LCs) display many of the flow characteristics of liquids but exhibit long range orientational order. In the nematic phase, the coupling of structure and flow leads to complex hydrodynamic effects that remain to be fully elucidated. Here, we consider the hydrodynamics of a nematic LC in a hybrid cell, where opposite walls have conflicting anchoring boundary conditions, and we employ a 3D lattice Boltzmann method to simulate the time-dependent flow patterns that can arise. Due to the symmetry breaking of the director field within the hybrid cell, we observe that at low to moderate shear rates, the volumetric flow rate under Couette and Poiseuille flows is different for opposite flow directions. At high shear rates, the director field may undergo a topological transition which leads to symmetric flows. By applying an oscillatory pressure gradient to the channel, a net volumetric flow rate is found to depend on the magnitude and frequency of the oscillation, as well as the anchoring strength. Taken together, our findings suggest several intriguing new applications for LCs in microfluidic devices.

  5. Lattice Boltzmann simulation of asymmetric flow in nematic liquid crystals with finite anchoring.

    PubMed

    Zhang, Rui; Roberts, Tyler; Aranson, Igor S; de Pablo, Juan J

    2016-02-28

    Liquid crystals (LCs) display many of the flow characteristics of liquids but exhibit long range orientational order. In the nematic phase, the coupling of structure and flow leads to complex hydrodynamic effects that remain to be fully elucidated. Here, we consider the hydrodynamics of a nematic LC in a hybrid cell, where opposite walls have conflicting anchoring boundary conditions, and we employ a 3D lattice Boltzmann method to simulate the time-dependent flow patterns that can arise. Due to the symmetry breaking of the director field within the hybrid cell, we observe that at low to moderate shear rates, the volumetric flow rate under Couette and Poiseuille flows is different for opposite flow directions. At high shear rates, the director field may undergo a topological transition which leads to symmetric flows. By applying an oscillatory pressure gradient to the channel, a net volumetric flow rate is found to depend on the magnitude and frequency of the oscillation, as well as the anchoring strength. Taken together, our findings suggest several intriguing new applications for LCs in microfluidic devices. PMID:26931724

  6. Enhanced magnetic-field-induced optical properties of nanostructured magnetic fluids by doping nematic liquid crystals

    PubMed Central

    2012-01-01

    Ferronematic materials composed of 4-cyano-4′-pentylbiphenyl nematic liquid crystal and oil-based Fe3O4 magnetic fluid were prepared using ultrasonic agitation. The birefringence (Δn) and figure of merit of optical properties (Q = Δn/α, where α is the extinction coefficient) of pure magnetic fluids and the as-prepared ferronematic materials were examined and compared. The figure of merit of optical properties weighs the birefringence and extinction of the materials and is more appropriate to evaluate their optical properties. Similar magnetic-field- and magnetic-particle-concentration-dependent properties of birefringence and figure of merit of optical properties were obtained for the pure magnetic fluids and the ferronematic materials. For the ferronematic materials, the values of Q increase with the volume fractions of nematic liquid crystal under certain fixed field strength and are larger than those of their corresponding pure magnetic fluids at high field region. In addition, the enhancement of Q value increases monotonously with the magnetic field and becomes remarkable when the applied magnetic field is beyond 50 mT. The maximum relative enhanced value of QR exceeds 6.8% in our experiments. The results of this work may conduce to extend the pragmatic applications of nanostructured magnetic fluids in optical field. PMID:22587542

  7. In situ prepared polymer films as alignment layers for nematic liquid crystals

    SciTech Connect

    Pires, David; Galerne, Yves

    2006-12-15

    By means of UV-visible irradiations and convenient photoinitiators, we realize the cross-linked polymerization of a triacrylate monomer in solution in a nematic liquid crystal (p-pentyl-p{sup '}-cyanobiphenyl) at low concentrations (a few wt %), i.e., under conditions opposite to the synthesis of polymer-dispersed liquid crystals. As atomic force microscope measurements show, when operating close to, but below, the percolation transition, a thin polymer layer is synthesized in situ, directly covering and coating all the substrate. These observations therefore confirm that the properties of anchoring and of alignment memory previously observed in such nematic cells effectively originate from the synthesized polymer film. According to the photoinitiator used, bulk or surface polymerizations dominate and respectively produce continuous or discontinuous films (i.e., with separate clusters). In the former case, polymer aggregates are first synthesized. They then diffuse in the volume until they meet a surface, where they definitely stick if they are large enough. An estimate of the entropy and interaction energy differences between the two states, stuck or free, shows that the aggregates stick on the substrates if their size exceeds the length of about three monomers, i.e., if they contain more than 20-30 monomers. Interestingly, these films may be used to replicate nonuniform alignment patterns that are difficult to realize otherwise. The method may be considered as an imprinting method.

  8. Miscibility and alignment effects of mixed monolayer cyanobiphenyl liquid-crystal-capped gold nanoparticles in nematic cyanobiphenyl liquid crystal hosts.

    PubMed

    Qi, Hao; Kinkead, Brandy; Marx, Vanessa M; Zhang, Huai R; Hegmann, Torsten

    2009-06-01

    Against the rule: Liquid crystal hosts (5CB and 8CB) are doped with different thiol decorated gold nanoparticles (see figure). The "simple" hexanethiol and dodecanethiol capped nanoparticles (Au1 and Au2) are more compatible to the nematic cyanobiphenyl liquid crystals than nanoparticles capped simultaneously with alkylthiols and a nematic cyanobiphenyl thiol (Au3 and Au4).This study focuses on the miscibility of liquid crystal (LC) decorated gold nanoparticles (NPs) in nematic LCs. To explore if LC functional groups on the gold NP corona improve the compatibility (miscibility) with structurally related LC hosts, we examined mixtures of two LC hosts, 5CB and 8CB, doped at 5 wt % with different types of gold NPs. Four alkanethiol-capped NPs were synthesized; two homogeneously coated with alkanethiols (Au1 with C(6)H(13)SH and Au2 with C(12)H(25)SH), and two that were additionally capped at a different ratio with a mesogenic cyanobiphenyl end-functionalized alkanethiol HS10OCB (C(6)H(13)SH + HS10OCB for Au3 and C(12)H(25)SH + HS10OCB for Au4). Investigating these mixtures in the bulk for settling of the NPs, and in thin films using polarized optical microscopy (POM) between untreated glass slides as well as POM studies and electro-optic tests in planar ITO/polyimide test cells, reveal that the alkanethiol capped NPs Au1 and Au2 are more compatible with the two polar cyanobiphenyl hosts in comparison to the NPs decorated with the cyanobiphenyl moieties. All NPs induce homeotropic alignment in 5CB and 8CB between untreated glass slides, with Au1 and Au2 showing characteristic birefringent stripes, and Au3 and A4 exhibiting clear signs of aggregation. In rubbed polyimide cells, however, Au3 and Au4 fail to induce homeotropic alignment and show clear signs of macroscopic aggregation. PMID:19334026

  9. Toroidal Nematics

    NASA Astrophysics Data System (ADS)

    Fernandez-Nieves, Alberto

    We will discuss how nematic liquid crystals organize inside toroidal droplets. When the director is parallel to the bounding surface, we find spontaneous reflection symmetry breaking, which we attribute to the role played by saddle-splay contributions to the Frank free energy. When the director is perpendicular to the bounding surface, we find that the structure is reminiscent of the escape radial configuration seen in cylinders, but with a central doubly-twisted organization, which we attribute to the geometry of the torus. We will end by presenting recent experiments with active nematics on the toroidal surface. In this case, topology and activity both affect the structure and dynamics of the material.

  10. Asymmetric motion of bubble in nematic liquid crystal induced by symmetry-broken evaporation

    NASA Astrophysics Data System (ADS)

    Kim, Sung-Jo; Lev, Bohdan; Kim, Jong-Hyun

    2016-07-01

    The size of air bubbles in nematic liquid crystals can be continuously decreased through the absorption of air molecules into the host liquid crystal. A bubble and its accompanying hyperbolic hedgehog point defect undergo a continuous asymmetric motion, while the bubble decreases in size. In this study, a mechanism is proposed to theoretically explain both the motion of the air bubble and the point defect observed experimentally. Anisotropic evaporation of air molecules may occur because of the symmetry breaking of the director configuration near the point defect. The motion of the center of the air bubble to the hyperbolic hedgehog point defect is induced by the anisotropic force due to evaporation of air molecules and Stokes drag force.

  11. A random laser made of nematic liquid crystal doped with a laser dye

    NASA Astrophysics Data System (ADS)

    Sznitko, L.; Kaliciak, K.; Adamow, A.; Mysliwiec, J.

    2016-06-01

    We report on random laser emission obtained in 5CB and E7 nematic liquid crystal (LC) mixtures doped with 1% weight to weight ratio of DCM laser dye. The LC cell was used as asymmetric planar waveguide were emission was collected from the edge of the sample. Variable stripe length method was utilized to estimate the gain and the losses coefficients. Both systems have shown the threshold energy fluence in order of several mJ/cm2. In both cases above Fredericks potential, significant increase of emission intensity was observed due to the increase of light scattering on liquid crystalline domains. Moreover the use of fifth order of diffraction grating covered with thin alumina film resulted in strong multimode and directional laser emission.

  12. All-optical measurement of elastic constants in nematic liquid crystals.

    PubMed

    Klus, Bartłomiej; Laudyn, Urszula A; Karpierz, Mirosław A; Sahraoui, Bouchta

    2014-12-01

    In this article we present a new all-optical method to measure elastic constants connected with twist and bend deformations. The method is based on the optical Freedericksz threshold effect induced by the linearly polarized electro-magnetic wave. In the experiment elastic constants are measured of commonly used liquid crystals 6CHBT and E7 and two new nematic mixtures with low birefringence. The proposed method is neither very sensitive on the variation of cell thickness, beam waist or the power of a light beam nor does it need any special design of a liquid crystal cell. The experimental results are in good agreement with the values obtain by other methods based on an electro-optical effect. PMID:25606956

  13. Competition of lattice and basis for alignment of nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    DeBenedictis, Andrew; Atherton, Timothy J.; Anquetil-Deck, Candy; Cleaver, Douglas J.; Emerson, David B.; Wolak, Mathew; Adler, James H.

    2015-10-01

    Due to elastic anisotropy, two-dimensional patterning of substrates can promote weak azimuthal alignment of adjacent nematic liquid crystals. Here we consider how such alignment can be achieved using a periodic square lattice of circular or elliptical motifs. In particular, we examine ways in which the lattice and motif can combine to favor differing orientations. Using Monte Carlo simulation and continuum elasticity we find, for circular motifs, that the coverage fraction controls both the polar anchoring angle and a transition in the azimuthal orientation. If the circles are generalized to ellipses, arbitrary control of the effective easy axis and effective anchoring potential becomes achievable by appropriate tuning of the ellipse motif relative to the periodic lattice patterning. This has possible applications in both monostable and bistable liquid crystal device contexts.

  14. Thermal switching of the reflection in chiral nematic mesoporous organosilica films infiltrated with liquid crystals.

    PubMed

    Giese, Michael; De Witt, Joanna C; Shopsowitz, Kevin E; Manning, Alan P; Dong, Ronald Y; Michal, Carl A; Hamad, Wadood Y; MacLachlan, Mark J

    2013-08-14

    Materials that undergo stimulus-induced optical changes are important for many new technologies. In this paper, we describe a new free-standing silica-based composite film that exhibits reversible thermochromic reflection, induced by a liquid crystalline guest in the pores of iridescent mesoporous films. We demonstrate that selective reflection from the novel mesoporous organosilica material with chiral nematic organization can be reversibly switched by thermal cycling of the 8CB guest between its isotropic and liquid crystalline states, which was proven by solid-state NMR experiments. The switching of the optical properties of the chiral solid-state host by stimulus-induced transitions of the guest opens the possibility of applications for these novel materials in sensors and displays. PMID:23859140

  15. Competition of lattice and basis for alignment of nematic liquid crystals.

    PubMed

    DeBenedictis, Andrew; Atherton, Timothy J; Anquetil-Deck, Candy; Cleaver, Douglas J; Emerson, David B; Wolak, Mathew; Adler, James H

    2015-10-01

    Due to elastic anisotropy, two-dimensional patterning of substrates can promote weak azimuthal alignment of adjacent nematic liquid crystals. Here we consider how such alignment can be achieved using a periodic square lattice of circular or elliptical motifs. In particular, we examine ways in which the lattice and motif can combine to favor differing orientations. Using Monte Carlo simulation and continuum elasticity we find, for circular motifs, that the coverage fraction controls both the polar anchoring angle and a transition in the azimuthal orientation. If the circles are generalized to ellipses, arbitrary control of the effective easy axis and effective anchoring potential becomes achievable by appropriate tuning of the ellipse motif relative to the periodic lattice patterning. This has possible applications in both monostable and bistable liquid crystal device contexts. PMID:26565259

  16. Competition of lattice and basis for alignment of nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Debenedictis, Andrew; Anquetil-Deck, Candy; Cleaver, Douglas J.; Emerson, David B.; Wolak, Mathew; Adler, James H.; Atherton, Timothy J.

    Due to elastic anisotropy, two-dimensional patterning of substrates can promote weak azimuthal alignment of adjacent nematic liquid crystals. We consider a periodic square lattice of elliptical motifs to examine ways in which the lattice and motif can combine to favor differing orientations. Using semi-analytic elastic continuum theory and Monte Carlo simulations, we find, for circular motifs, that the coverage fraction controls both the polar anchoring angle and a transition in the azimuthal orientation. If the circles are generalized to ellipses, arbitrary control of the effective easy axis and effective anchoring potential becomes achievable by appropriate tuning of the orientation of the ellipse motif relative to the lattice vectors. To determine the behavior of liquid crystals near the domain boundaries, we additionally formulate and solve the full 3D Euler-Lagrange equations directly. We additionally comment on the role of weak anchoring and saddle-splay elasticity.

  17. A self-quenched defect glass in a colloid-nematic liquid crystal composite.

    PubMed

    Wood, T A; Lintuvuori, J S; Schofield, A B; Marenduzzo, D; Poon, W C K

    2011-10-01

    Colloidal particles immersed in liquid crystals frustrate orientational order. This generates defect lines known as disclinations. At the core of these defects, the orientational order drops sharply. We have discovered a class of soft solids, with shear moduli up to 10(4) pascals, containing high concentrations of colloidal particles (volume fraction φ ≳ 20%) directly dispersed into a nematic liquid crystal. Confocal microscopy and computer simulations show that the mechanical strength derives from a percolated network of defect lines entangled with the particles in three dimensions. Such a "self-quenched glass" of defect lines and particles can be considered a self-organized analog of the "vortex glass" state in type II superconductors. PMID:21980107

  18. Electric field effects in nematic liquid crystals doped with carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Cîrtoaje, Cristina; Petrescu, Emil; Moţoc, Cornelia

    2013-12-01

    The aim of this paper was to investigate electric field induced effects in mixtures of nematic liquid crystals (NLCs) with positive electric anisotropies (MCL 6601 Merck) with carbon nanotubes (MWCNT from Aldrich). In planar alignment, the current-electric field dependence and the current-temperature dependence were explained by assuming a Poole-Frenkel effect (i.e. a tunnelling mechanism) and good agreement with the experimental data was obtained. Within this high field range it resulted that in planar aligned NLC-CNTs mixture the conductivity decreases when the temperature was increased. In homeotropic aligned mixture, the conduction mechanism is similar to the one occurring in a semiconductor: the conductivity increases when increasing temperature. This happens because in thin liquid crystal cells there is a possibility to realize an inner contact between nanotubes and electrodes so the mixture behaves like a semiconductor.

  19. Optically driven translational and rotational motions of microrod particles in a nematic liquid crystal

    PubMed Central

    Eremin, Alexey; Hirankittiwong, Pemika; Chattham, Nattaporn; Nádasi, Hajnalka; Stannarius, Ralf; Limtrakul, Jumras; Haba, Osamu; Yonetake, Koichiro; Takezoe, Hideo

    2015-01-01

    A small amount of azo-dendrimer molecules dissolved in a liquid crystal enables translational and rotational motions of microrods in a liquid crystal matrix under unpolarized UV light irradiation. This motion is initiated by a light-induced trans-to-cis conformational change of the dendrimer adsorbed at the rod surface and the associated director reorientation. The bending direction of the cis conformers is not random but is selectively chosen due to the curved local director field in the vicinity of the dendrimer-coated surface. Different types of director distortions occur around the rods, depending on their orientations with respect to the nematic director field. This leads to different types of motions driven by the torques exerted on the particles by the director reorientations. PMID:25624507

  20. Homeotropic orientation of a nematic liquid crystal by bent-core molecules adsorbed on its surface

    NASA Astrophysics Data System (ADS)

    Hwang, Jiyong; Yang, Seungbin; Lee, Hyojin; Kim, Jongyoon; Lee, Ji-Hoon; Kang, Shin-Woong; Choi, E.-Joon

    2015-06-01

    We reported the promotion of a homeotropic alignment of a nematic liquid crystal (NLC) by bent-core liquid-crystal (BLC) Molecules adsorbed its surface. The BLC was mixed at various concentrations with the NLC, and the mixtures were injected into an empty cell with a cell gap of 13 μm. Although the pure NLC showed a heterogeneous orientation, the BLC-NLC mixture was gradually transformed to a homeotropic alignment with increasing concentration of the BLC. We investigated the surface topography of the samples by using an atomic force microscopy (AFM) and found that the BLC molecules were segregated into a polyimide (PI) surface and formed protrusion domains with diameters of 50-100 nm. The BLC protrusions might promote the homeotropic orientation of the NLC molecules.

  1. Length Selection in Dendritic Growth of Electrohydrodynamic Convection in a Nematic Liquid Crystal

    NASA Astrophysics Data System (ADS)

    Gheorghiu, Nadina; Gleeson, J. T.

    2001-03-01

    Dendritic growth of electrohydrodynamic convection (EHC) with parallel magnetic field in a nematic liquid crystal (NLC) has been already subjected to one important experiment (J.T.Gleeson, Nature, 385, 511 (1997)). Further exploration of this interesting pattern-forming system is presented here. The most important question is: What sets the length scale for the dendrite? In order to find this, we use two control parameters in our experiment: the thickness d of the liquid crystal film, and the intensity H of the magnetic field. The first one is proportional to the pattern wavelength in the traditional EHC experiment, while the second determines the distance of externally imposed anisotropy, the magnetic coherence length ξ_m. By systematically varying d and ξ_m, we relate these two imposed lengths to those that characterize the dendrite: the tip radius of curvature ρ and the interface width w. An estimate of the critical field HC for the subcritical bifurcation is also provided.

  2. Stripe domains in a nearly homeotropic nematic liquid crystal: a bend escaped state at a nematic-smectic-A transition.

    PubMed

    Pergamenshchik, V M; Lelidis, I; Uzunova, V A

    2008-04-01

    We report an observation and mechanism of spontaneous periodic modulations of the nematic director close to the temperature T(NA) of a nematic-to-smectic-A phase transition if the surface alignment slightly differs from a pure homeotropic one. Stripe domains appear in the nematic phase about one degree above T(NA) and persist into the Sm A phase. The instability of the homogeneous state with respect to stripe domains is shown to be related to a very large bend constant which is much larger than the twist and splay elastic constants. The instability mechanism consists of reduction of the highly energetic bend deformation, induced by small surface director tilts, at the expense of a spontaneous periodic splay-twist modulation. Using smallness of the twist-to-bend and splay-to-bend elastic constant ratios, the critical condition of the instability and the modulation period are found analytically. Both the experimentally obtained and theoretically predicted domain period scales very closely to a square root of the cell thickness. PMID:18517639

  3. Nematic and blue phase liquid crystals for temperature stabilization and active optical tuning of silicon photonic devices (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Ptasinski, Joanna N.; Khoo, Iam Choon; Fainman, Yeshaiahu

    2015-10-01

    We describe the underlying theories and experimental demonstrations of passive temperature stabilization of silicon photonic devices clad in nematic liquid crystal mixtures, and active optical tuning of silicon photonic resonant structures combined with dye-doped nematic and blue phase liquid crystals. We show how modifications to the resonator device geometry allow for not only enhanced tuning of the resonator response, but also aid in achieving complete athermal operations of silicon photonic circuits. [Ref.: I.C. Khoo, "DC-field-assisted grating formation and nonlinear diffractions in methyl-red dye-doped blue phase liquid crystals," Opt. Lett. 40, 60-63 (2015); J. Ptasinski, I.C. Khoo, and Y. Fainman, "Enhanced optical tuning of modified-geometry resonators clad in blue phase liquid crystals," Opt. Lett. 39, 5435-5438 (2014); J. Ptasinski, I.C. Khoo, and Y. Fainman, "Passive Temperature Stabilization of Silicon Photonic Devices Using Liquid Crystals," Materials 7(3), 2229-2241 (2014)].

  4. Computational studies of history dependence in nematic liquid crystals in random environments

    NASA Astrophysics Data System (ADS)

    Ranjkesh, Amid; Ambrožič, Milan; Kralj, Samo; Sluckin, Timothy J.

    2014-02-01

    Glassy liquid crystalline systems are expected to show significant history-dependent effects. Two model glassy systems are the RAN and SSS (sprinkled silica spin) lattice models. The RAN model is a Lebwohl-Lasher lattice model with locally coupled nematic spins, together with uncorrelated random anisotropy fields at each site, while the SSS model has a finite concentration of impurity spins frozen in random directions. Here Brownian simulation is used to study the effect of different sample histories in the low temperature regime in a three-dimensional (d =3) model intermediate between SSS and RAN, in which a finite concentration p nematic spins with coupling W. Simulations were performed at temperature T ˜TNI/2 (TNI the bulk nematic-isotropic transition temperature) for temperature-quenched and field-quenched histories (TQH and FQH, respectively), as well as for temperature-annealed histories (AH). The first two of these limits represent extreme histories encountered in typical experimental studies. Using long-time averages for equilibrated systems, we calculate orientational order parameters and two-point correlation functions. Finite-size scaling was used to determine the range of the orientational ordering, as a function of coupling strength W ,p and sample history. Sample history plays a significant role; for given concentration p, as disorder strength W is increased, TQH systems sustain quasi-long-range order (QLRO) and short-range order (SRO). The data are also consistent with a long-range order (LRO) phase at very low disorder strength. By contrast, for FQH and p ≤0.1, only LRO and QLRO occur within the range of parameters investigated. The crossover between regimes depends on history, but in general, the FQH phase is more ordered than the AH phase, which is more ordered than the TQH phase. However, at temperatures close to the isotropic-nematic phase transition of pure samples

  5. Computational studies of history dependence in nematic liquid crystals in random environments.

    PubMed

    Ranjkesh, Amid; Ambrožič, Milan; Kralj, Samo; Sluckin, Timothy J

    2014-02-01

    Glassy liquid crystalline systems are expected to show significant history-dependent effects. Two model glassy systems are the RAN and SSS (sprinkled silica spin) lattice models. The RAN model is a Lebwohl-Lasher lattice model with locally coupled nematic spins, together with uncorrelated random anisotropy fields at each site, while the SSS model has a finite concentration of impurity spins frozen in random directions. Here Brownian simulation is used to study the effect of different sample histories in the low temperature regime in a three-dimensional (d = 3) model intermediate between SSS and RAN, in which a finite concentration p < p(c) (p(c) the percolation threshold) of frozen spins interacts with neighboring nematic spins with coupling W. Simulations were performed at temperature T ∼ T(NI)/2 (T(NI) the bulk nematic-isotropic transition temperature) for temperature-quenched and field-quenched histories (TQH and FQH, respectively), as well as for temperature-annealed histories (AH). The first two of these limits represent extreme histories encountered in typical experimental studies. Using long-time averages for equilibrated systems, we calculate orientational order parameters and two-point correlation functions. Finite-size scaling was used to determine the range of the orientational ordering, as a function of coupling strength W,p and sample history. Sample history plays a significant role; for given concentration p, as disorder strength W is increased, TQH systems sustain quasi-long-range order (QLRO) and short-range order (SRO). The data are also consistent with a long-range order (LRO) phase at very low disorder strength. By contrast, for FQH and p ≤ 0.1, only LRO and QLRO occur within the range of parameters investigated. The crossover between regimes depends on history, but in general, the FQH phase is more ordered than the AH phase, which is more ordered than the TQH phase. However, at temperatures close to the isotropic-nematic phase transition of

  6. Detection of a new 'nematic-like' phase in liquid crystal-amphiphile mixture by differential scanning calorimetry

    SciTech Connect

    Dan, Kaustabh Roy, Madhusudan Datta, Alokmay

    2014-04-24

    Differential Scanning Calorimetry (DSC) studies on phase transitions of the pure liquid crystalline material N-4-methoxybenzylidene-4-butylaniline (MBBA) and mixtures of MBBA and the amphiphile Stearic Acid (StA) show significant changes in the behavior of mixture from pure MBBA, as regards the nematic-isotropic (N-I) transition temperature (T{sub c}) and other thermodynamic parameters like enthalpy, specific heat and activation energy with concentration of StA. In particular, the convexity of the Arrhenius plot in pure MBBA vanishes with StA concentration pointing to the formation of a new, perhaps 'nematic-like', phase in the mixtures.

  7. A charge transfer complex nematic liquid crystalline gel with high electrical conductivity

    NASA Astrophysics Data System (ADS)

    Bhargavi, R.; Nair, Geetha G.; Krishna Prasad, S.; Majumdar, R.; Bag, Braja G.

    2014-10-01

    We describe the rheological, dielectric and elastic properties of a nematic liquid crystal gel created using an anthrylidene derivative of arjunolic acid, a chiral triterpenoid, obtained from the extracts of the wood of Terminalia arjuna. In this novel gel, having the electron-donor and acceptor components as minority constituents, the gelation and strengthening of charge-transfer complex (CTC) formation are seen to be occurring concomitantly. In addition to being mechanically strong with a large storage modulus, the gel with the maximized CTC exhibits Frank bend elastic constant values that approach nanonewton levels. The highlight of the study is the observation of 4-5 orders of magnitude increase in electrical conductivity for this gel, a value that is higher than even in the CT complexes of 2-d ordered columnar structures. A further important advantage of the present system over the columnar complex is that the high conductivity is seen for ac probing also, and owing to the nematic nature can be switched between its anisotropic limits. Some of these features are ascribed to a specific molecular packing architecture, which reduces the trapping of the charge carriers.

  8. Nematic liquid crystalline alignment on graphitic carbon film surfaces and its electrooptical characteristics

    NASA Astrophysics Data System (ADS)

    Nakagaki, Takamitsu; Yamada, Kenji; Nakamura, Atsushi; Temmyo, Jiro; Kubono, Atsushi

    2015-09-01

    A graphitic carbon (g-C) film directly grown on a synthetic quartz glass substrate was applied to a liquid crystal (LC) device as an alignment layer combined with a transparent electrode for a demonstration of high performance. The as-grown g-C films showed a nanometer-size domain with 91.6% transmittance at 550 nm and with a sheet resistance of 5.9 kΩ/sq. The nanodomain of the g-C film surface was associated with a random orientation of the twisted nematic LC (4-pentyl-4‧-n-cyanobiphenyl, 5CB) molecules in an in-plane randomly parallel alignment that was analyzed by polarized optical microscopy (POM). We also demonstrated an LC display (LCD) in an in-plane random hybrid twisted nematic (IPR-HTN) configuration using the g-C films compared with a previously proposed configuration using a hydroxypropyl cellulose (HPC) sublayer and a TN configuration using a polyimide film with a rubbing treatment. It was found that the combined g-C alignment layer/electrode provides a low turn-on voltage, a fast response, and a wide viewing angle as an orientation sublayer and an electrode.

  9. Dynamics of colloidal particles in electrohydrodynamic convection of nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Takahashi, Kentaro; Kimura, Yasuyuki

    2014-07-01

    We have studied the dynamics of micrometer-sized colloidal particles in electrohydrodynamic convection of nematic liquid crystal. Above the onset voltage of electroconvection, the parallel array of convection rolls appears to be perpendicular to the nematic field at first. The particles are forced to rotate by convection flow and are trapped within a single roll in this voltage regime. A slow glide motion along the roll axis is also observed. The frequency of rotational motion and the glide velocity increase with the applied voltage. Under a much larger voltage where the roll axis temporally fluctuates, the particles occasionally hop to the neighbor rolls. In this voltage regime, the motion of the particles becomes two-dimensional. The motion perpendicular to the roll axis exhibits diffusion behavior at a long time period. The effective diffusion constant is 103-104 times larger than the molecular one. The observed behavior is compared with the result obtained by a simple stochastic model for the transport of the particles in convection. The enhancement of diffusion can be quantitatively described well by the rotation frequency in a roll, the width of the roll, and the hopping probability to the neighbor rolls.

  10. Annihilation dynamics of topological monopoles on a fiber in nematic liquid crystals.

    PubMed

    Nikkhou, M; Škarabot, M; Muševič, I

    2016-06-01

    We use the laser tweezers to create isolated pairs of topological point defects in a form of radial and hyperbolic hedgehogs, located close and attracted to a thin fiber with perpendicular surface orientation of nematic liquid crystal molecules in a thin planar nematic cell. We study the time evolution of the interaction between the two monopoles by monitoring their movement and reconstructing their trajectories and velocities. We find that there is a crossover in the pair interaction force between the radial and hyperbolic hedgehog. At small separation d, the elastic force between the opposite monopoles results in an increase of the attractive force with respect to the far field, and their relative velocity v scales as a v(d)∝d^{-2±0.2} power law. At large separations, the two oppositely charged monopoles can either attract or repel with constant interaction force. We explain this strange far-field behavior by the experimental inaccuracy in setting the fiber exactly perpendicular to the cell director. PMID:27415330

  11. Annihilation dynamics of topological monopoles on a fiber in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Nikkhou, M.; Škarabot, M.; Muševič, I.

    2016-06-01

    We use the laser tweezers to create isolated pairs of topological point defects in a form of radial and hyperbolic hedgehogs, located close and attracted to a thin fiber with perpendicular surface orientation of nematic liquid crystal molecules in a thin planar nematic cell. We study the time evolution of the interaction between the two monopoles by monitoring their movement and reconstructing their trajectories and velocities. We find that there is a crossover in the pair interaction force between the radial and hyperbolic hedgehog. At small separation d , the elastic force between the opposite monopoles results in an increase of the attractive force with respect to the far field, and their relative velocity v scales as a v (d ) ∝d-2 ±0.2 power law. At large separations, the two oppositely charged monopoles can either attract or repel with constant interaction force. We explain this strange far-field behavior by the experimental inaccuracy in setting the fiber exactly perpendicular to the cell director.

  12. Microscopic origins of anisotropic active stress in motor-driven nematic liquid crystals.

    PubMed

    Blackwell, Robert; Sweezy-Schindler, Oliver; Baldwin, Christopher; Hough, Loren E; Glaser, Matthew A; Betterton, M D

    2016-03-14

    The cytoskeleton, despite comprising relatively few building blocks, drives an impressive variety of cellular phenomena ranging from cell division to motility. These building blocks include filaments, motor proteins, and static crosslinkers. Outside of cells, these same components can form novel materials exhibiting active flows and nonequilibrium contraction or extension. While dipolar extensile or contractile active stresses are common in nematic motor-filament systems, their microscopic origin remains unclear. Here we study a minimal physical model of filaments, crosslinking motors, and static crosslinkers to dissect the microscopic mechanisms of stress generation in a two-dimensional system of orientationally aligned rods. We demonstrate the essential role of filament steric interactions which have not previously been considered to significantly contribute to active stresses. With this insight, we are able to tune contractile or extensile behavior through the control of motor-driven filament sliding and crosslinking. This work provides a roadmap for engineering stresses in active liquid crystals. The mechanisms we study may help explain why flowing nematic motor-filament mixtures are extensile while gelled systems are contractile. PMID:26742483

  13. Dynamics of colloidal particles in electrohydrodynamic convection of nematic liquid crystal.

    PubMed

    Takahashi, Kentaro; Kimura, Yasuyuki

    2014-07-01

    We have studied the dynamics of micrometer-sized colloidal particles in electrohydrodynamic convection of nematic liquid crystal. Above the onset voltage of electroconvection, the parallel array of convection rolls appears to be perpendicular to the nematic field at first. The particles are forced to rotate by convection flow and are trapped within a single roll in this voltage regime. A slow glide motion along the roll axis is also observed. The frequency of rotational motion and the glide velocity increase with the applied voltage. Under a much larger voltage where the roll axis temporally fluctuates, the particles occasionally hop to the neighbor rolls. In this voltage regime, the motion of the particles becomes two-dimensional. The motion perpendicular to the roll axis exhibits diffusion behavior at a long time period. The effective diffusion constant is 10(3)-10(4) times larger than the molecular one. The observed behavior is compared with the result obtained by a simple stochastic model for the transport of the particles in convection. The enhancement of diffusion can be quantitatively described well by the rotation frequency in a roll, the width of the roll, and the hopping probability to the neighbor rolls. PMID:25122319

  14. Influences of surface and flexoelectric polarization on the effective anchoring energy in nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Guan, Rong-Hua; Ye, Wen-Jiang; Xing, Hong-Yu

    2015-10-01

    The physical effects on surface and flexoelectric polarization in a weak anchoring nematic liquid crystal cell are investigated systematically. We derive the analytic expressions of two effective anchoring energies for lower and upper substrates respectively as well as their effective anchoring strengths and corresponding tilt angles of effective easy direction. All of these quantities are relevant to the magnitudes of both two polarizations and the applied voltage U. Based on these expressions, the variations of effective anchoring strength and the tilt angle with the applied voltage are calculated for the fixed values of two polarizations. For an original weak anchoring hybrid aligned nematic cell, it may be equivalent to a planar cell for a small value of U and has a threshold voltage. The variation of reduced threshold voltage with reduced surface polarization strength is also calculated. The role of surface polarization is important without the adsorptive ions considered. Project supported by the National Natural Science Foundation of China (Grant Nos. 11274088, 11374087, and11304074), the Natural Science Foundation of Hebei Province, China (Grant No. A2014202123), the Research Project of Hebei Provincial Education Department, China (Grant No. QN2014130), and the Key Subject Construction Project of Hebei Provincial University, China.

  15. A charge transfer complex nematic liquid crystalline gel with high electrical conductivity

    SciTech Connect

    Bhargavi, R.; Nair, Geetha G. E-mail: skpras@gmail.com; Krishna Prasad, S. E-mail: skpras@gmail.com; Majumdar, R.; Bag, Braja G.

    2014-10-21

    We describe the rheological, dielectric and elastic properties of a nematic liquid crystal gel created using an anthrylidene derivative of arjunolic acid, a chiral triterpenoid, obtained from the extracts of the wood of Terminalia arjuna. In this novel gel, having the electron-donor and acceptor components as minority constituents, the gelation and strengthening of charge-transfer complex (CTC) formation are seen to be occurring concomitantly. In addition to being mechanically strong with a large storage modulus, the gel with the maximized CTC exhibits Frank bend elastic constant values that approach nanonewton levels. The highlight of the study is the observation of 4–5 orders of magnitude increase in electrical conductivity for this gel, a value that is higher than even in the CT complexes of 2-d ordered columnar structures. A further important advantage of the present system over the columnar complex is that the high conductivity is seen for ac probing also, and owing to the nematic nature can be switched between its anisotropic limits. Some of these features are ascribed to a specific molecular packing architecture, which reduces the trapping of the charge carriers.

  16. Optical transmission of nematic liquid crystal 5CB doped by single-walled and multi-walled carbon nanotubes.

    PubMed

    Lisetski, L N; Fedoryako, A P; Samoilov, A N; Minenko, S S; Soskin, M S; Lebovka, N I

    2014-08-01

    Comparative studies of optical transmission of single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs), dispersed in nematic liquid crystal matrix 5CB, were carried out. The data evidence violations of Beer-Lambert-Bouguer (BLB) law both in cell thickness and concentration dependencies. The most striking is the fact that optical transmission dependencies for SWCNTs and MWCNTs were quite different in the nematic phase, but they were practically indistinguishable in the isotropic phase. Monte Carlo simulations of the impact of aggregation on direct transmission and violation of BLB law were also done. The results were discussed accounting for the tortuous shape of CNTs, their physical properties and aggregation, as well as strong impact of perturbations of the nematic 5CB structure inside coils and in the vicinity of CNT aggregates. PMID:25106504

  17. Electroclinic effect in a chiral paranematic liquid-crystal layer above the bulk nematic-to-isotropic transition temperature

    NASA Astrophysics Data System (ADS)

    Nemitz, Ian R.; Lacaze, Emmanuelle; Rosenblatt, Charles

    2016-02-01

    Electroclinic measurements are reported for two chiral liquid crystals above their bulk chiral isotropic-nematic phase transition temperatures. It is found that an applied electric field E induces a rotation θ [∝Ε] of the director in the very thin paranematic layers that are induced by the cell's two planar-aligning substrates. The magnitude of the electroclinic coefficient dθ/dE close to the transition temperature is comparable to that of a bulk chiral nematic, as well as to that of a parasmectic region above a bulk isotropic-to-chiral smectic-A phase. However, dθ/dE in the paranematic layer varies much more slowly with temperature than in the parasmectic phase, and its relaxation time is slower by more than three orders of magnitude than that of the bulk chiral nematic electroclinic effect.

  18. Domain walls and anchoring transitions mimicking nematic biaxiality in the oxadiazole bent-core liquid crystal C7.

    PubMed

    Kim, Young-Ki; Cukrov, Greta; Xiang, Jie; Shin, Sung-Tae; Lavrentovich, Oleg D

    2015-05-28

    We investigate the origin of "secondary disclinations" that were recently described as new evidence of a biaxial nematic phase in an oxadiazole bent-core thermotropic liquid crystal C7. Using an assortment of optical techniques such as polarizing optical microscopy, LC PolScope, and fluorescence confocal polarizing microscopy, we demonstrate that the secondary disclinations represent non-singular domain walls formed in a uniaxial nematic phase during the surface anchoring transition, in which surface orientation of the director changes from tangential (parallel to the bounding plates) to tilted. Each domain wall separates two regions with the director tilted in opposite azimuthal directions. At the centre of the wall, the director remains parallel to the bounding plates. The domain walls can be easily removed by applying a moderate electric field. The anchoring transition is explained by the balance of (a) the intrinsic perpendicular surface anchoring produced by the polyimide aligning layer and (b) tangential alignment caused by ionic impurities forming electric double layers. The model is supported by the fact that the temperature of the tangentially tilted anchoring transition decreases as the cell thickness increases and as the concentration of ionic species (added salt) increases. We also demonstrate that the surface alignment is strongly affected by thermal degradation of the samples. This study shows that C7 exhibits only a uniaxial nematic phase and demonstrates yet another mechanism (formation of "secondary disclinations") by which a uniaxial nematic phase can mimic a biaxial nematic behaviour. PMID:25820380

  19. Determination of azimuthal anchoring strength in twisted nematic liquid crystal cells using heterodyne polarimeter.

    PubMed

    Yu, Tsung-Chih; Lo, Yu-Lung; Huang, Rei-Rong

    2010-09-27

    Two external-field-free methods are presented for measuring the azimuthal anchoring strength in twisted nematic liquid crystal (TNLC) cells. For asymmetrical TNLC samples, the twist angle is derived from the phase of the detected signal in a phase-sensitive heterodyne polarimeter and is then used to calculate the weak anchoring strength directly. The measurement resolution which is found to be about 0.01 μJ/m(2) makes the present method sensitive enough for the LC-based bio-sensing application. Using the proposed method, the weak azimuthal anchoring strength of a composite liquid crystal mixture (40% LCT-061153 + 60% MJO-42761) in contact with a plasma-alignment layer is found to be 7.19 μJ/m(2). For symmetrical TNLC samples, the liquid crystals are injected into a wedge cell, and the two-dimensional distributions of the twist angle and cell gap are extracted from the detected phase distribution using a genetic algorithm (GA). The azimuthal anchoring strength is then obtained by applying a fitting technique to the twist angle vs. cell gap curve. Utilizing the proposed approach, it is shown that the strong anchoring strength between a rubbed polyimide (PI) alignment layer and E7 liquid crystal is around 160 μJ/m(2) while that between a rubbed PI alignment layer and MLC-7023 liquid crystal is approximately 32 μJ/m(2). PMID:20941014

  20. Charge transport due to photoelectric interface activation in pure nematic liquid-crystal cells

    NASA Astrophysics Data System (ADS)

    Pagliusi, P.; Cipparrone, G.

    2002-11-01

    We report a study of the crucial role of liquid-crystal-polymer interface on photoinduced transport and redistribution of charges in pure nematic liquid-crystal cells that exhibit a photorefractivelike effect. A stationary photocurrent that is 30% of the dark current has been measured for very low power illumination (few mW) and low applied dc electric field (about 0.1 V/mum). The experimental results indicate a clear dependence of the effect on the light wavelength. The absence of photocurrent in cells with only one component, liquid-crystal, or polymer, suggests that both are not intrinsically photoconductive, rules out light-induced charge injection by the electrodes, and indicates the polymer-liquid-crystal interface as the photoactive element in the effect. The photocurrent dynamics indicate the presence of various mechanisms. We suppose that the effect is due to photoinduced carriers injection through the liquid-crystal-polymer interface and recombination process with the counterions present on the opposite side. Different hypotheses are made and discussed.

  1. A Technique for determining the director pretilt angle in cells with hybrid or homeotropic alignment of a nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Vakulin, D. A.

    2015-12-01

    A new technique for determining the director pretilt angle in cells with hybrid or homeotropic alignment of a nematic liquid crystal has been developed. To use this technique, it is necessary to experimentally determine the transmission of an optical system in parallel polarizers and maximum transmission of a cell in crossed polarizers. The technique makes it possible to locally control the liquid crystal director alignment on an aligning surface.

  2. Temperature dependences of the electrooptical properties of rodlike nematic liquid crystals doped with hockey-stick-shaped liquid crystals

    NASA Astrophysics Data System (ADS)

    Yeo, Sunggu; Srivastava, Anoop Kumar; Lee, Hyojin; Lee, Ji-Hoon; Choi, E.-Joon

    2016-01-01

    We investigated the temperature dependences of the dielectric anisotropy, birefringence, order parameter, splay elastic constant, and rotational viscosity of rodlike nematic liquid crystals (RLCs) doped with hockey-stick-shaped liquid crystals (HLCs). Although the order parameter of the HLC-RLC mixtures was similar to that of the pure RLC, the dielectric anisotropy and the birefringence of the mixtures were decreased or increased depending on the structure of the HLC molecule. In addition, the activation energies of the mixtures were different, which implies that the intramolecular structure of the HLC molecule had more influence on the electrooptical properties of the HLC-RLC binary mixtures than the inter-molecular interaction between the HLC and the RLC molecules.

  3. Optically isotropic liquid crystal media formulated by doping star-shaped cyclic oligosiloxane liquid crystal surfactants in twin nematic liquid crystals.

    PubMed

    Kim, Namil; Kim, Dae-Yoon; Park, Minwook; Choi, Yu-Jin; Kim, Soeun; Lee, Seung Hee; Jeong, Kwang-Un

    2015-05-21

    The formation of optically isotropic liquid crystal (LC) media has been investigated by doping the star-shaped LC molecular surfactants (SiLC) into the rod-shaped twin LC host molecules (DiLC). The experimental phase diagram was constructed on the basis of differential scanning calorimetry (DSC) and then a theoretical calculation was conducted through a combined Flory-Huggins (FH)/Maier-Saupe-McMillan (MSM)/phase field (PF) model to account for the experimental results. The phase diagram of the SiLC/DiLC mixtures revealed the broad coexistence regions such as smectic A + crystal (SmA1 + Cr2), liquid + crystal (L1 + Cr2), and liquid + nematic (L1 + N2) at the intermediate composition along with the narrow single phase crystal (Cr2), smectic (SmA1), and nematic (N2) regions. The morphologies and structures of these coexistence regions were further confirmed by polarized optical microscopy (POM) and wide-angle X-ray diffraction (WAXD). At the 80/20 SiLC/DiLC composition, the optical anisotropy was induced under an alternating current (AC) electric field above its isotropization temperature. The formation of an optically isotropic LC medium in mixtures of the SiLC molecular surfactants and nematic LC host may allow us to develop new electro-optical devices. PMID:25779205

  4. Patterns driven by combined ac and dc electric fields in nematic liquid crystals.

    PubMed

    Krekhov, Alexei; Decker, Werner; Pesch, Werner; Eber, Nándor; Salamon, Péter; Fekete, Balázs; Buka, Agnes

    2014-05-01

    The effect of superimposed ac and dc electric fields on the formation of electroconvection and flexoelectric patterns in nematic liquid crystals was studied. For selected ac frequencies, an extended standard model of the electrohydrodynamic instabilities was used to characterize the onset of pattern formation in the two-dimensional parameter space of the magnitudes of the ac and dc electric field components. Numerical as well as approximate analytical calculations demonstrate that depending on the type of patterns and on the ac frequency, the combined action of ac and dc fields may either enhance or suppress the formation of patterns. The theoretical predictions are qualitatively confirmed by experiments in most cases. Some discrepancies, however, seem to indicate the need to extend the theoretical description. PMID:25353815

  5. Electric method for studying reorientation dynamics of the nematic liquid crystal director

    NASA Astrophysics Data System (ADS)

    Shcherbinin, D. P.; Vakulin, D. A.; Konshina, E. A.

    2016-07-01

    A method has been proposed for studying the reorientation dynamics of the nematic liquid crystal (NLC) director using the results of measurements of the electric response of an LC cell. The simulation of the time dependences of the current in an LC cell with a homogeneous orientation is carried out upon variation of the applied voltage, the initial tilt angle of the director, dielectric anisotropy, and the elasticity coefficient, as well as the dynamic viscosity, density, and ion mobility in the NLC. A comparison of the experimental and computational curves of the electric response for NLC 5CB shows their good agreement. The method makes it possible to monitor the steady-state current, the density, and the ion mobility in NLCs.

  6. Splitting of surface plasmon frequencies of metal particles in a nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Park, Sung Yong; Stroud, D.

    2004-10-01

    We calculate the effective dielectric function for a suspension of small metallic particles immersed in a nematic liquid crystal (NLC) host. For a random suspension of such particles in the dilute limit, we calculate the effective dielectric tensor exactly and show that the surface plasmon resonance of such particles splits into two resonances, polarized parallel and perpendicular to the NLC director. At higher concentrations, we calculate this splitting using a generalized Maxwell-Garnett approximation (MGA), which can also be applied to a small metal particle coated with NLC. To confirm the accuracy of the MGA for NLC-coated spheres, we also use the discrete dipole approximation. The calculated splitting is comparable to that observed in recent experiments on NLC-coated small metal particles.

  7. Anisotropic shift of surface plasmon resonance of gold nanoparticles doped in nematic liquid crystal

    PubMed Central

    Choudhary, Amit; Li, Guoqiang

    2014-01-01

    Study of the liquid crystal (LC) director around nanoparticles has been an important topic of research very recently, since it allows design and fabrication of next-generation LC devices that are impossible in the past. In our experiment, alkanethiol-capped gold nanoparticles (GNPs) were dispersed in nematic LC. Analysis of the LC director around GNPs was performed by investigating the behavior of surface plasmon polariton (SPP) absorption peaks of the GNPs using spectrophotometry technique. It is found that the incident linearly polarized light orientated at 0°, 45°, and 90° angles with respect to the rubbing direction experiences varying interaction with the LC medium. The corresponding transmission of light reveals the anisotropic shift in wavelength of SPP peak. The anisotropic behavior of SPPs of the GNPs is in agreement with theoretical calculations. PMID:25322010

  8. Separation-independent attractive force between like particles mediated by nematic-liquid-crystal distortions.

    PubMed

    Fukuda, Jun-Ichi; Yokoyama, Hiroshi

    2005-04-15

    We investigate numerically with the aid of the Landau-de Gennes continuum theory the interaction between two spherical particles carrying the same topological charges +1 mediated by the elastic distortion of a nematic liquid crystal. We consider the case where an escaped nontopological ring disclination is situated between the particles; the director is continuous everywhere and no counterdefects are present. We find that the interaction is attractive and its potential energy depends linearly on the interparticle distance D. This behavior yields the D-independent interaction force, which was observed experimentally by Poulin, Cabuil, and Weitz [Phys. Rev. Lett. 79, 4862 (1997)] in the presence of narrow strings of birefringent regions ("bubble-gum" configuration) between the particles. PMID:15904120

  9. Simulation and optimization of liquid crystal gratings with alternate twisted nematic and planar aligned regions.

    PubMed

    Li, Jia-Nan; Hu, Xi-Kui; Wei, Bing-Yan; Wu, Zi-Jian; Ge, Shi-Jun; Ji, Wei; Hu, Wei; Lu, Yan-Qing

    2014-08-01

    Electro-optical properties of liquid crystal (LC) gratings with alternate twisted nematic (TN) and planar aligned (PA) regions are simulated. Three typical steps are introduced: first, the LC director distributions of the two different regions are simulated. Then, the phase and amplitude of the emergent light in each region are calculated through Jones matrix. Based on this information, the voltage-dependent diffraction efficiency is achieved by Fourier transformation, finally. It gives an exact explanation for the mechanism of this kind of gratings. Experiments with optimized parameters are carried out through photopatterning. The trend of the measured voltage-dependent efficiency fits the simulation result very well. This method can be used to optimize the performance of LC gratings with alternate TN and PA regions, and exhibits great potential in the simulation of corresponding photonics and display applications. PMID:25090348

  10. Transient Current of Nematic Liquid Crystals with Negative Dielectric Anisotropy Induced by Step-Voltage Excitation

    NASA Astrophysics Data System (ADS)

    Iwata, Yosuke; Naito, Hiroyoshi; Inoue, Masaru; Ichinose, Hideo; Klasen-Memmer, Melanie; Tarumi, Kazuaki

    2004-12-01

    A simple theory for measuring the rotational viscosity has been proposed from the analysis of transient current, induced by step-voltage excitation, in nematic liquid crystal cells (NLCs) with positive dielectric anisotropy [M. Imai et al.: Jpn. J. Appl. Phys. 33 (1994) L119]. The applicability of the theory to NLCs with negative dielectric anisotropy has been examined. It is found that the transient current shape of NLCs with negative dielectric anisotropy is different from that of NLCs with positive dielectric anisotropy, and hence, the theory cannot directly be applied to the analysis of the transient current of NLCs with negative dielectric anisotropy. Computer simulation shows that the transient current of NLCs with negative dielectric anisotropy is successfully reproduced by taking into account the flow effects with an appropriate boundary condition and that the flow effects play a key role in eliciting a faster electrooptic response in vertically aligned NLC displays.

  11. Fiber optic dynamic electric field sensor based on nematic liquid crystal Fabry-Perot etalon

    NASA Astrophysics Data System (ADS)

    Ko, Myeong Ock; Kim, Sung-Jo; Kim, Jong-Hyun; Jeon, Min Yong

    2014-05-01

    We propose a fiber-optic dynamic electric field sensor using a nematic liquid crystal (NLC) Fabry-Perot etalon and a wavelength-swept laser. The transmission wavelength of the NLC Fabry-Perot etalon depends on the applied electric field intensity. The change in the effective refractive index of the NLC is measured while changing the applied electric field intensity. It decreases from 1.67 to 1.51 as the applied the electric field intensity is increased. Additionally, we successfully measure the dynamic variation of the electric field using the high-speed wavelength-swept laser. By measuring the modulation frequency of the transmission peaks in the temporal domain, the frequency of the modulated electric field can be estimated.

  12. Wavelength, temperature, and voltage dependent calibration of a nematic liquid crystal multispectral polarization generating device

    SciTech Connect

    Baba, Justin S; Boudreaux, Philip R

    2007-01-01

    Rapid calibration of liquid crystal variable retarder (LCVR) devices is critical for successful clinical implementation of a LC-based Mueller matrix imaging system being developed for noninvasisve skin cancer detection. For multispectral implementation of such a system, the effect of wavelength (), temperature (T), and voltage (V) on the retardance () required to generate each desired polarization state needs to be clearly understood. Calibration involves quantifying this interdependence such that for a given set of system input variables, T, the appropriate voltage is applied across a LC cell to generate a particular retardance. This paper presents findings that elucidate the dependence of voltage, for a set retardance, on the aforementioned variables for a nematic LC cell: 253 mv100 nm-dependence andd 10 mVC T-dependence. Additionally, an empirically derived model is presented that enables initial voltage calibration of retardance for any desired input wavelength within the calibration range of 460-905 nm. copyright 2007 Optical Society of America

  13. Influence of interface stabilisers and surrounding aqueous phases on nematic liquid crystal shells.

    PubMed

    Noh, JungHyun; Reguengo De Sousa, Kevin; Lagerwall, Jan P F

    2016-01-14

    We investigate the nematic-isotropic (N-I) transition in shells of the liquid crystal 5CB, surrounded by aqueous phases that conventionally are considered to be immiscible with 5CB. The aqueous phases contain either sodium dodecyl sulfate (SDS) or polyvinyl alcohol (PVA) as stabiliser, the former additionally promoting homeotropic director alignment. For all shell configurations we find a depression of the clearing point compared to pure 5CB, indicating that a non-negligible fraction of the constituents of the surrounding phases enter the shell, predominantly water. In hybrid-aligned shells, with planar outer and homeotropic inner boundary (or vice versa), the N-I transition splits into two steps, with a consequent three-step textural transformation. We explain this as a result of the order-enhancing effect of a monolayer of radially aligned SDS molecules adsorbed at the homeotropic interface. PMID:26512764

  14. Homeotropic orientation behavior of nematic liquid crystals induced by copper ions.

    PubMed

    Li, Guang; Gao, Bin; Yang, Meng; Chen, Long-Cong; Xiong, Xing-Liang

    2015-06-01

    A homeotropic ordering film of nematic liquid crystal (LC) induced by copper ions (Cu(2+)) had been developed. The Cu(ClO4)2 was directly spin-coated on the glass substrate without any other chemical modification. A homeotropic orientation of LC thin-film was generated by the interfacial chemical interaction between nitrile-containing LC and copper ions on the surface. Results showed that an appropriate density of Cu(2+) could shorten the response time of orientation, but a shelf-time was prolonged. The LC film fabrication not only offered a simple process, but also presented a great repeatability to detect organophosphonates (DMMP). This study provided guidance for the design of LC films responding to organic molecules as a biosensor. PMID:25935262

  15. Fluctuating hydrodynamics of nematics for models of liquid-crystal based biosensors via lattice Boltzmann simulations

    NASA Astrophysics Data System (ADS)

    Guzman, Orlando; Velez, Jose Antonio; Castañeda, David

    2008-03-01

    Experimental biosensors based on liquid crystals (LC) use nematics to detect the presence of specific analytes, via the optical textures exhibited by the LC at long times. Efforts to model the time evolution of these textures have relied on relaxational models, ignoring transport phenomena. In this work we include hydrodynamics into a model for these LC biosensors, using lattice Boltzmann (LB) methods and assess the effect on the lifetime of multidomain structures, characteristic of high concentrations of analyte. We apply Yeoman's et al. LB algorithm, which reproduces the hydrodynamic equations developed by Beris and Edwards for LCs. We also take into account thermal fluctuations, by adding random perturbations to the hydrodynamic modes. Following Adhikari et al., their amplitude is determined by the Fluctuation-Dissipation theorem and we excite both hydrodynamic and the sub-hydrodynamic modes (also called ghost modes). As a result, we analyze the influence of the fluctuations and hydrodynamics on the movement of topological defects.

  16. Anisotropic shift of surface plasmon resonance of gold nanoparticles doped in nematic liquid crystal.

    PubMed

    Choudhary, Amit; Li, Guoqiang

    2014-10-01

    Study of the liquid crystal (LC) director around nanoparticles has been an important topic of research very recently, since it allows design and fabrication of next-generation LC devices that are impossible in the past. In our experiment, alkanethiol-capped gold nanoparticles (GNPs) were dispersed in nematic LC. Analysis of the LC director around GNPs was performed by investigating the behavior of surface plasmon polariton (SPP) absorption peaks of the GNPs using spectrophotometry technique. It is found that the incident linearly polarized light orientated at 0°, 45°, and 90° angles with respect to the rubbing direction experiences varying interaction with the LC medium. The corresponding transmission of light reveals the anisotropic shift in wavelength of SPP peak. The anisotropic behavior of SPPs of the GNPs is in agreement with theoretical calculations. PMID:25322010

  17. Long-time behavior of solution for the compressible nematic liquid crystal flows in R3

    NASA Astrophysics Data System (ADS)

    Gao, Jincheng; Tao, Qiang; Yao, Zheng-an

    2016-08-01

    In this paper, we investigate the global existence and long-time behavior of classical solution for the compressible nematic liquid crystal flows in three-dimensional whole space. First of all, the global existence of classical solution is established under the condition that the initial data are close to the constant equilibrium state in HN (R3) (N ≥ 3)-framework. Then, one establishes algebraic time decay for the classical solution by weighted energy method. Finally, the algebraic decay rate of classical solution in Lp (R3)-norm with 2 ≤ p ≤ ∞ and optimal decay rate of their spatial derivative in L2 (R3)-norm are obtained if the initial perturbation belong to L1 (R3) additionally.

  18. Nematic liquid crystals in a spatially step-wise magnetic field.

    PubMed

    Napoli, Gaetano; Scaraggi, Michele

    2016-01-01

    We study the molecular reorientation induced by a textured external field in a nematic liquid crystal (nLC). In particular, we consider an infinitely wide cell with strong planar anchoring boundary conditions, subjected to a spatially periodic piecewise magnetic field. In the framework of the Frank's continuum theory, we use the perturbation analysis to study in detail the field-induced splay-bend Fréedericksz transition. A numerical approach, based on the finite differences method, is instead employed to solve the fully nonlinear equations. At high field strengths, an analytic approach allows us to draw the bulk profile of the director in terms of elliptic integrals. Finally, through the application of the Bruggeman texture hydrodynamics theory, we qualitatively discuss on the LCs piecewise director configuration under sliding interfaces, which can be adopted to actively regulate friction. Our study opens the pathway for the application of highly controlled nLC texturing for tribotronics. PMID:26871129

  19. Nematic liquid crystals in a spatially step-wise magnetic field

    NASA Astrophysics Data System (ADS)

    Napoli, Gaetano; Scaraggi, Michele

    2016-01-01

    We study the molecular reorientation induced by a textured external field in a nematic liquid crystal (nLC). In particular, we consider an infinitely wide cell with strong planar anchoring boundary conditions, subjected to a spatially periodic piecewise magnetic field. In the framework of the Frank's continuum theory, we use the perturbation analysis to study in detail the field-induced splay-bend Fréedericksz transition. A numerical approach, based on the finite differences method, is instead employed to solve the fully nonlinear equations. At high field strengths, an analytic approach allows us to draw the bulk profile of the director in terms of elliptic integrals. Finally, through the application of the Bruggeman texture hydrodynamics theory, we qualitatively discuss on the LCs piecewise director configuration under sliding interfaces, which can be adopted to actively regulate friction. Our study opens the pathway for the application of highly controlled nLC texturing for tribotronics.

  20. Behaviors of random laser in dye-doped nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Yao, Fengfeng; Bian, Huanting; Pei, Yanbo; Hou, Chunfeng; Sun, Xiudong

    2016-01-01

    Random lasing in the nematic liquid crystals (NLCs) with a high doping concentration of the laser dye was observed and characterized. With increasing the pump energy after the occurrence of the random laser (RL), the RL intensity first increases gradually to a maximum, then drops sharply to zero, accompanied by the gradual enhancement of scattering manifested by the growth of far-field diffraction rings of the transmitted pump beam in number. The threshold energy per unit pump area, slope efficiency, and maximal output intensity of the NLC RL depend heavily and nonmonotonically on the pump angle. A model involving the pump pulse induced molecular reorientation in NLCs leading to the pump angle dependent enhancement of scattering is proposed to explain the pump angle dependent properties of RLs.

  1. Non-Monotonic Concentration Effects in the Phase Behavior and Nematic Orders: Mixtures of Side-Chain Liquid Crystalline Polymers and Low-Molecular-Weight Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Zhuang, Bilin; Wang, Zhen-Gang

    2012-02-01

    Mixtures of side-chain liquid crystal polymers (SCLCPs) and low-molecular-weight liquid crystals (LMWLCs) are novel materials with applications such as optical data storage, non-linear optics, solid polymer electrolytes, chromatography and display materials. Recent experiments showed that the nematic-isotropic transition temperature and the nematic orders of each component vary non-monotonically with concentration. Existing theories, which combine the Flory-Huggins theory for isotropic mixing and the Maier-Saupe theory for nematic order, cannot explain such non-monotonicity. Here, we extend the existing theories by, first, incorporating the local steric constraints between the side-chain and the polymer backbone on the SCLCPs, and second, accounting for the crowding effects at high SCLCP concentrations. The new extended theory is able to resolve the discrepancies between the predictions of existing theories and the experimental observations.

  2. Pairing instabilities of a Non-Fermi liquid in the presence of nematic and gauge fluctuations

    NASA Astrophysics Data System (ADS)

    Mesaros, Andrej; Lawler, Michael J.; Kim, Eun-Ah

    2015-03-01

    In the absence of Fermi-liquid starting point, instabilities of non-Fermi liquids are theoretically challenging problems. Here we note that a non-Fermi liquid state occurring at ν = 1 / 2 may be a promising concrete case for theoretical investigation of the issue for two reasons. Firstly, exotic ordered states observed in half-filled Landau levels, namely the FQH state at ν = 5 / 2 which is most likely best described as a paired state, and the quantum Hall nematic state at ν = 9 / 2 , present a compelling possibility that the non-Fermi liquid state with gauge fluctuations at ν = 1 / 2 is close to instabilities towards these ordered states. Secondly, a recent theoretical progress [Metlitski et al., arXiv:1403.3694] offers a scheme for a controlled renormalization group study of the problem. We will discuss competition between the two fluctuations in promoting or suppressing a superconducting instability, based on the phase diagram we obtain from a renormalization group calculation. This research was supported by NSF through CAREER Grant DMR-0955822.

  3. Ultraweak azimuthal anchoring of a nematic liquid crystal on a planar orienting photopolymer

    SciTech Connect

    Nespoulous, Mathieu; Blanc, Christophe; Nobili, Maurizio

    2007-10-01

    The search of weak anchoring is an important issue for a whole class of liquid crystal displays. In this paper we present an orienting layer showing unreached weak planar azimuthal anchoring for 4-n-pentyl-4{sup '}-cyanobiphenyl nematic liquid crystal (5CB). Azimuthal extrapolation lengths as large as 80 {mu}m are easily obtained. Our layers are made with the commercial photocurable polymer Norland optical adhesive 60. The anisotropy of the film is induced by the adsorption of oriented liquid crystal molecules under a 2 T magnetic field applied parallel to the surfaces. We use the width of surface {pi}-walls and a high-field electro-optical method to measure, respectively, the azimuthal and the zenithal anchorings. The azimuthal anchoring is extremely sensitive to the ultraviolet (UV) dose and it also depends on the magnetic field application duration. On the opposite, the zenithal anchoring is only slightly sensitive to the preparation parameters. All these results are discussed in terms of the adsorption/desorption mechanisms of the liquid crystal molecules on the polymer layer and of the flexibility of the polymer network.

  4. Thin film polarizer and color filter based on photo-polymerizable nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Mohammadimasoudi, Mohammad; Neyts, Kristiaan; Beeckman, Jeroen

    2015-03-01

    We present a method to fabricate a thin film color filter based on a mixture of photo-polymerizable liquid crystal and chiral dopant. A chiral nematic liquid crystal layer reflects light for a certain wavelength interval Δλ (= Δn.P) with the period and Δn the birefringence of the liquid crystal. The reflection band is determined by the chiral dopant concentration. The bandwidth is limited to 80nm and the reflectance is at most 50% for unpolarized incident light. The thin color filter is interesting for innovative applications like polarizer-free reflective displays, polarization-independent devices, stealth technologies, or smart switchable reflective windows to control solar light and heat. The reflected light has strong color saturation without absorption because of the sharp band edges. A thin film polarizer is developed by using a mixture of photo-polymerizable liquid crystal and color-neutral dye. The fabricated thin film absorbs light that is polarized parallel to the c axis of the LC. The obtained polarization ratio is 80% for a film of only 12 μm. The thin film polarizer and the color filter feature excellent film characteristics without domains and can be detached from the substrate which is useful for e.g. flexible substrates.

  5. Effect of molecular architecture on the electrorheological behavior of liquid crystal polymers in nematic solvents

    NASA Astrophysics Data System (ADS)

    Chiang, Yen-Ching

    1998-11-01

    The Miesowicz viscosities of dilute nematic solutions of liquid crystal polymers (LCP) in low molar mass nematic solvents have been measured by a cone-and-plate rheometer in the presence of a saturated electric field applied perpendicular to the shear plane. For mixtures with a positive dielectric anisotropy in the presence of the electric field the nematic director is perpendicular to the velocity gradient and the viscosity measured is the Miesowicz viscosity ηc. With the electric field off the nematic director orients parallel to the shear flow direction and the viscosity measured is closed to the Miesowicz viscosity η b. Specifically, we show that main-chain LCPs strongly increase the magnitude of the electrorheological (ER) response, ηc-ηb, a side-on side chain LCP moderately increases the response, and an end- on side-chain LCP weakly increases the response. The diverse behaviors can be interpreted using theoretical arguments which assume that the LCP conformation is an ellipsoid of revolution whose orientation relative to the flow is determined by the balance between the hydrodynamic and electric torques on the fluid. For the main-chain LCP TPB10 in 5OCB, which has mesogenic groups separated by decamethylene spacers, the intrinsic Miesowicz viscosity [ηc] was found to follow a Mark-Houwink-Sakurada relationship [ηc]/propto M/sp/alpha with α~1 and the configurational relaxation time (τR) shows a strong dependence on molecular weight, τR/propto M/sp/beta with β~2. Applying a theoretical description by Brochard, these results suggest that TPB10 behaves hydrodynamically like a free-draining random coil stretched along the director. The temperature dependence of Miesowicz viscosities η c and η b of LCPs dissolved in nematic solvent E48 was also investigated. The variations in δeta c and δeta c with temperature can be described by the Brochard theory in terms of the corresponding variation of the configurational anisotropy (R///R/sb/perp) with

  6. Non-equilibrium nature of two-dimensional isotropic and nematic coexistence in amyloid fibrils at liquid interfaces.

    PubMed

    Jordens, Sophia; Isa, Lucio; Usov, Ivan; Mezzenga, Raffaele

    2013-01-01

    Two-dimensional alignment of shape-anisotropic colloids is ubiquitous in nature, ranging from interfacial virus assembly to amyloid plaque formation. The principles governing two-dimensional self-assembly have therefore long been studied, both theoretically and experimentally, leading, however, to diverging fundamental interpretations on the nature of the two-dimensional isotropic-nematic phase transition. Here we employ single-molecule atomic force microscopy, cryogenic scanning electron microscopy and passive probe particle tracking to study the adsorption and liquid crystalline ordering of semiflexible β-lactoglobulin fibrils at liquid interfaces. Fibrillar rigidity changes on increasing interfacial density, with a maximum caused by alignment and a subsequent decrease stemming from crowding and domain bending. Coexistence of nematic and isotropic regions is resolved and quantified by a length scale-dependent order parameter S(2D)(d). The nematic surface fraction increases with interfacial fibril density, but depends, for a fixed interfacial density, on the initial bulk concentration, ascribing the observed two-dimensional isotropic-nematic coexistence to non-equilibrium phenomena. PMID:23715276

  7. Non-equilibrium nature of two-dimensional isotropic and nematic coexistence in amyloid fibrils at liquid interfaces

    NASA Astrophysics Data System (ADS)

    Jordens, Sophia; Isa, Lucio; Usov, Ivan; Mezzenga, Raffaele

    2013-05-01

    Two-dimensional alignment of shape-anisotropic colloids is ubiquitous in nature, ranging from interfacial virus assembly to amyloid plaque formation. The principles governing two-dimensional self-assembly have therefore long been studied, both theoretically and experimentally, leading, however, to diverging fundamental interpretations on the nature of the two-dimensional isotropic-nematic phase transition. Here we employ single-molecule atomic force microscopy, cryogenic scanning electron microscopy and passive probe particle tracking to study the adsorption and liquid crystalline ordering of semiflexible β-lactoglobulin fibrils at liquid interfaces. Fibrillar rigidity changes on increasing interfacial density, with a maximum caused by alignment and a subsequent decrease stemming from crowding and domain bending. Coexistence of nematic and isotropic regions is resolved and quantified by a length scale-dependent order parameter S2D(d). The nematic surface fraction increases with interfacial fibril density, but depends, for a fixed interfacial density, on the initial bulk concentration, ascribing the observed two-dimensional isotropic-nematic coexistence to non-equilibrium phenomena.

  8. Superconductivity from a confinement transition out of a fractionalized Fermi liquid with Z2 topological and Ising-nematic orders

    NASA Astrophysics Data System (ADS)

    Chatterjee, Shubhayu; Qi, Yang; Sachdev, Subir; Steinberg, Julia

    2016-07-01

    The Schwinger boson theory of the frustrated square lattice antiferromagnet yields a stable, gapped Z2 spin liquid ground state with time-reversal symmetry, incommensurate spin correlations, and long-range Ising-nematic order. We obtain an equivalent description of this state using fermionic spinons (the fermionic spinons can be considered to be bound states of the bosonic spinons and the visons). Upon doping, the Z2 spin liquid can lead to a fractionalized Fermi liquid (FL*) with small Fermi pockets of electronlike quasiparticles, while preserving the Z2 topological and Ising-nematic orders. We describe a Higgs transition out of this deconfined metallic state into a confining superconducting state which is almost always of the Fulde-Ferrell-Larkin-Ovchinnikov type, with spatial modulation of the superconducting order.

  9. Far-Field Patterns from Dye-Doped Planar-Aligned Nematic Liquid Crystals Under nanosecond Laser Irradiation

    SciTech Connect

    Lukishova, S.G.; Lepeshkin, N.; Boyd, R.W.; Marshall, K.L.

    2006-08-18

    High-definition patterns were observed under 10-Hz-pulse-repetition-rate, nanosecond laser irradiation of azodye-doped planar-nematic liquid crystal layers at incident intensities I ~ 5-10 MW/cm^2 in a single beam configuration and without any feedback involved. An incident polarization parallel to the nematic director was used. Under periodic pulsed laser irradiation, far-field beam patterns at the output of a dye-doped liquid crystal layer changed kaleidoscopically from rings and stripes to multiple hexagons. This pattern-formation regime had a buildup time of several seconds to minutes. We explain the observed effect by diffraction of the laser beam on light-induced micrometer-size inhomogeneities inside the liquid crystal layer with absorption and refraction properties different from the surrounding area. Possible mechanisms of the formation of the inhomogeneities are discussed.

  10. Hierarchical Organization in Liquid Crystal-in-Liquid Crystal Emulsions

    PubMed Central

    Mushenheim, Peter C.

    2014-01-01

    We report the formation and characterization of hierarchical ordering in systems comprised of micrometer-sized droplets of thermotropic nematic liquid crystals (LCs) dispersed in continuous nematic phases of a lyotropic chromonic LC (disodium cromoglycate (DSCG)). Significantly, we find the orientations of the two LC phases to be coupled, with nematic droplets of 4′-pentyl-4-cyanobiphenyl (5CB) exhibiting a bipolar configuration with an axis of symmetry aligned orthogonal to the far-field director of the DSCG phase. We determine that this coupling of orientations does not result from either anisometric LC droplet shape or interfacial ionic phenomena but rather is consistent with the influence of van der Waals interactions that arise from the anisotropic polarizabilities of nematic 5CB (Δn = + 0.18) and DSCG (Δn = − 0.02) phases. We also find that it is possible to rotate and uniformly align the nematic droplets by using a weak magnetic field (B ∼ 0.3 T). An analysis of the dynamics of relaxation of the orientations of the 5CB droplets following removal of the magnetic field reveals the DSCG and 5CB droplets to be coupled by energies of ∼104kT, consistent with a simple theoretical estimate of the influence of anisotropic van der Waals interactions. We also observed the nematic 5CB droplets to form dimers and larger assemblies mediated by the elasticity of the nematic DSCG. Overall, these results reveal that LC-in-LC emulsions define a new class of hierarchically ordered soft matter in which both thermotropic and lyotropic LCs are coupled in their ordering. PMID:25278032

  11. Hierarchical organization in liquid crystal-in-liquid crystal emulsions.

    PubMed

    Mushenheim, Peter C; Abbott, Nicholas L

    2014-11-21

    We report the formation and characterization of hierarchical ordering in systems comprised of micrometer-sized droplets of thermotropic nematic liquid crystals (LCs) dispersed in continuous nematic phases of a lyotropic chromonic LC (disodium cromoglycate (DSCG)). Significantly, we find the orientations of the two LC phases to be coupled, with nematic droplets of 4'-pentyl-4-cyanobiphenyl (5CB) exhibiting a bipolar configuration with an axis of symmetry aligned orthogonal to the far-field director of the DSCG phase. We determine that this coupling of orientations does not result from either anisometric LC droplet shape or interfacial ionic phenomena but rather is consistent with the influence of van der Waals interactions that arise from the anisotropic polarizabilities of nematic 5CB (Δn = +0.18) and DSCG (Δn = -0.02) phases. We also find that it is possible to rotate and uniformly align the nematic droplets by using a weak magnetic field (B ∼ 0.3 T). An analysis of the dynamics of relaxation of the orientations of the 5CB droplets following removal of the magnetic field reveals the DSCG and 5CB droplets to be coupled by energies of ∼10(4) kT, consistent with a simple theoretical estimate of the influence of anisotropic van der Waals interactions. We also observed the nematic 5CB droplets to form dimers and larger assemblies mediated by the elasticity of the nematic DSCG. Overall, these results reveal that LC-in-LC emulsions define a new class of hierarchically ordered soft matter in which both thermotropic and lyotropic LCs are coupled in their ordering. PMID:25278032

  12. Dual electrically and thermally responsive broadband reflectors based on polymer network stabilized chiral nematic liquid crystals: the role of crosslink density.

    PubMed

    Khandelwal, Hitesh; Timmermans, Gilles H; Debije, Michael G; Schenning, Albertus P H J

    2016-08-01

    A broadband reflector based on a polymer stabilized chiral nematic liquid crystal has been fabricated. The reflection bandwidth can be manually controlled by an electric field and autonomously by temperature. PMID:27357239

  13. Director-density coupling theory of the acousto-optic effect in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Sátiro, Caio; Vitoriano, Carlindo

    2011-10-01

    Experiments with nematic liquid crystals have proved that an ultrasonic wave exerts a torque on the liquid-crystal molecules, causing a change in its optical properties (acousto-optic effect). In this work we report a theoretical study on the theory proposed by Selinger [Phys. Rev. EPLEEE81539-375510.1103/PhysRevE.66.051708 66, 051708 (2002).] and, independently, by Boneto [Chem. Phys. Lett.CHPLBC0009-261410.1016/S0009-2614(02)00906-5 361, 237 (2002).] for this effect. We solved exactly the Euler-Lagrange equation, which determines the equilibrium configuration of the director profile. The liquid-crystal director is also calculated in powers of the acoustic intensity and a comparison of this expansion with the solution in a closed form is given. We show the existence of minimizers that does not satisfy the Euler-Lagrange equation and report the possibility of observing a Fréedericksz-type transition. Finally, a possibility of controlling light by ultrasonic wave is also discussed in the limit of low acoustic intensity.

  14. Surface induced phase separation and pattern formation at the isotropic interface in chiral nematic liquid crystals.

    PubMed

    Zola, R S; Evangelista, L R; Yang, Y-C; Yang, D-K

    2013-02-01

    We study the pattern formation of a chiral nematic liquid crystal under a wetting transition. In the isotropic-liquid crystal transition, a surface-enhanced effect happens and a thin liquid crystal layer forms at the substrates of the cell. In this confined system, chirality, elastic anisotropy, surface anchoring, and wetting strength interplay. A striped pattern is formed due to the chiral nature of the material and the tilted anchoring at the isotropic boundary. As the wetting layer grows from cooling the sample, first the stripes rotate through a process where dislocation defects are formed. As the wetting layer grows further, the periodicity of the stripe structure changes, and finally a splitting of the stripes occurs. Because of the unique properties of this system, new insights about pitch-thickness ratio, interface anchoring, and elastic anisotropy effect are found. Since the anchoring at the isotropic boundary is weak, the critical ratio between the thickness of the wetting layer and the helical pitch is different from that reported in the literature. We also discover that the elastic anisotropy and elastic constant ratios play a critical role in stripe formation. Because of the similarity with biological fibrous composites (twisted plywood), our system may be used as a synthetic version to mimic the naturally occurring one. We carry out a simulation study to explain the experimental results. PMID:23414046

  15. Surface Induced Phase Separation and Pattern Formation at the Isotropic Interface in Chiral Nematic Liquid Crystals

    NASA Astrophysics Data System (ADS)

    Zola, R. S.; Evangelista, L. R.; Yang, Y.-C.; Yang, D.-K.

    2013-02-01

    We study the pattern formation of a chiral nematic liquid crystal under a wetting transition. In the isotropic-liquid crystal transition, a surface-enhanced effect happens and a thin liquid crystal layer forms at the substrates of the cell. In this confined system, chirality, elastic anisotropy, surface anchoring, and wetting strength interplay. A striped pattern is formed due to the chiral nature of the material and the tilted anchoring at the isotropic boundary. As the wetting layer grows from cooling the sample, first the stripes rotate through a process where dislocation defects are formed. As the wetting layer grows further, the periodicity of the stripe structure changes, and finally a splitting of the stripes occurs. Because of the unique properties of this system, new insights about pitch-thickness ratio, interface anchoring, and elastic anisotropy effect are found. Since the anchoring at the isotropic boundary is weak, the critical ratio between the thickness of the wetting layer and the helical pitch is different from that reported in the literature. We also discover that the elastic anisotropy and elastic constant ratios play a critical role in stripe formation. Because of the similarity with biological fibrous composites (twisted plywood), our system may be used as a synthetic version to mimic the naturally occurring one. We carry out a simulation study to explain the experimental results.

  16. Wetting of liquid-crystal surfaces and induced smectic layering at a nematic-liquid interface: an x-ray reflectivity study.

    PubMed

    Fukuto, Masafumi; Gang, Oleg; Alvine, Kyle J; Ocko, Benjamin M; Pershan, Peter S

    2008-03-01

    We report the results of a synchrotron x-ray reflectivity study of bulk liquid-crystal surfaces that are coated by thin wetting films of an immiscible liquid. The liquid-crystal subphase consisted of the nematic or isotropic phase of 4-octyl- 4;{'} -cyanobiphenyl (8CB), and the wetting film was formed by the fluorocarbon perfluoromethylcyclohexane (PFMC), a volatile liquid. The thickness of the wetting film was controlled by the temperature difference DeltaT(micro) between the sample and a reservoir of bulk PFMC, contained within the sealed sample cell. Phase information on the interfacial electron density profiles has been extracted from the interference between the scattering from the PFMC-vapor interface and the surface-induced smectic order of the 8CB subphase. The liquid-crystal side of the nematic-liquid (8CB-PFMC) interface is characterized by a density oscillation whose period corresponds to the smectic layer spacing and whose amplitude decays exponentially toward the underlying nematic subphase. The decay length xi of the smectic amplitude is independent of the PFMC film thickness but increases as the nematic-smectic- A transition temperature T(NA) is approached, in agreement with the longitudinal correlation length xi(parallel) proportional, variant(T-T(NA))(-0.7} for the smectic fluctuations in the bulk nematic. The results indicate that the homeotropic orientation of the 8CB molecules is preferred at the 8CB-PFMC interface and that the observed temperature dependence of the smectic layer growth is consistent with the critical adsorption mechanism. The observed DeltaT(micro) dependence of the PFMC film thickness, L proportional, variant(DeltaT(micro))(-1/3) , implies that PFMC completely wets the 8CB surface and is dominated by the nonretarded dispersion interactions between hydro- and fluorocarbons. The complete wetting behavior of PFMC is nearly independent of the degree of interfacial smectic order in the subphase. PMID:18517395

  17. Controlling defects in nematic and smectic liquid crystals through boundary geometry

    NASA Astrophysics Data System (ADS)

    Beller, Daniel A.

    Liquid crystals (LCs), presently the basis of the dominant electronics display technology, also hold immense potential for the design of new self-assembling, self-healing, and "smart" responsive materials. Essential to many of these novel materials are liquid crystalline defects, places where the liquid crystalline order is forced to break down, replacing the LC locally with a higher-symmetry phase. Despite the energetic cost of this local melting, defects are often present at equilibrium when boundary conditions frustrate the material order. These defects provide micron-scale tools for organizing colloids, focusing light, and generating micropatterned materials. Manipulating the shapes of the boundaries thus offers a route to obtaining new and desirable self-assembly outcomes in LCs, but each added degree of complexity in the boundary geometry increases the complexity of the liquid crystal's response. Therefore, conceptually minimal changes to boundary geometry are investigated for their effects on the self-assembled defect arrangements that result in nematic and smectic-A LCs in three dimensions as well as two-dimensional smectic LCs on curved substrates. In nematic LCs, disclination loops are studied in micropost confining environments and in the presence of sharp-edged colloidal inclusions, using both numerical modeling and topological reasoning. In both scenarios, sharp edges add new possibilities for the shape or placement of disclinations, permitting new types of colloidal self-assembly beyond simple chains and hexagonal lattices. Two-dimensional smectic LCs on curved substrates are examined in the special cases where the substrate curvature is confined to points or curves, providing an analytically tractable route to demonstrate how Gaussian curvature is associated with disclinations and grain boundaries, as well as these defects' likely experimental manifestations. In three-dimensional smectic-A LCs, novel self-assembled arrangements of focal conic domains

  18. Interactions of carbon nanotubes in a nematic liquid crystal. I. Theory

    NASA Astrophysics Data System (ADS)

    Galerne, Yves

    2016-04-01

    Elongated and rodlike objects such as carbon nanotubes (CNTs) are studied when immersed in a nematic liquid crystal. Their interaction energy in a uniform nematic field depends on their orientation relative to the director n , and its minimum determines if they stabilize parallel or perpendicular to n . Using free energy calculations, we deduce the orientation at equilibrium that they choose in a uniform director field n or when they are in contact with a splay-bend disclination line. Naturally, the CNT orientations also depend on the anchoring conditions at their surface. Essentially, three types of anchorings are considered, planar, homeotropic, and Janus anchorings in the cases of weak and strong anchoring strengths. In the presence of a splay-bend disclination line, they are attracted toward it and ultimately, they get out of the colloidal dispersion to stick on it. Their orientation relative to the line is found to be parallel or perpendicular to it, again depending on the anchoring conditions. When a sufficient number of particles are deposited on a disclination line, we finally obtain a micro- or nanonecklace in the shape of a thin thread or of a bottle brush, according to the CNTs being oriented parallel or perpendicular to the disclination line, respectively. The system exhibits a rich versatility even if up to now the weak anchorings appear to be difficult to control. As discussed in the associated experimental paper, these necklaces could be a step toward interesting applications for realizing nanowires self-connected in three dimensions to predesignated electrodes. This method could provide a way to increase the number of transistors that may be connected together on a small volume.

  19. Study of anchoring behavior of nematic fluids at the interface of polymer-dispersed liquid crystals

    NASA Astrophysics Data System (ADS)

    Zhou, Jian

    A liquid crystal (LC) at its boundary surface adopts a preferential alignment, which is referred to as anchoring. The direction of this alignment (i.e., anchoring direction) may be perpendicular, parallel or tilted with respect to the surface. Transitions from one anchoring condition to another may occur when the parameters (e.g., temperature) charactering the surface change, as referred to as anchoring transitions. In the LC-polymer composite systems under our study, the anchoring and temperature-driven anchoring transitions of nematic fluids is very sensitive to the structure of the side chain of poly (alkyl acrylate) matrixes that encapsulate the LC. We have shown that the anchoring transition temperature of these systems can be tuned far below the nematic-to-isotropic transition temperature, by varying either the length, branching structure of the side chains of homopolymers, or the composition of copolymer of two dissimilar monomers. Both sharp and broad anchoring transitions with respect to the temperature range over which a transition occurs were observed. It is postulated that microscopic interactions between the polymer side chains and LC molecules play an important role in determining the anchoring. In particular, the conformation of the polymer side chain is proposed to have important control over the anchoring. Anchoring strength and tilt angle as a function of temperature during the anchoring transitions were also experimentally investigated, which contribute to understanding of the microscopic mechanism for such transitions. Based on the LC-polymer composites with controlled anchoring, a LC display with reverse switching mode and a novel electrically switchable diffraction grating have been demonstrated. The advantages of these devices are ease of manufacturing, low operation voltage, and mechanical stability offered by polymer matrix. Moreover, a detailed study of the director configuration of wall defects found in these composite films was carried

  20. Matched elastic constants for a perfect helical planar state and a fast switching time in chiral nematic liquid crystals.

    PubMed

    Yu, Meina; Zhou, Xiaochen; Jiang, Jinghua; Yang, Huai; Yang, Deng-Ke

    2016-05-11

    Chiral nematic liquid crystals possess a self-assembled helical structure and exhibit unique selective reflection in visible and infrared light regions. Their optical properties can be electrically tuned. The tuning involves the unwinding and restoring of the helical structure. We carried out an experimental study on the mechanism of the restoration of the helical structure. We constructed chiral nematic liquid crystals with variable elastic constants by doping bent-dimers and studied their impact on the restoration. With matched twist and bend elastic constants, the helical structure can be restored dramatically fast from the field-induced homeotropic state. Furthermore, defects can be eliminated to produce a perfect planar state which exhibits high selective reflection. PMID:27116620

  1. Electronic structure and pair potential energy analysis of 4-n-methoxy-4'-cyanobiphenyl: A nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Sharma, Dipendra; Dwivedi, M. K.; Tiwari, S. N.

    2016-05-01

    Electronic structure properties of 4-n-methoxy-4'-cyanobiphenyl, a pure nematic liquid crystal have been examined using an ab‒initio, HF/6‒31G(d,p) technique with GAMESS program. Conformational and charge distribution analysis have been carried out. MEP, HOMO and LUMO surfaces have been scanned. Ionization potential, electron affinity, electronegativity, global hardness and softness of the liquid crystal molecule have been calculated. Further, stacking, side by side and end to end interactions between a molecular pair have been evaluated. Results have been used to elucidate the physico-chemical and liquid crystalline properties of the system.

  2. Design and synthesis of new type I bicontinuous cubic lyotropic liquid crystal monomers based on the gemini framework for molecular-size separation applications

    NASA Astrophysics Data System (ADS)

    Wiesenauer, Brian R.

    The overall objective of this thesis research was the design and synthesis of new type I bicontinuous cubic (QI) phase-forming, gemini-shaped lyotropic liquid crystal (LLC) monomers for the preparation of nanoporous polymer membrane materials. These new QI-phase LLC monomers were designed to overcome several shortcomings of previously developed QI-phase LLC monomers in the Gin research group that include expensive and difficult synthesis, poor film processibility, and limited blendability with additives. The first method for obtaining this objective was the synthesis of six homologues of a new gemini ammonium LLC monomer, two of which exhibit a QI phase with water. Both of these LLCs form a robust Q I phase such that a gel of these materials can be fully infused into a microporous support membrane and then cross-linked to maintain the LLC phase structure. The resulting QI-phase polymer film showed a uniform pore size of 0.86 nm in water nanofiltration and desalination experiments. This QI monomer platform is less costly and less rigorous to synthesize than previously synthesized phosphonium-based gemini QI LLC monomers. These new LLC monomers also have the ability to blend with the hydrophobic, commercially available cross-linkable elastomer vinyl-EPDM (v-EPDM) to form breathable composite barrier materials. In the appropriate composition, melt-infused gemini ammonium monomer/v-EPDM polymer membranes exhibit extremely high pure water vapor fluxes, and high rejection of toxic industrial chemical vapors. A new cross-linkable gemini LLC monomer based on charged imidazolium units was also developed that forms a QI phase with glycerol. This new LLC monomer can be solution-cast from MeOH and UV-irradiated to form cross-linked thin-film composite QI membranes with slightly larger effective pore size (0.96 nm) than the previous systems. A related goal of this thesis research was to develop methods for systematically tuning the effective pore size of nanoporous QI polymer

  3. Pullback attractors of the two-dimensional non-autonomous simplified Ericksen-Leslie system for nematic liquid crystal flows

    NASA Astrophysics Data System (ADS)

    You, Bo; Li, Fang

    2016-08-01

    This paper is concerned with the long-time behaviour of the two-dimensional non-autonomous simplified Ericksen-Leslie system for nematic liquid crystal flows introduced in Lin and Liu (Commun Pure Appl Math, 48:501-537, 1995) with a non-autonomous forcing bulk term and order parameter field boundary conditions. In this paper, we prove the existence of pullback attractors and estimate the upper bound of its fractal dimension under some suitable assumptions.

  4. Light-induced first-order orientational transitions in a nematic liquid crystal in the presence of an ordinary wave

    SciTech Connect

    Zolot'ko, A S; Smaev, Mikhail P; Shvetsov, S A; Boiko, N I; Barnik, M I

    2012-04-30

    The effects of light-induced reorientation of the director of a nematic liquid crystal doped with dendrimer are investigated experimentally. The influence of light polarisation on the firstorder orientational transition that occurs with changing the light beam power is studied. An irreversible first-order orientational transition when changing the polarisation of light is discovered and examined. A theoretical description of the observed effects is presented.

  5. Self-action of a light beam in nematic liquid crystals in the presence of a DC electric field

    SciTech Connect

    Budagovsky, I. A.; Zolot'ko, A. S. Smayev, M. P.; Barnik, M. I.

    2010-07-15

    The results of experimental study of the light beam self-action in a nematic liquid crystal placed in a dc electric field are presented, and a theory of this effect is developed. This self-action of a light beam is shown to cause a hyperbolic umbilic caustic. The intensity distribution and caustics calculated in the far diffraction zone of the light beam agree well with the experimental data.

  6. All-optical and electro-optical switches based on the interaction with disclination lines in chiral nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Laudyn, U. A.; Kwasny, M.; Sala, F. A.; Karpierz, M. A.

    2016-05-01

    We outline the main features of spatial solitons called nematicons in chiral nematic liquid crystal confined in a wedge cell. We focus on electro-optic readdressing via the interaction with the disclination line to obtain highly steerable beam propagation. Nematicons can be effectively deviated by using the electro-optics response of the medium leading to voltage-control reconfiguration of light-induced guided-wave circuits and signal readdressing.

  7. Photorefractivity in nematic liquid crystals doped with a conjugated polymer: Mechanisms for enhanced charge transport

    SciTech Connect

    Wiederrecht, G.P.; Niemczyk, M.P.; Svec, W.A.; Wasielewski, M.R. |

    1999-06-01

    New organic materials that exhibit photorefractive effects are of wide interest for potential optical signal processing applications. The authors report on a photorefractive nematic liquid crystal composite containing the conjugated polymer poly(2,5-bis(2{prime}-ethylhexyloxy)-1,4-phenylenevinylene), BEH-PPV that exhibits a novel fringe spacing dependent inversion of the polarity of the space-charge field due to competition between the ionic diffusion and charge drift transport mechanisms. A eutectic mixture of 35% (wt %) 4{prime}-(n-octyloxy)-4-cyanobiphenyl, 8OCB, and 65% 4{prime}(n-pentyl)-4-cyanobiphenyl, 5CB, was doped with 10{sup {minus}5} M BEH-PPV (200 kD by GPC), as the electron donor. The molecular weight of the BEH-PPV polymer implies that 500 repeat units of the monomer are present with an extended chain length of 0.35 {micro}m. N,N{prime}-Dioctyl-1,4:5,8-naphthalenediimide, NI, 8 {times} 10{sup {minus}3} M, was added as the electron acceptor. The free energy change for the photoinduced electron-transfer reaction, (BEH-PPV) + NI {yields} (BEH-PPV){sup +} + NI{sup {minus}}, is {minus}1.0 eV. Two other liquid-crystal composites were also studied as controls.

  8. Side-polished fiber sensing for determination of azimuthal orientation of nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Han, Yuqi; Chen, Zhe; Yu, Jianhui; Li, Haozhi; He, Xiaoli

    2013-09-01

    The orientation of nematic liquid crystal (NLC) can be used in biosensor. The sensing characteristics of side-polished fiber (SPF) for determination of azimuthal orientation of NLC have been investigated. The relationship between the azimuthal angle of NLC director and the optical transmission power in SPF was derived by empirical approach. Experimental results showed that the azimuthal transition of liquid crystal affected the optical transmission power in SPF. While the azimuthal angle increased from 0° to 90°, the optical transmission power increased by 28.10dB, which is similar to the variation tendency of the empirical analysis. When it changes from 0° to 30°, the azimuthal angle is linear to the change of optical transmission power. The respondence of azimuthal angle for optical sensing is averagely 0.359dB/°. Experiments indicate that SPF can be used in determination of the azimuzal transition of NLC. It would be used for a new fiber optical biosensor based on the SPF and NLC.

  9. Nematic long-range ordering of topological defects in active liquid crystals

    NASA Astrophysics Data System (ADS)

    Dunkel, Jorn; Oza, Anand

    2015-11-01

    Identifying the ordering principles of intracellular matter is key to understanding the physics of microbiological systems. Recent experiments demonstrated that ATP-driven microtubule-kinesin bundles can self-assemble into two-dimensional active liquid crystals that exhibit a rich creation and annihilation dynamics of topological defects, reminiscent of particle-pair production processes in quantum systems. This remarkable discovery has sparked considerable theoretical and experimental interest, yet a satisfactory mathematical description remains elusive. Here, we present and validate a continuum theory for this new class of active matter systems by merging universality ideas with the classical Landau-de Gennes theory. The resulting model agrees quantitatively with recently published data and, in particular, predicts correctly a previously unexplained regime of long-range nematic ordering of defects observed in experiments. Our analysis implies that active liquid crystals are governed by the same generic ordering principles that determine the non-equilibrium dynamics of dense bacterial suspensions and elastic bilayer materials. Moreover, the theory suggests an energetic analogy with strongly interacting quantum gases.

  10. Disclination loops, standing alone and around solid particles, in nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Terentjev, E. M.

    1995-02-01

    A suspended particle with specific director anchoring on its surface introduces a complex distortion field in a nematic liquid crystal matrix. Topological defects-disclination loops, boojums, and hedgehogs, are needed to match the director near the particle surface with that at the far distance, which is determined by boundary conditions on the sample. This paper analyzes the elastic energy and stability of a singular loop of wedge disclination and the first-order transition of the radial hedgehog into a wide singular loop, driven by an external magnetic field. The far field of distortions, created by a ``Saturn ring'' of disclination around the spherical radial particle, allows one to calculate the potential of interaction between such particles and with the surface of the liquid crystal. Particles are repelled from each other and from the rigidly anchored surface with the potential U~1/r3. If the sample surface has soft anchoring, the particle is attracted to it at close distances and is repelled, if beyond the anchoring coherence length ξw. Several experiments to test these conclusions are suggested.

  11. Competition between local disordering and global ordering fields in nematic liquid crystals

    PubMed Central

    Ambrožič, Milan; Kralj, Samo

    2010-01-01

    Summary We study the influence of external electric or magnetic field B on orientational ordering of nematic liquid crystals or of other rod-like objects (e.g. nanotubes immersed in a liquid) in the presence of random anisotropy field type of disorder. The Lebwohl–Lasher lattice type of semi-microscopic approach is used at zero temperature. Therefore, results are valid well below the transition into the isotropic phase. We calculate the correlation function of systems as a function of B, concentration p of impurities imposing random anisotropy field disorder, the disorder strength W and system dimensionality (2D and 3D systems). In order to probe memory effects we calculate correlation length ξ for random and homogeneous initial configurations. We determine the crossover fields B c(p) separating roughly the ordered and disordered regime. Memory effects are apparent only in the latter case, i.e. for B < B c. PACS numbers: 47.51.+a, 47.54.-r, 07.05.Tp, 61.30.-v PMID:20502609

  12. Extremely sensitive light-induced reorientation in nondoped nematic liquid crystal cells due to photoelectric activation of the interface

    NASA Astrophysics Data System (ADS)

    Pagliusi, P.; Cipparrone, G.

    2003-06-01

    We report an investigation of the extremely sensitive molecular reorientation in pure nematic liquid crystal film induced by the combined application of low dc electric field (less than 0.1 V/μm) and very low intensity optical irradiation (few mW/cm2). The effect is observed in planar cells of well-known commercial nematic mixture (E7) aligned with rubbed polyvinyl alcohol layers, which exhibit photorefractive-like effect. We analyze the dependence of the photoinduced changes in birefringence upon the applied dc voltage and the light intensity. According to our results we believe that the effect is due to photoinduced recombination of the opposite charged carriers accumulated near the interface. In the low dc voltage regime (a few volts) the voltage mainly drops on the electric double layers at the interfaces as a consequence of dc field collected charge carriers from liquid crystalline and polymeric films to the border surfaces. Irradiation with appropriate wavelength reduces the interfacial charges density, because of photoinduced carrier injection and recombination processes, and consequently, induces a relocation of the electric field from the surface to the liquid crystal bulk. The light-induced additional electric field component in the nematic film results in a lowering of the Fréedericksz threshold or an enhanced molecular reorientation.

  13. Molecular dynamics simulation of the nematic liquid crystal phase in the presence of an intense magnetic field.

    PubMed

    Satoh, Katsuhiko

    2006-04-14

    The influence of an intense external field on the dynamics of the nematic liquid crystal phase is investigated using a molecular dynamics simulation for the Gay-Berne nematogen under isobaric-isothermal conditions. The molecular dynamics as a function of the second-rank orientational order parameter P<2> for a system consisting of a nematic liquid crystal in the presence of an intense magnetic field is compared with that of a similar system without the field. The translational motion of molecules is determined as a function of the translational diffusion coefficient tensor and the anisotropy and compared with the values predicted theoretically. The rotational dynamics of molecules is analyzed using the first- and the second-rank orientational time correlation functions. The translational diffusion coefficient parallel with respect to the director is constrained by the intense field, although the perpendicular one is decreased as the P<2> is increased, just as it is in the system without the field. However, no essential effect of the strong magnetic field is observed in the rotational molecular dynamics. Further, the rotational diffusion coefficient parallel with respect to the director obtained from the first-rank orientational time correlation function in the simulation is qualitatively in agreement with that in the real nematic liquid crystalline molecules. The P<2> dependence of the rotational diffusion coefficient for the system with the intense magnetic field shows a tendency similar to that for the system without the field. PMID:16626239

  14. Molecular dynamics simulation of the nematic liquid crystal phase in the presence of an intense magnetic field

    NASA Astrophysics Data System (ADS)

    Satoh, Katsuhiko

    2006-04-01

    The influence of an intense external field on the dynamics of the nematic liquid crystal phase is investigated using a molecular dynamics simulation for the Gay-Berne nematogen under isobaric-isothermal conditions. The molecular dynamics as a function of the second-rank orientational order parameter ⟨P2⟩ for a system consisting of a nematic liquid crystal in the presence of an intense magnetic field is compared with that of a similar system without the field. The translational motion of molecules is determined as a function of the translational diffusion coefficient tensor and the anisotropy and compared with the values predicted theoretically. The rotational dynamics of molecules is analyzed using the first- and the second-rank orientational time correlation functions. The translational diffusion coefficient parallel with respect to the director is constrained by the intense field, although the perpendicular one is decreased as the ⟨P2⟩ is increased, just as it is in the system without the field. However, no essential effect of the strong magnetic field is observed in the rotational molecular dynamics. Further, the rotational diffusion coefficient parallel with respect to the director obtained from the first-rank orientational time correlation function in the simulation is qualitatively in agreement with that in the real nematic liquid crystalline molecules. The ⟨P2⟩ dependence of the rotational diffusion coefficient for the system with the intense magnetic field shows a tendency similar to that for the system without the field.

  15. Anomalous viscoelasticity near the isotropic-nematic phase transition in liquid crystals.

    PubMed

    Jose, Prasanth P; Bagchi, Biman

    2004-10-01

    Recent optical Kerr effect experiments have shown that orientational relaxation of nematogens shows a pronounced slow down of the response function at intermediate times and also a power law decay near the isotropic-nematic (I-N) transition. In many aspects, this behavior appears to be rather similar to the ones observed in the supercooled liquid near-glass transition. We have performed molecular dynamics simulations of model nematogens (Gay-Berne with aspect ratio 3) to explore the viscoelasticity near the I-N transition and also investigated the correlation of viscoelasticity (if any) with orientational relaxation. It is found that although the viscosity indeed undergoes a somewhat sharper than normal change near the I-N transition, it is not characterized by any divergence-like behavior (like the ones observed in the supercooled liquid). The rotational friction, on the other hand, shows a much sharper rise as the I-N transition is approached. Interestingly, the probability distribution of the amplitude of the three components of the stress tensor shows anisotropy near the I-N transition-similar anisotropy has also been seen in the deeply supercooled liquid. Frequency dependence of viscosity shows several unusual behaviors: (a) There is a weak, power law dependence on frequency [eta(')(omega) approximately omega(-alpha)] at low frequencies and (b) there is a rapid increase in the sharp peak observed in eta(')(omega) in the intermediate frequency on approach to the I-N transition density. These features can be explained from the stress-stress time correlation function. The angular velocity correlation function also exhibits a power law decay in time. The reason for this is discussed. PMID:15473759

  16. Anomalous viscoelasticity near the isotropic-nematic phase transition in liquid crystals

    NASA Astrophysics Data System (ADS)

    Jose, Prasanth P.; Bagchi, Biman

    2004-10-01

    Recent optical Kerr effect experiments have shown that orientational relaxation of nematogens shows a pronounced slow down of the response function at intermediate times and also a power law decay near the isotropic-nematic (I-N) transition. In many aspects, this behavior appears to be rather similar to the ones observed in the supercooled liquid near-glass transition [Cang et al., J. Chem. Phys. 118, 9303 (2003)]. We have performed molecular dynamics simulations of model nematogens (Gay-Berne with aspect ratio 3) to explore the viscoelasticity near the I-N transition and also investigated the correlation of viscoelasticity (if any) with orientational relaxation. It is found that although the viscosity indeed undergoes a somewhat sharper than normal change near the I-N transition, it is not characterized by any divergencelike behavior (like the ones observed in the supercooled liquid). The rotational friction, on the other hand, shows a much sharper rise as the I-N transition is approached. Interestingly, the probability distribution of the amplitude of the three components of the stress tensor shows anisotropy near the I-N transition—similar anisotropy has also been seen in the deeply supercooled liquid [Phys. Rev. Lett. 89, 25504 (2002)]. Frequency dependence of viscosity shows several unusual behaviors: (a) There is a weak, power law dependence on frequency [η'(ω)˜ω-α] at low frequencies and (b) there is a rapid increase in the sharp peak observed in η'(ω) in the intermediate frequency on approach to the I-N transition density. These features can be explained from the stress-stress time correlation function. The angular velocity correlation function also exhibits a power law decay in time. The reason for this is discussed.

  17. Molecular ordering in the high-temperature nematic phase of an all-aromatic liquid crystal.

    PubMed

    Vita, Francesco; Hegde, Maruti; Portale, Giuseppe; Bras, Wim; Ferrero, Claudio; Samulski, Edward T; Francescangeli, Oriano; Dingemans, Theo

    2016-02-28

    We report the structural characterization of the nematic phase of 2,6-biphenyl naphthalene (PPNPP). This lath-like all-aromatic mesogen provides a valuable benchmark for classical theories of nematic order. PPNPP exhibits a very high temperature nematic phase (417-489 °C) above an enantiotropic smectic A phase. X-ray diffraction reveals a surprisingly strong tendency towards molecular layering in the nematic phase, indicative of "normal cybotaxis" (i.e. SmA-like stratification within clusters of mesogens). Although stronger at low temperatures, the layering is evident well above the smectic A-nematic transition. The nematic order parameter is evaluated as a function of temperature from the broadening of the wide-angle diffuse diffraction feature. Measured values of the orientational order parameter are slightly larger than those predicted by the Maier-Saupe theory over the entire nematic range except for a narrow region just below the clearing point where they significantly drop below the theoretical prediction. PMID:26781457

  18. Better Actuation Through Chemistry: Using Surface Coatings to Create Uniform Director Fields in Nematic Liquid Crystal Elastomers.

    PubMed

    Xia, Yu; Lee, Elaine; Hu, Hao; Gharbi, Mohamed Amine; Beller, Daniel A; Fleischmann, Eva-Kristina; Kamien, Randall D; Zentel, Rudolf; Yang, Shu

    2016-05-18

    Controlling the molecular alignment of liquid crystal monomers (LCMs) within nano- and microstructures is essential in manipulating the actuation behavior of nematic liquid crystal elastomers (NLCEs). Here, we study how to induce uniformly vertical alignment of nematic LCMs within a micropillar array to maximize the macroscopic shape change using surface chemistry. Landau-de Gennes numerical modeling suggests that it is difficult to perfectly align LCMs vertically in every pore within a poly(dimethylsiloxane) (PDMS) mold with porous channels during soft lithography. In an untreated PDMS mold that provides homeotropic anchoring of LCMs, a radially escaped configuration of LCMs is observed. Vertically aligned LCMs, a preferred configuration for actuation, are only observed when using a PDMS mold with planar anchoring. Guided by the numerical modeling, we coat the PDMS mold with a thin layer of poly(2-hydroxyethyl methacrylate) (PHEMA), leading to planar anchoring of LCM. Confirmed by polarized optical microscopy, we observe monodomains of vertically aligned LCMs within the mold, in agreement with modeling. After curing and peeling off the mold, the resulting NLCE micropillars showed a relatively large and reversible radial strain (∼30%) when heated above the nematic to isotropic transition temperature. PMID:27152975

  19. Flexoelectric instability and a spontaneous chiral-symmetry breaking in a nematic liquid crystal cell with asymmetric boundary conditions.

    PubMed

    Palto, S P; Mottram, N J; Osipov, M A

    2007-06-01

    Using both numerical simulations and an approximate analytical theory we describe a flexoelectric-induced instability in a thin nematic liquid crystal layer with asymmetric boundary conditions subjected to an applied electric field. The dependence of the threshold value of the electric field on principal material parameters of the nematic liquid crystal and the director distribution in different regions of the cell have been studied in detail numerically. The results have been compared with a simple analytical theory that enables us to obtain explicit expressions for the threshold electric field and the period of modulation above the threshold. It has been found that in the hybrid aligned nematic cell with homeotropic anchoring on one surface and planar homogeneous anchoring on the other surface, a periodic flexoelectric-induced domain structure appears, above a critical threshold, with a chiral director distribution. The director rotates about the alignment axis when moving along a perpendicular direction in the plane of the cell. The absolute value of the threshold field has been found to depend on the direction of the field due to the initial symmetry of the hybrid aligned cell and the presence of flexoelectricity. PMID:17677283

  20. A molecular nematic liquid crystalline material for high-performance organic photovoltaics

    PubMed Central

    Sun, Kuan; Xiao, Zeyun; Lu, Shirong; Zajaczkowski, Wojciech; Pisula, Wojciech; Hanssen, Eric; White, Jonathan M.; Williamson, Rachel M.; Subbiah, Jegadesan; Ouyang, Jianyong; Holmes, Andrew B.; Wong, Wallace W.H.; Jones, David J.

    2015-01-01

    Solution-processed organic photovoltaic cells (OPVs) hold great promise to enable roll-to-roll printing of environmentally friendly, mechanically flexible and cost-effective photovoltaic devices. Nevertheless, many high-performing systems show best power conversion efficiencies (PCEs) with a thin active layer (thickness is ~100 nm) that is difficult to translate to roll-to-roll processing with high reproducibility. Here we report a new molecular donor, benzodithiophene terthiophene rhodanine (BTR), which exhibits good processability, nematic liquid crystalline behaviour and excellent optoelectronic properties. A maximum PCE of 9.3% is achieved under AM 1.5G solar irradiation, with fill factor reaching 77%, rarely achieved in solution-processed OPVs. Particularly promising is the fact that BTR-based devices with active layer thicknesses up to 400 nm can still afford high fill factor of ~70% and high PCE of ~8%. Together, the results suggest, with better device architectures for longer device lifetime, BTR is an ideal candidate for mass production of OPVs. PMID:25586307

  1. Superior electro-optic response in multiferroic bismuth ferrite nanoparticle doped nematic liquid crystal device.

    PubMed

    Nayek, Prasenjit; Li, Guoqiang

    2015-01-01

    A superior electro-optic (E-O) response has been achieved when multiferroic bismuth ferrite (BiFeO3/BFO) nanoparticles (NPs) were doped in nematic liquid crystal (NLC) host E7 and the LC device was addressed in the large signal regime by an amplitude modulated square wave signal at the frequency of 100 Hz. The optimized concentration of BFO is 0.15 wt%, and the corresponding total optical response time (rise time + decay time) for a 5 μm-thick cell is 2.5 ms for ~7 V(rms). This might be exploited for the construction of adaptive lenses, modulators, displays, and other E-O devices. The possible reason behind the fast response time could be the visco-elastic constant and restoring force imparted by the locally ordered LCs induced by the multiferroic nanoparticles (MNPs). Polarized optical microscopic textural observation shows that the macroscopic dislocation-free excellent contrast have significant impact on improving the image quality and performance of the devices. PMID:26041701

  2. A molecular nematic liquid crystalline material for high-performance organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Sun, Kuan; Xiao, Zeyun; Lu, Shirong; Zajaczkowski, Wojciech; Pisula, Wojciech; Hanssen, Eric; White, Jonathan M.; Williamson, Rachel M.; Subbiah, Jegadesan; Ouyang, Jianyong; Holmes, Andrew B.; Wong, Wallace W. H.; Jones, David J.

    2015-01-01

    Solution-processed organic photovoltaic cells (OPVs) hold great promise to enable roll-to-roll printing of environmentally friendly, mechanically flexible and cost-effective photovoltaic devices. Nevertheless, many high-performing systems show best power conversion efficiencies (PCEs) with a thin active layer (thickness is ~100 nm) that is difficult to translate to roll-to-roll processing with high reproducibility. Here we report a new molecular donor, benzodithiophene terthiophene rhodanine (BTR), which exhibits good processability, nematic liquid crystalline behaviour and excellent optoelectronic properties. A maximum PCE of 9.3% is achieved under AM 1.5G solar irradiation, with fill factor reaching 77%, rarely achieved in solution-processed OPVs. Particularly promising is the fact that BTR-based devices with active layer thicknesses up to 400 nm can still afford high fill factor of ~70% and high PCE of ~8%. Together, the results suggest, with better device architectures for longer device lifetime, BTR is an ideal candidate for mass production of OPVs.

  3. Electrorheological Behavior of Main Chain Liquid Crystal Polymers in Thermotropic Nematic Solvents

    NASA Astrophysics Data System (ADS)

    Chiang, Yen-Ching; Jamieson, Alex. M.

    1998-03-01

    The increment in Miesowicz viscosity, δ η c on dissolving a main-chain liquid crystal polymer (LCP) in a nematic solvent was measured by cone-and-plate rheometry in the presence of a saturation electric field, applied perpendicular to the flow direction. In addition, the corresponding increment in the Leslie viscosity coefficient, δ α 2 was obtained from the dependence of the apparent viscosity response on the applied field strength, by curve-fitting to the torque balance equation using the 2D Ericksen-Leslie-Parodi theory. For the main-chain LCP TPB10, which has mesogenic groups separated by decamethylene spacers, both δ η c and δ α 2 exhibit, within experimental uncertainty, a linear dependence on the molecular weight. Using a hydrodynamic model of Brochard, this observation suggests that the chain behaves as a free-draining random coil, biased along the director. The temperature dependence of the relative viscosity increments, δ η c / η c ^o and δ α 2 / α 2 ^o, where η c ^o and α 2 ^o are the relevant solvent viscosities, exhibits Arrhenius behavior with an activation energy comparable to that for formation of hairpin turns in the spacer groups.

  4. A molecular nematic liquid crystalline material for high-performance organic photovoltaics.

    PubMed

    Sun, Kuan; Xiao, Zeyun; Lu, Shirong; Zajaczkowski, Wojciech; Pisula, Wojciech; Hanssen, Eric; White, Jonathan M; Williamson, Rachel M; Subbiah, Jegadesan; Ouyang, Jianyong; Holmes, Andrew B; Wong, Wallace W H; Jones, David J

    2015-01-01

    Solution-processed organic photovoltaic cells (OPVs) hold great promise to enable roll-to-roll printing of environmentally friendly, mechanically flexible and cost-effective photovoltaic devices. Nevertheless, many high-performing systems show best power conversion efficiencies (PCEs) with a thin active layer (thickness is ~100 nm) that is difficult to translate to roll-to-roll processing with high reproducibility. Here we report a new molecular donor, benzodithiophene terthiophene rhodanine (BTR), which exhibits good processability, nematic liquid crystalline behaviour and excellent optoelectronic properties. A maximum PCE of 9.3% is achieved under AM 1.5G solar irradiation, with fill factor reaching 77%, rarely achieved in solution-processed OPVs. Particularly promising is the fact that BTR-based devices with active layer thicknesses up to 400 nm can still afford high fill factor of ~70% and high PCE of ~8%. Together, the results suggest, with better device architectures for longer device lifetime, BTR is an ideal candidate for mass production of OPVs. PMID:25586307

  5. Lagrangian chaos and particle diffusion in electroconvection of planar nematic liquid crystals.

    PubMed

    Hidaka, Yoshiki; Hashiguchi, Megumi; Oikawa, Noriko; Kai, Shoichi

    2015-09-01

    Two types of spatiotemporal chaos in the electroconvection of nematic liquid crystals, such as defect turbulence and spatiotemporal intermittency, have been statistically investigated according to the Lagrangian picture. Here fluctuations are traced using the motion of a single particle driven by chaotic convection. In the defect turbulence (fluctuating normal rolls), a particle is mainly trapped in a roll but sometimes jumps to a neighboring roll. Its activation energy is then obtained from the jumping (hopping) rate. This research clarifies that diffusion in the defect turbulence regime in electroconvection can be regarded as a kind of hopping process. The spatiotemporal intermittency appears as a coexistent state of ordered grid domains and turbulent domains. The motion of a single particle shows weak and strong diffusion, respectively, in the ordered and turbulent domains. The diffusion characteristics intermittently change from one to another with certain durations as the domains change. This research has found that the distribution function of the duration that a particle remains in an ordered area has a power-law decay for which the index is different from that obtained by the Eulerian measurement. PMID:26465542

  6. Nematic liquid crystal in the wedge and edge geometry in the case of homeotropic alignment.

    PubMed

    Poniewierski, A

    2010-02-01

    Nematic liquid crystal confined to a wedge or edge is studied on the assumption that the confining surfaces provide strong and weak homeotropic anchorings, respectively. Both infinite and finite systems are considered. The model based on the Frank-Oseen and Rapini-Papoular formalisms predicts two textures of opposite rotations of the director as in the case of strong anchoring on both surfaces. However, the presence of weak anchoring results in a length scale lambda which characterizes the crossover between the regions close to the apex and far from it. The ratio lambda/b , where b is the extrapolation length, is a function of the opening angle alpha. Both stable and metastable textures are considered and the mechanism by which a texture loses its stability is found. It is related to the formation of a defect-like structure at the surface of weak anchoring whose distance from the apex is lambda(alpha) and the loss of stability is signalled by the divergence of lambda. Only in the limit alpha --> 2tau, the defect-like structure transforms into a defect of strength -1/2 located at a finite distance from the apex. PMID:20195687

  7. Superior electro-optic response in multiferroic bismuth ferrite nanoparticle doped nematic liquid crystal device

    PubMed Central

    Nayek, Prasenjit; Li, Guoqiang

    2015-01-01

    A superior electro-optic (E-O) response has been achieved when multiferroic bismuth ferrite (BiFeO3/BFO) nanoparticles (NPs) were doped in nematic liquid crystal (NLC) host E7 and the LC device was addressed in the large signal regime by an amplitude modulated square wave signal at the frequency of 100 Hz. The optimized concentration of BFO is 0.15 wt%, and the corresponding total optical response time (rise time + decay time) for a 5 μm-thick cell is 2.5 ms for ~7 Vrms. This might be exploited for the construction of adaptive lenses, modulators, displays, and other E-O devices. The possible reason behind the fast response time could be the visco-elastic constant and restoring force imparted by the locally ordered LCs induced by the multiferroic nanoparticles (MNPs). Polarized optical microscopic textural observation shows that the macroscopic dislocation-free excellent contrast have significant impact on improving the image quality and performance of the devices. PMID:26041701

  8. Using chemically patterns with different anchoring behavior to control the orientation of nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Li, Xiao; Armas Perez, Julio; Martinez-Gonzalez, Jose Adrian; Xie, Helou; de Pablo, Juan; Nealey, Paul

    2015-03-01

    We present experimental and theoretical study of nematic liquid crystal (5CB) confined to a thin cell between homeotropic anchoring top surface and chemically patterned planar/homeotropic anchoring bottom substrates. The chemically patterned substrate with different dimensions and ~ 4 nm depth topography induce the 5CB to align as the pattern direction as non-degenerate behavior, until the width of the straight line pattern is too wide to confine the 5CB to one direction and back to degenerate behavior. By changing the width of the straight line pattern, a brightness change of the intensity is shown by their corresponding crossed polarizer images. This change is mainly due to a discontinuity of the average angle between the molecules and the surface in function of line width, which is in excellent agreement with the Landan-de Gennes theory when the balance between the elastic deformation in the bulk and orientation of molecules close to the surface is simulated for different pattern dimensions. An elastic free energy transition is also observed from the numerical analysis when the strong planar anchoring for presented experiments is changed to weak. This 3D confinement by chemically patterns and small depth topography offers a new way to generate any geometry pattern controllable non-degenerate orientation, achieving switchable optical properties.

  9. Dielectric and electro-optic measurements of nematic liquid crystals doped with carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Peterson, Matthew; Georgiev, Georgi; Atherton, Timothy; Cebe, Peggy

    We studied the effects of carbon nanotubes (CNTs) on the dielectric and electro-optic properties of nematic 5CB liquid crystals (LCs). Samples containing 0.01%, 0.10% and 1.00% CNTs by weight were prepared. Anti- parallel rubbed cells with a nominal thickness of 10 μm were prepared using indium tin oxide coated glass cells and a polyimide alignment layer. The capacitance and dissipation factor were measured using an Agilent 4284A precision LCR meter. From these measurements, the complex dielectric permittivity was determined as a function of frequency. Analysis of the low frequency regime (f <1000 Hz) indicates that 5CB samples containing CNTs have a higher conductance than neat samples. The Fréedericksz transition critical voltage was noted by a sharp increase in capacitance after an initial plateau. Numerical simulations of CNT-facilitated switching show that polarization induced on the nanotubes from capacitive effects can significantly reduce the critical voltage in DC electric fields, in agreement with experimental results. Measurements of the critical voltage over a range of frequencies will also be presented. Research was supported by the National Science Foundation, DMR1206010.

  10. Molecular organization of nematic liquid crystals between concentric cylinders: Role of the elastic anisotropy

    NASA Astrophysics Data System (ADS)

    Chiccoli, C.; Pasini, P.; Evangelista, L. R.; Teixeira-Souza, R. T.; Zannoni, C.

    2015-02-01

    The orientational order in a nematic liquid crystal sample confined to an annular region between two concentric cylinders is investigated by means of lattice Monte Carlo simulations. Strong anchoring and homeotropic orientations, parallel to the radial direction, are implemented at the confining surfaces. The elastic anisotropy is taken into account in the bulk interactions by using the pair potential introduced by Gruhn and Hess [T. Gruhn and S. Hess, Z. Naturforsch. A 51, 1 (1996)] and parametrized by Romano and Luckhurst [S. Romano, Int. J. Mod. Phys. B 12, 2305 (1998), 10.1142/S0217979298001344; Phys. Lett. A 302, 203 (2002), 10.1016/S0375-9601(02)01042-3; G. R. Luckhurst and S. Romano, Liq. Cryst. 26, 871 (1999), 10.1080/026782999204561], i.e., the so-called GHRL potential. In the case of equal elastic constants, a small but appreciable deformation along the cylinder axis direction is observed, whereas when the values of K11/K33 if K22=K33 are low enough, all the spins in the bulk follow the orientation imposed by the surfaces. For larger values of K11/K33 , spontaneous deformations, perpendicular to the polar plane, increase significantly. Our findings indicate that the onset of these deformations also depends on the ratio K22/K33 and on the radius of the cylindrical surfaces. Although expected from the elastic theory, no tangential component of the deformations was observed in the simulations for the set of parameters analyzed.

  11. Homogeneous alignment of nematic liquid crystals by ion beam etched surfaces

    NASA Technical Reports Server (NTRS)

    Wintucky, E. G.; Mahmood, R.; Johnson, D. L.

    1979-01-01

    A wide range of ion beam etch parameters capable of producing uniform homogeneous alignment of nematic liquid crystals on SiO2 films are discussed. The alignment surfaces were generated by obliquely incident (angles of 5 to 25 deg) argon ions with energies in the range of 0.5 to 2.0 KeV, ion current densities of 0.1 to 0.6 mA sq cm and etch times of 1 to 9 min. A smaller range of ion beam parameters (2.0 KeV, 0.2 mA sq cm, 5 to 10 deg and 1 to 5 min.) were also investigated with ZrO2 films and found suitable for homogeneous alignment. Extinction ratios were very high (1000), twist angles were small ( or = 3 deg) and tilt-bias angles very small ( or = 1 deg). Preliminary scanning electron microscopy results indicate a parallel oriented surface structure on the ion beam etched surfaces which may determine alignment.

  12. Topology and self-assembly of defect-colloidal superstructure in confined chiral nematic liquid crystals

    NASA Astrophysics Data System (ADS)

    Pandey, M. B.; Ackerman, P. J.; Burkart, A.; Porenta, T.; Žumer, S.; Smalyukh, Ivan I.

    2015-01-01

    We describe formation of defect-colloidal superstructures induced by microspheres with normal surface anchoring dispersed in chiral nematic liquid crystals in confinement-unwound homeotropic cells. Using three-dimensional nonlinear optical imaging of the director field, we demonstrate that some of the induced defects have nonsingular solitonic nature while others are singular point and line topological defects. The common director structures induced by individual microspheres have dipolar symmetry. These topological dipoles are formed by the particle and a hyperbolic point defect (or small disclination loop) of elementary hedgehog charge opposite to that of a sphere with perpendicular boundary conditions, which in cells with thickness over equilibrium cholesteric pitch ratio approaching unity are additionally interspaced by a looped double-twist cylinder of continuous director deformations. The long-range elastic interactions are probed by holographic optical tweezers and videomicroscopy, providing insights to the physical underpinnings behind self-assembled colloidal structures entangled by twisted solitons. Computer-simulated field and defect configurations induced by the colloidal particles and their assemblies, which are obtained by numerically minimizing the Landau-de Gennes free energy, are in agreement with the experimental findings.

  13. Direct mapping of local director field of nematic liquid crystals at the nano-scale

    NASA Astrophysics Data System (ADS)

    Xia, Yu; Serra, Francesca; Yang, Shu; Kamien, Randall

    2015-03-01

    The director field in liquid crystals (LCs) has been characterized mainly via polarized optical microscopy, fluorescence confocal microscopy, and Raman spectroscopy, all of which are limited by optical wavelengths - from hundreds of nanometers to several micrometers. Since LC orientation cannot be resolved directly by these methods, theory is needed to interpret the local director field of LC alignment. In this work, we introduce a new approach to directly visualize the local director field of a nematic LC (NLC) at the nano-scale using scanning electron microscopy (SEM). A new type of NLC monomer bearing crosslinkable groups was designed and synthesized. It can be well-oriented at particle surfaces and patterned polymer substrates, including micron-sized silica colloids, porous membranes, micropillar arrays, and 1D channels. After carefully crosslinking, the molecular orientation of NLCs around the particles or within the patterns could be directly visualized by SEM, showing oriented nanofibers representing LC director from the fractured samples. Here, we could precisely resolve not only the local director field by this approach, but the defect structures of NLCs, including hedgehogs and line defects. The direct mapping of LC directors at the nanoscale using this method will improve our understanding of NLC local director field, and thus their manipulation and applications. More importantly, a theoretical interpretation will no longer be a necessity to resolve a new material system in this field.

  14. Frequency dependence of the onset voltage of electroconvection in the nematic liquid crystal N4

    NASA Astrophysics Data System (ADS)

    Xu, Xiaochao; Bowers, Steve; Bajaj, Kapil; Ahlers, Guenter

    2003-03-01

    Onset voltages Vc of electroconvection in a nematic liquid crystal (NLC) cell were measured as a function of the drive frequency ω/ 2 π. The cell (from E.H.C Co, Ltd Japan) had a nominal spacing of 25 μm and planar alignment. It was filled with the NLC Merck phase IV (N4). The NLC was doped with 0.1% by weight of tetra butylammonium bromide(TBAB) and the conductivity was near 1.0 × 10-6 (Ω m)-1 at 30^oC. At low frequencies (15 to 80Hz) the onset voltage dropped as the frequency increased. This is contrary to the usual interpretation of the standard model which yields Vc (1+ω^2 τ^2)/[ξ^2-(1+ω^2 τ^2)] (ξ is related to NLC material properities), with the charge relaxation time τ=ɛ/ ( 4π σ) assumed to be independent of ω. Measurements at higher frequencies agreed reasonably with the standard model prediction. Further measurements using an AC bridge revealed that the dielectric constant ɛ is strongly frequency dependent at low frequencies, whereas the conductivity σ was roughly constant. Taking into account the frequency dependence of ɛ (and thus of τ), the onset-voltage measurements agreed fairly well with the standard-model prediction.

  15. Fluctuations below a stationary supercritical bifurcation to electroconvection in a nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Qiu, Xin-Liang; Ahlers, Guenter

    2003-03-01

    We report measurements of thermally driven fluctuations near the onset of electroconvection in a nematic liquid crystal (NLC). The cell (from E.H.C Co, Ltd Japan) had a nominal spacing of 25 μm and planar alignment. It was filled with the NLC Merck phase IV (N4). The NLC was doped with 0.1% by weight of tetra butylammonium bromide(TBAB) and the conductivity was near 9 × 10-7 (Ω m)-1 at 30^oC. The system was driven by an alternating voltage of frequency 25 Hz and amplitude V. The initial bifurcation to electroconvection was supercritical and yielded oblique stationary rolls. For small but negative ɛ ≡ V^2/V_c^2 - 1 the mean-square amplitude of the fluctuations was proportional to |ɛ|^-γ with γ larger than the value γ_LT = 1/2 given by linear theory (LT). This result differs from the one obtained earlier (M.A. Scherer ,G. Ahlers, F. Hörner, and I. Rehberg, Phys. Rev. Lett. 85), 3754 (2000); M.A. Scherer and G. Ahlers, Phys. Rev. E 65, 051101 (2002) for the NLC 5CB, which undergoes a supercritical Hopf bifurcation to oblique rolls and which yields γ ˜= 0.25 < γ_LT . We conclude that the two systems belong to different universality classes.

  16. Multi-domain vertical alignment of nematic liquid crystals for reduced off-axis gamma shift

    NASA Astrophysics Data System (ADS)

    Yoon, Tae-Hoon; Park, Byung Wok; Kim, Ki-Han; Kim, Hoon; Shin, Ki-Chul; Kim, Hee Seop

    2013-03-01

    Several liquid crystal (LC) modes, such as twisted nematic, vertical alignment (VA), and in-plane switching, have been in competition with each other in the LC display market. Among them, the VA mode has been widely used because of the high contrast ratio. Since the LC molecules are aligned perpendicular to the substrate in the initial state, an excellent dark state can be obtained at normal viewing direction. However, effective phase retardation of LC layer at oblique viewing direction differs greatly from that at normal viewing direction. Thus, gamma distortion phenomenon occurs at oblique view direction. To reduce the gamma shift in the VA mode at oblique viewing direction, multi-domain VA modes were proposed. Although gamma shifts of these modes are smaller than that of the single domain VA mode, the problems still remain. Recently, several technologies for 8-domain alignment have been proposed to decrease the gamma shift at off-axis. However, additional driving circuits are required to realize the eight-domain structure. In this paper we report technologies for the multi-domain VA mode with no additional driving circuits. By using the proposed technologies, we can obtain the dual threshold voltage in each sub-pixel to realize the multi-domain VA mode with no decrease of contrast ratio.

  17. Theoretical model applicable to the experimental determination of surface anchoring energies of nematic liquid crystals. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Wintucky, E. G.

    1980-01-01

    For a cell configuration consisting of a thin nematic layer bounded by two parallel plane surfaces, with opposing surfaces suitably treated to produce dissimilar molecular orientations, the elastic continuum theory for nematic liquid crystals was applied to derive an expression relating surface anchoring energies to elastic constants, director orientations at the substrate surfaces, and cell thickness. A numerical comparison with the elastically isotropic result over a range K sub 3 = 1.5 K sub 1 to K sub 3 = 10 K sub 1 showed the effect of elastic anisotropy could be quite significant. Surface anchoring energies calculated for anisotropic of K sub 3 = 2 K sub 1 and K sub 3 + 10 K sub 1 were approximately 50% and 500%, respectively, than the isotropic values.

  18. Density of photon states in dye-doped chiral nematic liquid crystal cells in the presence of losses and gain.

    PubMed

    Mavrogordatos, Th K; Morris, S M; Castles, F; Hands, P J W; Ford, A D; Coles, H J; Wilkinson, T D

    2012-07-01

    We calculate the density of photon states (DOS) of the normal modes in dye-doped chiral nematic liquid crystal (LC) cells in the presence of various loss mechanisms. Losses and gain are incorporated into the transmission characteristics through the introduction of a small imaginary part in the dielectric constant perpendicular and along the director, for which we assume no frequency dispersion. Theoretical results are presented on the DOS in the region of the photonic band gap for a range of values of the loss coefficient and different values of the optical anisotropy. The obtained values of the DOS at the photonic band gap edges predict a reversal of the dominant modes in the structure. Our results are found to be in good agreement with the experimentally obtained excitation thresholds in chiral nematic LC lasers. The behavior of the DOS is also discussed for amplifying LC cells providing additional insight to the lasing mechanism of these structures. PMID:23005435

  19. Synthesis and mesomorphic behaviour of achiral four-ring unsymmetrical bent-core liquid crystals: Nematic phases

    NASA Astrophysics Data System (ADS)

    Paul, Manoj Kumar; Kalita, Gayatri; Laskar, Atiqur Rahman; Debnath, Somen; Gude, Venkatesh; Sarkar, Dipika Debnath; Mohiuddin, Golam; Varshney, Sanjay Kumar; Nandiraju Rao, V. S.

    2013-10-01

    Achiral four ring unsymmetrical bent-core liquid crystals derived from 3-amino-2-methylbenzoic acid have been designed and synthesized with an imine, ester and photochromic azo linking moieties. These hockey-stick shape resembling bent molecules possess an alkoxy chain at one end of the molecule and methyl or methoxy group at the other end. The synthesis, phase transition temperatures and characterization of phase behaviour are discussed. The molecular structure characterization is consistent with data from elemental and spectroscopic analysis. The materials thermal behaviour and phase characterization have been investigated by differential scanning calorimetry and polarizing optical microscopy. All these compounds exhibit enantiotropic nematic phase over wide temperature range. Stable supercooling of nematic phase has been observed in methoxy homologues. The density functional theory (DFT) calculations were performed to obtain the stable molecular conformation, polarizability, dipole moment, Highest occupied molecular orbital (HOMO), Lowest unoccupied molecular orbital (LUMO) energies and bending angle of the compound.

  20. Gradient polymer-disposed liquid crystal single layer of large nematic droplets for modulation of laser light.

    PubMed

    Hadjichristov, Georgi B; Marinov, Yordan G; Petrov, Alexander G

    2011-06-01

    The light modulating ability of gradient polymer-disposed liquid crystal (PDLC) single layer of large droplets formed by nematic E7 in UV-cured polymer NOA65 is studied. Operating at relatively low voltages, such PDLC film with a of thickness 10-25 μm and droplet size up to 50 μm exhibits a good contrast ratio and is capable of producing a large phase shift for the propagating coherent light. For a linearly polarized He-Ne laser (λ=633 nm), an electrically commanded phase shift as large as π/2 can be obtained by the large-droplet region of the film. The electrically produced phase shift and its spatial profile controlled by the thickness of the gradient PDLC single layers of large nematic droplets can be useful for tunable spatial light modulators and other devices for active control of laser light. PMID:21629309

  1. Temperature effects on capillary instabilities in a thin nematic liquid crystalline fiber embedded in a viscous matrix.

    PubMed

    Cheong, A-G; Rey, A D

    2002-10-01

    Linear stability analysis of capillary instabilities in a thin nematic liquid crystalline cylindrical fiber embedded in an immiscible viscous matrix is performed by formulating and solving the governing nemato-capillary equations, that include the effect of temperature on the nematic ordering as well as the effect of the nematic orientation. A representative axial nematic orientation texture with the planar easy axis at the fiber surface is studied. The surface disturbance is expressed in normal modes, which include the azimuthal wave number m to take into account non-axisymmetric modes. Capillary instabilities in nematic fibers reflect the anisotropic nature of liquid crystals, such as the ordering and orientation contributions to the surface elasticity and surface normal and bending stresses. Surface gradients of normal and bending stresses provide additional anisotropic contributions to the capillary pressure that may renormalize the classical displacement and curvature forces that exist in any fluid fiber. The exact nature (stabilizing and destabilizing) and magnitude of the renormalization of the displacement and curvature forces depend on the nematic ordering and orientation, i.e. the anisotropic contribution to the surface energy, and accordingly capillary instabilities may be axisymmetric or non-axisymmetric. In addition, when the interface curvature effects are accounted for as contributions of the work of interfacial bending and torsion to the total energy of the system, the higher-order bending moment contribution to the surface stress tensor is critical in stabilizing the fiber instabilities. For the planar easy axis, the nematic ordering contribution to the surface energy, which renormalizes the effect of the fiber shape, plays a crucial role to determine the instability mechanisms. Moreover, the unstable modes, which are most likely observed, can be driven by the dependence of surface energy on the surface area. Low-ordering fibers display the

  2. Temperature effects on capillary instabilities in a thin nematic liquid crystalline fiber embedded in a viscous matrix

    NASA Astrophysics Data System (ADS)

    Cheong, A.-G.; Rey, A. D.

    2002-10-01

    Linear stability analysis of capillary instabilities in a thin nematic liquid crystalline cylindrical fiber embedded in an immiscible viscous matrix is performed by formulating and solving the governing nemato-capillary equations, that include the effect of temperature on the nematic ordering as well as the effect of the nematic orientation. A representative axial nematic orientation texture with the planar easy axis at the fiber surface is studied. The surface disturbance is expressed in normal modes, which include the azimuthal wave number m to take into account non-axisymmetric modes. Capillary instabilities in nematic fibers reflect the anisotropic nature of liquid crystals, such as the ordering and orientation contributions to the surface elasticity and surface normal and bending stresses. Surface gradients of normal and bending stresses provide additional anisotropic contributions to the capillary pressure that may renormalize the classical displacement and curvature forces that exist in any fluid fiber. The exact nature (stabilizing and destabilizing) and magnitude of the renormalization of the displacement and curvature forces depend on the nematic ordering and orientation, i.e. the anisotropic contribution to the surface energy, and accordingly capillary instabilities may be axisymmetric or non-axisymmetric. In addition, when the interface curvature effects are accounted for as contributions of the work of interfacial bending and torsion to the total energy of the system, the higher-order bending moment contribution to the surface stress tensor is critical in stabilizing the fiber instabilities. For the planar easy axis, the nematic ordering contribution to the surface energy, which renormalizes the effect of the fiber shape, plays a crucial role to determine the instability mechanisms. Moreover, the unstable modes, which are most likely observed, can be driven by the dependence of surface energy on the surface area. Low-ordering fibers display the

  3. Tunable microwave bandpass filter integrated power divider based on the high anisotropy electro-optic nematic liquid crystal.

    PubMed

    Liu, Yupeng; Liu, Yang; Li, Haiyan; Jiang, Di; Cao, Weiping; Chen, Hui; Xia, Lei; Xu, Ruimin

    2016-07-01

    A novel, compact microwave tunable bandpass filter integrated power divider, based on the high anisotropy electro-optic nematic liquid crystal, is proposed in this letter. Liquid crystal, as the electro-optic material, is placed between top inverted microstrip line and the metal plate. The proposed structure can realize continuous tunable bandpass response and miniaturization. The proposed design concept is validated by the good performance of simulation results and experimental results. The electro-optic material has shown great potential for microwave application. PMID:27475583

  4. Tunable microwave bandpass filter integrated power divider based on the high anisotropy electro-optic nematic liquid crystal

    NASA Astrophysics Data System (ADS)

    Liu, Yupeng; Liu, Yang; Li, Haiyan; Jiang, Di; Cao, Weiping; Chen, Hui; Xia, Lei; Xu, Ruimin

    2016-07-01

    A novel, compact microwave tunable bandpass filter integrated power divider, based on the high anisotropy electro-optic nematic liquid crystal, is proposed in this letter. Liquid crystal, as the electro-optic material, is placed between top inverted microstrip line and the metal plate. The proposed structure can realize continuous tunable bandpass response and miniaturization. The proposed design concept is validated by the good performance of simulation results and experimental results. The electro-optic material has shown great potential for microwave application.

  5. Global Existence and Large Time Behavior of Strong Solutions to the 2-D Compressible Nematic Liquid Crystal Flows with Vacuum

    NASA Astrophysics Data System (ADS)

    Wang, Teng

    2016-02-01

    This paper is concerned with the strong solutions to the Cauchy problem of a simplified Ericksen-Leslie system of compressible nematic liquid crystals in two or three dimensions with vacuum as far field density. For strong solutions, some a priori decay rate (in large time) for the pressure, the spatial gradient of velocity field and the second spatial gradient of liquid crystal director field are obtained provided that the initial total energy is suitably small. Furthermore, with the help of the key decay rates, we establish the global existence and uniqueness of strong solutions (which may be of possibly large oscillations) in two spatial dimensions.

  6. Photoreactive self-assembled monolayer for the stabilization of tilt orientation of a director in vertically aligned nematic liquid crystals.

    PubMed

    Oh, Su Yeon; Kang, Shin-Woong

    2013-12-16

    Photo-reactive self-assembled monolayer (PR-SAM) is employed to mediate alignment of liquid crystals (LC) and stabilize the tilt orientation of a nematic director for a vertically aligned liquid crystal. Bifunctional PR-SAM formed by silane coupling reaction to oxide surfaces efficiently induces a homeotropic alignment and stabilizes LC director by the photo-polymerization under applied electric field. As a result, the substantial enhancement of electro-optic performance has been achieved after the PR-SAM assisted stabilization of tilt orientation of director. This approach for pretilt stabilization has multifarious advantages over the conventional PSVA. PMID:24514711

  7. Electro-optical study of chiral nematic liquid crystal/chiral ionic liquid composites with electrically controllable selective reflection characteristics.

    PubMed

    Hu, Wang; Zhang, Lipei; Cao, Hui; Song, Li; Zhao, Haiyan; Yang, Zhou; Cheng, Zihui; Yang, Huai; Guo, Lin

    2010-03-20

    A chiral nematic liquid crystal (N*-LC)/chiral ionic liquid (CIL) composite with unique electro-optical characteristics was prepared and filled into a planar treated cell. When an electric field was applied to the cell, the anions and the cations of CIL moved towards the anode and the cathode of the power supply, respectively, thus forming a density gradient of the chiral groups, which resulted in wideband reflection. By adjusting the intensity of the electric field, the reflection bandwidth can be controlled accurately and reversibly. Moreover, the electric field-induced states can be memorized after the applied electric field is turned off. The reflective properties of the composite are investigated in the visible and near-infrared region, respectively. Additionally, the changes of the reflection bandwidths with the intensity and the applied time of the electric field were also investigated. From scanning electron microscopy (SEM) investigations, the mechanism of the electrically controllable reflection was demonstrated. Potential applications of the composite are related to reflective, color electronic paper (E-paper) and smart reflective windows for the solar light management. PMID:20200740

  8. Interactions of carbon nanotubes in a nematic liquid crystal. II. Experiment

    NASA Astrophysics Data System (ADS)

    Agha, Hakam; Galerne, Yves

    2016-04-01

    Multiwall carbon nanotube (CNT) colloids with different anchoring conditions are dispersed in pentyl-cyanobiphenyl (5CB), a thermotropic liquid crystal (LC) that exhibits a room-temperature nematic phase. The experiments make use of CNTs treated for strong planar, homeotropic, or Janus anchorings. Observations with a polarizing microscope show that the CNTs placed in a uniform nematic field stabilize parallel or perpendicular to n depending on their anchoring conditions. In the presence of a splay-bend disclination line, they are first attracted toward it and ultimately, they get trapped on it. Their orientation relative to the line is then found to be parallel or perpendicular to it, again depending on the anchoring conditions. When a sufficient number of particles are deposited on a disclination line, they form a micro- or nanonecklace in the shape of a thin thread or of a bottle brush, with the CNTs being oriented parallel or perpendicular to the disclination line according to the anchoring treatment. The system exhibits a rich versatility, even if until now the weak anchorings appear to be difficult to control. In a next step, the necklaces may be glued by means of pyrrole electropolymerization. In this manner, we realize a true materialization of the disclination lines, and we obtain nanowires capable of conducting the electricity in the place of the initial disclinations that just worked as templates. The advantage of the method is that it finally provides nanowires that are automatically connected to predesignated three-dimensional (3D) electrodes. Such a 3D nanowiring could have important applications, as it could allow one to develop electronic circuits in the third dimension. They could thus help with increasing the transistor density per surface unit, although downsizing of integrated circuits will soon be limited to atomic sizes or so. In other words, the predicted limitation to Moore's law could be avoided. For the moment, the nanowires that we obtain

  9. Anisotropic nanoparticles immersed in a nematic liquid crystal: defect structures and potentials of mean force.

    PubMed

    Hung, Francisco R; Guzmán, Orlando; Gettelfinger, Brian T; Abbott, Nicholas L; de Pablo, Juan J

    2006-07-01

    We report results for the potential of mean force (PMF) and the defect structures that arise when spherocylindrical nanoparticles are immersed in a nematic liquid crystal. Using a dynamic field theory for the tensor order parameter Q of the liquid crystal, we analyzed configurations, including one, two, and three elongated particles, with strong homeotropic anchoring at their surfaces. For systems with one nanoparticle, the most stable configuration is achieved when the spherocylinder is placed with its long axis perpendicular to the far-field director, for which the defect structure consists of an elongated Saturn ring. For systems with two or three nanoparticles with their long axes placed perpendicular to the far-field director, at small separations the defect structures consist of incomplete Saturn rings fused with new disclination rings orthogonal to the original ones, in analogy to results previously observed for spherical nanoparticles. The shape of these orthogonal rings depends on the nanoparticles' configuration, i.e., triangular, linear, or parallel with respect to their long axis. A comparison of the PMFs indicates that the latter configuration is the most stable. The stability of the different arrays depends on whether orthogonal disclination rings form or not, their size, and the curvature effects in the interparticle regions. Our results suggest that the one-elastic-constant approximation is valid for the considered systems; similar results were obtained when a three-constant expression is used to represent the elastic free energy. The attractive interactions between the elongated particles were compared to those observed for spheres of similar diameters. Similar interparticle energies were observed for linear arrays; in contrast, parallel and triangular arrays of spherocylinders yielded interactions that were up to 3.4 times stronger than those observed for spherical particles. PMID:16907115

  10. Three-dimensional control of the helical axis of a chiral nematic liquid crystal by light

    NASA Astrophysics Data System (ADS)

    Zheng, Zhi-Gang; Li, Yannian; Bisoyi, Hari Krishna; Wang, Ling; Bunning, Timothy J.; Li, Quan

    2016-03-01

    Chiral nematic liquid crystals—otherwise referred to as cholesteric liquid crystals (CLCs)—are self-organized helical superstructures that find practical application in, for example, thermography, reflective displays, tuneable colour filters and mirrorless lasing. Dynamic, remote and three-dimensional control over the helical axis of CLCs is desirable, but challenging. For example, the orientation of the helical axis relative to the substrate can be changed from perpendicular to parallel by applying an alternating-current electric field, by changing the anchoring conditions of the substrate, or by altering the topography of the substrate’s surface; separately, in-plane rotation of the helical axis parallel to the substrate can be driven by a direct-current field. Here we report three-dimensional manipulation of the helical axis of a CLC, together with inversion of its handedness, achieved solely with a light stimulus. We use this technique to carry out light-activated, wide-area, reversible two-dimensional beam steering—previously accomplished using complex integrated systems and optical phased arrays. During the three-dimensional manipulation by light, the helical axis undergoes, in sequence, a reversible transition from perpendicular to parallel, followed by in-plane rotation on the substrate surface. Such reversible manipulation depends on experimental parameters such as cell thickness, surface anchoring condition, and pitch length. Because there is no thermal relaxation, the system can be driven either forwards or backwards from any light-activated intermediate state. We also describe reversible photocontrol between a two-dimensional diffraction state, a one-dimensional diffraction state and a diffraction ‘off’ state in a bilayer cell.

  11. Liquid crystalline polymers in good nematic solvents: Free chains, mushrooms, and brushes

    SciTech Connect

    Williams, D.R.M. . Lab. de Physique de la Matiere Condensee); Halperin, A. . Dept. of Materials)

    1993-08-02

    The swelling of main chain liquid crystalline polymers (LCPs) in good nematic solvents is theoretically studied, focusing on brushes of terminally anchored, grafted LCPs. The analysis is concerned with long LCPs, of length L, with n[sub 0] >> 1 hairpin defects. The extension behavior of the major axis, R[parallel], of these ellipsoidal objects gives rise to an Ising elasticity with a free energy penalty of F[sub el](R[parallel])/kT [approx] n[sub 0] [minus] n[sub 0](1 [minus] R[parallel][sup 2]/L[sup 2])[sup 1/2]. The theory of the extension behavior enables the formulation of a Flory type theory of swelling of isolated LCPs yielding R[parallel] [approx] exp(2U[sub h]/5kT)N[sup 3/5] and R [perpendicular] [approx] exp([minus]U[sub h]/10kT)N[sup 3/5], with N the degree of polymerization and U[sub h] the hairpin energy. It also allows the generalization of the Alexander model for polymer brushes to the case of grafted LCPs. The behavior of LCP brushes depends on the alignment imposed by the grafting surface and the liquid crystalline solvent. A tilting phase transition is predicted as the grafting density is increased for a surface imposing homogeneous, parallel anchoring. A related transition is expected upon compression of a brush subject to homeotropic, perpendicular alignment. The effect of magnetic or electric fields on these phase transitions is also studied. The critical magnetic/electric field for the Frederiks transition can be lowered to arbitrarily small values by using surfaces coated by brushes of appropriate density.

  12. Three-dimensional control of the helical axis of a chiral nematic liquid crystal by light.

    PubMed

    Zheng, Zhi-gang; Li, Yannian; Bisoyi, Hari Krishna; Wang, Ling; Bunning, Timothy J; Li, Quan

    2016-03-17

    Chiral nematic liquid crystals--otherwise referred to as cholesteric liquid crystals (CLCs)--are self-organized helical superstructures that find practical application in, for example, thermography, reflective displays, tuneable colour filters and mirrorless lasing. Dynamic, remote and three-dimensional control over the helical axis of CLCs is desirable, but challenging. For example, the orientation of the helical axis relative to the substrate can be changed from perpendicular to parallel by applying an alternating-current electric field, by changing the anchoring conditions of the substrate, or by altering the topography of the substrate's surface; separately, in-plane rotation of the helical axis parallel to the substrate can be driven by a direct-current field. Here we report three-dimensional manipulation of the helical axis of a CLC, together with inversion of its handedness, achieved solely with a light stimulus. We use this technique to carry out light-activated, wide-area, reversible two-dimensional beam steering--previously accomplished using complex integrated systems and optical phased arrays. During the three-dimensional manipulation by light, the helical axis undergoes, in sequence, a reversible transition from perpendicular to parallel, followed by in-plane rotation on the substrate surface. Such reversible manipulation depends on experimental parameters such as cell thickness, surface anchoring condition, and pitch length. Because there is no thermal relaxation, the system can be driven either forwards or backwards from any light-activated intermediate state. We also describe reversible photocontrol between a two-dimensional diffraction state, a one-dimensional diffraction state and a diffraction 'off' state in a bilayer cell. PMID:26950601

  13. The Relaxation of Twisted Chiral Nematic Liquid Crystals with Side-Chain Polymeric Layer

    NASA Astrophysics Data System (ADS)

    Zhou, Xuan; Zhang, Zhidong

    2013-09-01

    A generalized form of surface dissipation function, for the description of the relative motion of the nematic director with respect to the polymer side chains in twisted chiral nematic samples is proposed, and the relaxation time of such samples are investigated, using the perturbation analysis method proposed by Alexe-Ionescu et al. Our results show that the presence of both the surface dissipation and the polymer side chains increase the relaxation time.

  14. Angular dependence of optical scattering in mixed nematic-cholesteric liquid crystals.

    NASA Technical Reports Server (NTRS)

    Oron, N.; Yu, J. L.; Labes, M. M.

    1973-01-01

    The basic ternary cholesteric mixture used in the investigations reported contained by weight 1.1 parts of cholesteryl chloride, 0.9 parts of cholesteryl nonanoate, and 2.0 parts cholesteryl oleyl carbonate. Samples were prepared by adding a nematic dopant to the cholesteric mixture. Measurements of the wavelength of maximum scattering at different angles for the doped samples show that the angular color distortion is reduced with increasing concentrations of nematic dopant.

  15. Condensation of Self-Assembled Lyotropic Chromonic Liquid Crystal Sunset Yellow in Aqueous Solutions Crowded with Polyethylene Glycol and Doped with Salt

    SciTech Connect

    Park, Heung-Shik; Kang, Shin-Woong; Tortora, Luana; Kumar, Satyendra; Lavrentovich, Oleg D.

    2012-10-10

    We use optical and fluorescence microscopy, densitometry, cryo-transmission electron microscopy (cryo-TEM), spectroscopy, and synchrotron X-ray scattering to study the phase behavior of the reversible self-assembled chromonic aggregates of an anionic dye Sunset Yellow (SSY) in aqueous solutions crowded with an electrically neutral polymer polyethylene glycol (PEG) and doped with the salt NaCl. PEG causes the isotropic SSY solutions to condense into a liquid-crystalline region with a high concentration of SSY aggregates, coexisting with a PEG-rich isotropic (I) region. PEG added to the homogeneous nematic (N) phase causes separation into the coexisting N and I domains; the SSY concentration in the N domains is higher than the original concentration of PEG-free N phase. Finally, addition of PEG to the highly concentrated homogeneous N phase causes separation into the coexisting columnar hexagonal (C) phase and I phase. This behavior can be qualitatively explained by the depletion (excluded volume) effects that act at two different levels: at the level of aggregate assembly from monomers and short aggregates and at the level of interaggregate packing. We also show a strong effect of a monovalent salt NaCl on phase diagrams that is different for high and low concentrations of SSY. Upon the addition of salt, dilute I solutions of SSY show appearance of the condensed N domains, but the highly concentrated C phase transforms into a coexisting I and N domains. We suggest that the salt-induced screening of electric charges at the surface of chromonic aggregates leads to two different effects: (a) increase of the scission energy and the contour length of aggregates and (b) decrease of the persistence length of SSY aggregates.

  16. Influence of the nematic order on the rheology and conformation of stretched comb-like liquid crystalline polymers

    NASA Astrophysics Data System (ADS)

    Fourmaux-Demange, V.; Brûlet, A.; Boué, F.; Davidson, P.; Keller, P.; Cotton, J. P.

    2000-04-01

    We have studied the rheology and the conformation of stretched comb-like liquid-crystalline polymers. Both the influence of the comb-like structure and the specific effect of the nematic interaction on the dynamics are investigated. For this purpose, two isomers of a comb-like polymetacrylate polymer, of well-defined molecular weights, were synthesized: one displays a nematic phase over a wide range of temperature, the other one has only an isotropic phase. Even with high degrees of polymerization N, between 40 and 1000, the polymer chains studied were not entangled. The stress-strain curves during the stretching and relaxation processes show differences between the isotropic and nematic comb-like polymers. They suggest that, in the nematic phase, the chain dynamics is more cooperative than for a usual linear polymer. Small-angle neutron scattering has been used in order to determine the evolution of the chain conformation after stretching, as a function of the duration of relaxation t_r. The conformation can be described with two parameters only: λ_p, the global deformation of the polymer chain, and p, the number of statistical units of locally relaxed sub-chains. For the comb-like polymer, the chain deformation is pseudo-affine: λ_p is always smaller than λ (the deformation ratio of the whole sample). In the isotropic phase, λ_p has a constant value, while p increases as t_r. This latter behavior is not that expected for non-entangled chains, in which p varies as {t_r}^{1/2} (Rouse model). In the nematic phase, λ_p decreases as a stretched exponential function of t_r, while p remains constant. The dynamics of the comb-like polymers is discussed in terms of living clusters from which junctions are produced by interactions between side chains. The nematic interaction increases the lifetime of these junctions and, strikingly, the relaxation is the same at all scales of the whole polymer chain.

  17. A possible critical point for nematic order on the basis of Landau free energy having dual instabilities for nano-segregated smectic liquid crystals.

    PubMed

    Saito, Kazuya; Hishida, Mafumi; Yamamura, Yasuhisa

    2015-11-21

    Landau expansion of free energy assuming dual instabilities for the nano-segregated SmA phase is analyzed. In addition to known phase sequences (on cooling, disordered isotropic liquidnematic phase → smectic phase, and disordered isotropic liquid → smectic phase), a new sequence (disordered isotropic liquid → density wave with subsidiary nematic order → smectic phase) and the existence of a critical point are demonstrated in the case where the instability for density wave formation occurs at a higher temperature. PMID:26372214

  18. Dielectric spectroscopy of isotropic liquids and liquid crystal phases with dispersed graphene oxide

    PubMed Central

    Al-Zangana, Shakhawan; Iliut, Maria; Boran, Gökçen; Turner, Michael; Vijayaraghavan, Aravind; Dierking, Ingo

    2016-01-01

    Graphene oxide (GO) flakes of different sizes were prepared and dispersed in isotropic and nematic (anisotropic) fluid media. The dielectric relaxation behaviour of GO-dispersions was examined for a wide temperature (25–60 oC) and frequency range (100 Hz–2 MHz). The mixtures containing GO flakes exhibited varying dielectric relaxation processes, depending on the size of the flakes and the elastic properties of the dispersant fluid. Relaxation frequencies of the GO doped isotropic media, such as isopropanol IPA, were observed to be much lower than the GO doped thermotropic nematic medium 5CB. It is anticipated that the slow relaxation frequencies (~10 kHz) could be resulting from the relaxation modes of the GO flakes while the fast relaxation frequencies (~100 kHz) could indicate strongly slowed down molecular modes of the nematogenic molecules, which are anchored to the GO flakes via dispersion interactions. The relaxation frequencies decreased as the size of the GO flakes in the isotropic solvent was increased. Polarizing microscopy showed that GO flakes with a mean diameter of 10 μm, dispersed in water, formed a lyotropic nematic liquid crystal phase. This lyotropic nematic exhibited the slowest dielectric relaxation process, with relaxation frequencies in the order of 2 kHz, as compared to the GO-isotropic suspension and the GO-doped 5CB. PMID:27555475

  19. Dielectric spectroscopy of isotropic liquids and liquid crystal phases with dispersed graphene oxide.

    PubMed

    Al-Zangana, Shakhawan; Iliut, Maria; Boran, Gökçen; Turner, Michael; Vijayaraghavan, Aravind; Dierking, Ingo

    2016-01-01

    Graphene oxide (GO) flakes of different sizes were prepared and dispersed in isotropic and nematic (anisotropic) fluid media. The dielectric relaxation behaviour of GO-dispersions was examined for a wide temperature (25-60 (o)C) and frequency range (100 Hz-2 MHz). The mixtures containing GO flakes exhibited varying dielectric relaxation processes, depending on the size of the flakes and the elastic properties of the dispersant fluid. Relaxation frequencies of the GO doped isotropic media, such as isopropanol IPA, were observed to be much lower than the GO doped thermotropic nematic medium 5CB. It is anticipated that the slow relaxation frequencies (~10 kHz) could be resulting from the relaxation modes of the GO flakes while the fast relaxation frequencies (~100 kHz) could indicate strongly slowed down molecular modes of the nematogenic molecules, which are anchored to the GO flakes via dispersion interactions. The relaxation frequencies decreased as the size of the GO flakes in the isotropic solvent was increased. Polarizing microscopy showed that GO flakes with a mean diameter of 10 μm, dispersed in water, formed a lyotropic nematic liquid crystal phase. This lyotropic nematic exhibited the slowest dielectric relaxation process, with relaxation frequencies in the order of 2 kHz, as compared to the GO-isotropic suspension and the GO-doped 5CB. PMID:27555475

  20. Second harmonic light scattering induced by defects in the twist-bend nematic phase of liquid crystal dimers.

    PubMed

    Pardaev, Shokir A; Shamid, S M; Tamba, M G; Welch, C; Mehl, G H; Gleeson, J T; Allender, D W; Selinger, J V; Ellman, B; Jakli, A; Sprunt, S

    2016-05-11

    The nematic twist-bend (NTB) phase, exhibited by certain thermotropic liquid crystalline (LC) dimers, represents a new orientationally ordered mesophase - the first distinct nematic variant discovered in many years. The NTB phase is distinguished by a heliconical winding of the average molecular long axis (director) with a remarkably short (nanoscale) pitch and, in systems of achiral dimers, with an equal probability to form right- and left-handed domains. The NTB structure thus provides another fascinating example of spontaneous chiral symmetry breaking in nature. The order parameter driving the formation of the heliconical state has been theoretically conjectured to be a polarization field, deriving from the bent conformation of the dimers, that rotates helically with the same nanoscale pitch as the director field. It therefore presents a significant challenge for experimental detection. Here we report a second harmonic light scattering (SHLS) study on two achiral, NTB-forming LCs, which is sensitive to the polarization field due to micron-scale distortion of the helical structure associated with naturally-occurring textural defects. These defects are parabolic focal conics of smectic-like "pseudo-layers", defined by planes of equivalent phase in a coarse-grained description of the NTB state. Our SHLS data are explained by a coarse-grained free energy density that combines a Landau-deGennes expansion of the polarization field, the elastic energy of a nematic, and a linear coupling between the two. PMID:27089236