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Articles 1 - 25 of 25
Full-Text Articles in Physics
Coexistence Of Two Colloidal Crystals At The Nematic-Liquid-Crystal-Air Interface, A. B. Nych, V. M. Pergamenshchik, B. I. Lev, V. G. Nazarenko, I. Muševič, M. Škarabot, Oleg Lavrentovich
Coexistence Of Two Colloidal Crystals At The Nematic-Liquid-Crystal-Air Interface, A. B. Nych, V. M. Pergamenshchik, B. I. Lev, V. G. Nazarenko, I. Muševič, M. Škarabot, Oleg Lavrentovich
Oleg Lavrentovich
Glycerol droplets at a nematic-liquid-crystal–air interface form two different lattices—hexagonal and dense quasihexagonal—which are separated by the energy barrier and can coexist. Director distortions around each droplet form an elastic dipole. The first order transition between the two lattices is driven by a reduction of the dipole-dipole repulsion through reorientation of these dipoles. The elastic-capillary attraction is essential for the both lattices. The effect has a many-body origin.
Pretransitional Fluctuations In The Isotropic Phase Of A Lyotropic Chromonic Liquid Crystal, Yuriy A. Nastishin, Sergij V. Shiyanovskii, Oleg Lavrentovich, A. F. Kostko, M. A. Anisimov
Pretransitional Fluctuations In The Isotropic Phase Of A Lyotropic Chromonic Liquid Crystal, Yuriy A. Nastishin, Sergij V. Shiyanovskii, Oleg Lavrentovich, A. F. Kostko, M. A. Anisimov
Oleg Lavrentovich
We have studied isotropic-to-nematic pretransitional fluctuations in an aqueous solution of disodium cromoglycate (cromolyn) by static and dynamic light scattering. Cromolyn is a representative of lyotropic chromonic liquid crystals with building units being elongated rods formed by aggregates of disk-like molecules. By combining light-scattering and viscosity measurements we have determined the correlation length and relaxation time of the orientational order-parameter fluctuations and estimated the size of the cromolyn aggregates. The pretransitional behavior of light scattering does not completely follow the classic Landau-de Gennes model. This feature is most probably associated with the variable length of cromolyn aggregates. We have observed …
Undulations In A Confined Lamellar System With Surface Anchoring, T. Ishikawa, Oleg Lavrentovich
Undulations In A Confined Lamellar System With Surface Anchoring, T. Ishikawa, Oleg Lavrentovich
Oleg Lavrentovich
We visualize undulations in layered systems using a cholesteric stripe phase with a macroscopic supramicron periodicity. The wave vector of stripe pattern is in the cell's plane. The-undulation is induced by an in-plane magnetic field normal to the stripes. The observed displacement of layers is much larger than the value predicted by the Helfrich-Hurault classic theory. We propose a model of undulations that explains the data by finite surface anchoring of layers.
Curvature Energy Of A Focal Conic Domain With Arbitrary Eccentricity, Maurice Kleman, Oleg Lavrentovich
Curvature Energy Of A Focal Conic Domain With Arbitrary Eccentricity, Maurice Kleman, Oleg Lavrentovich
Oleg Lavrentovich
The most frequently observed focal conic domains (FCD’s) in lamellar phases are those based on confocal paris of ellipse and hyperbola. Experimentally, the eccentricity of the ellipse takes a broad range of values 0<~eeisolated FCD reaches a minimum only at e⃗1 (under the constraint of a fixed major semiaxis of the ellipse); exceptions include situations with large saddle-splay elastic constant and small domains where the applicability of the elastic theory is limited. In realistic cases, a value of eccentricity smaller than 1 is stabilized by factors other than the curvature energy: by dislocations emerging from the FCD’s …
Stripe Domain Phase Of A Thin Nematic Film And The K13 Divergence Term, Oleg Lavrentovich, V. M. Pergamenshchik
Stripe Domain Phase Of A Thin Nematic Film And The K13 Divergence Term, Oleg Lavrentovich, V. M. Pergamenshchik
Oleg Lavrentovich
To verify the status of the divergence K13 term in the elastic theory of liquid crystals we study submicron films placed onto an isotropic fluid substrate in the Langmuir trough (Langmuir liquid crystal, LLC). The upper and lower surfaces favor normal and tangential molecular orientation, respectively. The periodic domain phase is observed in a nematic LLC. The dependence of the periodicity L of the domains vs film thickness h can be explained only if the elastic energy is accompanied by divergence terms with nonzero constants K13 and K24. It is found that for 5CB K13 almost-equal-to -0.2K11.
Tensor And Complex Anchoring In Liquid Crystals, Sergij V. Shiyanovskii, Anatoliy Glushchenko, Yuri Reznikov, Oleg Lavrentovich, John L. West
Tensor And Complex Anchoring In Liquid Crystals, Sergij V. Shiyanovskii, Anatoliy Glushchenko, Yuri Reznikov, Oleg Lavrentovich, John L. West
Oleg Lavrentovich
We propose a tensor description of surface anchoring of liquid crystals ~LCs!. The model allows one to consider both the homogeneous and inhomogeneous parts of LC anchoring and to calculate the cumulative effect of different treatments as a sum of corresponding tensors. For the planar alignment the tensor representation is reduced to the complex azimuthal anchoring coefficient, whose amplitude and phase determine, respectively, the strength of azimuthal anchoring and the azimuthal angle of the easy axis. We predict and experimentally confirm that two consecutive photoalignment treatments with beams of perpendicular polarizations can compensate each other and restore the initial anchoring.
Effect Of Director Distortions On Morphologies Of Phase Separation In Liquid Crystals, D. Voloschenko, Oleg P. Pishnyak, Sergij V. Shiyanovskii, Oleg Lavrentovich
Effect Of Director Distortions On Morphologies Of Phase Separation In Liquid Crystals, D. Voloschenko, Oleg P. Pishnyak, Sergij V. Shiyanovskii, Oleg Lavrentovich
Oleg Lavrentovich
We study phase separation from a nematic liquid crystal with spatially nonuniform director gradients. Particles of a phase-separated component, which is either an isotropic fluid (silicone oil) or a nonmesogenic photopolymer, accumulate in the regions with the strongest director distortions, thus reducing the overall energy of the system.
Anchoring-Mediated Interaction Of Edge Dislocations With Bounding Surfaces In Confined Cholesteric Liquid Crystals, Ivan I. Smalyukh, Oleg Lavrentovich
Anchoring-Mediated Interaction Of Edge Dislocations With Bounding Surfaces In Confined Cholesteric Liquid Crystals, Ivan I. Smalyukh, Oleg Lavrentovich
Oleg Lavrentovich
We employ the fluorescent confocal polarizing microscopy to image edge dislocations in cholesteric liquid crystals. Surface anchoring at the bounding plates determines the structure and behavior of defects. Two types of plates set in-plane director orientation but differ in the type of associated anchoring potentials. Plates with strong polar anchoring and nonzero azimuthal anchoring repel the dislocations, while plates with weak polar anchoring and no azimuthal anchoring allow the dislocations to escape through the boundary. To explain the results, we propose a coarse-grained model of cholesteric anchoring.
Tilted Photoalignment Of A Nematic Liquid Crystal Induced By A Magnetic Field, Denis Andrienko, Yuri Kurioz, Yuri Reznikov, Charles Rosenblatt, Rolfe Petschek, Oleg Lavrentovich, Darius Subacius
Tilted Photoalignment Of A Nematic Liquid Crystal Induced By A Magnetic Field, Denis Andrienko, Yuri Kurioz, Yuri Reznikov, Charles Rosenblatt, Rolfe Petschek, Oleg Lavrentovich, Darius Subacius
Oleg Lavrentovich
Nematic liquid crystal cells with polyvinyl cinnamate coated substrates were subjected to ultraviolet light. When this was done in the presence of an oblique magnetic field the photoalignment was found to be temporally and thermally robust, with a large pretilt angle and weak polar anchoring. Moreover, two easy axes with equal and opposite pretilt angle were obtained, such that a magnetic field could switch the director from one easy axis to the other. (C) 1998 American Institute of Physics.
Electrorotation Of Colloidal Particles In Liquid Crystals, Guangxun Liao, Ivan I. Smalyukh, J. R. Kelly, Oleg D. Lavrentovich, Antal Jakli
Electrorotation Of Colloidal Particles In Liquid Crystals, Guangxun Liao, Ivan I. Smalyukh, J. R. Kelly, Oleg D. Lavrentovich, Antal Jakli
Oleg Lavrentovich
We present the first observations of dc electric-field-induced rotational motion of finite particles in liquid crystals. We show that the electrorotation is essentially identical to the well-known Quincke rotation, which in liquid crystals triggers an additional translational motion at higher fields. In the smectic phase the translational motion is confined to the two-dimensional geometry of smectic layers, in contrast to the isotropic and nematic phases, where the particles can move in all three dimensions. We demonstrate that by a proper analysis of the electrorotation, one can determine the in-plane viscosity of smectic liquid crystals. This method needs only a small …
Optical Characterization Of The Nematic Lyotropic Chromonic Liquid Crystals: Light Absorption, Birefringence, And Scalar Order Parameter, Yuriy A. Nastishin, H. Liu, T. Schneider, V. G. Nazarenko, Sergij V. Shiyanovskii, Oleg Lavrentovich
Optical Characterization Of The Nematic Lyotropic Chromonic Liquid Crystals: Light Absorption, Birefringence, And Scalar Order Parameter, Yuriy A. Nastishin, H. Liu, T. Schneider, V. G. Nazarenko, Sergij V. Shiyanovskii, Oleg Lavrentovich
Oleg Lavrentovich
We report on the optical properties of the nematic (N) phase formed by lyotropic chromonic liquid crystals (LCLCs) in well aligned planar samples. LCLCs belong to a broad class of materials formed by one-dimensional molecular self-assembly and are similar to other systems such as “living polymers” and “wormlike micelles.” We study three water soluble LCLC forming materials: disodium chromoglycate, a derivative of indanthrone called Blue 27, and a derivative of perylene called Violet 20. The individual molecules have a planklike shape and assemble into rodlike aggregates that form the N phase once the concentration exceeds about 0.1M. The uniform surface …
Levitation, Lift, And Bidirectional Motion Of Colloidal Particles In An Electrically Driven Nematic Liquid Crystal, Oleg P. Pishnyak, S. Tang, J. R. Kelly, Sergij V. Shiyanovskii, Oleg Lavrentovich
Levitation, Lift, And Bidirectional Motion Of Colloidal Particles In An Electrically Driven Nematic Liquid Crystal, Oleg P. Pishnyak, S. Tang, J. R. Kelly, Sergij V. Shiyanovskii, Oleg Lavrentovich
Oleg Lavrentovich
We study electric-field-induced dynamics of colloids in a nematic cell, experimentally and by computer simulations. Solid particles in the nematic bulk create director distortions of dipolar type. Elastic repulsion from the walls keeps the particles in the middle of cell. The ac electric field reorients the dipoles and lifts them to top or bottom, depending on dipole orientation. Once near the walls, the colloids are carried along two antiparallel horizontal directions by nematic backflow. Computer simulations of the backflow agree with the experiment.
Surface Alignment And Anchoring Transitions In Nematic Lyotropic Chromonic Liquid Crystal, V. G. Nazarenko, O. P. Boiko, H. S. Park, O. M. Brodyn, M. M. Omelchenko, L. Tortora, Yuriy A. Nastishin, Oleg Lavrentovich
Surface Alignment And Anchoring Transitions In Nematic Lyotropic Chromonic Liquid Crystal, V. G. Nazarenko, O. P. Boiko, H. S. Park, O. M. Brodyn, M. M. Omelchenko, L. Tortora, Yuriy A. Nastishin, Oleg Lavrentovich
Oleg Lavrentovich
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.
Real-Time Microbe Detection Based On Director Distortions Around Growing Immune Complexes In Lyotropic Chromonic Liquid Crystals, Sergij V. Shiyanovskii, T. Schneider, Ivan I. Smalyukh, T. Ishikawa, G. D. Niehaus, K. J. Doane, C. J. Woolverton, Oleg Lavrentovich
Real-Time Microbe Detection Based On Director Distortions Around Growing Immune Complexes In Lyotropic Chromonic Liquid Crystals, Sergij V. Shiyanovskii, T. Schneider, Ivan I. Smalyukh, T. Ishikawa, G. D. Niehaus, K. J. Doane, C. J. Woolverton, Oleg Lavrentovich
Oleg Lavrentovich
We describe director distortions in the nematic liquid crystal (LC) caused by a spherical particle with tangential surface orientation of the director and show that light transmittance through the distorted region is a steep function of the particle's size. The effect allows us to propose a real-time microbial sensor based on a nontoxic lyotropic chromonic LC (LCLC) that detects and amplifies the presence of immune complexes. A cassette is filled with LCLC, antibody, and antigen-bearing particles. Small and isolated particles cause no macroscopic distortions of the LCLC. Upon antibody-antigen binding, the growing immune complexes distort the director and cause detectable …
Directed Vertical Alignment Liquid Crystal Display With Fast Switching, Mingxia Gu, Ivan I. Smalyukh, Oleg Lavrentovich
Directed Vertical Alignment Liquid Crystal Display With Fast Switching, Mingxia Gu, Ivan I. Smalyukh, Oleg Lavrentovich
Oleg Lavrentovich
We describe a directed vertical alignment (VA) display mode based on a nematic liquid crystal (LC) doped with a chiral dopant and confined between two substrates, one of which is pretreated, say, by unidirectional rubbing or photoalignment. The design allows one to eliminate umbilical defects that appear during switching of the conventional VA cells and thus to obtain better contrast. Switching is similar to 30% faster than for VA cells when optimized concentration of a chiral dopant is added and LC molecules at one of the substrates are slightly tilted from the cell normal due to the unidirectional surface treatment.
Thermodielectric Bistability In Dual Frequency Nematic Liquid Crystal, Y. Yin, Sergij V. Shiyanovskii, Oleg Lavrentovich
Thermodielectric Bistability In Dual Frequency Nematic Liquid Crystal, Y. Yin, Sergij V. Shiyanovskii, Oleg Lavrentovich
Oleg Lavrentovich
We report on a thermodielectric bistability in dual frequency nematic liquid crystals (LCs) caused by the anisotropic nature of dielectric heating and director reorientation in an electric field. The bistability is a result of the positive feedback loop: director reorientation -> anisotropic dielectric heating -> dielectric anisotrophy -> director reorientation. We demonstrate both experimentally and theoretically that two states with different temperature and director orientation, namely, a cold planar state and a hot homeotropic state coexist in a LC cell for a certain frequency and amplitude range of the applied voltage.
Monte Carlo Simulations Of Stable Point Defects In Hybrid Nematic Films, C. Chiccoli, Oleg Lavrentovich, P. Pasini, C. Zannoni
Monte Carlo Simulations Of Stable Point Defects In Hybrid Nematic Films, C. Chiccoli, Oleg Lavrentovich, P. Pasini, C. Zannoni
Oleg Lavrentovich
Monte Carlo (MC) simulations based exclusively on nearest-neighbor intermolecular interactions reveal the existence of stable long-range deformations and topological defects in a thin nematic film confined between two surfaces with antagonistic (normal and tangential) molecular orientations. Thus the MC technique allows one to describe a delicate balance of bulk elasticity and surface energy usually treated only with macroscopic theories.
Cholesteric Gratings With Field-Controlled Period, Darius Subacius, Sergij V. Shiyanovskii, Philip J. Bos, Oleg Lavrentovich
Cholesteric Gratings With Field-Controlled Period, Darius Subacius, Sergij V. Shiyanovskii, Philip J. Bos, Oleg Lavrentovich
Oleg Lavrentovich
Diffractive gratings with period varied by an electric field are developed using a cholesteric liquid crystal confined between two transparent electrodes with unidirectionally treated alignment layers. In the initial state (zero field), the cholesteric layers are parallel to the cell planes. The electric field creates an in-plane modulated structure of variable period. Diffraction regimes of both Raman-Nath and Bragg types are demonstrated. (C) 1997 American Institute of Physics.
Viscoelasticity, Dielectric Anisotropy, And Birefringence In The Nematic Phase Of Three Four-Ring Bent-Core Liquid Crystals With An L-Shaped Molecular Frame, Nejmettin Acvi, Volodymyr Borshch, Dipika Debnath Sarkar, Rahul Deb, Gude Venkatesh, Taras Turiv, Sergij V. Shiyanovskii, Nandiraju V. S. Rao, Oleg Lavrentovich
Viscoelasticity, Dielectric Anisotropy, And Birefringence In The Nematic Phase Of Three Four-Ring Bent-Core Liquid Crystals With An L-Shaped Molecular Frame, Nejmettin Acvi, Volodymyr Borshch, Dipika Debnath Sarkar, Rahul Deb, Gude Venkatesh, Taras Turiv, Sergij V. Shiyanovskii, Nandiraju V. S. Rao, Oleg Lavrentovich
Oleg Lavrentovich
Molecular shape is an important factor in determining the material properties of thermotropic liquid crystals (LCs). We synthesized and investigated several LC compounds formed by asymmetrically bent molecules with a rigid four-ring core in the shape of the letter 'L'. We measured the temperature dependencies of dielectric permittivities, birefringence, splay K-1 and bend K-3 elastic constants, splay viscosity eta(splay) and flow viscosities eta(parallel to) and eta(perpendicular to). The bend-splay anisotropy delta K-31 - K-3 - K-1 is negative, similar to the case of nematic LCs formed by symmetrically bent molecules of V-shape. The dielectric anisotropy Delta epsilon and birefringence are …
Liquid Crystals, Photonic Crystals, Metamaterials, And Transformation Optics, Oleg Lavrentovich
Liquid Crystals, Photonic Crystals, Metamaterials, And Transformation Optics, Oleg Lavrentovich
Oleg Lavrentovich
No abstract provided.
Self-Assembly, Condensation, And Order In Aqueous Lyotropic Chromonic Liquid Crystals Crowded With Additives, Luana Tortora, Heung-Shik Park, Shin-Woong Kang, Victoria Savaryn, Seung-Ho Hong, Konstantine Kaznatcheev, Daniele Finotello, Samuel Sprunt, Satyendra Kumar, Oleg Lavrentovich
Self-Assembly, Condensation, And Order In Aqueous Lyotropic Chromonic Liquid Crystals Crowded With Additives, Luana Tortora, Heung-Shik Park, Shin-Woong Kang, Victoria Savaryn, Seung-Ho Hong, Konstantine Kaznatcheev, Daniele Finotello, Samuel Sprunt, Satyendra Kumar, Oleg Lavrentovich
Oleg Lavrentovich
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 covalentpolymerization. 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 …
Switchable Two-Dimensional Gratings Based On Field-Induced Layer Undulations In Cholesteric Liquid Crystals, B. I. Senyuk, I. I. Smalyukh, Oleg Lavrentovich
Switchable Two-Dimensional Gratings Based On Field-Induced Layer Undulations In Cholesteric Liquid Crystals, B. I. Senyuk, I. I. Smalyukh, Oleg Lavrentovich
Oleg Lavrentovich
We propose switchable two-dimensional (2D) diffractive gratings with periodic refractive-index modulation arising from layer undulations in cholesteric liquid crystals. The cholesteric cell can be switched between two states: (1) f lat layers of a planar cholesteric texture and (2) a square lattice of periodic director modulation associated with layer undulations that produces 2D diffraction patterns. The intensities of the diffraction maxima can be tuned by changing the applied field. The diffractive properties can be optimized for different wavelengths by appropriately choosing cholesteric pitch, cell thickness, and surface treatment.
Crossing Of Disclinations In Nematic Slabs, T. Ishikawa, Oleg Lavrentovich
Crossing Of Disclinations In Nematic Slabs, T. Ishikawa, Oleg Lavrentovich
Oleg Lavrentovich
It is shown experimentally that crossing and intercommutation of disclinations in a bounded nematic cell depend on surface orientation of the director and the relative strength of disclinations. Lines of opposite strength switch the pinned ends between the bounding plates and vanish independently of each other if the surface orientation is tangential. In contrast, tilted surface orientation preserves the stability of lines.
X-Ray Studies Of Bond-Orientational Order In Liquid-Crystalline Orthogonal Hexatic-B Phase, E. Gorecka, Li Chen, Oleg Lavrentovich, W. Pyzuk
X-Ray Studies Of Bond-Orientational Order In Liquid-Crystalline Orthogonal Hexatic-B Phase, E. Gorecka, Li Chen, Oleg Lavrentovich, W. Pyzuk
Oleg Lavrentovich
X-ray scattering measurements have been carried out for free-standing, thick . monodomain films of the orthogonal hexatic-B phase. From Fourier analysis of X-scans, 6n-fold-symmetry order parameters were determined and proved to fulfill the scaling relation C6n = C6n+lambdan(n-1). The temperature behavior of C6 and lambda was found nonuniversal when comparing homologues, PIR5 and PIR7, differing in their range of the hexatic phase. The hexatic order parameter varies with the critical exponents 0.25, 0.20 (+/- 0.03), respectively. For comparison results for compound RFL6, of other homologue series, are presented.
Biaxiality In A Cyclic Thermotropic Nematic Liquid-Crystal, Jian-Feng Li, V. Percec, Ch. Rosenblatt, Oleg Lavrentovich
Biaxiality In A Cyclic Thermotropic Nematic Liquid-Crystal, Jian-Feng Li, V. Percec, Ch. Rosenblatt, Oleg Lavrentovich
Oleg Lavrentovich
Birefringence and textural data are presented for a ring-shaped trimeric liquid crystal. The material apparently undergoes a uniaxial-to-biaxial nematic phase transition as a function of temperature.