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Articles 1 - 12 of 12

Full-Text Articles in Physics

Unusual Sequences Of Tilted Smectic Phases In Liquid Crystals Of Bent-Shape Molecules, Antal Jakli, P. Toledano Dec 2002

Unusual Sequences Of Tilted Smectic Phases In Liquid Crystals Of Bent-Shape Molecules, Antal Jakli, P. Toledano

Chemical Physics Publications

The first theoretical description of the experimentally often-observed isotropic-polar smectic phase transitions of symmetric and asymmetric bent-shape molecules is presented. The isotropic-tilted polar smectic phase transition requires a coupling among three types of ordering processes: polar packing, director tilt, and layer ordering. For explaining the unusual triclinic-monoclinic phase transition with the lower symmetry phase at higher temperature, observed in fluoro-containing compounds recently, a mechanism is proposed in which the layer ordering triggers the simultaneous onset of the tilt and polar order.


Dynamics Of The Nematic Phase Of A Bent-Core Liquid Crystal, S. Stojadinovic, A. Adorjan, Samuel N. Sprunt, Hans Sawade, Antal Jakli Dec 2002

Dynamics Of The Nematic Phase Of A Bent-Core Liquid Crystal, S. Stojadinovic, A. Adorjan, Samuel N. Sprunt, Hans Sawade, Antal Jakli

Chemical Physics Publications

The dielectric fluctuations in the uniaxial nematic phase of a bent-core liquid crystal have been studied by dynamic light scattering. Polarization selection of the scattering cross-section reveals one mode due to ordinary director fluctuations and, in the lower part of the nematic phase, a second mode attributable to fluctuations of the biaxial order parameter. The director fluctuations are similar to100 times slower than observed in typical nematics based on straight-core molecules, suggesting that the bent core nematogenic units may be microscopic smectic domains ("cybotactic" clusters).


Three-Dimensional Director Structures Of Defects In Grandjean-Cano Wedges Of Cholesteric Liquid Crystals Studied By Fluorescence Confocal Polarizing Microscopy, Ivan I. Smalyukh, Oleg Lavrentovich Nov 2002

Three-Dimensional Director Structures Of Defects In Grandjean-Cano Wedges Of Cholesteric Liquid Crystals Studied By Fluorescence Confocal Polarizing Microscopy, Ivan I. Smalyukh, Oleg Lavrentovich

Chemical Physics Publications

We use a nondestructive technique of fluorescence confocal polarizing microscopy to visualize three-dimensional director patterns of defects in Grandjean-Cano wedges filled with a cholesteric liquid crystal of pitch p=5 mum. Strong surface anchoring of the director causes a stable lattice of dislocations in the bulk. Optical slicing in the vertical cross sections of the wedges allows us to establish the detailed structure of dislocations and their kinks. Dislocations of Burgers vector b=p/2 are located in the thin part of the sample, very close to the bisector plane. Their cores are split into a pair of tau(-1 ...


Evolution Of Disclinations In Cholesteric Liquid Crystals, F. Zhang, Deng-Ke Yang Oct 2002

Evolution Of Disclinations In Cholesteric Liquid Crystals, F. Zhang, Deng-Ke Yang

Chemical Physics Publications

We studied the evolution of defect lines (oily streaks) in cholesteric liquid crystals. In contrast to nematic liquid crystals, there were no interactions between the defect lines in cholesteric liquid crystals. We observed experimentally that individual open defect segments shrank with time with a linear relation, and individual defect loops shrank with time with a square root relation. We also observed that the defects in cholesteric liquid crystals were mainly interconnected loops, and the total length of the defect lines decreased with time logarithmically because of the distribution of loop size. The decay constant depended on the helical pitch of ...


Topological Defects In Schlieren Textures Of Biaxial And Uniaxial Nematics, C. Chiccoli, I. Feruli, Oleg Lavrentovich, P. Pasini, Sergij V. Shiyanovskii, C. Zannoni Sep 2002

Topological Defects In Schlieren Textures Of Biaxial And Uniaxial Nematics, C. Chiccoli, I. Feruli, Oleg Lavrentovich, P. Pasini, Sergij V. Shiyanovskii, C. Zannoni

Chemical Physics Publications

Monte Carlo and theoretical studies of thin 3D films of biaxial and uniaxial nematics with tangential boundary conditions show distinct differences in structure and evolution of topological defects. In the uniaxial films, defects of strength k=+/-1 are point defects that bear no bulk singularity and disappear by annihilation with each other. In the biaxial films, k=+/-1 defects are true singular bulk disclinations that split into pairs of k=+/-1/2 lines; the latter disappear by annihilation processes of the type +1/2-1/2=0. These observed differences are of relevance for the current debate on the existence of ...


Nanophase Segregation Of Nonpolar Solvents In Smectic Liquid Crystals Of Bent-Shape Molecules, M.Y.M. Huang, A.M. Pedreira, O.G. Martins, A.M.F. Neto, Antal Jakli Sep 2002

Nanophase Segregation Of Nonpolar Solvents In Smectic Liquid Crystals Of Bent-Shape Molecules, M.Y.M. Huang, A.M. Pedreira, O.G. Martins, A.M.F. Neto, Antal Jakli

Chemical Physics Publications

Electro-optical, calorimetric, x-ray, and dielectric measurements are reported on a mixture containing a bent-core liquid crystal 4-chloro-1,3-phenylinebis [4-(4-n-tetradecyloxyphenyliminomethyl) benzoate] mixed with the nonpolar solvent n-hexadecane (HEX). It is observed that the addition of HEX depresses the isotropic-to-smectic phase transition temperature, but the crystallization temperature does not change considerably. Instead, the texture of the crystalline phase changes and, at sufficiently high concentrations of HEX (>20 wt %), an optically isotropic phase appears. Above 40 wt % HEX concentrations, the mesophase completely disappears and a direct isotropic solid-to-isotropic liquid transition takes place. At increasing HEX concentration, the transition enthalpies, the layer ordering ...


Ferroelectric-Chiral-Antiferroelectric-Racemic Liquid Crystal Phase Transition Of Bent-Shape Molecules, S. Rauch, P. Bault, Hans Sawade, G. Heppke, Geetha G. Nair, Antal Jákli Aug 2002

Ferroelectric-Chiral-Antiferroelectric-Racemic Liquid Crystal Phase Transition Of Bent-Shape Molecules, S. Rauch, P. Bault, Hans Sawade, G. Heppke, Geetha G. Nair, Antal Jákli

Chemical Physics Publications

Detailed dielectric, polarization current, electro-optical, and textural observations are reported on an asymmetric banana-shaped compound 1,3-biphenylene-bis[4-(3-fluoro-4-octyloxyphenyliminomethyl)benzoate]. The material possesses a chiral-ferroelectric-racemic-antiferroelectric phase transition. Our studies reveal that the higher temperature ferroelectric phase has a polar double-tilted smectic structure, where both the molecular plane and the long axis are tilted with respect to the layer normal. Accordingly, it has a chiral triclinic structure with an out-of-plane polarization component. The lower temperature phase has a monoclinic symmetry, which is higher than that of the higher temperature phase. To our knowledge, among liquid crystals such situations were previously observed ...


Piezoelectricity Of A Ferroelectric Liquid Crystal With A Glass Transition, Antal Jakli, T. Toth-Katona, T. Scharf, M. Schadt, A. Saupe Jul 2002

Piezoelectricity Of A Ferroelectric Liquid Crystal With A Glass Transition, Antal Jakli, T. Toth-Katona, T. Scharf, M. Schadt, A. Saupe

Chemical Physics Publications

Pressure-electric (hydrostatic piezoelectric) measurements are reported on bookshelf textures of a ferroelectric smectic-C (Sm C(*)) liquid crystal with a glass transition. The continuous variation of a partially fluid state to the solid glass enables one to trace how the piezoelectric effect depends on the consistency of the material. It was observed that in the Sm C(*) samples with poled glass the piezoelectric constants are comparable to conventional piezoelectric crystals and poled piezoelectric polymers. This implies their application possibilities. The magnitude of the piezoelectric constant in the glassy state depends very much on the poling conditions. The studies indicate that there ...


Effect Of Director Distortions On Morphologies Of Phase Separation In Liquid Crystals, D. Voloschenko, Oleg P. Pishnyak, Sergij V. Shiyanovskii, Oleg Lavrentovich Jun 2002

Effect Of Director Distortions On Morphologies Of Phase Separation In Liquid Crystals, D. Voloschenko, Oleg P. Pishnyak, Sergij V. Shiyanovskii, Oleg Lavrentovich

Chemical Physics Publications

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.


Synthesis Of A Color Image Display Using Birefringent Filters, Salman Morgan Saeed, Philip J. Bos Jan 2002

Synthesis Of A Color Image Display Using Birefringent Filters, Salman Morgan Saeed, Philip J. Bos

Chemical Physics Publications

A new method of generating color in liquid crystal displays using birefringent filters is shown. This method has the benefit of high light transmission and color saturation compared to traditional spatial or temporal multiplexing methods, which include highly absorptive color filters. We discuss the design and optimization of a double-layer supertwisted nematic color display based on polarization interference filters. The viewing angle of such a device is also modeled and improvements are shown. The device is capable of high light transmission (90% that of parallel polarizers) while retaining color saturation.


Imprinting The Quasi Bookshelf Texture Of A Ferroelectric Liquid Crystal Into Nano-Scaled Polymer Fibrils, S. H. Kim, S. Suresh, Liang-Chy Chien Jan 2002

Imprinting The Quasi Bookshelf Texture Of A Ferroelectric Liquid Crystal Into Nano-Scaled Polymer Fibrils, S. H. Kim, S. Suresh, Liang-Chy Chien

Chemical Physics Publications

Polymer-stabilized ferroelectric liquid crystals (PSFLCs) are made by photopolymerizing 3% reactive mesogenic monomer on a quasi bookshelf texture of a ferroelectric liquid crystal (FLC). We observe the formation of nano-scaled polymer fibrils templated by the two dimensionally ordered host. The polymer fibrils capture the orientation of the host with thin polymer fibrils interweaving the smectic layers. The SEM study highlights the difference in morphology of the polymer fibrils depending on polymerization conditions; that is, polymerizing with or without the presence of an electric field. The polymer networks suppress the cone of rotation of FLC and thus, facilitate the switching and ...


A Novel Polymer Patterning Method Based On Pattern Forming States Of Liquid Crystals As Templates, Liang-Chy Chien, Samuel N. Sprunt, Shin-Woong Kang Jan 2002

A Novel Polymer Patterning Method Based On Pattern Forming States Of Liquid Crystals As Templates, Liang-Chy Chien, Samuel N. Sprunt, Shin-Woong Kang

Chemical Physics Publications

We describe a new polymer patterning technique that produces controllable morphological and optical anisotropy in a polymer network. This technique is based on the use of pattern-forming states of nematic and cholesteric liquid crystals as templates for forming ordered polymer networks. One and two-dimensional optical patterns are induced by applying an electric field across a narrow gap of an electro-optical cell. These field-induced optical patterns are then stabilized by UV-induced polymerization of a typically 5 wt% reactive monomer in liquid crystal host. Depending on specific conditions (e.g., thickness to pitch ratio of a cholesteric, applied electric field, and wavelength ...