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Articles 1 - 27 of 27
Full-Text Articles in Physics
Direct Piezoelectric Responses Of Soft Composite Fiber Mats, M. Varga, J. Morvan, Nicholas Diorio, E. Buyuktanir, John Harden, John L. West, Antal Jákli
Direct Piezoelectric Responses Of Soft Composite Fiber Mats, M. Varga, J. Morvan, Nicholas Diorio, E. Buyuktanir, John Harden, John L. West, Antal Jákli
Antal Jakli
Recently soft fiber mats electrospun from solutions of Barium Titanate (BT) ferroelectric ceramics particles and polylactic acid (PLA) were found to have large (d(33) similar to 1 nm/V) converse piezoelectric signals offering a myriad of applications ranging from active implants to smart textiles. Here, we report direct piezoelectric measurements (electric signals due to mechanical stress) of the BT/PLA composite fiber mats at several BT concentrations. A homemade testing apparatus provided AC stresses in the 50 Hz-1.5 kHz-frequency range. The piezoelectric constant d(33) similar to 0.5 nC/N and the compression modulus Y similar to 10(4)-10(5) Pa found are in agreement with …
Glass Forming Banana-Shaped Compounds: Vitrified Liquid Crystal States, S. Rauch, C. Selbmann, P. Bault, Hans Sawade, G. Heppke, O. Morales-Saavedra, M. Y. M. Huang, Antal Jákli
Glass Forming Banana-Shaped Compounds: Vitrified Liquid Crystal States, S. Rauch, C. Selbmann, P. Bault, Hans Sawade, G. Heppke, O. Morales-Saavedra, M. Y. M. Huang, Antal Jákli
Antal Jakli
The synthesis and physical properties, in particular electro-optic switching behavior, of 3-chloro-biphenyl-3('),4-bis{4-[4-(3,7-dimethyloctyloxy)-phenyliminomethyl]} benzoate are reported. The compound exhibits an antiferroelectric tilted smectic liquid crystalline phase (Sm-CP) in a broad temperature range. Below 20 degreesC the sample goes over to a glassy state and no crystallization appeares down to -50 degreesC. It is observed that below the glass transition temperature both achiral and chiral structures of the Sm-CP phase can be frozen. Each of them can have three polarization states (two ferroelectric and one antiferroelectric), thus giving six different vitrified textures. This enables atomic force microscopy studies of the different liquid …
Effect Of A Polymer Network On The Alignment And The Rotational Viscosity Of A Nematic Liquid-Crystal, Antal Jákli, D. R. Kim, Liang-Chy Chien, A. Saupe
Effect Of A Polymer Network On The Alignment And The Rotational Viscosity Of A Nematic Liquid-Crystal, Antal Jákli, D. R. Kim, Liang-Chy Chien, A. Saupe
Antal Jakli
Polymer dispersions were made by photoinduced polymerization of 4,4'-bisacryloyl-biphenyl in liquid crystal 4-4'-cyano pentyl biphenyl as nematic solvent. Samples were prepared with 0.5, 1, and 1.5 wt % monomer. The polymerization was done in the isotropic phase. The rotational viscosities of the two lower concentration samples increased only moderately after UV curing (3 mW/cm2, 25 min). The 1.5 wt % sample gave under the same condition a nematic with a fairly rigid anisotropic network that did not realign in magnetic field up to 20 kG. We estimate that the mesh size of the network was in the order of 1 …
Biaxial Nematic Order Induced By Smectic Fluctuations, C. Zhang, S. Chakraborty, T. Ostapenko, Samuel N. Sprunt, Antal Jakli, Jim T. Gleeson
Biaxial Nematic Order Induced By Smectic Fluctuations, C. Zhang, S. Chakraborty, T. Ostapenko, Samuel N. Sprunt, Antal Jakli, Jim T. Gleeson
Antal Jakli
We report on a series of measurements on the microscopic structure and the magneto-optical properties of a calamitic liquid crystalline compound in its nematic phase. Structural studies show the existence of short-range, tilted smectic order consistent with pretransitional effects above an underlying smectic phase. Concomitantly, magneto-optical results exhibit the existence of an optic axis not collinear with the uniaxial director. This apparent biaxial nature is discussed within the context of coupling between the tensor nematic and the smectic order parameters.
Highly Piezoelectric Biocompatible And Soft Composite Fibers, J. Morvan, E. Buyuktanir, John L. West, Antal Jakli
Highly Piezoelectric Biocompatible And Soft Composite Fibers, J. Morvan, E. Buyuktanir, John L. West, Antal Jakli
Antal Jakli
We report the fabrication of highly piezoelectric biocompatible soft fibers containing barium titanate ferroelectric ceramic particles dispersed in electrospun poly lactic acid (PLA). These fibers form mats that have two orders of magnitude larger piezoelectric constant per weight than single crystal barium titanate films. We propose that the observed apparent piezoelectricity results from the electrospinning induced polar alignment of the ferroelectric particles that pole the fibers similar to ferroelectret polymer foams that are poled by corona discharge. Due to the biocompatibility of PLA that encases the ferroelectric particles, these mats can be used in biological applications such as bio-sensors, artificial …
Optical Waveguiding In Bent-Core Liquid-Crystal Filaments, Jake Fontana, C. Bailey, Wolfgang Weissflog, I. Janossy, Antal Jakli
Optical Waveguiding In Bent-Core Liquid-Crystal Filaments, Jake Fontana, C. Bailey, Wolfgang Weissflog, I. Janossy, Antal Jakli
Antal Jakli
We demonstrate optical waveguiding in recently discovered free-standing bent-core liquid-crystal filaments. The bent-core liquid-crystal molecules in air self-assemble into a cylindrical geometry that is "solidlike" along the radial direction of the filament and liquid in the axial direction of the filament. These filaments are unique not only because they are fluids, but also because they are anisotropic. For this reason, their waveguiding properties not predictable need to be characterized. The light power transmitted through the filament was found to be independent of temperature from 180 degrees C to near room temperature. Initial defects of newly pulled filaments were found to …
Optically Isotropic Liquid-Crystal Phase Of Bent-Core Molecules With Polar Nanostructure, Guangxun Liao, S. Stojadinovic, Gerhard Pelzl, Wolfgang Weissflog, Samuel N. Sprunt, Antal Jakli
Optically Isotropic Liquid-Crystal Phase Of Bent-Core Molecules With Polar Nanostructure, Guangxun Liao, S. Stojadinovic, Gerhard Pelzl, Wolfgang Weissflog, Samuel N. Sprunt, Antal Jakli
Antal Jakli
We found that the optically isotropic (I-M) mesophase observed recently below the nematic phase of the bent-core liquid crystal 4-chlororesorcinol bis[4-(4-n-dodecyloxybenzoyloxy)benzoate] shows ferroelectric-type switching. Polarizing microscopic, electric current, dielectric, and dynamic light scattering studies lead us to propose that the I-M phase is composed of interconnected orthoconic racemic smectic (Sm-CaPF) nanodomains with random layer orientations. Near the nematic phase, where the polarization can be saturated by electric fields, the system responds in a fashion analogous to the granular structure of a magnetic spin glass-in particular, we observed that the relaxation back to the nonpoled structure follows a similar, inverse logarithmic …
Dielectric Relaxation Behavior Of A Liquid Crystal Showing An Unusual Type Of Antiferroelectric-Ferroelectric-Antiferroelectric Phase Sequence, S. K. Kundu, B. K. Chaudhuri, A. Seed, Antal Jakli
Dielectric Relaxation Behavior Of A Liquid Crystal Showing An Unusual Type Of Antiferroelectric-Ferroelectric-Antiferroelectric Phase Sequence, S. K. Kundu, B. K. Chaudhuri, A. Seed, Antal Jakli
Antal Jakli
The temperature and frequency dependent dielectric relaxation behavior of a liquid crystalline (S)-(+)-1-methylheptyl 4-[2-(4-alkoxyphenyl) thiophene-5-carbonylthiooxy] benzoate system is reported. Interesting successive antiferroelectric-ferroelectric-antiferroelectric (AF-FE-AF) phase transitions are observed in this system resembling the successive phase transitions observed in crystalline Rochelle salt. The smectic-C*(SmC*) to AF1 phase transition (around 103.0 °C) is first order in nature, predicted from the use of Orihara and Ishibashi theory. It is also found that a contribution of the ferroelectric SmC* phase ordering penetrates even in the antiferroelectric AF1 (SmCA*) and AF2 (Sm …
Macroscopic Chirality Of A Liquid Crystal From Nonchiral Molecules, Antal Jákli, Geetha G. Nair, C. K. Lee, R. Sun, Liang-Chy Chien
Macroscopic Chirality Of A Liquid Crystal From Nonchiral Molecules, Antal Jákli, Geetha G. Nair, C. K. Lee, R. Sun, Liang-Chy Chien
Antal Jakli
The transfer of chirality from nonchiral polymer networks to the racemic B2 phase of nonchiral banana-shaped molecules is demonstrated. This corresponds to the transfer of chirality from an achiral material to another achiral material. There are two levels of chirality transfers. (a) On a microscopic level the presence of a polymer network (chiral or nonchiral) favors a chiral state over a thermodynamically stable racemic state due to the inversion symmetry breaking at the polymer-liquid crystal interfaces. (b) A macroscopically chiral (enantimerically enriched) sample can be produced if the polymer network has a helical structure, and/or contains chemically chiral groups. The …
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
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
Antal Jakli
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 …
Converse Flexoelectric Effect In A Bent-Core Nematic Liquid Crystal, John Harden, R. Teeling, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli
Converse Flexoelectric Effect In A Bent-Core Nematic Liquid Crystal, John Harden, R. Teeling, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli
Antal Jakli
Flexoelectricity is a unique property of liquid crystals; it is a linear coupling between electric polarizations and bend and/or splay distortions of the direction of average molecular orientation. Recently it was shown [J. Harden et al., Phys. Rev. Lett. 97, 157802 (2006)] that the bend flexoelectric coefficient in bent-core nematic liquid crystals can be three orders of magnitude higher than the effect with calamitic (rod-shaped) molecular shape. Here we report the converse of the flexoelectric effect: An electric field applied across a bent-core liquid crystal sandwiched between thin flexible substrates produces a director distortion which is manifested as a polarity-dependent …
Liquid Crystal Fibers Of Bent-Core Molecules, Antal Jákli, Daniel Krüerke, Geetha G. Nair
Liquid Crystal Fibers Of Bent-Core Molecules, Antal Jákli, Daniel Krüerke, Geetha G. Nair
Antal Jakli
Although the liquid-crystal research is well established in science, there are newly emerging exciting systems, that deserve extensive basic studies. One of these areas is the research of the bent-shaped molecules (so-called "banana liquid crystals"), which have delicate chirality and polarity properties. In this paper we show that these materials also have very unusual rheological features, such as the formation of stable fluid fibers and bridges. Under electric fields, these objects present striking mechanical effects, such as horizontal and transversal vibrations. Studies indicate that the research of banana-liquid-crystal fibers may lead to new type of artificial muscle systems.
Light-Induced Changes Of Optical And Electrical Properties In Bent-Core Azo Compounds, Antal Jakli, V. Prasad, D.S.S. Rao, Guangxun Liao, I. Janossy
Light-Induced Changes Of Optical And Electrical Properties In Bent-Core Azo Compounds, Antal Jakli, V. Prasad, D.S.S. Rao, Guangxun Liao, I. Janossy
Antal Jakli
We have studied the optical and electrical properties of two bent-core substances with an azo linkage in their cores. Pump-probe laser studies, direct textural observations, and spectrophotometric recordings show an initial decrease of light transmission, which at larger light intensities (similar to 1 mW/mm(2)) is followed by a bleaching. Simultaneously the electrical properties (electric conductivity, antiferroelectric polarization, switching threshold, and switching time) decreased monotonically with increasing light intensities. The monotonic decrease of electrical properties indicates that the darkening and bleaching have the same origin, namely, the photochemical isomerization of the azo linkage from the trans to the cis isomer. The …
Large Flow Birefringence Of Nematogenic Bent-Core Liquid Crystals, C. Bailey, Katalin Fodor-Csorba, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli
Large Flow Birefringence Of Nematogenic Bent-Core Liquid Crystals, C. Bailey, Katalin Fodor-Csorba, Rafael Verduzco, Jim T. Gleeson, Samuel N. Sprunt, Antal Jakli
Antal Jakli
We have found that bent-core liquid crystalline materials show exceptionally large intrinsic flow birefringence in their isotropic liquid phase. This effect is more than 100 times larger than typical values measured for low molecular weight liquid crystals. The specific flow birefringence (i.e., normalized by the flow viscosity) is an order of magnitude larger than in both side-chain polymeric as well as low molecular weight liquid crystals. We propose that this large enhancement for bent-core compounds may be attributed to nanoscale smecticlike clusters that persist above the nematic-isotropic transition temperature, and shear align under shear flow; however, this mechanism has not …
Evidence For Triclinic Symmetry In Smectic Liquid Crystals Of Bent-Shape Molecules, Antal Jakli, D. Kruerke, Hans Sawade, G. Heppke
Evidence For Triclinic Symmetry In Smectic Liquid Crystals Of Bent-Shape Molecules, Antal Jakli, D. Kruerke, Hans Sawade, G. Heppke
Antal Jakli
The first experimental evidence for triclinic symmetry of bulk smectic liquid-crystal samples of achiral banana-shaped molecules is presented. This phase corresponds to the so-called Sm-C-G phase consisting of biaxial molecules and characterized by two tilt directions with respect to the layer normal: tilt of the molecular plane (clinic) and tilt of the molecular kink direction (leaning). Each smectic layer has a polarization component normal to the smectic layers (C-1 symmetry). The observations suggest that the phase tentatively labeled as B-7 is identical with the Sm-C-G phase.
A Comparison Of Short-Range Molecular Order In Bent-Core And Rod-Like Nematic Liquid Crystals, S. Chakraborty, J. T. Gleeson, Antal Jákli, Samuel Sprunt
A Comparison Of Short-Range Molecular Order In Bent-Core And Rod-Like Nematic Liquid Crystals, S. Chakraborty, J. T. Gleeson, Antal Jákli, Samuel Sprunt
Antal Jakli
Thermotropic liquid crystals exhibit strongly temperature-dependent positional correlations among molecules in the nematic phase above the transition to a smectic-A or C phase. However, even in the absence of a lower temperature smectic phase, nematics composed of reduced symmetry molecules (bent-core mesogens, for example) reveal small angle X-ray scattering (SAXS) patterns with features similar to those associated with pretransitional smectic order. We report on a quantitative analysis and comparison of two-dimensional SAXS data on a bent-core nematic compound (lacking a smectic phase) and a rod-like nematic (exhibiting a nematic to smectic-C transition). This analysis demonstrates that a nanostructure based on …
Search For Biaxiality In A Shape-Persistent Bent-Core Nematic Liquid Crystal, Young-Ki Kim, Madhabi Majumdar, Bohdan I. Senyuk, Luana Tortora, Jens Seltmann, Matthias Lehmann, Antal Jakli, Jim T. Gleeson, Oleg Lavrentovich, Samuel Sprunt
Search For Biaxiality In A Shape-Persistent Bent-Core Nematic Liquid Crystal, Young-Ki Kim, Madhabi Majumdar, Bohdan I. Senyuk, Luana Tortora, Jens Seltmann, Matthias Lehmann, Antal Jakli, Jim T. Gleeson, Oleg Lavrentovich, Samuel Sprunt
Antal Jakli
Using a range of optical techniques, we have probed the nature of orientational order in a thermotropic bent-core liquid crystal, which features a shape-persistent molecular architecture designed to promote a biaxial nematic phase. In the upper range of the nematic phase (enantiotropic regime), dynamic light scattering reveals strong fluctuations attributable to the biaxial order parameter, in addition to the usual uniaxial director modes. Assuming a Landau-type expansion of the orientational free energy, we estimate the correlation length associated with these fluctuations to be similar to 100 nm. At lower temperatures, and mainly in the monotropic regime of the nematic, we …
Unexpected Liquid Crystalline Behaviour Of Three-Ring Bent-Core Mesogens: Bis(4-Subst.-Phenyl) 2-Methyl-Iso-Phthalates, Wolfgang Weissflog, Ute Baumeister, Maria-Gabriela Tamba, Gerhard Pelzl, Horst Kresse, Rudolf Friedemann, Gunther Hempel, Ricardo Kurz, Matthias Roos, Kurt Merzwiler, Antal Jakli, Cuiyu Zhang, Nicholas Diorio, Ralf Stannarius, Alexey Eremin, Ulrike Kornek
Unexpected Liquid Crystalline Behaviour Of Three-Ring Bent-Core Mesogens: Bis(4-Subst.-Phenyl) 2-Methyl-Iso-Phthalates, Wolfgang Weissflog, Ute Baumeister, Maria-Gabriela Tamba, Gerhard Pelzl, Horst Kresse, Rudolf Friedemann, Gunther Hempel, Ricardo Kurz, Matthias Roos, Kurt Merzwiler, Antal Jakli, Cuiyu Zhang, Nicholas Diorio, Ralf Stannarius, Alexey Eremin, Ulrike Kornek
Antal Jakli
Three-ring bent-core bis(4-subst.-phenyl) 2-methyl-iso-phthalates exhibiting nematic, SmA and SmC phases are reported. The occurring mesophases have been identified by their optical textures and X-ray diffraction measurements which give also geometrical structural parameters like layer spacing and molecular tilt. Quantum chemical calculations on single molecules and X-ray structure analysis in the crystalline state indicate wide opening angles (about 155 degrees) of the molecular legs due to the lateral methyl group in position 2 of the central phenyl ring. However solid state NMR spectroscopy in the liquid crystalline phases finds stronger molecular bending (bending angle to be about 138 degrees in the …
Short-Range Smectic Order In Bent-Core Nematic Liquid Crystals, S. H. Hong, R. Verduzco, J. C. Williams, R. J. Twieg, E. Dimasi, R. Pindak, Antal Jakli, J. T. Gleeson, Samuel Sprunt
Short-Range Smectic Order In Bent-Core Nematic Liquid Crystals, S. H. Hong, R. Verduzco, J. C. Williams, R. J. Twieg, E. Dimasi, R. Pindak, Antal Jakli, J. T. Gleeson, Samuel Sprunt
Antal Jakli
Small angle X-ray diffraction from the uniaxial nematic phase of certain bent-core liquid crystals is shown to be consistent with the presence of molecular clusters possessing short-range tilted smectic (smectic-C) order. Persistence of these clusters throughout the nematic phase, and even into the isotropic state, likely accounts for the unusual macroscopic behavior previously reported in bent-core nematics, including an anomalously large flexoelectric effect (similar to 1000 times that of conventional calamitic nematics), very large orientational and flow viscosities (similar to 10 100 and similar to 100 1000 times, respectively, typical values for calamitics), and an extraordinary flow birefringence observed in …
Bent-Core Liquid Crystal Elastomers, Rafael Verduzco, Paul Luchette, Seung Ho Hong, John Harden, Elaine Dimasi, Peter Palffy-Muhoray, S. Michael Kilbey Ii, Jim T. Gleeson, Antal Jákli
Bent-Core Liquid Crystal Elastomers, Rafael Verduzco, Paul Luchette, Seung Ho Hong, John Harden, Elaine Dimasi, Peter Palffy-Muhoray, S. Michael Kilbey Ii, Jim T. Gleeson, Antal Jákli
Antal Jakli
Liquid crystal (LC) elastomers with bent-core side-groups incorporate the properties of bent-core liquid crystals in a flexible and self-supporting polymer network. Bent-core liquid crystal elastomers (BCEs) with uniform alignment were prepared by attaching a reactive bent-core LC to poly(hydrogenmethylsiloxane) and crosslinking with a divinyl crosslinker. Phase behavior studies indicate a nematic phase over a wide temperature range that approaches room temperature, and thermoelastic measurements show that these BCEs can reversibly change their length by more than a factor of two upon heating and cooling. Small-angle X-ray scattering studies reveal multiple, broad low-angle peaks consistent with short-range smectic C order of …
Flexoelectricity Of A Calamitic Liquid Crystal Elastomer Swollen With A Bent-Core Liquid Crystal, M. Chambers, R. Verduzco, J. T. Gleeson, S. Sprunt, Antal Jakli
Flexoelectricity Of A Calamitic Liquid Crystal Elastomer Swollen With A Bent-Core Liquid Crystal, M. Chambers, R. Verduzco, J. T. Gleeson, S. Sprunt, Antal Jakli
Antal Jakli
We have measured the electric current induced by mechanical distortion of a calamitic liquid crystal elastomer (LCE) swollen with a low molecular weight bent-core nematic (BCN) liquid crystal, and have determined, for the first time, the bend flexoelectric coefficient e(3) of such a BCN-LCE composite. In one method, we utilise air-pressure to induce a mechanical bend deformation and flexoelectric polarization in a BCN-LCE film, and then measure the polarization current as a function of time. An alternative technique uses a rotary-motor driven scotch yoke to periodically flex the BCN-LCE; in this case, the magnitude and phase of the induced current …
Rheological Properties Of Bent-Core Liquid Crystals, C. Bailey, K. Fodor-Csorba, J. T. Gleeson, Samuel N. Sprunt, Antal Jákli
Rheological Properties Of Bent-Core Liquid Crystals, C. Bailey, K. Fodor-Csorba, J. T. Gleeson, Samuel N. Sprunt, Antal Jákli
Antal Jakli
We show that bent-core liquid crystalline materials exhibit non-Newtonian flow in their optically isotropic liquid phase. We conjecture that this behavior is due to the existence of nanostructured, fluctuating clusters composed of a few smectic-like layers. Shear alignment of these clusters explains the shear thinning observed in bent-core liquid crystals having either a nematic phase or non-modulated smectic phase. By contrast, smectogens having a modulated smectic phase do not shear thin at low shear rates, but even show a slight shear thickening which may be due to entanglements of wormlike and/or helical clusters.
Acoustically Driven Oscillations Of Freely Suspended Liquid Crystal Filaments, J. Petzold, A. Nemes, A. Eremin, C. Bailey, N. Diorio, Antal Jakli, R. Stannarius
Acoustically Driven Oscillations Of Freely Suspended Liquid Crystal Filaments, J. Petzold, A. Nemes, A. Eremin, C. Bailey, N. Diorio, Antal Jakli, R. Stannarius
Antal Jakli
Some liquid crystalline phases of bent-core mesogens are known to form stable freely-suspended filaments with length to diameter ratios of 1000 and larger. These structures can behave like thin liquid chords. We study filament oscillations excited with harmonic sound waves. From amplitudes of the filament motion and phase shifts respective to the harmonic excitation signal we develop a model for the filament dynamics. Like in solid chords, the resonance frequency f(0) is inversely proportional to their length. The dependence of f(0) upon the filament radius allows one to draw conclusions on the nature of the filament tension. For thin filaments, …
Colloidal Micromotor In Smectic A Liquid Crystal Driven By Dc Electric Field, Antal Jakli, Bohdan Senyuk, Guangxun Liao, Oleg Lavrentovich
Colloidal Micromotor In Smectic A Liquid Crystal Driven By Dc Electric Field, Antal Jakli, Bohdan Senyuk, Guangxun Liao, Oleg Lavrentovich
Antal Jakli
Converting linear stimulus to rotation has endless examples in virtually all scales of the universe. One of the interesting examples is Quincke rotation, a spinning rotation of a dielectric sphere neutrally buoyant in an isotropic fluid caused by a unidirectional DC electric field. Recently Quincke rotation has been reported in liquid crystalline (LC) phases, and it was noted that spinning triggers a translational motion normal to the electric field and the rotation axis. In this work, we explain the translation of spinning spheres as a result of hydrodynamic interaction with the bounding walls. We also describe a unique orbiting motion: …
Bistable Linear Electro-Optical Switching In The B-7 ' Phase Of Novel Bent-Core, S. Umadevi, Antal Jakli, B. K. Sadashiva
Bistable Linear Electro-Optical Switching In The B-7 ' Phase Of Novel Bent-Core, S. Umadevi, Antal Jakli, B. K. Sadashiva
Antal Jakli
Three novel symmetrical bent-core compounds were synthesized where the terminal alkoxy linkages of the original bent-core inesogen forming a B-2 phase was converted to n-alkyl carboxylates. It is found that instead of the B-2 phase, all three compounds exhibit a transition between B-7' and B-2 mesophases. The physical and electro-optical properties have been investigated by polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction and electric field experiments. The higher temperature B-7' phase has been shown to exhibit bistable but analogous linear electro-optical Switching Without,my observable polarization peak. We analyze two theoretical models and find that a local triclinic symmetry may …
Ester Type Banana-Shaped Liquid Crystalline Monomers: Synthesis And Physical Properties, Katalin Fodor-Csorba, Aniko Vajda, Antal Jakli, Christian Slugovc, Gregor Trimmel, Dietrich Demus, Eszter Gacz-Baitz, Sandor Holly, Giancarlo Galli
Ester Type Banana-Shaped Liquid Crystalline Monomers: Synthesis And Physical Properties, Katalin Fodor-Csorba, Aniko Vajda, Antal Jakli, Christian Slugovc, Gregor Trimmel, Dietrich Demus, Eszter Gacz-Baitz, Sandor Holly, Giancarlo Galli
Antal Jakli
New ester-type banana (bent-shaped) monomers, 1,3-phenylene bis[4'-(alken-1-yloxy)-biphenyl-4-carboxylate] s Ia - Vb, with different substituent(s) on the central phenyl ring (H, CH3, Cl or NO2) and alkenyl tails in the side arms ( decenyl or undecenyl) were prepared. The analogues IIIa - IVb with 4-chloro- or 4,6-dichloro-substituents exhibited a nematic phase, while Va, Vb with 2-nitro-substituent showed a B-7 phase at relatively low temperature. All the compounds were stable, no degradation or polymerization was observed under applied electric fields or heat treatments. Electro-hydrodynamic instabilities were observed in the nematic phase of each sample. In the B-7 phase of Vb there was …
Optically Induced Periodic Structures In Smectic-C Liquid Crystals, Antal Jákli, A. Vajda, E. Benkler, Janossy, Peter Palffy-Muhoray
Optically Induced Periodic Structures In Smectic-C Liquid Crystals, Antal Jákli, A. Vajda, E. Benkler, Janossy, Peter Palffy-Muhoray
Antal Jakli
We explore periodic structures of smectic-C (SmC) liquid crystals, induced optically by a polarization grating. The studied cells contain a passive surface of rubbed polyimide and an active photosensitive substrate of ate-dye doped polyimide. In a nematic phase the director field can be periodic independent of the angle between the grating vector and the rubbing direction. In the SmA phase periodic structure can be induced only by layer undulations. The SmC behaves similarly to the nematic phase, but the director can rotate only on a cone, which results in a more complex geometry. The periodic pattern is superimposed with four …