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Articles 1 - 15 of 15
Full-Text Articles in Physical Sciences and Mathematics
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.