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Physics

Selected Works

2013

Articles 31 - 60 of 304

Full-Text Articles in Physical Sciences and Mathematics

A Cellulose Liquid Crystal Motor: A Steam Engine Of The Second Kind, Yong Geng, Pedro Lucio Almeida, Cheng Cheng, Peter Palffy-Muhoray, Maria Helena Godinho, Susete Nogueira Fernandes Oct 2013

A Cellulose Liquid Crystal Motor: A Steam Engine Of The Second Kind, Yong Geng, Pedro Lucio Almeida, Cheng Cheng, Peter Palffy-Muhoray, Maria Helena Godinho, Susete Nogueira Fernandes

Peter Palffy-Muhoray

The salient feature of liquid crystal elastomers and networks is strong coupling between orientational order and mechanical strain. Orientational order can be changed by a wide variety of stimuli, including the presence of moisture. Changes in the orientation of constituents give rise to stresses and strains, which result in changes in sample shape. We have utilized this effect to build soft cellulose-based motor driven by humidity. The motor consists of a circular loop of cellulose film, which passes over two wheels. When humid air is present near one of the wheels on one side of the film, with drier air …

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Nonlinear Schrodinger Equation In Nematic Liquid Crystals, Peter Palffy-Muhoray, J. A. Reyes Oct 2013

Nonlinear Schrodinger Equation In Nematic Liquid Crystals, Peter Palffy-Muhoray, J. A. Reyes

Peter Palffy-Muhoray

We derive the amplitude equation, in the weakly nonlinear regime, for an optical wave packet that propagates in an initially undistorted nematic liquid crystal. By using the dyad representation Q(ij), we find the retarded and nonlocal equation for the nematic configuration and solve it in Fourier space. This allows us to calculate the amplitude dependent dispersion relation for a nematic liquid crystal in a given initial undistorted stationary state. We consider a linearly polarized wave packet that travels along the principal axis of the nematic dielectric tensor. We find a nonlinear Schrodinger equation for the amplitude, which includes an additional …

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Pattern Formation In Non-Newtonian Hele-Shaw Flow, P. Fast, L. Kondic, M. J. Shelley, Peter Palffy-Muhoray Oct 2013

Pattern Formation In Non-Newtonian Hele-Shaw Flow, P. Fast, L. Kondic, M. J. Shelley, Peter Palffy-Muhoray

Peter Palffy-Muhoray

We study theoretically the Saffman-Taylor instability of an air bubble expanding into a non-Newtonian fluid in a Hele-Shaw cell, with the motivation of understanding suppression of tip-splitting and the formation of dendritic structures observed in the flow of complex fluids, such as polymeric liquids or liquid crystals. A standard visco-elastic flow model is simplified in the case of flow in a thin gap, and it is found that there is a distinguished limit where shear thinning and normal stress differences are apparent, but elastic response is negligible. This observation allows formulation of a generalized Darcy's law, where the pressure satisfies …

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Nonphotochemical Laser-Induced Nucleation Of Nematic Phase And Alignment Of Nematic Director From A Supercooled Thermotropic Liquid Crystal, Xiaoying Sun, Bruce A. Garetz, Michele F. Moreira, Peter Palffy-Muhoray Oct 2013

Nonphotochemical Laser-Induced Nucleation Of Nematic Phase And Alignment Of Nematic Director From A Supercooled Thermotropic Liquid Crystal, Xiaoying Sun, Bruce A. Garetz, Michele F. Moreira, Peter Palffy-Muhoray

Peter Palffy-Muhoray

A nonphotochemical laser-induced phase transition was studied in a supercooled 4′‐n-pentyl-4-cyanobiphenyl (5CB, also referred to as PCB and K15) liquid crystal, using linearly polarized 45 ps light pulses at a wavelength of 532 nm. The laser induced nucleation from the metastable supercooled isotropic phase to the nematic phase during slow cooling (0.001 °C∕min) and high light intensity (3.9 MW∕cm2). The resulting nematic director tended to be aligned along the direction of the plane of polarization of the light. At the intensities used, there is no observable laser-induced realignment of the director once the sample is in the nematic …

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Cholesteric Liquid-Crystal Laser As An Optic Fiber-Based Temperature Sensor, M. F. Moreira, I.C.S. Carvalho, W. Cao, C. Bailey, Bahman Taheri, Peter Palffy-Muhoray Oct 2013

Cholesteric Liquid-Crystal Laser As An Optic Fiber-Based Temperature Sensor, M. F. Moreira, I.C.S. Carvalho, W. Cao, C. Bailey, Bahman Taheri, Peter Palffy-Muhoray

Peter Palffy-Muhoray

In this work, we have studied the temperature dependence of a cholesteric liquid-crystal laser coupled to an optical fiber, with a view towards optical fiber sensor applications. To stabilize the laser emission, we developed a procedure to align the liquid crystal placed in the fiber. Unexpected oscillations in the laser emission were observed as the temperature was varied, which can be understood in terms of the competition between bulk and surface anchoring torques. (C) 2004 American Institute of Physics.

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Distance Of Closest Approach Of Two Arbitrary Hard Ellipses In Two Dimensions, Xiaoyu Zheng, Peter Palffy-Muhoray Oct 2013

Distance Of Closest Approach Of Two Arbitrary Hard Ellipses In Two Dimensions, Xiaoyu Zheng, Peter Palffy-Muhoray

Peter Palffy-Muhoray

The distance of closest approach of hard particles is a key parameter of their interaction and plays an important role in the resulting phase behavior. For nonspherical particles, the distance of closest approach depends on orientation, and its calculation is surprisingly difficult. Although overlap criteria have been developed for use in computer simulations [ Vieillard-Baron J. Chem. Phys. 56 4729 (1972); Perram and Wertheim J. Comput. Phys. 58 409 (1985)], no analytic solutions have been obtained for the distance of closest approach of ellipsoids in three dimensions, or, until now, for ellipses in two dimensions. We have derived an analytic …

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Identified Baryon And Meson Distributions At Large Transverse Momenta From Au Plus Au Collisions At Root(S)(Nn)=200 Gev, B. I. Abelev, Quan Li, Star Collaboration Oct 2013

Identified Baryon And Meson Distributions At Large Transverse Momenta From Au Plus Au Collisions At Root(S)(Nn)=200 Gev, B. I. Abelev, Quan Li, Star Collaboration

Quan Li

Transverse momentum spectra of pi(+/-), p, and (p) over bar p up to 12 GeV/c at midrapidity in centrality selected Au + Au collisions at root s(NN) = 200 GeV are presented. In central Au + Au collisions, both pi(+/-) and p((p) over bar) show significant suppression with respect to binary scaling at p(T) greater than or similar to 4 GeV/c. Protons and antiprotons are less suppressed than pi(+/-), in the range 1.5 less than or similar to p(T) less than or similar to 6 GeV/c. The pi(-)/pi(+) and (p) over bar /p ratios show at most a weak pT …

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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 Oct 2013

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.

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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 Oct 2013

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 …

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Undulations In A Confined Lamellar System With Surface Anchoring, T. Ishikawa, Oleg Lavrentovich Oct 2013

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.

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Curvature Energy Of A Focal Conic Domain With Arbitrary Eccentricity, Maurice Kleman, Oleg Lavrentovich Oct 2013

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 …

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Stripe Domain Phase Of A Thin Nematic Film And The K13 Divergence Term, Oleg Lavrentovich, V. M. Pergamenshchik Oct 2013

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.

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Tensor And Complex Anchoring In Liquid Crystals, Sergij V. Shiyanovskii, Anatoliy Glushchenko, Yuri Reznikov, Oleg Lavrentovich, John L. West Oct 2013

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.

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Effect Of Director Distortions On Morphologies Of Phase Separation In Liquid Crystals, D. Voloschenko, Oleg P. Pishnyak, Sergij V. Shiyanovskii, Oleg Lavrentovich Oct 2013

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.

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Anchoring-Mediated Interaction Of Edge Dislocations With Bounding Surfaces In Confined Cholesteric Liquid Crystals, Ivan I. Smalyukh, Oleg Lavrentovich Oct 2013

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.

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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 Oct 2013

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.

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Electrorotation Of Colloidal Particles In Liquid Crystals, Guangxun Liao, Ivan I. Smalyukh, J. R. Kelly, Oleg D. Lavrentovich, Antal Jakli Oct 2013

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 …

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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 Oct 2013

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 …

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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 Oct 2013

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.

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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 Oct 2013

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.

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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 Oct 2013

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 …

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Directed Vertical Alignment Liquid Crystal Display With Fast Switching, Mingxia Gu, Ivan I. Smalyukh, Oleg Lavrentovich Oct 2013

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.

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Thermodielectric Bistability In Dual Frequency Nematic Liquid Crystal, Y. Yin, Sergij V. Shiyanovskii, Oleg Lavrentovich Oct 2013

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.

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Monte Carlo Simulations Of Stable Point Defects In Hybrid Nematic Films, C. Chiccoli, Oleg Lavrentovich, P. Pasini, C. Zannoni Oct 2013

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.

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Direct Piezoelectric Responses Of Soft Composite Fiber Mats, M. Varga, J. Morvan, Nicholas Diorio, E. Buyuktanir, John Harden, John L. West, Antal Jákli Oct 2013

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 …

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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 Oct 2013

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 …

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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 Oct 2013

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 …

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Biaxial Nematic Order Induced By Smectic Fluctuations, C. Zhang, S. Chakraborty, T. Ostapenko, Samuel N. Sprunt, Antal Jakli, Jim T. Gleeson Oct 2013

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.

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Highly Piezoelectric Biocompatible And Soft Composite Fibers, J. Morvan, E. Buyuktanir, John L. West, Antal Jakli Oct 2013

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 …

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Optical Waveguiding In Bent-Core Liquid-Crystal Filaments, Jake Fontana, C. Bailey, Wolfgang Weissflog, I. Janossy, Antal Jakli Oct 2013

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 …

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