PSSM

Poster Presentations

P1   Focusing properties of the liquid crystal lens with polymer network

Svitlana Bielykh, S. Subota, V. Yu. Reshetnyak, Kyiv National Taras Shevchenko University, Physics Department

Abstract: We study a tunable-focus lens in which the key element is a gradient-polymer-stabilized liquid crystal (G-PSLC) structure [1]. It means that in the nematic liquid crystal cell there is a spatially inhomogeneous polymer network. This network creates an additional torque on the LC director forcing it to preserve planar orientation despite the applied voltage.

The electro-optical response of the system to a uniform electric field is inhomogeneous but centrally symmetric. The refractive index profile is qualitatively similar to the director spatial distribution. The cell acts as a positive lens for extraordinary polarized light. By varying the applied voltage one can change the refractive index profile and hence control the focal length of the lens.

We have employed a recent theoretical model [1], to calculate the properties of this lens. We have performed calculations of the director reorientation in the external electric field, using several trial functions for polymer profile form. The result is a focal length dependence on electric field.

[1] V. Reshetnyak, S. Subota, T. Galstian, Mol. Cryst. Liq. Cryst., 484, 187/[589] (2006).

P2   Photo-luminescent properties and defect Structures of novel bent-core liquid crystal

Rajdeep Deb^1,2; Nandiraju V S Rao², Noel A Clark¹ and Ivan I Smalyukh^1
1 Department of Physics; University of Colorado, Boulder CO 80309, USA.
² Department of Chemistry; Assam University, Silchar-788011, India.

Abstract: A great deal of light has been shed on Photo-luminescent properties of liquid crystal owing to the light generating capacity and the potential use in the Emissive type liquid crystal displays (LCDs). Early work in the area of emissive LCs involved the incorporation of fluorescent dyes into conventional LC phases of rod-like molecules such as the nematic and smectic thermotropic phases. One of the common problems encountered with organic dye-LC mixtures is limited solubility of the fluorescent dye in the LC host. Luminescent thermotropic LCs have traditionally been designed around a fluorescent moiety. However, research in this area has been limited, in part, as the shape and structure of many fluorescent moieties are not always conducive to LC phase formation. Only a small number of attempts have been made to synthesize and study functional LCs with intrinsic luminescence properties. Moreover, there were no reports of fluyoresent bent-core molecules forming liquid crystal phases.

Here in we will demonstrated a modular approach to designing a novel type liquid crystal with intrinsic light generating capabilities based on bent-core platform. The synthesis and mesogenic behaviour of the homologous series of compounds with different bent-core structure will be presented. In addition, taking advantage of their photo-luminescent property we, visualise the most intricate and poorly understood B7 defect structure formed by those mesogens using a non-destructive techniques of fluorescence confocal polarizing microscopy. Comparative textural analysis of their phase structures in light of the fluorescence imaging will be detailed.

We acknowledge support of The Institute for Complex Adaptive Matter (ICAM-I2CAM) and Department of Science and Technology, New Delhi.

P3   Experimental studies of anomalous diffusion in gel-membrane system

Kazimierz Dworecki, Institute of Physics,The Jan Kochanowski University

Abstract: We study diffusion in a membrane system consisting of three glass cuvettes separated by horizontally located polymer membranes. Initially,we fill the lower and upper cuvettes with the agarose hydrogel solvent while in the middle cuvette there is an aqueous gel solution of transported substance.Then, the substance diffusis from the middle cuvette to the exterior ones through the membranes.The substance concentration is measured by meanslaser interferometric method.The analysis of the interferograms allows one reconstruct the time-space dependent concentration profiles of the substance transported (polyethylene glycol 2000) from middle cuvette across the top and bottom membranes to outside cuvettes and time evolution of the so-called near-membrane layer or diffusion boundary layer.The initial concentration of solute in the gel was fixed to be 0.00375, 0.0050, 0.0075 and 0.01125 mol/dm3.We conclude that the measured spatiotemporal concentration profles of PEG2000 in agarose gel and temporal evolution of the near-membrane layer thickness indicate subdiffusion behawiour with the subdiffusion coefficient of PEG2000- 2.25 10(-10) m2/s0.43 and anomalous diffusion exponent - 0.86.

P4   Self-assembly of quantum rods into defects of cholesteric liquid crystals

Dennis Gardner, University of Colorado at Boulder

Abstract: We study the interactions of CdSe quantum rods in dilute liquid crystal (LC) suspensions using various microscopy techniques including fluorescent confocal microcopy (FCM) and freeze fracture transmission electron microscopy (FFTEM). FCM employs the strong, non-bleaching, fluorescent signals from the quantum rods to image the 3-D spatial location of the quantum rods. Using FFTEM enables us to image individual nanoparticles in LCs. We demonstrate that LC defects and structures allow for controlled localization, alignment, and assembly of these quantum particles. Generalizing our studies for various nanoparticles of different compositions may provide new self-assembly-based methods of nanofabrication of metamaterials needed for applications such as cloaking at optical wavelengths, optical circuits, and super lenses.

This research was supported by the NSF, Colorado Alliance for Graduate Education and the Professoriate, and by the CU SMART & UROP Programs, and the Institute for Complex Adaptive Matter.

P5   Folding dynamics of the Trp-cage protein by action-derived molecular dynamics

Seung-Yeon Kim, Chungju National University, South Korea

Abstract: The folding dynamics of a 20-residue protein, Trp-cage, is investigated by using action-derived molecular dynamics simulations with the AMBER all-atom force field and the GB/SA solvation potential. In the early stages, a nativelike unfolded state appears with partially formed native contacts and native hydrogen bonds. The radius of gyration changes little but RMSD decreases continuously after the formation of the nativelike unfolded state. Also, the method of principal component analysis is applied to the understanding of the Trp-cage folding dynamics. This analysis indicates that the slow adjustment processes of the near-native states into the native state are dominant in the late stages.

P6   Instability of the nematic liquid crystal filled with sphere-like magnetic-impurity particles against formation of the modulated structures

Andrii V. Kleshchonok and Victor Yu. Reshetnyak, Faculty of Physics, Taras Shevchenko National University of Kyiv, Prospekt Glushkova 2, Building 1, Kyiv, Ukraine, Valentin A. Tatarenko, Department of Solid State Theory, G. V. Kurdyumov Institute for Metal Physics, NAS of Ukraine, 36 Academician Vernadsky Blvd., UA-03142 Kyiv, Ukraine

Abstract: In the last decade, much attention has been attracted to Filled Liquid Crystals – highly disperse suspension of impurity particles in nematic liquid carrier. The tested objects are filled nematic liquid crystals – highly-disperse suspension of impurity particles within the nematic liquid carrier. The spatial distribution of rigid-sphere-like magnetic-impurity particles (with radii of 5 μm) within the host nematic liquid crystal is studied. Both the indirect effective interaction between the impurity particles by means of nematic medium and the direct magnetic interaction are considered as being responsible for the formation of (modulated) structures. In the general case, total interaction between the impurity particles includes several contributions – direct Van der Waals-type interaction (at short distances between the particles) and magnetic one as well as indirect interactions (through both the director-field distortions and the density inhomogeneities). The last one depends on temperature, density of nematic host medium and impurities concentration. Such effective interaction controls the structure formation and properties of a system. Using continuum-mechanics and statistical-thermodynamics approaches, we analyze the necessary thermodynamic conditions for formation of modulated lamellar structures. This condition allows to calculate temperature of homogeneous-distribution stability loss and to estimate period of formed structures. The offered theoretical approach can be used to forecasting other anisotropic and inhomogeneous mesomorphic systems, which can find application by development of integrated-optics facilities to govern the light-beam passing (diffraction gratings of an optical range etc.).

P7   On the theory of bulk properties of ionic liquid crystals

Svyatoslav Kondrat, Max-Planck-Institut für Metallforschung

Abstract: The density functional theory and a molecular field theory are used to provide some theoretical insight into mechanisms responsible for the formation of bulk liquid crystalline phases in ionic liquid crystals.

P8   Angle-dependent cyclotron resonance in highly anisotropic conducting systems

Stepanenko, B.I.Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of the Ukraine

Abstract: Highly anisotropic organic conductors have attracted considerable interest in recent years because their physical properties, in particular behavior in a strong magnetic field, essentially differ both from properties of quasi-isotropic metals, and properties of true two-dimensional or one-dimensional conducting systems. The Fermi surface of these substances may consist of topologically different elements in the form of cylinder weakly corrugated along the least conductivity direction or slightly warped sheets which are perpendicular to the direction of highest conductivity. The resonant absorption of high-frequency electromagnetic field in the highly anisotropic organic conductors in presence of an external magnetic field $\mathbf{B_{0}}$ differs in a number of features due to the topology of the Fermi surface. The electron drift velocity is the oscillatory function of the angle of the magnetic field direction. As a result the location of Landau damping regions depends on the orientation of $\mathbf{B_{0}}$. In the case of weak spatial dispersion one can neglect by Landau damping and the angle-dependence of the kinetic coefficients is defined by the angle-dependence of cyclotron frequency. Under condition of anomalous skin effect when the skin depth is much smaller then the Larmor radius, the Landau absorption may be essential and the additional angle-dependent oscillations of high-frequency conductivity and surface impedance result from the angular dependence of drift velocity should appear. At some orientations of a magnetic field, the drift velocity in quasi-two-dimensional conductor is close to zero. For these directions of the collisionless attenuation of electromagnetic field is determined by the cyclotron absorption when the wave frequency is multiple to the cyclotron frequency and there takes place the cyclotron resonance similar that in the magnetic field parallel to the sample surface. The impedance shows corresponding oscillation dependence on a magnetic field.

P9   Three dimensional holographic optical trapping and manipulation

Rahul P. Trivedi, University of Colorado at Boulder

Abstract: Simultaneous manipulation of multiple colloidal particles and defects in liquid crystals is performed using holographic optical trapping implemented with a liquid-crystal phase-only spatial light modulator. We have used nematic and chiral-nematic liquid crystals for this purpose. Polarization dependence of the trapping forces is studied which arises in liquid crystalline media due to their anisotropic nature. The same optical anisotropy makes the tight focusing of the laser beam difficult and thus weakens the optical trapping forces. Hence liquid crystal materials with low birefringence are used so as to mitigate these undesirable effects. We have first determined the trap stiffness at different laser powers by using two approaches: (a) dragging the particle in the LC medium and measuring the viscous drag forces exerted on them as well as (b) by studying the change in the rms displacement in the Brownian motion of the particles with increasing the laser power. Trap stiffness variation along the depth of the liquid crystal is also analysed. These calibration measurements are then used to probe inter-particle and defect-particle interaction forces as well as to characterize the line tension of disclinations and linear defect clusters in the bulk of liquid crystals.

We acknowledge the support of the Institute for Complex Adaptive Matter (ICAM), International Institute for Complex Adaptive Matter (I2CAM) and the NSF grants no. DMR 0645461, DMR-0820579 and DMR-0847782.

P10   Enhanced microwave dielectric anisotropy of nematic liquid crystals loaded with carbon nanotubes

Oksana Trushkevych, Cambridge University

Abstract: Liquid crystals are attractive materials for microwave applications due to low losses and high anisotropy of dielectric properties. LCs can be loaded with various types of nanoparticles for enhanced performance. In the present work we employ carbon nanotubes (CNT) as an additive to LC to increase the anisotropy at microwave frequencies. When dispersed in liquid crystal, CNTs can be ordered with a high order parameter, up to 0.9. This ordering can be dynamically reconfigured with electric or magnetic fields. Loading with CNTs changes the low frequency electrical and dielectric properties of LCs.

We show that the high frequency dielectric anisotropy Δε of nematic liquid crystals can be increased by loading with carbon nanotubes. CNT-LC suspension stability is sufficient to perform a measurement, but it must be improved to be practically usable. The studies were performed at 1 - 4 GHz using a capacitor termination of the transmission line, and at 30 GHz using a cavity resonator. Both experiments revealed an increase of the microwave Δε when CNTs are added to the liquid crystal. We report up to two times increase in the Δε in the 1-4GHz range and up to two and a half times increase in the Δε at 30GHz for liquid crystals with 0.01% wt carbon nanotube loading. The loss also increased in these materials. The effects correlate with CNT concentration.

The authors acknowledge funding from the Centre for Advanced Photonics and Electronics (CAPE). Current CAPE partners are Dow Corning Ltd. and Alps Electric Co., Ltd.

P11   Optically-generated diffraction gratings in cholesteric liquid crystals

Christopher Twombly, University of Colorado at Boulder

Abstract: We demonstrate that tightly-focused infrared laser beams can be used for optical switching of structures in cholesteric liquid crystals. This is employed to generate periodic diffraction gratings and, thus, to optically control diffraction patterns observed in the far field. Moreover, in addition to the optical fields, the obtained structures can be also switched and tuned by electric field applied using transparent electrodes on the confining substrates of the cholesteric liquid crystal cell. Potential applications include all-optical diffraction gratings and data storage devices.

We acknowledge support of the International Institute for Complex Adaptive Matter.

P12   Chiral symmetry breaking in bent-core liquid crystals

Tomasz Wydro, Laboratoire de Physique des Matériaux, Université Henri Poincaré, Nancy I

Abstract: By molecular modeling we demonstrate that nematic long-range order (uniaxial and biaxial) discovered in bent-core liquid crystal systems reveals two further spatially homogeneous phases predicted by symmetry arguments [1]. The new phases are tetrahedratic nematic (T) with D2d symmetry and a chiral tetrahedratic nematic (NT ) phase with D2 symmetry. These new phases were found for a lattice model with quadrupolar and octupolar anisotropic interactions using Mean Field theory and Monte Carlo simulations. Our results show that an interplay between quadrupolar and octupolar interactions stabilizes the new phases. To our knowledge, this is the 1-rst molecular model with spontaneous (homo-)chiral symmetry breaking in non-layered liquid crystals composed of bent-core molecules.

[1] T. C. Lubensky and L. Radzihovsky, Phys. Rev. E 66 (2002) 031704.

P13   Colloidal gold nanoparticle dispersions in lamellar liquid crystals

R. Pratibha^1,2, W. Park¹, Ivan Smalyukh¹;
¹University of Colorado at Boulder, USA.
²Raman Research Institutre, India.

Abstract: We demonstrate that the layered structure and elasticity of smectic liquid crystals allow for stable dispersion of colloidal nanoparticles in these anisotropic fluids. To probe average inter-particle distances on the nanometer scales in concentrated suspensions of nanoparticles in the liquid crystal medium, we use the strong sensitivity of plasmonic resonance to the proximity of nanospheres when probing the dispersions in the bulk of lamellar liquid crystals and atomic force microscopy when studying their thin (<100nm) films. We show how limited permeability of particles across the layers and repulsive interactions of nanocolloids entrapped within the same layers preclude irreversible aggregation of these nanoparticles and open possibilities for building novel tunable optical metamaterials.

P14   Ion ordering near the charged nanocylinders

Andrij Trokhymchuk¹, Eugene Soviak¹, Eckhard Spohr²;
¹Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine
²Lehrstuhl für Theoretische Chemie, Universität Duisburg-Essen, Germany.

Abstract: In this report we present some theoretical and computer simulations results which show remarkable effects that can be produced by a charged nano-sized surface on the macroscopic behavior of nearby charged species, where the shape and size of the surface itself is equally or even more important than the direct interaction between the particles. In the case of charged planar surface the equilibrium position for a single counter-charge is above the center of the charged area. If more than one counter-charge is present, these charges compete for this equilibrium position and, at the same time, repel each other due to Coulomb forces, that effectively lead to a rather stable equilibrium between particle-particle Coulomb repulsion and surface-induced Coulomb attraction due to the surface finiteness. We find that the like-charged ions, independent of their number, all become confined on the oppositely charged area if the surface charge balances the total charge carried by the particles. The local density of the particles above the charged area is not homogeneous; a higher particle density is found near the boundaries of the charged area with a clear tendency of layer formation along the area.

An extension of the finite confinement effect to cylindrical geometry helps to illustrate the principal forces that would govern the behavior of charged species in oppositely charged nanopores. We find that one of the consequences of a charged pore wall is the aggregation of mobile charges in the pore with arrangements characteristic for different occupancies. Applications to study occupancy and valence selectivity in biological ion channels will be discussed.

P15   Life and scientific activity of Prof. Julius Planer

Rostyslav Bilyy^1,2, Alexander Lutsyk²;
¹Institute of Cell Biology, NAS of Ukraine
²Danylo Halytskyi Lviv National Medical University

Abstract: Prof. Julius Planer (Julius Planner von Plan) (13.VIII.1827 - 25.VII.1881) is an outstanding scientist who greatly contributed to both our understanding of malaria and of liquid crystals.

Julius Planer was born in Vienna where he obtained medical education and started his work in a famous Viennese pathologico-anatomical school. During 1855-1863 Prof. Planer headed Department of Anatomy at Lviv University. In 1863 he moved to the city of Graz, where he headed Chair of Department of Anatomy, Medical Faculty, University of Graz during 1863 - 1881.

Scientific interests of Prof. Planner mainly included descriptive and topographical anatomy. He founded Museum of pathological-anatomy at Lviv University as well as enriched physiological and anatomical collections of the University. Besides the studies of cholesterol derivatives which led to the observation of selective reflection in cholesteric liquid crystals while Prof. Planer was working in Lviv University, he also have made several landmark contributions to bio-medical science. Among them the study of the occurrence of pigment granules in the blood, particularly the indication of their relation to the course of intermittent fever and study of gases in biological fluids.

P16   Density functional study of flexible chain molecules at curved surfaces

Stepan Hlushak¹, W. Rzysko², S. Sokolowski²;
¹Institute for Condensed Matter Physics, Svientsitskoho 1, 79011, Lviv, Ukraine
² Department for the Modelling of Physico-Chemical Processes, Maria Curie Sklodowska University, 20031 Lublin, Poland

Abstract: Density profiles of flexible hard-sphere chain molecules in hard cylindrical pores and around hard cylindrical rods of various diameters were obtained by means of density functional theory of Yu and Wu (Y.-X. Yu, J. Wu, J. Chem. Phys., 117, 2368 (2002)) and grand-canonical Monte-Carlo simulation. The density profiles show stronger depletion of long chain molecules from narrow cylindrical pores at low densities, when compared to slit pores of the same width. Additionally, positive surface curvature of cylindrical pores increases the magnitude of wall depletion of chain molecules at low and intermediate densities. For negative surfaces curvature around the cylindrical rod, the wall depletion of chains is weaker than for a flat surface.

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Important Dates

June 10, 2009:	Final Program
June 22, 2009:	PSSM Workshop

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