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Topnani NB, Posnjak G, Nagaraja P, Neogi A, Musevic I, Ramarao P. Self-assembled toron-like structures in inverse nematic gels. Soft Matter 2020; 16:2933-2940. [PMID: 32095804 DOI: 10.1039/c9sm02547b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
A novel form of nematic gel (N-gel) wherein bright flower-like domains (BFDs) rich in gelator fibres are embedded in a matrix of liquid crystal (LC) molecules has been reported. These gels which we denote as inverse N-gels are unlike typical N-gels in which the LC is encapsulated within an aggregated network of gelator molecules. The self-organization of the helical gelator fibres within the BFDs leads to the creation of localized toron-like structures that are topologically protected due to their skyrmion director profile. Optical and confocal microscopy have been used to deduce the LC director configuration, in order to understand possible intermolecular interactions that can lead to the formation of the twisted structures and the inverse N-gels.
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Affiliation(s)
- Neha B Topnani
- Soft Condensed Matter Lab, Raman Research Institute, Bangalore 560080, India.
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2
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Venkata Sai D, Mirri G, Kouwer PHJ, Sahoo R, Musevic I, Dhara S. Unusual temperature dependence of elastic constants of an ambient-temperature discotic nematic liquid crystal. Soft Matter 2016; 12:2960-2964. [PMID: 26883494 DOI: 10.1039/c6sm00065g] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
We report the first experimental studies on the temperature dependence of viscoelastic properties of a room temperature discotic nematic liquid crystal. The splay elastic constant is greater than the bend elastic constant and both show unusual temperature and order parameter dependence. The rotational viscosity is remarkably larger than conventional calamitic liquid crystals. We provide a simple physical explanation based on the columnar short-range order to account for the the unusual temperature dependence of the elastic constants.
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Affiliation(s)
- D Venkata Sai
- School of Physics, University of Hyderabad, Hyderabad-500046, India.
| | - G Mirri
- Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands and Soft Matter Materials Lab, Solid State Physics Department, Jožef Stefan Institute, Jamova cesta 39, 1000, Ljubljana, Slovenia and Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000, Ljubljana, Slovenia
| | - P H J Kouwer
- Institute for Molecules and Materials, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands
| | - R Sahoo
- School of Physics, University of Hyderabad, Hyderabad-500046, India.
| | - I Musevic
- Soft Matter Materials Lab, Solid State Physics Department, Jožef Stefan Institute, Jamova cesta 39, 1000, Ljubljana, Slovenia and Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000, Ljubljana, Slovenia
| | - Surajit Dhara
- School of Physics, University of Hyderabad, Hyderabad-500046, India.
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3
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Abstract
We review and discuss recent progress in the field of nematic colloids, with an emphasis on possible future applications in photonics. The role of the topology is described, based on experimental manipulations of the topological defects in nematic colloids. The topology of the ordering field in nematics provides the forces between colloidal particles that are unique to these materials. We also discuss recent progress in the new field of active microphotonic devices based on liquid crystals (LCs), where chiral nematic microlasers and tuneable nematic microresonators are just two of the recently discovered examples. We conclude that the combination of topology and microphotonic devices based on LCs provides an interesting platform for future progress in the field of LCs.
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Affiliation(s)
- I Musevic
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
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4
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Sathyanarayana P, Jampani VSR, Skarabot M, Musevic I, Le KV, Takezoe H, Dhara S. Viscoelasticity of ambient-temperature nematic binary mixtures of bent-core and rodlike molecules. Phys Rev E Stat Nonlin Soft Matter Phys 2012; 85:011702. [PMID: 22400578 DOI: 10.1103/physreve.85.011702] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2011] [Indexed: 05/31/2023]
Abstract
We report measurements of the temperature variations of physical parameters in ambient-temperature nematic liquid crystal mixtures of bent-core (BC) and rodlike molecules (5CB): birefringence Δn; static dielectric constants ε(||) and ε(⊥); splay K(11) and bend K(33) elastic constants; rotational viscosity γ(1); and diffusion coefficients D(||) and D(⊥) of a microsphere. Both Δn and ε(||) decreases rapidly with increasing BC concentration, whereas ε(⊥) remains almost constant. At a shifted temperature (e.g., T-T(NI)=-10 °C), K(11) increases by ~50% and K(33) decreases by ~80% compared to pure 5CB when the BC concentration is increased to ~43 mol % in the mixture. Viscosities parallel and perpendicular to the director, η(||), η(⊥), which are nearly equal to the Miesowicz viscosities η(2) and η(3), respectively, were obtained by D(||) and D(⊥) using the Stokes-Einstein relation. Both the viscosities at room temperature increase by 60 and 50 times, respectively, whereas γ(1) increases by 180 times (at ~43 mol %) compared to the corresponding values of pure 5CB. The stiffening of K(11) and exorbitantly large enhancement in all the viscosities at a higher mol % of BC indicate that the viscoelastic properties are highly impacted by the presence of smectic clusters of BC molecules that results from the restricted free rotation of the molecules along the bow axis in the nematic phase. A possible attachment model of smectic type clusters of BC molecules surrounding the microparticle is presented.
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Affiliation(s)
- P Sathyanarayana
- School of Physics, University of Hyderabad, Hyderabad 500046, India
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5
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Zager U, Irman S, Lunder M, Skarabot M, Musevic I, Hodnik V, Anderluh G, Cucnik S, Kveder T, Rozman B, Bozic B. Immunochemical properties and pathological relevance of anti- 2-glycoprotein I antibodies of different avidity. Int Immunol 2011; 23:511-8. [DOI: 10.1093/intimm/dxr043] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
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6
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Carbone G, Zappone B, Barberi R, Bartolino R, Musevic I. Direct nanomechanical measurement of layer thickness and compressibility of smectic liquid crystals. Phys Rev E Stat Nonlin Soft Matter Phys 2011; 83:051707. [PMID: 21728556 DOI: 10.1103/physreve.83.051707] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/28/2010] [Revised: 04/12/2011] [Indexed: 05/31/2023]
Abstract
Using an atomic force microscope (AFM) we confined a smectic-A liquid crystal (LC) between a flat glass plate and a 10-μm glass sphere attached to the free end of the AFM cantilever. Both surfaces were treated with a surfactant that induces normal alignment of the LC molecules. We measured the force F acting on the cantilever while varying the plate-sphere distance D with subnanometer precision. For D < 50 nm, the force was periodically oscillating and decayed as D was increased. Analyzing the force in the framework of a simple model of elastic deformation of the smectic layers, we have evaluated the undeformed layer thickness a(0) and compressibility modulus B. Compared to other techniques used to determine a(0) and B, AFM measurements are faster and require a much smaller amount (microliters) of LC. Moreover, they are based on purely mechanical deformations of the LC structure and do not require any static or radiative electromagnetic field.
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7
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Abstract
We demonstrate a tunable and omnidirectional microlaser in the form of a microdroplet of a dye-doped, cholesteric liquid crystal in a carrier fluid. The cholesteric forms a Bragg-onion optical microcavity and the omnidirectional 3D lasing is due to the stimulated emission of light from the dye molecules in the liquid crystal. The lasing wavelength depends solely on the natural helical period of the cholesteric and can be tuned by varying the temperature. Millions of microlasers can be formed simply by mixing a liquid crystal, a laser dye and a carrier fluid, thus providing microlasers for soft-matter photonic devices.
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Affiliation(s)
- M Humar
- J. Stefan Institute, Ljubljana, Slovenia
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8
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Zupanic E, Zitko R, van Midden HJP, Musevic I, Prodan A. Pinning of adsorbed cobalt atoms by defects embedded in the copper (111) surface. Phys Rev Lett 2010; 104:196102. [PMID: 20866982 DOI: 10.1103/physrevlett.104.196102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/04/2010] [Indexed: 05/29/2023]
Abstract
Using a low-temperature scanning tunneling microscope (STM), we observe that Co adatoms are unusually strongly bound to a particular type of pinning centers on the Cu(111) surface. Using density-functional-theory calculations, the pinning centers are identified as Ag substitutional atoms embedded in the topmost atomic layer of the surface. These impurities are hardly detectable in the STM images as they have low topographic height and produce no standing-wave patterns. They do not affect the exchange coupling of the Co adsorbate with the substrate electrons; thus, the Kondo resonances measured on pinned and free Co adatoms show no detectable differences. Whereas free Co adatoms undergo significant surface diffusion already above 8 K, Ag-stabilized Co adatoms remain pinned up to 12.7 K.
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Affiliation(s)
- Erik Zupanic
- J. Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
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9
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Abstract
We present an experimental analysis of different equilibrium orientations and light driven transformations of Janus particles in the nematic liquid crystal 5CB. Depending on the preparation technique of homeotropic (DMOAP) and planar (Au) hemispheres we have observed two types of director field configurations: dipolar-like in the case of Au/DMOAP capped colloids and boojum-like in the case of DMOAP/Au capped colloids. Using the manipulation of Au/DMOAP capped colloids with laser tweezers we report on light driven irreversible orientational transformations into Saturn-ring and a novel, boojum-ring configuration. On the contrary, boojum-like DMOAP/Au capped colloids can act as rotators when exposed to the laser filed. Observed rotation is continuous around an axis perpendicular to the laser beam axis, with the frequency increasing linearly with the laser power.
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Affiliation(s)
- M Conradi
- Institute of Metals and Technology, Ljubljana, Slovenia.
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10
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Ognysta U, Nych A, Nazarenko V, Skarabot M, Musevic I. Design of 2D binary colloidal crystals in a nematic liquid crystal. Langmuir 2009; 25:12092-12100. [PMID: 19757827 DOI: 10.1021/la901719t] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/28/2023]
Abstract
In this paper, we examine directed self-assembly in a 2D binary system of dipolar and quadrupolar colloidal particles with normal surface boundary conditions, dispersed in the nematic liquid crystal. Using the laser tweezers, we assembled a large variety of stable 2D colloidal crystal structures. In all analyzed structures, the particles, their surface treatment and the cell conditions were the same, which gives us the ability to systematically follow the evolution of colloidal assembly when many particles are present. We present an analogy between molecular self-assembly and organization of colloidal microspheres in liquid crystalline medium to extend the strategy for designing colloidal crystalline structures of different level of complexity.
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Affiliation(s)
- U Ognysta
- Institute of Physics, 46 Nauky avenue, Kyiv 680028, Ukraine
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11
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Carbone G, Lombardo G, Barberi R, Musevic I, Tkalec U. Mechanically induced biaxial transition in a nanoconfined nematic liquid crystal with a topological defect. Phys Rev Lett 2009; 103:167801. [PMID: 19905724 DOI: 10.1103/physrevlett.103.167801] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2008] [Indexed: 05/28/2023]
Abstract
Using an atomic force microscopy, we have measured the separation dependence of the force between an atomically flat mica sheet and a micrometer-sized glass sphere immersed in the nematic liquid crystal. As the mica surface induces a strong parallel alignment and the treated glass sphere induces a strong perpendicular alignment on the liquid crystal, a repulsive force is observed due to the elastically deformed nematic liquid crystal. We observe that below a critical separation d(th) approximately 10 nm, the system undergoes a structural transition, thus relaxing the distortion. The results are interpreted within the eigenvalue exchange mechanism using the Landau-de Gennes tensorial approach.
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Affiliation(s)
- Giovanni Carbone
- CNR-INFM LiCryL, c/o Physics Department, University of Calabria, 87036 Rende (CS), Italy.
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12
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Tkalec U, Ravnik M, Zumer S, Musevic I. Vortexlike topological defects in nematic colloids: chiral colloidal dimers and 2D crystals. Phys Rev Lett 2009; 103:127801. [PMID: 19792458 DOI: 10.1103/physrevlett.103.127801] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/26/2008] [Indexed: 05/28/2023]
Abstract
We show that chiral ordering of the underlying complex fluid strongly influences defect formation and colloidal interactions. Nonsingular defect loops with a topological charge -2 are observed, with a cross section identical to hyperbolic vortices in magnetic systems. These loops are binding spontaneously formed pairs of colloidal particles and dimers, which are chiral objects. Chiral dimer-dimer interaction weakly depends on the chirality of dimers and leads to the assembly of 2D nematic colloidal crystals of pure or "mixed" chirality, intercalated with a lattice of nonsingular vortexlike defects.
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Affiliation(s)
- U Tkalec
- J. Stefan Institute, 1000 Ljubljana, Slovenia
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13
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Humar M, Skarabot M, Ravnik M, Zumer S, Poberaj I, Babic D, Musevic I. Electrically tunable diffraction of light from 2D nematic colloidal crystals. Eur Phys J E Soft Matter 2008; 27:73-79. [PMID: 19230228 DOI: 10.1140/epje/i2008-10353-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/27/2023]
Abstract
We show that diffraction of visible light from 2D dipolar nematic colloidal crystals can be tuned electrically. When the external electric field of approximately 1 V/microm is applied in a direction perpendicular to the plane of the 2D colloidal crystal, the induced strain is highly anisotropic, and the inter-colloidal spacing changes by as much as 20% along one direction and approximately 2% along the perpendicular one. Although the speed of response is in the range of several seconds, this novel mechanism could provide interesting photonic applications.
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Affiliation(s)
- M Humar
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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14
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Skarabot M, Ravnik M, Zumer S, Tkalec U, Poberaj I, Babic D, Musevic I. Hierarchical self-assembly of nematic colloidal superstructures. Phys Rev E Stat Nonlin Soft Matter Phys 2008; 77:061706. [PMID: 18643286 DOI: 10.1103/physreve.77.061706] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/10/2007] [Indexed: 05/26/2023]
Abstract
We show that colloidal superstructures could be assembled in mixtures of large and small colloidal particles dispersed in a nematic liquid crystal. Using elastic interaction of small colloidal particles with the disclination lines we succeed to demonstrate how one can decorate with small particles a topological matrix of defect rings and loops formed by an array of large colloidal particles. Our simulations show that this concept of colloidal self-assembly in nematics could be extended down to the nanoscale particles.
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Affiliation(s)
- M Skarabot
- J Stefan Institute, Jamova 39, Ljubljana, Slovenia
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15
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Ognysta U, Nych A, Nazarenko V, Musevic I, Skarabot M, Ravnik M, Zumer S, Poberaj I, Babic D. 2D interactions and binary crystals of dipolar and quadrupolar nematic colloids. Phys Rev Lett 2008; 100:217803. [PMID: 18518636 DOI: 10.1103/physrevlett.100.217803] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/15/2008] [Indexed: 05/26/2023]
Abstract
In this Letter, we demonstrate that the symmetry of the elastic interaction between the dipolar and quadrupolar colloidal particles in the nematic liquid crystal leads to a novel variety of 2D nematic "binary" colloidal crystals, which have not been observed in any colloidal system. The dipolar-quadrupolar interaction is highly anisotropic and shows a power-law dependence when the particles approach each other along the director field with a pair-binding energy of the order of several thousands of k(B)T for 4 microm diameter colloids.
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Affiliation(s)
- U Ognysta
- Institute of Physics, 46 Nauky avenue, Kyiv 680028, Ukraine
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16
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Skarabot M, Ravnik M, Zumer S, Tkalec U, Poberaj I, Babic D, Osterman N, Musevic I. Interactions of quadrupolar nematic colloids. Phys Rev E Stat Nonlin Soft Matter Phys 2008; 77:031705. [PMID: 18517404 DOI: 10.1103/physreve.77.031705] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/09/2008] [Indexed: 05/26/2023]
Abstract
We present experimental and theoretical study of colloidal interactions in quadrupolar nematic liquid crystal colloids, confined to a thin planar nematic cell. Using the laser tweezers, the particles have been positioned in the vicinity of other colloidal particles and their interactions have been determined using particle tracking video microscopy. Several types of interactions have been analyzed: (i) quadrupolar pair interaction, (ii) the interaction of an isolated quadrupole with a quadrupolar chain, and (iii) the interaction of an isolated quadrupolar colloidal particle with a two-dimensional (2D) quadrupolar crystallite. In all cases, the interactions are of the order of several 100k(B)T for 2 microm particles, which gives rise to relatively stable 2D colloidal crystals. The experimental results are compared to the predictions of Landau-de Gennes theory and we find a relatively good qualitative agreement.
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Affiliation(s)
- M Skarabot
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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17
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Ravnik M, Skarabot M, Zumer S, Tkalec U, Poberaj I, Babic D, Osterman N, Musevic I. Entangled nematic colloidal dimers and wires. Phys Rev Lett 2007; 99:247801. [PMID: 18233489 DOI: 10.1103/physrevlett.99.247801] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2007] [Indexed: 05/25/2023]
Abstract
It has been predicted, but never confirmed, that colloidal particles in a nematic liquid crystal could be self-assembled by delocalized topological defects and entangled disclinations. We show experimentally and theoretically that colloidal dimers and 1D structures bound by entangled topological defect loops can indeed be created by locally thermally quenching a thin layer of the nematic liquid crystal around selected colloidal particles. The topological entanglement provides a strong stringlike binding, which is ten thousand times stronger compared to water-based colloids. This unique binding mechanism could be used to assemble resonator optical waveguides and robust chiral and achiral structures of topologically entangled colloids that we call colloidal wires.
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Affiliation(s)
- M Ravnik
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
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18
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Skarabot M, Ravnik M, Zumer S, Tkalec U, Poberaj I, Babic D, Osterman N, Musevic I. Two-dimensional dipolar nematic colloidal crystals. Phys Rev E Stat Nonlin Soft Matter Phys 2007; 76:051406. [PMID: 18233658 DOI: 10.1103/physreve.76.051406] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2007] [Indexed: 05/25/2023]
Abstract
We study the interactions and directed assembly of dipolar nematic colloidal particles in planar nematic cells using laser tweezers. The binding energies for two stable configurations of a colloidal pair with homeotropic surface alignment are determined. It is shown that the orientation of the dipolar colloidal particle can efficiently be controlled and changed by locally quenching the nematic liquid crystal from the laser-induced isotropic phase. The interaction of a single colloidal particle with a single colloidal chain is determined and the interactions between pairs of colloidal chains are studied. We demonstrate that dipolar colloidal chains self-assemble into the two-dimensional (2D) dipolar nematic colloidal crystals. An odd-even effect is observed with increasing number of colloidal chains forming the 2D colloidal crystal.
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Affiliation(s)
- M Skarabot
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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19
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Skarabot M, Tkalec U, Musevic I. Transport and crystallization of colloidal particles in a thin nematic cell. Eur Phys J E Soft Matter 2007; 24:99-107. [PMID: 17882351 DOI: 10.1140/epje/i2007-10218-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2007] [Accepted: 08/07/2007] [Indexed: 05/17/2023]
Abstract
In a thin planar nematic cell, the application of an AC electric field induces a macroscopic transport of micrometer-sized colloidal particles along the nematic director. We have analyzed the dependence of particle velocities on the electric-field amplitude and frequency and found that it decreases exponentially with increasing frequency. Using specially designed electrodes we have observed that colloidal particles could be pumped and accelerated across the field-no-field interface, and measured the structural force and the corresponding potential, which is of the order of 10000 kBT for 4 microm particles. We demonstrate that spatially periodic close-packed crystalline colloidal structures can be obtained, which are thermodinamically metastable for many days after turning off the electric field and slowly decay into linear chains. Above the nematic-isotropic phase transition, such crystalline structures are non-stable and decay in few minutes.
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Affiliation(s)
- M Skarabot
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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20
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Nych AB, Ognysta UM, Pergamenshchik VM, Lev BI, Nazarenko VG, Musevic I, Skarabot M, Lavrentovich OD. Coexistence of two colloidal crystals at the nematic-liquid-crystal-air interface. Phys Rev Lett 2007; 98:057801. [PMID: 17358900 DOI: 10.1103/physrevlett.98.057801] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2006] [Indexed: 05/11/2023]
Abstract
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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Affiliation(s)
- A B Nych
- Institute of Physics, prospekt Nauky, 46, Kiev 03039, Ukraine
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21
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Abstract
The ability to generate regular spatial arrangements of particles is an important technological and fundamental aspect of colloidal science. We showed that colloidal particles confined to a few-micrometer-thick layer of a nematic liquid crystal form two-dimensional crystal structures that are bound by topological defects. Two basic crystalline structures were observed, depending on the ordering of the liquid crystal around the particle. Colloids inducing quadrupolar order crystallize into weakly bound two-dimensional ordered structure, where the particle interaction is mediated by the sharing of localized topological defects. Colloids inducing dipolar order are strongly bound into antiferroelectric-like two-dimensional crystallites of dipolar colloidal chains. Self-assembly by topological defects could be applied to other systems with similar symmetry.
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Affiliation(s)
- Igor Musevic
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
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22
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Lev B, Nych A, Ognysta U, Chernyshuk SB, Nazarenko V, Skarabot M, Poberaj I, Babic D, Osterman N, Musevic I. Anisotropic laser trapping in nematic colloidal dispersion. Eur Phys J E Soft Matter 2006; 20:215-9. [PMID: 16779526 DOI: 10.1140/epje/i2006-10015-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/24/2006] [Accepted: 05/26/2006] [Indexed: 05/10/2023]
Abstract
The interaction between a colloidal particle and a focused laser beam in a nematic liquid crystal reveals an unusual anisotropic Coulomb-like character. Experiments demonstrate two opposite directions in which the particle is attracted to and repelled from the nematic region deformed by the light-induced director reorientation. In this work we present analytical analysis of such behavior and derive the energy of interaction between colloidal particle and deformed director field. The analytical solution is in good agreement with recent results obtained by computer simulation.
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Affiliation(s)
- B Lev
- Institute of Physics, 46 Nauky ave., 03039, Kyiv-39, Ukraine
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23
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Conradi M, Ziherl P, Sarlah A, Musevic I. Colloids on free-standing smectic films. Eur Phys J E Soft Matter 2006; 20:231-6. [PMID: 16791457 DOI: 10.1140/epje/i2006-10016-2] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/08/2006] [Accepted: 05/29/2006] [Indexed: 05/10/2023]
Abstract
We study the structure of a free-standing smectic-A film around a micron-size polystyrene colloid adsorbed onto the film. We find that a colloid or a cluster of colloids is surrounded by an optically distinct and radially decorated meniscus ending with a sharp edge. The observed strong and finite-range attraction between the adsorbed colloids is driven by the fusion of menisci. We interpret the structure of the smectic meniscus in terms of a model dominated by the surface free energy and we argue that the characteristic appearance of the meniscus is due to layer undulations.
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Affiliation(s)
- M Conradi
- Jozef Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia
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24
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Skarabot M, Ravnik M, Babic D, Osterman N, Poberaj I, Zumer S, Musevic I, Nych A, Ognysta U, Nazarenko V. Laser trapping of low refractive index colloids in a nematic liquid crystal. Phys Rev E Stat Nonlin Soft Matter Phys 2006; 73:021705. [PMID: 16605354 DOI: 10.1103/physreve.73.021705] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2005] [Revised: 01/06/2006] [Indexed: 05/08/2023]
Abstract
We describe and analyze laser trapping of small colloidal particles in a nematic liquid crystal, where the index of refraction of colloids is smaller compared to the indices of the liquid crystal. Two mechanisms are identified that are responsible for this anomalous trapping: (i) below the optical Fréedericksz transition, the trapping is due to the anisotropic dielectric interaction of the polarized light with the inhomogeneous director field around the colloid, (ii) above the optical Fréedericksz transition, the optical trapping is accompanied by the elasticity-mediated interaction between the optically distorted region of a liquid crystal and the colloid. In the majority of the experiments, the trapping above the Fréedericksz transition is highly anisotropic. Qualitative agreement is found with a numerical analysis, considering the nematic director elastic distortion, dielectric director-light field coupling and optical repulsion due to low refraction index colloid in high index surroundings.
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Affiliation(s)
- M Skarabot
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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25
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Conradi M, Cepic M, Copic M, Musevic I. Test of clock model in ellipsometric study of thin and thick free-standing films of an antiferroelectric liquid crystal. Phys Rev E Stat Nonlin Soft Matter Phys 2005; 72:051711. [PMID: 16383624 DOI: 10.1103/physreve.72.051711] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2005] [Indexed: 05/05/2023]
Abstract
The temperature dependences of the ellipsometric parameters in a weak dc external field are studied in thin and thick free-standing films of MHPOBC. The results for thin films consisting of two, three, and four layers are analyzed within the discrete phenomenological model. We find very good quantitative agreement between the theory and experiment, which indicates an odd-even effect. We find that the XY structures are stable for an odd number of layers, whereas planar, Ising-like structures are stable for an even number of layers. The experiments on thick (several tens of layers) films show a combination of bulklike and free-surface behavior. This is most pronounced at high temperatures, where the interior of the film is not tilted, whereas the layers at the air interfaces show qualitatively similar temperature dependance of the ellipsometric parameters as in the four-layer film.
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Affiliation(s)
- M Conradi
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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26
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Carbone G, Barberi R, Musevic I, Krzic U. Atomic force microscope study of presmectic modulation in the nematic and isotropic phases of the liquid crystal octylcyanobiphenyl using piezoresistive force detection. Phys Rev E Stat Nonlin Soft Matter Phys 2005; 71:051704. [PMID: 16089548 DOI: 10.1103/physreve.71.051704] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2005] [Indexed: 05/03/2023]
Abstract
Using a temperature controlled atomic force microscope (AFM), we have studied surface induced pre-smectic order in the nematic and isotropic phases of 4-cyano- 4'-n -octylbiphenyl. A modified AFM head with piezoresitive cantilevers has been used to measure the structural force between a flat BK7 glass plate and a 10 microm glass sphere, both being treated to induce homeotropic alignment of the confined liquid crystal layer in between. We have observed surface-induced presmectic force not only in the isotropic, but also in the nematic phase. We have measured the temperature dependencies of the presmectic force, the smectic correlation length xi and the smectic order parameter psi at the surface. The correlation length xi(T) shows a power-law temperature dependence with a critical exponent of nu=0.67 +/- 0.03 and the bare correlation length of xi(0) = (0.39 +/- 0.08) nm, in good agreement with x-ray data. The smectic density at the surface is psi(2)(S) =0.4 in the nematic phase and decreases in the isotropic phase.
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Affiliation(s)
- G Carbone
- Licryl - Liquid Crystal Laboratory, INFM Research Unit of Calabria c/o Physics Department, University of Calabria, 87036 Rende (CS), Italy
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27
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Conradi M, Cepic M, Copic M, Musevic I. Structures and phase transitions in thin free standing films of an antiferroelectric liquid crystal. Phys Rev Lett 2004; 93:227802. [PMID: 15601118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Received: 06/22/2004] [Indexed: 05/24/2023]
Abstract
The premises of a discrete mean-field model for polar smectic liquid crystals are tested by analyzing the ellipsometric experiments on two, three, and four-layer freestanding films of MHPOBC. The measured temperature dependences of the ellipsometric parameters in a weak dc external field are compared to the predictions of a simple clock model. A very good quantitative agreement is found indicating an odd-even effect: XY structures are stable for odd and Ising-like structures for an even number of layers.
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Affiliation(s)
- M Conradi
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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28
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Musevic I, Skarabot M, Babic D, Osterman N, Poberaj I, Nazarenko V, Nych A. Laser trapping of small colloidal particles in a nematic liquid crystal: clouds and ghosts. Phys Rev Lett 2004; 93:187801. [PMID: 15525209 DOI: 10.1103/physrevlett.93.187801] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2004] [Indexed: 05/24/2023]
Abstract
We show that, contrary to intuition, small (< or =1 microm) transparent particles can be trapped and manipulated in a nematic liquid crystal using an intense laser beam, although their index of refraction is lower than both refractive indices of the surrounding birefringent fluid. Two mechanisms are identified that are responsible for this anomalous trapping: (i) surface-induced distortion of the birefringent media around the particle, creating a high-index "cloud" around the colloid, and (ii) laser-induced distortion or (partial) melting of a nematic, creating a ghost colloid.
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Affiliation(s)
- I Musevic
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia and Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia.
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29
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Jenko S, Skarabot M, Kenig M, Guncar G, Musevic I, Turk D, Zerovnik E. Different propensity to form amyloid fibrils by two homologous proteins-Human stefins A and B: searching for an explanation. Proteins 2004; 55:417-25. [PMID: 15048832 DOI: 10.1002/prot.20041] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
By using ThT fluorescence, X-ray diffraction, and atomic force microscopy (AFM), it has been shown that human stefins A and B (subfamily A of cystatins) form amyloid fibrils. Both protein fibrils show the 4.7 A and 10 A reflections characteristic for cross beta-structure. Similar height of approximately 3 nm and longitudinal repeat of 25-27 nm were observed by AFM for both protein fibrils. Fibrils with a double height of 5.6 nm were only observed with stefin A. The fibril's width for stefin A fibrils, as observed by transmission electron microscopy (TEM), was in the same range as previously reported for stefin B (Zerovnik et al., Biochem Biophys Acta 2002;1594:1-5). The conditions needed to undergo fibrillation differ, though. The amyloid fibrils start to form at pH 5 for stefin B, whereas in stefin A, preheated sample has to be acidified to pH < 2.5. In both cases, adding TFE, seeding, and alignment in a strong magnetic field accelerate the fibril growth. Visual analysis of the three-dimensional structures of monomers and domain-swapped dimers suggests that major differences in stability of both homologues stem from arrangement of specific salt bridges, which fix alpha-helix (and the alpha-loop) to beta-sheet in stefin A monomeric and dimeric forms.
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Affiliation(s)
- Sasa Jenko
- Department of Biochemistry and Molecular Biology, Jozef Stefan Institute, Ljubljana, Slovenia
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30
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Abstract
The structure of the fragile liquid-crystalline phases has a strong impact on the forces between bodies immersed in a liquid crystal (LC). We have equipped an atomic force microscope with a precise temperature control and measured various liquid-crystalline structural forces at temperatures close to the phase transitions. The observed forces agree well with predictions of Landau--de Gennes phenomenological theory of LCs, even at a nanoscale length. In addition to this, we have observed a molecular layer, adsorbed on the surfactant-covered glass surface, and determined its thickness and elastic properties.
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Affiliation(s)
- Klemen Kocevar
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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31
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Borstnik Bracic A, Kocevar K, Musevic I, Zumer S. Capillary forces in a confined isotropic-nematic liquid crystal. Phys Rev E Stat Nonlin Soft Matter Phys 2003; 68:011708. [PMID: 12935163 DOI: 10.1103/physreve.68.011708] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/20/2003] [Indexed: 05/24/2023]
Abstract
We have investigated nematic capillary condensation in the isotropic phase of nematic liquid crystals 5CB (4-cyano-4(')-n-pentylbiphenyl) and 8CB (4-cyano-4(')-n-octylbiphenyl) confined to nanometer thick layers between two orienting surfaces. The capillary condensation was induced by decreasing the liquid crystal layer thickness using an atomic force microscope, and the onset of condensation was detected by monitoring the structural force on a confining surface. Very strong and long-ranged capillary forces were observed at temperatures close to the isotropic-nematic transition. We have analyzed the temperature dependence of the thickness of the liquid crystal layer, at which the condensation occurs, with a thermodynamic Kelvin equation and determined the interfacial tension between the isotropic and nematic phases. The separation dependence of capillary forces was analyzed within the Landau-de Gennes approach, including electrostatic interaction due to surface charging. The quantitative agreement between the measured and calculated force profiles is very good, and a single set of parameters is needed to describe a set of measured force profiles at different temperatures. Surface charge density, surface potential, and Debye screening length were determined directly from the observed surface forces.
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Affiliation(s)
- A Borstnik Bracic
- Faculty of Education, University of Ljubljana, Kardeljeva ploscad 16, 1000 Ljubljana, Slovenia
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32
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Drevensek Olenik I, Kocevar K, Musevic I, Rasing T. Structure and polarity of 8CB films evaporated onto solid substrates. Eur Phys J E Soft Matter 2003; 11:169-175. [PMID: 15011057 DOI: 10.1140/epje/i2003-10013-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/27/2003] [Revised: 05/06/2003] [Indexed: 05/24/2023]
Abstract
Brewster-angle reflection ellipsometry and surface optical second harmonic generation were used to study the growth of 4'-n-octyl-4-cyanobiphenyl (8CB) films evaporated in air onto polymeric and quartz glass substrates. The layer-by-layer growth of the films terminates after formation of two distinctive interfacial layers. Both of these two layers are polar and tilted. In the first layer the molecules lie nearly flat on the surface, while in the second layer they point on average about 50 degrees toward the surface normal. The dipole moment of the second layer has a lower magnitude and an opposite direction with respect to the dipole moment of the first layer.
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Affiliation(s)
- I Drevensek Olenik
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI 1000, Ljubljana, Slovenia.
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33
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Conradi M, Musevic I, Cepic M. Structure and dynamics of freely suspended film of the smectic-C*alpha phase in an external transverse electric field. Phys Rev E Stat Nonlin Soft Matter Phys 2002; 65:061705. [PMID: 12188749 DOI: 10.1103/physreve.65.061705] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/19/2001] [Revised: 03/18/2002] [Indexed: 05/23/2023]
Abstract
We present a theoretical analysis of static and dynamic properties of freely suspended films of the smectic-C*alpha phase in an external electric field, applied along the smectic layers. The analysis is performed within the "clock" model, where the interactions up to next-nearest neighbors are considered. The calculated critical electric field for the unwinding of the smectic-C*alpha phase is of the order of several 100 V/mm and strongly depends on the interlayer interactions. The calculated relaxation rates of the eigenfluctuations of a system of N layers are in the kilohertz range for phase fluctuations and several megahertz for amplitude fluctuations.
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Affiliation(s)
- M Conradi
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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34
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Zerovnik E, Zavasnik-Bergant V, Kopitar-Jerala N, Pompe-Novak M, Skarabot M, Goldie K, Ravnikar M, Musevic I, Turk V. Amyloid fibril formation by human stefin B in vitro: immunogold labelling and comparison to stefin A. Biol Chem 2002; 383:859-63. [PMID: 12108553 DOI: 10.1515/bc.2002.092] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The mechanism by which proteins form amyloid fibrils is of high interest to the scientific community as its understanding could resolve questions relevant to conformational diseases. The structural and energetic basis of the process is still largely unknown. The main controversial issue is the co-existence of several protein conformations. Three models for the mechanism of protein fibrillogenesis have been proposed which need to be tested by experiments. In this report, amyloid fibrils grown from human stefin B (type I cystatin) are described. This physiologically relevant protein readily forms fibrils in vitro, in contrast to the homologue--human stefin A--which forms fibrils under extreme conditions only. In order to specifically label stefin B fibrils in vitro, rabbit polyclonal antibody and mouse monoclonal antibody A6/2 against human stefin B were used for immunogold labelling. Samples were examined by transmission electron microscopy. Fibrils of stefin B were strongly labelled using polyclonal antibody and Protein A gold, whereas no positive reaction was observed with monoclonal antibody A6/2.
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Affiliation(s)
- Eva Zerovnik
- Department of Biochemistry and Molecular Biology, Institute Jozef Stefan, Ljubljana, Slovenia
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35
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Kocevar K, Musevic I. Observation of an electrostatic force between charged surfaces in liquid crystals. Phys Rev E Stat Nonlin Soft Matter Phys 2002; 65:030703. [PMID: 11909018 DOI: 10.1103/physreve.65.030703] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2001] [Indexed: 05/23/2023]
Abstract
We report on the atomic force microscope observation of an electrostatic force between glass surfaces immersed in cyanobiphenil liquid crystals. The measured force is repulsive and decays exponentially with increasing surface separation. A mean field description of the electrostatic interaction in liquids has been used to determine the Debye screening length, the concentration of dissolved ions, and the surface electric potential. The effect of the observed interfacial electric field on the liquid crystal orientation at the surface has been discussed. It has been found that the coupling between the liquid crystal order and the surface electric field does not contribute considerably to the surface orienting action.
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Affiliation(s)
- K Kocevar
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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36
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Kocevar K, Musevic I. Surface-induced nematic and smectic order at a liquid-crystal-silanated-glass interface observed by atomic force spectroscopy and Brewster angle ellipsometry. Phys Rev E Stat Nonlin Soft Matter Phys 2002; 65:021703. [PMID: 11863541 DOI: 10.1103/physreve.65.021703] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/13/2001] [Indexed: 05/23/2023]
Abstract
We have investigated nematic and smectic surface-induced ordering in the isotropic phase of the 4-cyano-4'-n-octylbiphenyl liquid crystal on silanated BK7 and LaSF glass using atomic force spectroscopy and Brewster angle ellipsometry. We have observed complete wetting of the silanated glass surfaces with the nematic phase when approaching the isotropic-nematic phase transition from above. Using the atomic force spectroscopy at the same interfaces, we have detected a significant presmectic ordering that is enhanced at the nematic-isotropic transition. We have observed the first, strongly adsorbed layer of liquid-crystalline molecules underneath this presmectic ordering. This first molecular layer is laterally inhomogeneous with typically 100 nm voids and covers approximately 70% of the surface. It is stable far above the clearing point and is responsible for the surface-memory effect. The results have been analyzed using Landau-de Gennes theory. The surface coupling energies of the nematic and smectic order have been determined, as well as the coupling energy between the nematic and smectic order.
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Affiliation(s)
- K Kocevar
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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37
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Abstract
Human stefin B (cystatin B) is an intracellular cysteine proteinase inhibitor broadly distributed in different tissues. Here, we show that recombinant human stefin B readily forms amyloid fibrils in vitro. It dimerises and further oligomerises, starting from the native-like acid intermediate, I(N), populated at pH 5. On standing at room temperature it produces regular (over 4 microm long) fibrils over a period of several months. These have been visualised by transmission electron microscopy and atomic force microscopy. Their cross-sectional diameter is about 14 nm and blocks of 27 nm repeat longitudinally. The fibrils are smooth, of unbranched surface, consistent with findings of other amyloid fibrils. Thioflavin T fluorescence spectra as a function of time were recorded and Congo red dye binding to the fibrils was demonstrated. Adding 10% (v/v) trifluoroethanol resulted in an increased rate of fibrillation with a typical lag phase. The finding that human stefin B, in contrast to the homologue stefin A, forms amyloid fibrils rather easily should promote further studies of the protein's behaviour in vivo, and/or as a model system for fibrillogenesis.
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Affiliation(s)
- Eva Zerovnik
- Department of Biochemistry and Molecular Biology, Institute Jozef Stefan, Jamova 39, 1000 Ljubljana, Slovenia.
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38
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Kocevar K, Musevic I. Forces in the isotropic phase of a confined nematic liquid crystal 5CB. Phys Rev E Stat Nonlin Soft Matter Phys 2001; 64:051711. [PMID: 11735949 DOI: 10.1103/physreve.64.051711] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/15/2001] [Indexed: 05/23/2023]
Abstract
Using a temperature controlled atomic force microscope, we have measured the temperature dependence of the force between a flat silanated glass surface and a silanated glass microsphere, immersed in the isotropic phase of the nematic liquid crystal 5CB (4'-n-pentyl 4-cyanobiphenyl). At separations of several nanometers, we observed a weak, short range attractive force of the order of 100 pN, which was increased by decreasing the temperature. The temperature dependence of the amplitude and the range of this attractive force can be described by a combination of van der Waals and a mean-field prenematic force due to the surface-induced nematic order. This is supported by ellipsometric study and allows for the determination of the surface coupling energy of 5CB on a silanated glass surface.
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Affiliation(s)
- K Kocevar
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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39
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Musevic I, Skarabot M. Optical rotation and structure of ferrielectric smectic phases. Phys Rev E Stat Nonlin Soft Matter Phys 2001; 64:051706. [PMID: 11735944 DOI: 10.1103/physreve.64.051706] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2001] [Revised: 07/10/2001] [Indexed: 05/23/2023]
Abstract
We analyze the measured optical rotation in three- and four-layer smectic ferrielectric phases within the matrix approach to the light propagation. We show that "perfect" three- and four-layer structures with 120 degrees and 90 degrees phase rotation of the director in neighboring layers give negligible optical rotation of polarized light travelling along the normal to the smectic layers. Significant optical rotation is obtained in deformed three- and four-layer smectic phases. The analysis of the measured optical rotatory power clearly shows that three-layer ferrielectric phases of [4-(1-methylheptyloxycarbonylphenyl)-octylbiphenyl-4-carboxylate] and 4-[(4-[[1(*)-methyl]heptycarboxy]phenyl)carboxy]phenyl-4'-decyloxy-1-benzencarbatioate (10OTBBB1M7) are deformed with the deformation angle of 35 degrees-45 degrees. The deformation angle in the four-layer smectic phase of 10OTBBB1M7 is 70 degrees-90 degrees. This is in reasonable agreement with other experiments and suggests the validity of the "deformed clock model."
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Affiliation(s)
- I Musevic
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
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40
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Kocevar K, Borstnik A, Musevic I, Zumer S. Capillary condensation of a nematic liquid crystal observed by force spectroscopy. Phys Rev Lett 2001; 86:5914-5917. [PMID: 11415392 DOI: 10.1103/physrevlett.86.5914] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2001] [Indexed: 05/23/2023]
Abstract
We have observed capillary condensation in nanometer-thin films of nematic liquid crystals using force spectroscopy. The liquid crystal was confined to a submicron gap between a flat substrate and a microsphere, attached to the cantilever of an atomic force microscope. A long-ranged and strongly attractive force due to capillary condensation of a nematic phase was observed at temperatures close to the bulk isotropic-nematic phase transition. The critical point, terminating the first-order confined isotropic-nematic transition line, was determined for the first time.
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Affiliation(s)
- K Kocevar
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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Abstract
The glassy state of felodipine was prepared by melting crystals of felodipine on a clean glass slide and cooling to room temperature. It has been confirmed that glassy felodipine is a metastable state, and undergoes transformation to the more stable crystalline form. Crystallization occurred slowly and spontaneously at room temperature, below the glassy state transition temperature (Tg). The contact mode of atomic force microscopy was used for topographical imaging of the glassy and crystalline states of felodipine. When the glassy felodipine region next to the recrystallized zone was exposed to controlled mechanical stress through the tip, rapid additional crystallization was observed. This crystallization process can be induced and imaged in real time by atomic force microscopy.
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Affiliation(s)
- A Trojak
- University of Ljubljana, Faculty of Pharmacy, Askerceva 7, SI-1000, Ljubljana, Slovenia
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42
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Kocevar K, Blinc R, Musevic I. Atomic force microscope evidence for the existence of smecticlike surface layers in the isotropic phase of a nematic liquid crystal. Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics 2000; 62:R3055-R3058. [PMID: 11088877 DOI: 10.1103/physreve.62.r3055] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/23/2000] [Indexed: 05/23/2023]
Abstract
Using a temperature controlled atomic force microscope we have observed presmectic layering in the isotropic phase of 4-cyano-4(')-n-octylbiphenyl (8CB) on silanated glass. The first molecular layer shows a smecticlike compressibility modulus of B approximately 10(7) N/m(2) and is stable more than 20 K beyond the bulk clearing point. It is followed by a presmectic modulation that increases when cooling towards the isotropic-nematic transition. In the bulk isotropic phase, the layers cover approximately 70% of the glass surface, indicating a clusterlike organization.
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Affiliation(s)
- K Kocevar
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
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43
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Sepcić K, Musevic I, Lahajnar G, Turk T, Macek P. AFM imaging of surface adsorbed polymeric 3-alkylpyridinium salts from the marine sponge Reniera sarai. Int J Biol Macromol 1999; 26:353-6. [PMID: 10628537 DOI: 10.1016/s0141-8130(99)00106-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Bioactive 3-alkylpyridinium polymers (poly-APS) have recently been isolated from the marine sponge Reniera sarai. Previous results have shown that these molecules in aqueous solutions form supramolecular aggregates with an average hydrodynamic radius of 23 +/- 2 nm. To obtain additional evidences about the shape and the dimensions of poly-APS aggregates, we used atomic force microscopy (AFM) operating in tapping mode. The images clearly showed adsorbed aggregates with a lateral dimension of approximately 40 nm and a thickness of the order of approximately 1 nm. The distribution of volumes of the adsorbed aggregates is very similar to the distribution of hydrodynamic radii as obtained from the dynamic light scattering experiments. The volume distribution of these aggregates shows a maximum at 1750 nm3, which corresponds to a sphere with a radius of 7.5 nm.
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Affiliation(s)
- K Sepcić
- Department of Biology, Biotechnical Faculty, University of Ljubliana, Slovenia.
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Rastegar A, Rasing T, Musevic I, Heppke G. Slow mode of the smectic-A-smectic-C(*)(alpha) phase transition. Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics 1999; 60:6788-92. [PMID: 11970598 DOI: 10.1103/physreve.60.6788] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/12/1998] [Revised: 08/02/1999] [Indexed: 04/18/2023]
Abstract
Unusual slow fluctuations as revealed recently by dynamic light scattering close to the Sm-A-Sm-C(alpha)(*) phase transition in the antiferroelectric liquid crystal 4-(1-methylheptyloxy-carbonyl)phenyl 4(')-octyloxy biphenyl-4-carboxylate can be explained by the electrostatic coupling between impurity ions and director fluctuations. Within the vicinity of Sm-A-Sm-C(alpha)(*) transition, the relaxation rate of the slow mode depends linearly on temperature, but with a different slope in each phase. The square root of its intensity shows a clear Curie-Weiss divergence at the phase transition, which is a direct confirmation of the electrostatic coupling mechanism.
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Affiliation(s)
- A Rastegar
- Research Institute for Materials, University of Nijmegen, 6525 ED Nijmegen, The Netherlands
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Wittebrood MM, Luijendijk DH, Stallinga S, Rasing T, Musevic I. Thickness-dependent phase transition in thin nematic films. Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics 1996; 54:5232-5234. [PMID: 9965706 DOI: 10.1103/physreve.54.5232] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Musevic I, Rastegar A, Cepic M, Zeks B, Copic M, Moro D, Heppke G. Observation of an Opticlike Phase Mode in an Antiferroelectric Liquid Crystal. Phys Rev Lett 1996; 77:1769-1772. [PMID: 10063167 DOI: 10.1103/physrevlett.77.1769] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Kralj S, Zidansek A, Lahajnar G, Musevic I, Zumer S, Blinc R, Pintar MM. Nematic ordering in porous glasses: A deuterium NMR study. Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics 1996; 53:3629-3638. [PMID: 9964673 DOI: 10.1103/physreve.53.3629] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Musevic I, Zeks B, Blinc R, Rasing T. Phasons and broken symmetries in ferroelectric liquid crystals. Phys Rev B Condens Matter 1994; 49:9299-9311. [PMID: 10009726 DOI: 10.1103/physrevb.49.9299] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/12/2023]
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Musevic I, Blinc R, Zeks B, Copic M, Wittebrood MM, Rasing T, Orihara H, Ishibashi Y. Gapless phason in an antiferroelectric liquid crystal. Phys Rev Lett 1993; 71:1180-1183. [PMID: 10055470 DOI: 10.1103/physrevlett.71.1180] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
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Musevic I, Zeks B, Blinc R, Rasing T. Magnetic-field-induced biaxiality in an antiferroelectric liquid crystal. Phys Rev E Stat Phys Plasmas Fluids Relat Interdiscip Topics 1993; 47:1094-1100. [PMID: 9960110 DOI: 10.1103/physreve.47.1094] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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