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Sebastián N, Lovšin M, Berteloot B, Osterman N, Petelin A, Mandle RJ, Aya S, Huang M, Drevenšek-Olenik I, Neyts K, Mertelj A. Polarization patterning in ferroelectric nematic liquids via flexoelectric coupling. Nat Commun 2023; 14:3029. [PMID: 37230977 DOI: 10.1038/s41467-023-38749-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2023] [Accepted: 05/11/2023] [Indexed: 05/27/2023] Open
Abstract
The recently discovered ferroelectric nematic liquids incorporate to the functional combination of fluidity, processability and anisotropic optical properties of nematic liquids, an astonishing range of physical properties derived from the phase polarity. Among them, the remarkably large values of second order optical susceptibility encourage to exploit these new materials for non-linear photonic applications. Here we show that photopatterning of the alignment layer can be used to structure polarization patterns. To do so, we take advantage of the flexoelectric effect and design splay structures that geometrically define the polarization direction. We demonstrate the creation of periodic polarization structures and the possibility of guiding polarization by embedding splay structures in uniform backgrounds. The demonstrated capabilities of polarization patterning, open a promising new route for the design of ferroelectric nematic based photonic structures and their exploitation.
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Affiliation(s)
| | - Matija Lovšin
- Jožef Stefan Institute, Ljubljana, Slovenia
- University of Ljubljana, Faculty of Mathematics and Physics, Ljubljana, Slovenia
| | - Brecht Berteloot
- Liquid Crystals and Photonics Group, ELIS Department, Ghent University, Ghent, Belgium
| | - Natan Osterman
- Jožef Stefan Institute, Ljubljana, Slovenia
- University of Ljubljana, Faculty of Mathematics and Physics, Ljubljana, Slovenia
| | - Andrej Petelin
- Jožef Stefan Institute, Ljubljana, Slovenia
- University of Ljubljana, Faculty of Mathematics and Physics, Ljubljana, Slovenia
| | - Richard J Mandle
- School of Physics and Astronomy, University of Leeds, Leeds, UK
- School of Chemistry, University of Leeds, Leeds, UK
| | - Satoshi Aya
- South China Advanced Institute for Soft Matter Science and Technology (AISMST), School of Emergent Soft Matter, South China University of Technology, Guangzhou, China
- Guangdong Provincial Key Laboratory of Functional and Intelligent Hybrid Materials and Devices, South China University of Technology, Guangzhou, China
| | - Mingjun Huang
- South China Advanced Institute for Soft Matter Science and Technology (AISMST), School of Emergent Soft Matter, South China University of Technology, Guangzhou, China
- Guangdong Provincial Key Laboratory of Functional and Intelligent Hybrid Materials and Devices, South China University of Technology, Guangzhou, China
| | - Irena Drevenšek-Olenik
- Jožef Stefan Institute, Ljubljana, Slovenia
- University of Ljubljana, Faculty of Mathematics and Physics, Ljubljana, Slovenia
| | - Kristiaan Neyts
- Liquid Crystals and Photonics Group, ELIS Department, Ghent University, Ghent, Belgium
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2
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Gregorin Ž, Sebastián N, Osterman N, Hribar Boštjančič P, Lisjak D, Mertelj A. Dynamics of domain formation in a ferromagnetic fluid. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2022.120308] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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3
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Hribar Boštjančič P, Gregorin Ž, Sebastián N, Osterman N, Lisjak D, Mertelj A. Isotropic to nematic transition in alcohol ferrofluids of barium hexaferrite nanoplatelets. J Mol Liq 2022. [DOI: 10.1016/j.molliq.2021.118038] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
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4
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Stergar J, Osterman N. Thermophoretic tweezers for single nanoparticle manipulation. Beilstein J Nanotechnol 2020; 11:1126-1133. [PMID: 32802715 PMCID: PMC7404219 DOI: 10.3762/bjnano.11.97] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2020] [Accepted: 07/06/2020] [Indexed: 05/11/2023]
Abstract
We present the trapping and manipulation of a single nano-object in an aqueous medium by optically induced temporally varying temperature gradients. By real-time object tracking and control of the position of the heating laser focus, we can precisely employ thermophoretic drift to oppose the random diffusive motion. As a result, a nano-object is confined in a micrometer-sized trap. Numerical modeling gives a quantitative prediction of the effect. Traps can be dynamically created and relocated, which we demonstrate by the controlled independent manipulation of two nanoparticles.
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Affiliation(s)
- Jošt Stergar
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, Ljubljana, Slovenia
- J. Stefan Institute, Jamova 39, Ljubljana, Slovenia
| | - Natan Osterman
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, Ljubljana, Slovenia
- J. Stefan Institute, Jamova 39, Ljubljana, Slovenia
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5
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Emeršič T, Zhang R, Kos Ž, Čopar S, Osterman N, de Pablo JJ, Tkalec U. Sculpting stable structures in pure liquids. Sci Adv 2019; 5:eaav4283. [PMID: 30793033 PMCID: PMC6377271 DOI: 10.1126/sciadv.aav4283] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2018] [Accepted: 12/21/2018] [Indexed: 05/19/2023]
Abstract
Pure liquids in thermodynamic equilibrium are structurally homogeneous. In liquid crystals, flow and light pulses are used to create reconfigurable domains with polar order. Moreover, through careful engineering of concerted microfluidic flows and localized optothermal fields, it is possible to achieve complete control over the nucleation, growth, and shape of such domains. Experiments, theory, and simulations indicate that the resulting structures can be stabilized indefinitely, provided the liquids are maintained in a controlled nonequilibrium state. The resulting sculpted liquids could find applications in microfluidic devices for selective encapsulation of solutes and particles into optically active compartments that interact with external stimuli.
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Affiliation(s)
- Tadej Emeršič
- Institute of Biophysics, Faculty of Medicine, University of Ljubljana, Vrazov trg 2, 1000 Ljubljana, Slovenia
| | - Rui Zhang
- Institute for Molecular Engineering, University of Chicago, Chicago, IL 60637, USA
| | - Žiga Kos
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
| | - Simon Čopar
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
| | - Natan Osterman
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, 1000 Ljubljana, Slovenia
- Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
| | - Juan J. de Pablo
- Institute for Molecular Engineering, University of Chicago, Chicago, IL 60637, USA
- Material Science Division, Argonne National Laboratory, Lemont, IL 60439, USA
- Corresponding author. (J.J.d.P.); (U.T.)
| | - Uroš Tkalec
- Institute of Biophysics, Faculty of Medicine, University of Ljubljana, Vrazov trg 2, 1000 Ljubljana, Slovenia
- Jožef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
- Faculty of Natural Sciences and Mathematics, University of Maribor, Koroška 160, 2000 Maribor, Slovenia
- Corresponding author. (J.J.d.P.); (U.T.)
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6
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Sebastián N, Osterman N, Lisjak D, Čopič M, Mertelj A. Director reorientation dynamics of ferromagnetic nematic liquid crystals. Soft Matter 2018; 14:7180-7189. [PMID: 30141811 DOI: 10.1039/c8sm01377b] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Successful realization of ferromagnetic nematic liquid crystals has opened up the possibility to experimentally study a completely new set of fundamental physical phenomena. In this contribution we present a detailed investigation of some aspects of the static response and the complex dynamics of ferromagnetic liquid crystals under the application of an external magnetic field. Experimental results are then compared with a macroscopic model. Dynamics of the director were measured by optical methods and analyzed in terms of a theoretical macroscopic model. A dissipative cross-coupling coefficient describing the dynamic coupling between the two system order parameters, the magnetization and the nematic director, is needed to explain the results. In this contribution we examine the dependency of this coefficient on material parameters and the saturation magnetization and the liquid crystal host. Despite the complexity of the system, the theoretical description allows for a proper interpretation of the results and is connected to several microscopic aspects of the colloidal suspension.
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Affiliation(s)
- Nerea Sebastián
- J. Stefan Institute, P.O.B 3000, SI-1000 Ljubljana, Slovenia.
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7
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Vilfan M, Osterman N, Vilfan A. Magnetically driven omnidirectional artificial microswimmers. Soft Matter 2018; 14:3415-3422. [PMID: 29670984 DOI: 10.1039/c8sm00230d] [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: 06/08/2023]
Abstract
We present an experimental realisation of two new artificial microswimmers that swim at low Reynolds number. The swimmers are externally driven with a periodically modulated magnetic field that induces an alternating attractive/repulsive interaction between the swimmer parts. The field sequence also modulates the drag on the swimmer components, making the working cycle non-reciprocal. The resulting net translational displacement leads to velocities of up to 2 micrometers per second. The swimmers can be made omnidirectional, meaning that the same magnetic field sequence can drive swimmers in any direction in the sample plane. Although the direction of their swimming is determined by the momentary orientation of the swimmer, their motion can be guided by solid boundaries. We demonstrate their omnidirectionality by letting them travel through a circular microfluidic channel. We use simple scaling arguments as well as more detailed numerical simulations to explain the measured velocity as a function of the actuation frequency.
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Affiliation(s)
- Mojca Vilfan
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia.
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8
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Potisk T, Mertelj A, Sebastián N, Osterman N, Lisjak D, Brand HR, Pleiner H, Svenšek D. Magneto-optic dynamics in a ferromagnetic nematic liquid crystal. Phys Rev E 2018; 97:012701. [PMID: 29448417 DOI: 10.1103/physreve.97.012701] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2017] [Indexed: 06/08/2023]
Abstract
We investigate dynamic magneto-optic effects in a ferromagnetic nematic liquid crystal experimentally and theoretically. Experimentally we measure the magnetization and the phase difference of the transmitted light when an external magnetic field is applied. As a model we study the coupled dynamics of the magnetization, M, and the director field, n, associated with the liquid crystalline orientational order. We demonstrate that the experimentally studied macroscopic dynamic behavior reveals the importance of a dynamic cross-coupling between M and n. The experimental data are used to extract the value of the dissipative cross-coupling coefficient. We also make concrete predictions about how reversible cross-coupling terms between the magnetization and the director could be detected experimentally by measurements of the transmitted light intensity as well as by analyzing the azimuthal angle of the magnetization and the director out of the plane spanned by the anchoring axis and the external magnetic field. We derive the eigenmodes of the coupled system and study their relaxation rates. We show that in the usual experimental setup used for measuring the relaxation rates of the splay-bend or twist-bend eigenmodes of a nematic liquid crystal one expects for a ferromagnetic nematic liquid crystal a mixture of at least two eigenmodes.
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Affiliation(s)
- Tilen Potisk
- Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, SI-1000 Ljubljana, Slovenia
- Department of Physics, University of Bayreuth, 95440 Bayreuth, Germany
| | | | | | - Natan Osterman
- Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, SI-1000 Ljubljana, Slovenia
- J. Stefan Institute, SI-1000 Ljubljana, Slovenia
| | - Darja Lisjak
- J. Stefan Institute, SI-1000 Ljubljana, Slovenia
| | - Helmut R Brand
- Department of Physics, University of Bayreuth, 95440 Bayreuth, Germany
| | - Harald Pleiner
- Max Planck Institute for Polymer Research, 55021 Mainz, Germany
| | - Daniel Svenšek
- Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, SI-1000 Ljubljana, Slovenia
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9
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Mur J, Pirker L, Osterman N, Petkovšek R. Silicon crystallinity control during laser direct microstructuring with bursts of picosecond pulses. Opt Express 2017; 25:26356-26364. [PMID: 29041292 DOI: 10.1364/oe.25.026356] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2017] [Accepted: 10/11/2017] [Indexed: 06/07/2023]
Abstract
Laser ablation and modification using bursts of picosecond pulses and a tightly focused laser beam are used to manufacture structures in the bulk silicon. We demonstrate precise control of the surface crystallinity as well as the structure depth and topography of the processed areas, achieving homogeneous surface properties. The control is achieved with a combination of a well-defined pulse energy, systematic pulse positioning on the material, and the number of pulses in a burst. A custom designed fiber laser source is used to generate bursts of 1, 5, 10, and 20 pulses at a pulse repetition rate of 40 MHz and burst repetition rate of 83.3 kHz allowing for a fast and stable processing of silicon. We show a controlled transition through different laser-matter interaction regimes, from no observable changes of the silicon at low pulse energies, through amorphization below the ablation threshold energy, to the ablation with either complete, partial or nonexistent amorphization. Single micrometer-sized areas of desired shape and crystallinity were defined on the silicon surface with submicron precision, offering a promising tool for applications in the field of optics.
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10
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Potisk T, Svenšek D, Brand HR, Pleiner H, Lisjak D, Osterman N, Mertelj A. Dynamic Magneto-optic Coupling in a Ferromagnetic Nematic Liquid Crystal. Phys Rev Lett 2017; 119:097802. [PMID: 28949588 DOI: 10.1103/physrevlett.119.097802] [Citation(s) in RCA: 10] [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: 02/21/2017] [Indexed: 06/07/2023]
Abstract
Hydrodynamics of complex fluids with multiple order parameters is governed by a set of dynamic equations with many material constants, of which only some are easily measurable. We present a unique example of a dynamic magneto-optic coupling in a ferromagnetic nematic liquid, in which long-range orientational order of liquid crystalline molecules is accompanied by long-range magnetic order of magnetic nanoplatelets. We investigate the dynamics of the magneto-optic response experimentally and theoretically and find out that it is significantly affected by the dissipative dynamic cross-coupling between the nematic and magnetic order parameters. The cross-coupling coefficient determined by fitting the experimental results with a macroscopic theory is of the same order of magnitude as the dissipative coefficient (rotational viscosity) that governs the reorientation of pure liquid crystals.
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Affiliation(s)
- Tilen Potisk
- Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, SI-1000 Ljubljana, Slovenia
- Theoretische Physik III, Universität Bayreuth, 95440 Bayreuth, Germany
| | - Daniel Svenšek
- Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, SI-1000 Ljubljana, Slovenia
| | - Helmut R Brand
- Theoretische Physik III, Universität Bayreuth, 95440 Bayreuth, Germany
| | - Harald Pleiner
- Max Planck Institute for Polymer Research, 55021 Mainz, Germany
| | - Darja Lisjak
- J. Stefan Institute, SI-1000 Ljubljana, Slovenia
| | - Natan Osterman
- Department of Physics, Faculty of Mathematics and Physics, University of Ljubljana, SI-1000 Ljubljana, Slovenia
- J. Stefan Institute, SI-1000 Ljubljana, Slovenia
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11
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Škarabot M, Osterman N, Muševič I. Optothermally driven colloidal transport in a confined nematic liquid crystal. Soft Matter 2017; 13:2448-2452. [PMID: 28277573 DOI: 10.1039/c7sm00136c] [Citation(s) in RCA: 2] [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] [Indexed: 06/06/2023]
Abstract
We demonstrate transport of microparticles by rapid movement of a laser spot in a thin layer of a nematic liquid crystal. The transport is achieved by fluid flow, caused by two different mechanisms. The thermoviscous expansion effect induces colloidal transport in the direction opposite to the laser movement, whereas thermally induced local melting of the liquid crystal pulls the particles in the direction of the laser movement. We demonstrate control of colloidal transport by changing the speed of the laser trap movement and the laser power. We anticipate that complex optofluidic colloidal transport could be realized in the nematic liquid crystal using a channel-free optofluidic approach.
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Affiliation(s)
- M Škarabot
- J. Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia.
| | - N Osterman
- J. Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia. and Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000, Ljubljana, Slovenia
| | - I Muševič
- J. Stefan Institute, Jamova 39, SI-1000, Ljubljana, Slovenia. and Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000, Ljubljana, Slovenia
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12
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Abstract
Magnetic colloids in external time-dependent fields are subject to complex induced many-body interactions governing their self-assembly into a variety of equilibrium and out-of-equilibrium structures such as chains, networks, suspended membranes, and colloidal foams. Here, we report experiments, simulations, and theory probing the dynamic assembly of superparamagnetic colloids in precessing external magnetic fields. Within a range of field frequencies, we observe dynamic large-scale structures such as ordered phases composed of precessing chains, ribbons, and rotating fluidic vortices. We show that the structure formation is inherently coupled to the buildup of torque, which originates from internal relaxation of induced dipoles and from transient correlations among the particles as a result of short-lived chain formation. We discuss in detail the physical properties of the vortex phase and demonstrate its potential in particle-coating applications.
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Affiliation(s)
- Tomaž Mohorič
- International Research Center for Soft Matter, Beijing University of Chemical Technology , Beijing 100029, P.R. China
- Department of Chemistry, University of Ljubljana , Večna pot 113, 1000 Ljubljana, Slovenia
| | - Gašper Kokot
- Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia
| | - Natan Osterman
- Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia
| | - Alexey Snezhko
- Argonne National Laboratory, 9700 Cass Avenue, Lemont, Illinois 60439, United States
| | - Andrej Vilfan
- Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia
| | - Dušan Babič
- Department of Mathematics and Physics, Jadranska 19, 1000 Ljubljana, Slovenia
| | - Jure Dobnikar
- International Research Center for Soft Matter, Beijing University of Chemical Technology , Beijing 100029, P.R. China
- Department of Chemistry, University of Cambridge , Cambridge CB2 1TN, United Kingdom
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13
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Mertelj A, Osterman N, Lisjak D, Copič M. Magneto-optic and converse magnetoelectric effects in a ferromagnetic liquid crystal. Soft Matter 2014; 10:9065-9072. [PMID: 25244107 DOI: 10.1039/c4sm01625d] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We have studied the response of ferromagnetic liquid crystals to external magnetic and electric fields, and compared it to the usual response of nematic liquid crystals (NLCs). We have observed effects, which are not present in a pure NLC and are a consequence of the coupling between the nematic director and the magnetization. The electro-optic effect, which is in the ferromagnetic phase the same as in the pure NLC, is accompanied by a converse magnetoelectric effect. The magneto-optic effect differs completely from the one observed in the pure NLC, where it is a quadratic effect and it only appears when a magnetic field larger than a critical field is applied perpendicular to the director. In the ferromagnetic NLC in addition to the response to the perpendicular field, there is also a qualitatively different response to the parallel field. Contrary to the pure NLC no critical field needs to be exceeded for the system to respond to a perpendicular field, but a critical field needs to be exceeded to observe a response to the field parallel to the director and antiparallel to the magnetization. The critical field is in this case two orders of magnitude smaller than the critical field of the magnetic Frederiks transition in the pure NLC. The experimental observations are well described by a simple macroscopic theory.
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Affiliation(s)
- Alenka Mertelj
- J. Stefan Institute, P.O.B. 3000, SI-1001 Ljubljana, Slovenia.
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14
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Müller K, Osterman N, Babič D, Likos CN, Dobnikar J, Nikoubashman A. Pattern formation and coarse-graining in two-dimensional colloids driven by multiaxial magnetic fields. Langmuir 2014; 30:5088-5096. [PMID: 24742096 DOI: 10.1021/la500896e] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
We study the pattern formation in a two-dimensional system of superparamagnetic colloids interacting via spatially coherent induced interactions driven by an external precessing magnetic field. On the pair level, upon changing the opening angle of the external field, the interactions smoothly vary from purely repulsive (opening angle equal to zero) to purely attractive (time-averaged pair interactions at an opening angle of 90°). In the experiments, we observed ordered hexagonal crystals at the repulsive end and coarsening frothlike structures for purely attractive interactions. In both of these limiting cases, the dense colloidal systems can be sufficiently accurately described by assuming pairwise additivity of the interaction potentials. However, for a range of intermediate angles, pronounced many-body depolarization effects compete with the direct induced interactions, resulting in inherently anisotropic effective interactions. Under such conditions, we observed the decay of hexagonal order with the concomitant formation of short chains and percolated networks of chains coexisting with free colloids. In order to describe and investigate these systems theoretically, we developed a coarse-grained model of a binary mixture of patchy and nonpatchy particles with the ratio of patchy and nonpatchy colloids as the order parameter. Combining genetic algorithms with Monte Carlo simulations, we optimized the model parameters and quantitatively reproduced the experimentally observed sequence of colloidal structures. The results offer new insight into the anisotropy induced by the many-body effects. At the same time, they allow for a very efficient description of the system by means of a pairwise-additive Hamiltonian, whereupon the original, one-component system features a two-component mixture of isotropic and patchy colloids.
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Affiliation(s)
- Kathrin Müller
- Institute of Complex Systems: Theoretical Soft Matter and Biophysics, Forschungszentrum Jülich , Wilhelm-Johnen-Straße, 52428 Jülich, Germany
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15
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16
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Gog JR, Murcia A, Osterman N, Restif O, McKinley TJ, Sheppard M, Achouri S, Wei B, Mastroeni P, Wood JLN, Maskell DJ, Cicuta P, Bryant CE. Dynamics of Salmonella infection of macrophages at the single cell level. J R Soc Interface 2012; 9:2696-707. [PMID: 22552918 PMCID: PMC3427505 DOI: 10.1098/rsif.2012.0163] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Salmonella enterica causes a range of diseases. Salmonellae are intracellular parasites of macrophages, and the control of bacteria within these cells is critical to surviving an infection. The dynamics of the bacteria invading, surviving, proliferating in and killing macrophages are central to disease pathogenesis. Fundamentally important parameters, however, such as the cellular infection rate, have not previously been calculated. We used two independent approaches to calculate the macrophage infection rate: mathematical modelling of Salmonella infection experiments, and analysis of real-time video microscopy of infection events. Cells repeatedly encounter salmonellae, with the bacteria often remain associated with the macrophage for more than ten seconds. Once Salmonella encounters a macrophage, the probability of that bacterium infecting the cell is remarkably low: less than 5%. The macrophage population is heterogeneous in terms of its susceptibility to the first infection event. Once infected, a macrophage can undergo further infection events, but these reinfection events occur at a lower rate than that of the primary infection.
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Affiliation(s)
- Julia R Gog
- Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 0WA, UK
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17
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Vilfan M, Kokot G, Vilfan A, Osterman N, Kavčič B, Poberaj I, Babič D. Analysis of fluid flow around a beating artificial cilium. Beilstein J Nanotechnol 2012; 3:163-71. [PMID: 22428106 PMCID: PMC3304323 DOI: 10.3762/bjnano.3.16] [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] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2011] [Accepted: 01/31/2012] [Indexed: 05/07/2023]
Abstract
Biological cilia are found on surfaces of some microorganisms and on surfaces of many eukaryotic cells where they interact with the surrounding fluid. The periodic beating of the cilia is asymmetric, resulting in directed swimming of unicellular organisms or in generation of a fluid flow above a ciliated surface in multicellular ones. Following the biological example, externally driven artificial cilia have recently been successfully implemented as micropumps and mixers. However, biomimetic systems are useful not only in microfluidic applications, but can also serve as model systems for the study of fundamental hydrodynamic phenomena in biological samples. To gain insight into the basic principles governing propulsion and fluid pumping on a micron level, we investigated hydrodynamics around one beating artificial cilium. The cilium was composed of superparamagnetic particles and driven along a tilted cone by a varying external magnetic field. Nonmagnetic tracer particles were used for monitoring the fluid flow generated by the cilium. The average flow velocity in the pumping direction was obtained as a function of different parameters, such as the rotation frequency, the asymmetry of the beat pattern, and the cilium length. We also calculated the velocity field around the beating cilium by using the analytical far-field expansion. The measured average flow velocity and the theoretical prediction show an excellent agreement.
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Affiliation(s)
- Mojca Vilfan
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
| | - Gašper Kokot
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
| | - Andrej Vilfan
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
| | - Natan Osterman
- J. Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
| | - Blaž Kavčič
- LPKF Laser & Elektronika d.o.o, Polica 33, 4202 Naklo, Slovenia
| | - Igor Poberaj
- Department of Physics, Jadranska 19, University of Ljubljana, 1000 Ljubljana, Slovenia
| | - Dušan Babič
- Department of Physics, Jadranska 19, University of Ljubljana, 1000 Ljubljana, Slovenia
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Kokot G, Vilfan M, Osterman N, Vilfan A, Kavčič B, Poberaj I, Babič D. Measurement of fluid flow generated by artificial cilia. Biomicrofluidics 2011; 5:34103-341039. [PMID: 22662034 PMCID: PMC3364822 DOI: 10.1063/1.3608139] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2011] [Accepted: 06/02/2011] [Indexed: 05/23/2023]
Abstract
We observed and measured the fluid flow that was generated by an artificial cilium. The cilium was composed of superparamagnetic microspheres, in which magnetic dipole moments were induced by an external magnetic field. The interaction between the dipole moments resulted in formation of long chains-cilia, and the same external magnetic field was also used to drive the cilia in a periodic manner. Asymmetric periodic motion of the cilium resulted in generation of fluid flow and net pumping of the surrounding fluid. The flow and pumping performance were closely monitored by introducing small fluorescent tracer particles into the system. By detecting their motion, the fluid flow around an individual cilium was mapped and the flow velocities measured. We confirm that symmetric periodic beating of one cilium results in vortical motion only, whereas asymmetry is required for additional translational motion. We determine the effect of asymmetry on the pumping performance of a cilium, verify the theoretically predicted optimal pumping conditions, and determine the fluid behaviour around a linear array of three neighbouring cilia. In this case, the contributions of neighbouring cilia enhance the maximal flow velocity compared with a single cilium and contribute to a more uniform translational flow above the surface.
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19
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Osterman N, Kotar J, Terentjev EM, Cicuta P. Relaxation kinetics of stretched disclination lines in a nematic liquid crystal. Phys Rev E Stat Nonlin Soft Matter Phys 2010; 81:061701. [PMID: 20866426 DOI: 10.1103/physreve.81.061701] [Citation(s) in RCA: 6] [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: 02/09/2010] [Indexed: 05/29/2023]
Abstract
The dynamics of disclination defect lines in a nematic liquid crystal are measured experimentally and considered theoretically. An optical trap is used to deform the line, enabling the previously unexplored regime of large deformation to be accessed. The relaxation follows a linear decay at large amplitude, crossing over into the well understood exponential decay at small amplitude. Both regimes can be described by simple theoretical arguments. The crossover point is well described by the theory, but the experiments show a faster than expected dynamics, indicating that the effective viscosity in the models is overestimated.
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Affiliation(s)
- Natan Osterman
- Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK.
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20
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Osterman N, Poberaj I, Dobnikar J, Frenkel D, Ziherl P, Babić D. Field-induced self-assembly of suspended colloidal membranes. Phys Rev Lett 2009; 103:228301. [PMID: 20366126 DOI: 10.1103/physrevlett.103.228301] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2009] [Indexed: 05/29/2023]
Abstract
We report experiments that probe the self-assembly of micrometer-size colloids into one-particle-thick, robust, and self-healing membranes. In a magic-angle precessing magnetic field, superparamagnetic spheres experience isotropic pair attraction similar to the van der Waals force between atoms. But the many-body polarization interactions among them steer an ordered aggregation pathway consisting of growth of short chains, cross-linking and network formation, network coarsening, and consolidation of membrane patches. This generic aggregation scenario can be induced in any particles of large enough susceptibility.
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Affiliation(s)
- N Osterman
- Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana, Slovenia
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21
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Vilfan M, Osterman N, Copic M, Ravnik M, Zumer S, Kotar J, Babic D, Poberaj I. Confinement effect on interparticle potential in nematic colloids. Phys Rev Lett 2008; 101:237801. [PMID: 19113594 DOI: 10.1103/physrevlett.101.237801] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/09/2008] [Indexed: 05/27/2023]
Abstract
We studied the confinement effect on the interaction force in nematic liquid crystal colloids with spherical particles inducing planar anchoring. Using magneto-optical tweezers, we measured the spatial dependence of the quadrupolar structural interparticle force over 4 orders of magnitude. For small separations, the interparticle potential follows the power law, whereas for separations larger than the sample thickness, it decreases exponentially with the decay length proportional to the sample thickness. Experimental results are reproduced by using the Landau-de Gennes free-energy minimization approach.
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Affiliation(s)
- Mojca Vilfan
- J. Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
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22
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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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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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Osterman N, Babic D, Poberaj I, Dobnikar J, Ziherl P. Observation of condensed phases of quasiplanar core-softened colloids. Phys Rev Lett 2007; 99:248301. [PMID: 18233495 DOI: 10.1103/physrevlett.99.248301] [Citation(s) in RCA: 33] [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] [Subscribe] [Scholar Register] [Received: 07/25/2007] [Indexed: 05/25/2023]
Abstract
We experimentally study the condensed phases of repelling core-softened spheres in two dimensions. The dipolar pair repulsion between superparamagnetic spheres trapped in a thin cell is induced by a transverse magnetic field and softened by suitably adjusting the cell thickness. We scan a broad density range and we materialize a large part of the theoretically predicted phases in systems of core-softened particles, including expanded and close-packed hexagonal, square, chainlike, stripe or labyrinthine, and honeycomb phase. Further insight into their structure is provided by Monte Carlo simulations.
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Affiliation(s)
- N Osterman
- Department of Physics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana, Slovenia
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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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26
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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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Kotar J, Vilfan M, Osterman N, Babic D, Copic M, Poberaj I. Interparticle potential and drag coefficient in nematic colloids. Phys Rev Lett 2006; 96:207801. [PMID: 16803208 DOI: 10.1103/physrevlett.96.207801] [Citation(s) in RCA: 12] [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: 02/03/2006] [Indexed: 05/10/2023]
Abstract
Magneto-optic tweezers were used for measurements of liquid-crystal-mediated forces between spherical beads with tangential anchoring in thin nematic samples. Repulsive force, which results from the quadrupolar symmetry of defects around the immersed beads, decreases proportionally to 1/x6, with x being the bead separation. The velocity with which the particles are pushed apart also follows the same separation dependence. We thus find the effective drag coefficient gamma(eff) independent of x for surface-to-surface distances as small as 10% of the bead diameter.
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Affiliation(s)
- Jurij Kotar
- Department of Physics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana, Slovenia
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28
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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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29
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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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