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Sergan V, Sergan T, Dozov I, Joly S, Voss R. Orientational order induced by a polymer network in the isotropic phase of liquid crystal. Phys Rev E 2020; 101:052705. [PMID: 32575175 DOI: 10.1103/physreve.101.052705] [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] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Accepted: 03/16/2020] [Indexed: 11/07/2022]
Abstract
We studied the paranematic ordering induced by a polymer network in the isotropic phase of a liquid crystal (LC) that occurs in polymer-stabilized cells with bend configuration of the LC director (π cells) fabricated via photopolymerization of photoreactive monomer RM 82 added in small concentrations (3-5 wt %) to a nematic LC [4-cyano-4'-pentylbiphenyl (5CB)] when low voltage was applied across the cell. The polymer network formed in the nematic phase of the LC consists of fine fibrils that are aligned along the LC director and thus mirror the bend deformation of the LC at the time of polymerization. When heated to temperatures above the nematic-to-isotropic (N-I) phase transition such highly ordered polymer network anchors LC molecules providing ordering of the LC around the fibrils which results in unusually high optical retardation of the cell, R_{cell}. We present a theoretical model that relates R_{cell} to the degree of order of the fibrils, the anchoring energy of the LC molecules on the surface of the polymer fibrils, and the fibril radius r_{0}. Fitting of the experimental R_{cell}(T) curves with the developed model reveals correlation of r_{0} with the nematic correlation length ξ_{0} which characterizes penetration of the nematic order in the isotropic phase of the LC. Accepting ξ_{0} as a material constant of about 1 nm leads to a very small radius of the fibrils, r_{0}∼1nm, which is also supported by other reported experimental data. High optical retardation and fast electro-optical response of the cells at the temperatures deep into the isotropic phase point toward the enhancement of the polymer-induced paranematic order by a well-oriented layer of LC molecules that are absorbed on the surface of fibrils. Application of high voltage at the isotropic phase temperatures results in high variations of the optical retardation of the cells. Characteristic on and off response times were about 10-100 μs, independent of the cell gap. Combination of large voltage-driven changes of the optical retardation occurring in the low-viscosity isotropic state with switching times that are at least two orders of magnitude shorter than the typical relaxation times of the cells operating in the nematic phase make such polymer-stabilized π cells very promising for application in fast electro-optical switches and light modulators.
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Affiliation(s)
- V Sergan
- California State University, Sacramento, 6000 J Street, Sacramento, California 95608, USA
| | - T Sergan
- California State University, Sacramento, 6000 J Street, Sacramento, California 95608, USA
| | - I Dozov
- PSC, Université de Picardie Jules Verne, 80039 Amiens, France
| | - S Joly
- PEDL Laboratory, PSA Technical Center, Route de Gisy, Case courrier VV009, 78943 Vélizy-Villacoublay, France
| | - R Voss
- California State University, Sacramento, 6000 J Street, Sacramento, California 95608, USA
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Reznikov M, Andrienko D, Boychuk V, Bubnov A, Dolgov L, Dozov I, Davidson P, Gabovich A, Hegmann T, Ilchishin I, Karapinar R, Korniychuk P, Stepanchikov D, Tkachenko O, Kurioz Y, Manevich M, Negriyko A, Parka J, Pergamenshchik V, Rosenblatt C, Singer K, Terenetskaya I, Vashchenko V, Vasnetsov M, Soskin M, Wolinski T, Yaroshchuk O. Recollections of Professor Yuriy Reznikov. J Mol Liq 2018. [DOI: 10.1016/j.molliq.2018.08.127] [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: 10/28/2022]
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Sergan T, Dozov I, Sergan V, Voss R. Comparative study of the anchoring strength of reactive mesogens and industrial polyimides used for the alignment of liquid crystals. Phys Rev E 2017; 95:052706. [PMID: 28618526 DOI: 10.1103/physreve.95.052706] [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] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2017] [Indexed: 11/07/2022]
Abstract
We measured the Rapini-Papoular polar anchoring strength coefficient W for 4^{'}-pentyl-4-cyanobiphenyl (5CB) on alignment layers formed by the reactive mesogen photopolymers RM 257, RM 82, and RM 84 [4,4^{'}-bis(acryloyl)biphenyl] (by Merck). These materials are commonly used for the photostabilization of the liquid crystal (LC) director in the bulk as well as at the surface of the LC layer via the formation of a loose polymer network that captures the director orientation. We developed a method of fabrication of alignment layers from these polymers, and estimated W from the measurements of the optical retardation as a function of applied voltage in uniformly aligned cells. We found that RM 257 yielded W of about 6×10^{-4}J/m^{2}, whereas RM 82 and RM 84 provided anchoring strengths of about 2×10^{-4} and 4×10^{-4}J/m^{2}, respectively. Subsequent heating of the sample either destroyed the alignment layer, or substantially decreased W to about 1×10^{-4}J/m^{2}, which was comparable to the anchoring strength of weakly rubbed commercial polyimides.
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Affiliation(s)
- T Sergan
- California State University, Sacramento, 6000 J Street, Sacramento, California 95819, USA
| | - I Dozov
- Université de Picardie Jules Verne, 80039 Amiens, France
| | - V Sergan
- California State University, Sacramento, 6000 J Street, Sacramento, California 95819, USA
| | - R Voss
- California State University, Sacramento, 6000 J Street, Sacramento, California 95819, USA
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Meyer C, Rabette C, Gisse P, Antonova K, Dozov I. DH(*) in chiral smectics under electric field. Eur Phys J E Soft Matter 2016; 39:76. [PMID: 27465656 DOI: 10.1140/epje/i2016-16076-7] [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: 05/04/2016] [Accepted: 07/15/2016] [Indexed: 06/06/2023]
Abstract
The behavior of double helices (DH(*) formed in the temperature interval N(*) -SmA(*) in compounds of non-chiral liquid crystals doped with chiral molecules was investigated. Two different systems presenting left-handed and right-handed chirality were studied. A statistics of the handedness of the DH(*) revealed a correlation with the mixture chirality, as predicted theoretically in C. Meyer, Yu. A. Nastishin, M. Kleman, Phys. Rev. E 82, 031704 (2010). By applying a gradually increasing AC electric field, one can observe the shrinking of the cylinder circumscribing the DH(*) . This shrink is accompanied by a reduction of the DH(*) 's pitch. This effect was similar to the one produced by the decrease of temperature in the absence of the field.
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Affiliation(s)
- C Meyer
- Laboratoire de Physique des Systèmes Complexes, Université de Picardie Jules Verne, 33 rue Saint-Leu, 80039, Amiens, France.
| | - C Rabette
- Laboratoire de Physique des Systèmes Complexes, Université de Picardie Jules Verne, 33 rue Saint-Leu, 80039, Amiens, France
| | - P Gisse
- Laboratoire de Physique des Systèmes Complexes, Université de Picardie Jules Verne, 33 rue Saint-Leu, 80039, Amiens, France
| | - K Antonova
- Laboratoire de Physique des Systèmes Complexes, Université de Picardie Jules Verne, 33 rue Saint-Leu, 80039, Amiens, France
- Institute of Solid State Physics, Bulgarian Academy of Sciences, Tzarigradsko Chaussee 72, 1784, Sofia, Bulgaria
| | - I Dozov
- Laboratoire de Physique des Systèmes Complexes, Université de Picardie Jules Verne, 33 rue Saint-Leu, 80039, Amiens, France
- Laboratoire de Physique des Solides, UMR 8502 CNRS, Université Paris-Sud, Bât. 510, 91405, Orsay Cédex, France
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Abstract
The recently discovered twist-bend nematic phase of achiral bent-shaped molecules, NTB, has a doubly degenerate ground-state with a periodically modulated heliconical structure and unusual distortion elasticity, the theoretical description of which is still debated. We show that the NTB phase has the same macroscopic symmetry as another periodic mesophase, the chiral smectic-A, SmA*. Based on this NTB/SmA* analogy, we develop a coarse-grained elastic model for the NTB phase. Adopting one of the existing microscopic NTB elastic models, we calculate the coarse-grained elastic constants, coherence and penetration lengths in terms of a few Frank-like nematic elastic coefficients that can be measured in macroscopic experiments. The same coarse-grained approach, applied to different local elastic models, may provide an efficient experimental test of their validity. We show that the anisotropy of the NTB coarse-grained elasticity is opposite to that of the SmA*, leading probably to different configurations of some of the defects of the "layered" NTB structure. Moreover, we argue that the intrinsic chiral frustration of the NTB phase may be resolved by penetration of the twist field into the bulk through a network of screw dislocations of the NTB pseudo-layers, resulting in a twist-bend analogue of the twist grain boundary phase TGBA.
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Affiliation(s)
- C Meyer
- Physique des Systèmes Complexes, Université de Picardie Jules Verne, 80039 Amiens, France.
| | - I Dozov
- Physique des Systèmes Complexes, Université de Picardie Jules Verne, 80039 Amiens, France. and Laboratoire de Physique des Solides, UMR 8502 CNRS-Université Paris-Sud, Bât. 510, 91405 Orsay Cedex, France
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Meyer C, Luckhurst GR, Dozov I. Flexoelectrically driven electroclinic effect in the twist-bend nematic phase of achiral molecules with bent shapes. Phys Rev Lett 2013; 111:067801. [PMID: 23971614 DOI: 10.1103/physrevlett.111.067801] [Citation(s) in RCA: 58] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2013] [Indexed: 06/02/2023]
Abstract
We extend the twist-bend nematic (N(TB)) model to describe the electro-optics of this novel phase. We predict an electroclinic effect (ECE) subject to a dc electric field E applied perpendicular to the helix axis or wave vector q, with rotation of the N(TB) optic axis around E. This linear effect, with its flexoelectric origin, is a close analog to the electro-optic effects observed for chiral liquid crystals. However, in nematics composed of achiral molecules having a bent shape, it is the electro-optic signature of the N(TB) phase. We test our model experimentally in the low-temperature nematic phase of the odd liquid crystal dimer, CB7CB, with its molecules having, on average, a bent shape. The ECE measurements confirm the previously proposed twist-bend nematic structure of this phase, with its broken chiral symmetry, extremely short (<10 nm) doubly degenerate pitch and ultrafast, submicrosecond response times.
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Affiliation(s)
- C Meyer
- Physique des Systèmes Complexes, Université de Picardie Jules Verne, 80039 Amiens, France
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Dozov I, Paineau E, Davidson P, Antonova K, Baravian C, Bihannic I, Michot LJ. Electric-Field-Induced Perfect Anti-Nematic Order in Isotropic Aqueous Suspensions of a Natural Beidellite Clay. J Phys Chem B 2011; 115:7751-65. [DOI: 10.1021/jp201201x] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Affiliation(s)
- I. Dozov
- Laboratoire de Physique des Solides, UMR 8502 CNRS−Université Paris-Sud, Bât. 510, 91405 Orsay Cedex, France
| | - E. Paineau
- Laboratoire Environnement et Minéralurgie, Nancy University CNRS-INPL UMR 7569, BP40, 54501 Vandœuvre Cedex, France
| | - P. Davidson
- Laboratoire de Physique des Solides, UMR 8502 CNRS−Université Paris-Sud, Bât. 510, 91405 Orsay Cedex, France
| | - K. Antonova
- Institute of Solid State Physics, Bulgarian Academy of Sciences, Tzarigradsko Chaussee 72, 1784 Sofia, Bulgaria
| | - C. Baravian
- Laboratoire d’Energétique et de Mécanique Théorique et Appliquée, Nancy University UMR 7563 CNRS-INPL-UHP, 2, Avenue de la Forêt de Haye, BP160 54504 Vandœuvre Cedex, France
| | - I. Bihannic
- Laboratoire Environnement et Minéralurgie, Nancy University CNRS-INPL UMR 7569, BP40, 54501 Vandœuvre Cedex, France
| | - L. J. Michot
- Laboratoire Environnement et Minéralurgie, Nancy University CNRS-INPL UMR 7569, BP40, 54501 Vandœuvre Cedex, France
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van den Pol E, Verhoeff AA, Lupascu A, Diaconeasa MA, Davidson P, Dozov I, Kuipers BWM, Thies-Weesie DME, Vroege GJ. Magnetic-field-induced nematic-nematic phase separation and droplet formation in colloidal goethite. J Phys Condens Matter 2011; 23:194108. [PMID: 21525548 DOI: 10.1088/0953-8984/23/19/194108] [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] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
We demonstrate the suitability of polarization microscopy to study the recently discovered (parallel) nematic-(perpendicular) nematic phase separation. This novel type of phase transition is induced by applying an external magnetic field to a nematic liquid crystal of boardlike colloidal goethite and is due to an interplay between the intrinsic magnetic properties of goethite and the collective effect of liquid crystal formation. It is shown that the intense ochre colour of goethite does not preclude the use of polarization microscopy and interference colours, and that dichroism can give valuable qualitative information on the nature of the phases, their anchoring and their sedimentation and order parameter profiles. We also apply these techniques to study 'nematic-nematic tactoids': nematic droplets sedimenting within a nematic medium with mutually perpendicular orientations.
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Affiliation(s)
- E van den Pol
- Van' t Hoff Laboratory for Physical and Colloid Chemistry, Debye Institute for Nanomaterials Science, Utrecht University, Utrecht, The Netherlands
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Paineau E, Antonova K, Baravian C, Bihannic I, Davidson P, Dozov I, Impéror-Clerc M, Levitz P, Madsen A, Meneau F, Michot LJ. Liquid-Crystalline Nematic Phase in Aqueous Suspensions of a Disk-Shaped Natural Beidellite Clay. J Phys Chem B 2009; 113:15858-69. [DOI: 10.1021/jp908326y] [Citation(s) in RCA: 118] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- E. Paineau
- Laboratoire Environnement et Minéralurgie, Nancy University CNRS-INPL UMR 7569, BP40 54501 Vandœuvre Cedex France, Institute of Solid State Physics, Bulgarian Academy of Sciences, Boulevard Tzarigradsko Chaussee 72, Sofia, 1784, Bulgaria, Laboratoire d’Energétique et de Mécanique Théorique et Appliquée, Nancy University UMR 7563 CNRS-INPL-UHP, 2, Avenue de la Forêt de Haye, BP160 54504 Vandœuvre Cedex, France, Laboratoire de Physique des Solides, UMR 8502 CNRS-Université Paris-Sud Bât 510 91405 Orsay
| | - K. Antonova
- Laboratoire Environnement et Minéralurgie, Nancy University CNRS-INPL UMR 7569, BP40 54501 Vandœuvre Cedex France, Institute of Solid State Physics, Bulgarian Academy of Sciences, Boulevard Tzarigradsko Chaussee 72, Sofia, 1784, Bulgaria, Laboratoire d’Energétique et de Mécanique Théorique et Appliquée, Nancy University UMR 7563 CNRS-INPL-UHP, 2, Avenue de la Forêt de Haye, BP160 54504 Vandœuvre Cedex, France, Laboratoire de Physique des Solides, UMR 8502 CNRS-Université Paris-Sud Bât 510 91405 Orsay
| | - C. Baravian
- Laboratoire Environnement et Minéralurgie, Nancy University CNRS-INPL UMR 7569, BP40 54501 Vandœuvre Cedex France, Institute of Solid State Physics, Bulgarian Academy of Sciences, Boulevard Tzarigradsko Chaussee 72, Sofia, 1784, Bulgaria, Laboratoire d’Energétique et de Mécanique Théorique et Appliquée, Nancy University UMR 7563 CNRS-INPL-UHP, 2, Avenue de la Forêt de Haye, BP160 54504 Vandœuvre Cedex, France, Laboratoire de Physique des Solides, UMR 8502 CNRS-Université Paris-Sud Bât 510 91405 Orsay
| | - I. Bihannic
- Laboratoire Environnement et Minéralurgie, Nancy University CNRS-INPL UMR 7569, BP40 54501 Vandœuvre Cedex France, Institute of Solid State Physics, Bulgarian Academy of Sciences, Boulevard Tzarigradsko Chaussee 72, Sofia, 1784, Bulgaria, Laboratoire d’Energétique et de Mécanique Théorique et Appliquée, Nancy University UMR 7563 CNRS-INPL-UHP, 2, Avenue de la Forêt de Haye, BP160 54504 Vandœuvre Cedex, France, Laboratoire de Physique des Solides, UMR 8502 CNRS-Université Paris-Sud Bât 510 91405 Orsay
| | - P. Davidson
- Laboratoire Environnement et Minéralurgie, Nancy University CNRS-INPL UMR 7569, BP40 54501 Vandœuvre Cedex France, Institute of Solid State Physics, Bulgarian Academy of Sciences, Boulevard Tzarigradsko Chaussee 72, Sofia, 1784, Bulgaria, Laboratoire d’Energétique et de Mécanique Théorique et Appliquée, Nancy University UMR 7563 CNRS-INPL-UHP, 2, Avenue de la Forêt de Haye, BP160 54504 Vandœuvre Cedex, France, Laboratoire de Physique des Solides, UMR 8502 CNRS-Université Paris-Sud Bât 510 91405 Orsay
| | - I. Dozov
- Laboratoire Environnement et Minéralurgie, Nancy University CNRS-INPL UMR 7569, BP40 54501 Vandœuvre Cedex France, Institute of Solid State Physics, Bulgarian Academy of Sciences, Boulevard Tzarigradsko Chaussee 72, Sofia, 1784, Bulgaria, Laboratoire d’Energétique et de Mécanique Théorique et Appliquée, Nancy University UMR 7563 CNRS-INPL-UHP, 2, Avenue de la Forêt de Haye, BP160 54504 Vandœuvre Cedex, France, Laboratoire de Physique des Solides, UMR 8502 CNRS-Université Paris-Sud Bât 510 91405 Orsay
| | - M. Impéror-Clerc
- Laboratoire Environnement et Minéralurgie, Nancy University CNRS-INPL UMR 7569, BP40 54501 Vandœuvre Cedex France, Institute of Solid State Physics, Bulgarian Academy of Sciences, Boulevard Tzarigradsko Chaussee 72, Sofia, 1784, Bulgaria, Laboratoire d’Energétique et de Mécanique Théorique et Appliquée, Nancy University UMR 7563 CNRS-INPL-UHP, 2, Avenue de la Forêt de Haye, BP160 54504 Vandœuvre Cedex, France, Laboratoire de Physique des Solides, UMR 8502 CNRS-Université Paris-Sud Bât 510 91405 Orsay
| | - P. Levitz
- Laboratoire Environnement et Minéralurgie, Nancy University CNRS-INPL UMR 7569, BP40 54501 Vandœuvre Cedex France, Institute of Solid State Physics, Bulgarian Academy of Sciences, Boulevard Tzarigradsko Chaussee 72, Sofia, 1784, Bulgaria, Laboratoire d’Energétique et de Mécanique Théorique et Appliquée, Nancy University UMR 7563 CNRS-INPL-UHP, 2, Avenue de la Forêt de Haye, BP160 54504 Vandœuvre Cedex, France, Laboratoire de Physique des Solides, UMR 8502 CNRS-Université Paris-Sud Bât 510 91405 Orsay
| | - A. Madsen
- Laboratoire Environnement et Minéralurgie, Nancy University CNRS-INPL UMR 7569, BP40 54501 Vandœuvre Cedex France, Institute of Solid State Physics, Bulgarian Academy of Sciences, Boulevard Tzarigradsko Chaussee 72, Sofia, 1784, Bulgaria, Laboratoire d’Energétique et de Mécanique Théorique et Appliquée, Nancy University UMR 7563 CNRS-INPL-UHP, 2, Avenue de la Forêt de Haye, BP160 54504 Vandœuvre Cedex, France, Laboratoire de Physique des Solides, UMR 8502 CNRS-Université Paris-Sud Bât 510 91405 Orsay
| | - F. Meneau
- Laboratoire Environnement et Minéralurgie, Nancy University CNRS-INPL UMR 7569, BP40 54501 Vandœuvre Cedex France, Institute of Solid State Physics, Bulgarian Academy of Sciences, Boulevard Tzarigradsko Chaussee 72, Sofia, 1784, Bulgaria, Laboratoire d’Energétique et de Mécanique Théorique et Appliquée, Nancy University UMR 7563 CNRS-INPL-UHP, 2, Avenue de la Forêt de Haye, BP160 54504 Vandœuvre Cedex, France, Laboratoire de Physique des Solides, UMR 8502 CNRS-Université Paris-Sud Bât 510 91405 Orsay
| | - L. J. Michot
- Laboratoire Environnement et Minéralurgie, Nancy University CNRS-INPL UMR 7569, BP40 54501 Vandœuvre Cedex France, Institute of Solid State Physics, Bulgarian Academy of Sciences, Boulevard Tzarigradsko Chaussee 72, Sofia, 1784, Bulgaria, Laboratoire d’Energétique et de Mécanique Théorique et Appliquée, Nancy University UMR 7563 CNRS-INPL-UHP, 2, Avenue de la Forêt de Haye, BP160 54504 Vandœuvre Cedex, France, Laboratoire de Physique des Solides, UMR 8502 CNRS-Université Paris-Sud Bât 510 91405 Orsay
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Faget L, Lamarque-Forget S, Martinot-Lagarde P, Auroy P, Dozov I. Anticonical anchoring and surface transitions in a nematic liquid crystal. Phys Rev E Stat Nonlin Soft Matter Phys 2006; 74:050701. [PMID: 17279869 DOI: 10.1103/physreve.74.050701] [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] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/03/2006] [Indexed: 05/13/2023]
Abstract
Recent works reported planar and conical azimuthally degenerated nematic anchorings. Here we predict an additional "anticonical" degenerated anchoring. Its energy presents two minima, parallel and perpendicular to the substrate plane, separated by a conical energy barrier. We realize this bistable anchoring on a grafted polymer brush and we observe temperature-driven transitions between the conical, planar, and anticonical degenerated anchorings. Under electric field we break the anticonical anchoring and switch between its bistable states.
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Affiliation(s)
- L Faget
- Nemoptic, Parc du Mérantais, 1 rue Guynemer, F-78114 Magny-les-Hameaux, France
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Affiliation(s)
- H. Dreyfus-lambez
- a Lab. de Physique des Solides , Univ. Paris-Sud , Bǎt. 510, 91405 , Orsay , cedex , France
| | - D. Stoenescu
- a Lab. de Physique des Solides , Univ. Paris-Sud , Bǎt. 510, 91405 , Orsay , cedex , France
- b INCDFM-Mãgurele , POBox MG7, 76900 , Bucharest , Romania
| | - I. Dozov
- a Lab. de Physique des Solides , Univ. Paris-Sud , Bǎt. 510, 91405 , Orsay , cedex , France
- c Institue of Solid State Physics , 72 blvd Tsarigrasko Chaussee, 1784 , Sofia , Bulgaria
| | - Ph. Martinot-Lagarde
- a Lab. de Physique des Solides , Univ. Paris-Sud , Bǎt. 510, 91405 , Orsay , cedex , France
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Stoenescu DN, Nguyen HT, Barois P, Navailles L, Nobili M, Martinot-Lagarde P, Dozov I. Optical Studies of Chiral Mesophases in Sandwich Cells with Planar Degenerated Anchoring. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/10587250108028287] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- D. N. Stoenescu
- a Laboratoire de Physique des Solides, Université Paris-Sud , Bǎt. 510, 91405 , ORSAY , France
| | - H. T. Nguyen
- b Centre de Recherche Paul Pascal , Av. A. Schweitzer, 33600 , PESSAC , France
| | - P. Barois
- b Centre de Recherche Paul Pascal , Av. A. Schweitzer, 33600 , PESSAC , France
| | - L. Navailles
- c Université Montpellier II , Pl. E. Bataillon, 34095 , MONTPELLIER Cedex , 5 , France
| | - M. Nobili
- c Université Montpellier II , Pl. E. Bataillon, 34095 , MONTPELLIER Cedex , 5 , France
| | - Ph. Martinot-Lagarde
- a Laboratoire de Physique des Solides, Université Paris-Sud , Bǎt. 510, 91405 , ORSAY , France
| | - I. Dozov
- a Laboratoire de Physique des Solides, Université Paris-Sud , Bǎt. 510, 91405 , ORSAY , France
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Stoenescu DN, Dozov I, Martinot-Lagarde P. Long-Time Behavior of the Azimuthal Anchoring Strength and Easy Axis Gliding of Nematic Liquid Crystal. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/10587250008023294] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Affiliation(s)
- D. N. Stoenescu
- a Laboratoire de Physique des Solides , Université Paris-Sud , 91405 , Orsay , France
- b INCDFM - Mãgurele , POBox MG7, 76900 , Bucharest , Romania
| | - I. Dozov
- a Laboratoire de Physique des Solides , Université Paris-Sud , 91405 , Orsay , France
- c Institute of Solid State Physics , 72 blvd.Tsarigradsko Chaussee, 1784 , Sofia , Bulgaria
| | - Ph. Martinot-Lagarde
- a Laboratoire de Physique des Solides , Université Paris-Sud , 91405 , Orsay , France
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Affiliation(s)
- D. N. Stoenescu
- a Laboratoire de Physique des Solides , Université Paris-Sud , 91405 , Orsay , France
- b National Institute of Material Physics , CP. MG7, 76900 , Bucharest , Romania
| | - Ph. Martinot-Lagarde
- a Laboratoire de Physique des Solides , Université Paris-Sud , 91405 , Orsay , France
| | - I. Dozov
- a Laboratoire de Physique des Solides , Université Paris-Sud , 91405 , Orsay , France
- c Institute of Solid State Physics , Bvd. Lenin 72, Sofia , Bulgaria
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Kirov N, Dozov I, Jordanova J, Fontana M, Hadjichristov G. Elastic incoherent neutron scattering of rotational and translational dynamics in liquid crystals. J Mol Struct 2006. [DOI: 10.1016/j.molstruc.2005.09.040] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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Lemaire BJ, Davidson P, Petermann D, Panine P, Dozov I, Stoenescu D, Jolivet JP. Physical properties of aqueous suspensions of goethite (alpha-FeOOH) nanorods. Part II: In the nematic phase. Eur Phys J E Soft Matter 2004; 13:309-319. [PMID: 15103524 DOI: 10.1140/epje/i2003-10079-5] [Citation(s) in RCA: 24] [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: 05/24/2023]
Abstract
At volume fractions larger than 8.5%, aqueous suspensions of lath-like goethite (alpha-FeOOH) nanorods form a lyotropic nematic phase. In this article, we first discuss the nematic ordering within statistical-physics models of the isotropic/nematic phase transition. We then describe the influence of a magnetic field on the nematic phase. Because the nanorods bear permanent magnetic moments, the nematic suspensions have dipolar order and very low Frederiks thresholds. Moreover, the nematic phase aligns parallel to a small magnetic field but realigns perpendicular to a high field because of a competition between the permanent moments of the nanorods and their negative anisotropy of magnetic susceptibility. This magneto-optical study of the nematic phase is completely consistent with that of the isotropic phase of the same suspensions published in Part I (this issue, p. 291). Besides, we demonstrate the field-induced biaxiality of a nematic single domain aligned perpendicular to the field. We also describe here preliminary experiments where an a.c. electric field is applied to the nematic phase. Both field amplitude and frequency were found to control the alignment direction and homeotropic-to-planar alignment transitions were observed. From this data, simple models were used to estimate some physical constants of the nematic phase.
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Affiliation(s)
- B J Lemaire
- Laboratoire de Physique des Solides, UMR CNRS 8502, Université Paris-Sud, 91405, Orsay, France
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Lemaire BJ, Davidson P, Ferré J, Jamet JP, Petermann D, Panine P, Dozov I, Jolivet JP. Physical properties of aqueous suspensions of goethite (alpha-FeOOH) nanorods. Part I: In the isotropic phase. Eur Phys J E Soft Matter 2004; 13:291-308. [PMID: 15103523 DOI: 10.1140/epje/i2003-10078-6] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Depending on volume fraction, aqueous suspensions of goethite (alpha-FeOOH) nanorods form a liquid-crystalline nematic phase (above 8.5%) or an isotropic liquid phase (below 5.5%). In this article, we investigate by small-angle X-ray scattering, magneto-optics, and magnetometry the influence of a magnetic field on the isotropic phase. After a brief description of the synthesis and characterisation of the goethite nanorod suspensions, we show that the disordered phase becomes very anisotropic under a magnetic field that aligns the particles. Moreover, we observe that the nanorods align parallel to a small field (< 350 mT), but realign perpendicular to a large enough field (> 350 mT). This phenomenon is interpreted as due to the competition between the influence of the nanorod permanent magnetic moment and a negative anisotropy of magnetic susceptibility. Our interpretation is supported by the behaviour of the suspensions in an alternating magnetic field. Finally, we propose a model that explains all experimental observations in a consistent way.
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Affiliation(s)
- B J Lemaire
- Laboratoire de Physique des Solides, UMR CNRS 8502, Université Paris-Sud, 91405, Orsay, France
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Martinot-Lagarde P, Dreyfus-Lambez H, Dozov I. Biaxial melting of the nematic order under a strong electric field. Phys Rev E Stat Nonlin Soft Matter Phys 2003; 67:051710. [PMID: 12786167 DOI: 10.1103/physreve.67.051710] [Citation(s) in RCA: 5] [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: 11/05/2002] [Indexed: 05/24/2023]
Abstract
We study the action of a strong electric field on a nematic, topologically stabilized with director n perpendicular to E. Above a threshold field the nematic order on the cell midplane is "melted" and rapidly reconstructed with n axially E. In a Landau-de Gennes model, we show that the observed transient "melted" state is a biaxial nematic and not an isotropic liquid.
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Affiliation(s)
- Ph Martinot-Lagarde
- Laboratoire de Physique des Solides, Université Paris-Sud, bat. 510, F-91405 Orsay, France
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Bogi A, Martinot-Lagarde P, Dozov I, Nobili M. Anchoring screening of defects interaction in a nematic liquid crystal. Phys Rev Lett 2002; 89:225501. [PMID: 12485079 DOI: 10.1103/physrevlett.89.225501] [Citation(s) in RCA: 11] [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: 03/24/2002] [Indexed: 05/24/2023]
Abstract
The relaxation dynamic of a dipole of +1/2 and -1/2 parallel disclination lines in a confined geometry is measured. The confinement and the planar anchoring conditions force the disclinations to be normal to the glass plates. In a first asymptotic regime, the direct elastic interaction between disclination is completely screened out by the anchoring energy. In a second regime, corresponding to the final annihilation steps, the dynamic follows the square-root law predicted by de Gennes for two isolated and parallel disclinations. The annihilation dynamic, in the asymptotic regime, is in good agreement with an elastic model based on an electrostatic analogy.
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Affiliation(s)
- A Bogi
- Groupe de Dynamique des Phases Condensées, CNRS-Université Montpellier II, Place E. Bataillon, France
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Lemaire BJ, Davidson P, Ferré J, Jamet JP, Panine P, Dozov I, Jolivet JP. Outstanding magnetic properties of nematic suspensions of goethite (alpha-FeOOH) nanorods. Phys Rev Lett 2002; 88:125507. [PMID: 11909477 DOI: 10.1103/physrevlett.88.125507] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/11/2001] [Indexed: 05/23/2023]
Abstract
Aqueous suspensions of goethite (alpha-FeOOH) nanorods form a mineral lyotropic nematic phase that aligns in a very low magnetic field (20 mT for samples 20 microm thick). The particles orient along the field direction at intensities smaller than 350 mT, but they reorient perpendicular to the field beyond 350 mT. This outstanding behavior is also observed in the isotropic phase which has a very strong magnetic-field induced birefringence that could be interesting for applications. We interpret these magnetic effects as resulting from a competition between a nanorod remanent magnetic moment and a negative anisotropy of its magnetic susceptibility.
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Affiliation(s)
- B J Lemaire
- Laboratoire de Physique des Solides, UMR CNRS 8502, Bâtiment 510, Université Paris-Sud, 91405 Orsay, France
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Ramdane OO, Auroy P, Forget S, Raspaud E, Martinot-Lagarde P, Dozov I. Memory-free conic anchoring of liquid crystals on a solid substrate. Phys Rev Lett 2000; 84:3871-3874. [PMID: 11019227 DOI: 10.1103/physrevlett.84.3871] [Citation(s) in RCA: 20] [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: 08/05/1999] [Indexed: 05/23/2023]
Abstract
We show that the anchoring memory of liquid crystals on solid substrates can be completely removed by grafting highly mobile polymer chains. Using grafted polystyrene, we obtain uniform, stable, and reproducible memory-free and conically degenerated anchoring of the nematic 5CB. The symmetry of the conic anchoring enables two different zenithal anchoring breakings, towards homeotropic and planar states. Under external torques we observe both of them, with weak thresholds.
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Affiliation(s)
- OO Ramdane
- Institut Curie, UMR 168, 11 rue Pierre et Marie Curie, F-75231 Paris Cedex 05, France
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Kirov N, Dozov I. Vibrational spectroscopy of rotational dynamics in aligned systems (stochastic and inertial regimes). J Mol Liq 1992. [DOI: 10.1016/0167-7322(92)80046-k] [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: 10/17/2022]
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Dozov I, Kirov N, Temkin S. Translational contribution to incoherent neutron scattering in anisotropic fluids - new theoretical approach. J Mol Liq 1992. [DOI: 10.1016/0167-7322(92)80001-x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Kirov N, Dozov I, Temkin S. Uncorrelated jumps model for orientational relaxation in ordered fluids. J Mol Liq 1991. [DOI: 10.1016/0167-7322(91)80015-v] [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: 10/18/2022]
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Fournier JB, Dozov I, Durand G. Surface frustration and texture instability in smectic-A liquid crystals. Phys Rev A 1990; 41:2252-2255. [PMID: 9903348 DOI: 10.1103/physreva.41.2252] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [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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Rosi B, Fontana MP, Dozov I, Kirov N. Molecular biaxiality and reorientational correlation functions in nematic phases: Infrared spectroscopy. Phys Rev A Gen Phys 1987; 36:2879-2884. [PMID: 9899193 DOI: 10.1103/physreva.36.2879] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Dozov I, Kirov N, Petroff B. Molecular biaxiality and reorientational correlation functions in nematic phases: Theory. Phys Rev A Gen Phys 1987; 36:2870-2878. [PMID: 9899192 DOI: 10.1103/physreva.36.2870] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [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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Kirov N, Dozov I, Fontana M, Rosi B. Vibrational bandshape analysis and inertial-stochastic molecular motion in anisotropic ordered fluids. ACTA ACUST UNITED AC 1987. [DOI: 10.1051/jphys:01987004803045700] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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Fontana MP, Rosi B, Kirov N, Dozov I. Molecular orientational motions in liquid crystals: A study by Raman and infrared band-shape analysis. Phys Rev A Gen Phys 1986; 33:4132-4142. [PMID: 9897154 DOI: 10.1103/physreva.33.4132] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [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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Barbero G, Dozov I, Palierne JF, Durand G. Order electricity and surface orientation in nematic liquid crystals. Phys Rev Lett 1986; 56:2056-2059. [PMID: 10032846 DOI: 10.1103/physrevlett.56.2056] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.1] [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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Kirov N, Dozov I, Fontana MP. Determination of orientational correlation functions in ordered fluids: Raman scattering. J Chem Phys 1985. [DOI: 10.1063/1.449866] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Dozov I, Kirov N, Fontana MP. Determination of reorientational correlation functions in ordered fluids: IR absorption spectroscopy. J Chem Phys 1984. [DOI: 10.1063/1.447966] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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