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Burylov S, Petrov D, Lacková V, Zakutanská K, Burylova N, Voroshilov A, Skosar V, Agresti F, Kopčanský P, Tomašovičová N. Ferromagnetic and antiferromagnetic liquid crystal suspensions: Experiment and theory. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2020.114467] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Reshetnyak VY, Pinkevych IP, Evans DR. Flexoelectro-optic effect and two-beam energy exchange in a hybrid photorefractive cholesteric cell with a short-pitch horizontal helix. Phys Rev E 2018; 97:062701. [PMID: 30011427 DOI: 10.1103/physreve.97.062701] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Indexed: 11/07/2022]
Abstract
We develop a theoretical model to describe two-beam energy exchange in a hybrid photorefractive cholesteric cell with a short-pitch helix oriented parallel to the cell substrates (so-called uniformly lying helix configuration). Weak and strong light beams incident on the hybrid cell interfere and induce a periodic space-charge field in the photorefractive substrate of the cell, which penetrates into the cholesteric liquid crystal (LC). Due to the flexoelectro-optic effect an interaction of the photorefractive field with the LC flexopolarization causes the spatially periodic modulation of the helix axis in the plane parallel to the cell substrates. Coupling of a weak signal beam with a strong pump beam at the LC permittivity grating, induced by the periodically tilted helix axis, leads to the energy gain of the weak signal beam. Dependence of the signal beam gain coefficient on the parameters of the short-pitch cholesteric LC is studied.
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Affiliation(s)
- V Yu Reshetnyak
- Physics Faculty, Taras Shevchenko National University of Kyiv, Volodymyrska Street 64, Kyiv 01601, Ukraine
| | - I P Pinkevych
- Physics Faculty, Taras Shevchenko National University of Kyiv, Volodymyrska Street 64, Kyiv 01601, Ukraine
| | - D R Evans
- Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson Air Force Base, Ohio 45433, USA
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Khan RK, Turlapati S, Begum N, Mohiuddin G, Rao NS, Ghosh S. Impact of terminal polar substitution on elastic, electro-optic and dielectric properties of four-ring bent-core nematic liquid crystals. RSC Adv 2018; 8:11509-11516. [PMID: 35542808 PMCID: PMC9079133 DOI: 10.1039/c8ra00575c] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2018] [Accepted: 03/18/2018] [Indexed: 11/21/2022] Open
Abstract
Here we report the influence of terminal –F, –Cl and –NO2 substitution on the elastic, dielectric and polar switching behavior of four-ring bent-core liquid crystals (LCs).
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Affiliation(s)
- R. K. Khan
- Department of Physics
- University of Calcutta
- Kolkata 700 009
- India
| | - S. Turlapati
- Chemistry Department
- Assam University
- Silchar 788011
- India
| | - N. Begum
- Chemistry Department
- Assam University
- Silchar 788011
- India
| | - G. Mohiuddin
- Chemistry Department
- Assam University
- Silchar 788011
- India
| | - N. V. S. Rao
- Chemistry Department
- Assam University
- Silchar 788011
- India
| | - S. Ghosh
- Department of Physics
- University of Calcutta
- Kolkata 700 009
- India
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Babakhanova G, Parsouzi Z, Paladugu S, Wang H, Nastishin YA, Shiyanovskii SV, Sprunt S, Lavrentovich OD. Elastic and viscous properties of the nematic dimer CB7CB. Phys Rev E 2017; 96:062704. [PMID: 29347367 DOI: 10.1103/physreve.96.062704] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2017] [Indexed: 05/16/2023]
Abstract
We present a comprehensive set of measurements of optical, dielectric, diamagnetic, elastic, and viscous properties in the nematic (N) phase formed by a liquid crystalline dimer. The studied dimer, 1,7-bis-4-(4'-cyanobiphenyl) heptane (CB7CB), is composed of two rigid rodlike cyanobiphenyl segments connected by a flexible aliphatic link with seven methyl groups. CB7CB and other nematic dimers are of interest due to their tendency to adopt bent configurations and to form two states possessing a modulated nematic director structure, namely, the twist-bend nematic, N_{TB}, and the oblique helicoidal cholesteric, Ch_{OH}, which occurs when the achiral dimer is doped with a chiral additive and exposed to an external electric or magnetic field. We characterize the material parameters as functions of temperature in the entire temperature range of the N phase, including the pretransitional regions near the N-N_{TB} and N-to-isotropic (I) transitions. The splay constant K_{11} is determined by two direct and independent techniques, namely, detection of the Frederiks transition and measurement of director fluctuation amplitudes by dynamic light scattering (DLS). The bend K_{33} and twist K_{22} constants are measured by DLS. K_{33}, being the smallest of the three constants, shows a strong nonmonotonous temperature dependence with a negative slope in both N-I and N-N_{TB} pretransitional regions. The measured ratio K_{11}/K_{22} is larger than 2 in the entire nematic temperature range. The orientational viscosities associated with splay, twist, and bend fluctuations in the N phase are comparable to those of nematics formed by rodlike molecules. All three show strong temperature dependence, increasing sharply near the N-N_{TB} transition.
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Affiliation(s)
- Greta Babakhanova
- Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
- Chemical Physics Interdisciplinary Program, Kent State University, Kent, Ohio 44242, USA
| | - Zeinab Parsouzi
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
| | | | - Hao Wang
- Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
- Chemical Physics Interdisciplinary Program, Kent State University, Kent, Ohio 44242, USA
| | - Yu A Nastishin
- Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
- Hetman Petro Sahaidachnyi National Army Academy, 32, Heroes of Maidan Street, Lviv 79012, Ukraine
| | | | - Samuel Sprunt
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
| | - Oleg D Lavrentovich
- Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
- Chemical Physics Interdisciplinary Program, Kent State University, Kent, Ohio 44242, USA
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
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Vimala S, Nair GG, Prasad SK, Veerabhadraswamy BN, Hiremath US. Diminished Splay Stiffening in Weak Gels of Calamitic-Bent-Core Nematic Composites. J Phys Chem B 2016; 120:2596-603. [PMID: 26840783 DOI: 10.1021/acs.jpcb.5b12665] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Composites of calamitic and bent-core nematic molecules exhibiting a nematic to nematic-gel transformation have been investigated using thermal, electrical, X-ray, and mechanical probes. The studies focusing on the Frank elastic behavior show a surprising result that the thermal behavior of the threshold voltage and the dependent splay elastic constant (K11) are remarkably different in temperature regions identified as weak and strong gels. In the former gel, the parameters exhibit values significantly smaller than the higher-temperature fluid nematic, effectively canceling out the underlying thermal variation due to the order parameter. This is especially attractive from the viewpoint of display devices. The X-ray diffraction data suggest that the fibers have a plastic nature in the weak gel and 3D-crystalline ordering in the strong gel. We argue that the different elastic behavior in the two gel phases is caused by the nature of the fibers; they are stiff in both gels but the interfiber interaction is weaker in the weak gel allowing the splay elastic constant to be lowered. The X-ray and rheological data lend support to the characterization of the fibers.
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Affiliation(s)
- S Vimala
- Centre for Nano and Soft Matter Sciences , Jalahalli, Bengaluru 560 013, India
| | - Geetha G Nair
- Centre for Nano and Soft Matter Sciences , Jalahalli, Bengaluru 560 013, India
| | - S Krishna Prasad
- Centre for Nano and Soft Matter Sciences , Jalahalli, Bengaluru 560 013, India
| | | | - Uma S Hiremath
- Centre for Nano and Soft Matter Sciences , Jalahalli, Bengaluru 560 013, India
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Xiang Y, Zhou MJ, Xu MY, Salamon P, Éber N, Buka Á. Unusual polarity-dependent patterns in a bent-core nematic liquid crystal under low-frequency ac field. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2015; 91:042501. [PMID: 25974510 DOI: 10.1103/physreve.91.042501] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2015] [Indexed: 06/04/2023]
Abstract
Electric-field-induced patterns of diverse morphology have been observed over a wide frequency range in a recently synthesized bent-core nematic (BCN) liquid crystal. At low frequencies (up to ∼25 Hz), the BCN exhibited unusual polarity-dependent patterns. When the amplitude of the ac field was enhanced, these two time-asymmetrical patterns turned into time-symmetrical prewavylike stripes. At ac frequencies in the middle-frequency range (∼50-3000 Hz), zigzag patterns were detected whose obliqueness varied with the frequency. Finally, if the frequency was increased above 3 kHz, the zigzag pattern was replaced by another, prewavylike pattern, whose threshold voltage depended on the frequency; however, the wave vector did not. For a more complete characterization, material parameters such as elastic constants, dielectric permittivities, and the anisotropy of the diamagnetic susceptibility were also determined.
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Affiliation(s)
- Ying Xiang
- School of Information Engineering, Guangdong University of Technology, Guangzhou 510006, People's Republic of China
| | - Meng-jie Zhou
- School of Information Engineering, Guangdong University of Technology, Guangzhou 510006, People's Republic of China
| | - Ming-Ya Xu
- School of Information Engineering, Guangdong University of Technology, Guangzhou 510006, People's Republic of China
| | - Péter Salamon
- Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1121 Budapest, Konkoly Thege Miklós út 29-33, Hungary
| | - Nándor Éber
- Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1121 Budapest, Konkoly Thege Miklós út 29-33, Hungary
| | - Ágnes Buka
- Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, H-1121 Budapest, Konkoly Thege Miklós út 29-33, Hungary
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Zakhlevnykh A, Petrov D. Weak coupling effects and re-entrant transitions in ferronematic liquid crystals. J Mol Liq 2014. [DOI: 10.1016/j.molliq.2014.06.028] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Aya S, Ogino S, Hayashi Y, Okano K, Pociecha D, Le KV, Araoka F, Kawauchi S, Gorecka E, Vaupotič N, Takezoe H, Ishikawa K. Structure-sensitive bend elastic constants between piconewton and subnanonewton in diphenylacetylene-core-based liquid crystals. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 90:042506. [PMID: 25375514 DOI: 10.1103/physreve.90.042506] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Indexed: 06/04/2023]
Abstract
Elastic constants in liquid crystals are known to be in the range of pico- and several-tens piconewton (pN). We report herein that a bend elastic constant, K33, remarkably varies depending on a slight modification of the chemical structure in an analogous series of calamitic liquid crystals. In contrast to the record-high bend elastic constants (hundreds pN or sub-nN) reported previously in a compound with an azo linkage, analogous compounds with tolan and ester linkages show several-tens pN and pN, respectively. X-ray diffraction studies of these compounds reveal that smectic-like layer structures (cybotacticclusters) are formed in the nematic phase of only the homologous compounds with an azo linkage, certifying the idea that the existence of cybotactic clusters strongly enhances K33. Two theoretical considerations were made: (1) Based on molecular conformation calculation, flat molecules that have high torsional potential energy, such as the one with an azo linkage, easily pack to form cybotactic clusters. (2) Theoretical estimation was made of how much cluster volume ratio is necessary to give about 100-times-larger K33s.
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Affiliation(s)
- Satoshi Aya
- Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Meguro, Tokyo 152-8552, Japan
| | - Shohei Ogino
- Department of Pure and Applied Chemistry, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba, 278-8510, Japan
| | - Yoshihiro Hayashi
- Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Meguro, Tokyo 152-8552, Japan
| | - Kunihiko Okano
- Department of Pure and Applied Chemistry, Tokyo University of Science, 2641 Yamazaki, Noda-shi, Chiba, 278-8510, Japan and Department of Applied Chemistry, Faculty of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku, Yokohama, Kanagawa 223-8522, Japan
| | - Damian Pociecha
- University of Warsaw, Department of Chemistry, ul. Zwirki i Wigury 101, Warsaw, 02-089, Poland
| | - Khoa V Le
- RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Fumito Araoka
- Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Meguro, Tokyo 152-8552, Japan and RIKEN Center for Emergent Matter Science (CEMS), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
| | - Susumu Kawauchi
- Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Meguro, Tokyo 152-8552, Japan
| | - Ewa Gorecka
- University of Warsaw, Department of Chemistry, ul. Zwirki i Wigury 101, Warsaw, 02-089, Poland
| | - Nataša Vaupotič
- Department of Physics, Faculty of Natural Sciences and Mathematics, University of Maribor, Koroška 160, Maribor, Slovenia and Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
| | - Hideo Takezoe
- Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Meguro, Tokyo 152-8552, Japan
| | - Ken Ishikawa
- Department of Organic and Polymeric Materials, Tokyo Institute of Technology, O-okayama, Meguro, Tokyo 152-8552, Japan
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Gleeson HF, Kaur S, Görtz V, Belaissaoui A, Cowling S, Goodby JW. The nematic phases of bent-core liquid crystals. Chemphyschem 2014; 15:1251-60. [PMID: 24700653 PMCID: PMC4257080 DOI: 10.1002/cphc.201400014] [Citation(s) in RCA: 72] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Indexed: 11/07/2022]
Abstract
Over the last ten years, the nematic phases of liquid crystals formed from bent-core structures have provoked considerable research because of their remarkable properties. This Minireview summarises some recent measurements of the physical properties of these systems, as well as describing some new data. We concentrate on oxadiazole-based materials as exemplars of this class of nematogens, but also describe some other bent-core systems. The influence of molecular structure on the stability of the nematic phase is described, together with progress in reducing the nematic transition temperatures by modifications to the molecular structure. The physical properties of bent-core nematic materials have proven difficult to study, but patterns are emerging regarding their optical and dielectric properties. Recent breakthroughs in understanding the elastic and flexoelectric behaviour are summarised. Finally, some exemplars of unusual electric field behaviour are described.
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Affiliation(s)
- Helen F Gleeson
- [a] Prof. H. F. Gleeson, Dr. S. Kaur School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester, M13 9PL (UK) E-mail:
| | - Sarabjot Kaur
- [a] Prof. H. F. Gleeson, Dr. S. Kaur School of Physics and Astronomy, The University of Manchester, Oxford Road, Manchester, M13 9PL (UK) E-mail:
| | - Verena Görtz
- Department of ChemistryUniversity of York, Heslington, York YO10 5DD (UK)
- Department of ChemistryLancaster University, Lancaster LA1 4YB (UK)
| | - Abdel Belaissaoui
- Department of ChemistryUniversity of York, Heslington, York YO10 5DD (UK)
| | - Stephen Cowling
- Department of ChemistryUniversity of York, Heslington, York YO10 5DD (UK)
| | - John W Goodby
- Department of ChemistryUniversity of York, Heslington, York YO10 5DD (UK)
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Vaupotič N, Čepič M, Osipov MA, Gorecka E. Flexoelectricity in chiral nematic liquid crystals as a driving mechanism for the twist-bend and splay-bend modulated phases. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 89:030501. [PMID: 24730777 DOI: 10.1103/physreve.89.030501] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2014] [Indexed: 06/03/2023]
Abstract
We present a continuum theoretical model describing the impact of chirality on nematic systems with large flexoelectricity. As opposed to achiral materials, where only one type of the modulated structure can exist in a given material, the model predicts that chirality can stabilize several modulated phases, which have already been observed experimentally [A. Zep et al., J. Mater. Chem. C 1, 46 (2013)].
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Affiliation(s)
- Nataša Vaupotič
- Faculty of Natural Sciences and Mathematics, University of Maribor, Koroška 160, 2000 Maribor, Slovenia and Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia
| | - Mojca Čepič
- Jozef Stefan Institute, Jamova 39, 1000 Ljubljana, Slovenia and Faculty of Education, University of Ljubljana, Kardeljeva ploščad 16, 1000 Ljubljana
| | - Mikhail A Osipov
- Department of Mathematics and Statistics, University of Strathclyde, 26 Richmond St., G1 Glasgow, United Kingdom
| | - Ewa Gorecka
- Department of Chemistry, University of Warsaw, Zwirki i Wigury 101, 02-089 Warsaw, Poland
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Gornik K, Čepič M, Vaupotič N. Effect of a bias electric field on the structure and dielectric response of the ferroelectric smectic-A liquid crystal in thin planar cells. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 89:012501. [PMID: 24580240 DOI: 10.1103/physreve.89.012501] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Indexed: 06/03/2023]
Abstract
The phenomenological continuum model is used to study the director structure and dielectric response of the ferroelectric smectic-A phase in thin planar cells. The frequency of the phase mode and the dielectric permittivity are calculated numerically as a function of the bias external DC electric field, cell thickness, the strength of polar surface anchoring, and the ratio between the bend and splay elastic constants. The theoretically obtained dependencies are in agreement with the recently reported experimental measurements, which show that in thin planar cells both the phase mode frequency and the dielectric permittivity decrease with increasing external bias electric field.
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Affiliation(s)
- K Gornik
- Department of Physics, Faculty of Natural Sciences and Mathematics, University of Maribor, Koroška cesta 160, SI-2000 Maribor, Slovenia
| | - M Čepič
- Department of Physics and Technical Studies, Faculty of Education, University of Ljubljana, Kardeljeva ploščad 16, SI-1000 Ljubljana, Slovenia and Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
| | - N Vaupotič
- Department of Physics, Faculty of Natural Sciences and Mathematics, University of Maribor, Koroška cesta 160, SI-2000 Maribor, Slovenia and Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
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Effect of fluorinated nematic mesogens on phase behaviors and optical properties of chiral liquid crystalline polysiloxanes. Colloid Polym Sci 2013. [DOI: 10.1007/s00396-013-3049-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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