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Popov P, Lacks DJ, Jákli A, Mann EK. Insertion of liquid crystal molecules into hydrocarbon monolayers. J Chem Phys 2015; 141:054901. [PMID: 25106607 DOI: 10.1063/1.4891307] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Atomistic molecular dynamics simulations were carried out to investigate the molecular mechanisms of vertical surface alignment of liquid crystals. We study the insertion of nCB (4-Cyano-4'-n-biphenyl) molecules with n = 0,…,6 into a bent-core liquid crystal monolayer that was recently found to provide good vertical alignment for liquid crystals. The results suggest a complex-free energy landscape for the liquid crystal within the layer. The preferred insertion direction of the nCB molecules (core or tail first) varies with n, which can be explained by entropic considerations. The role of the dipole moments was found to be negligible. As vertical alignment is the leading form of present day liquid crystal displays (LCD), these results will help guide improvement of the LCD technology, as well as lend insight into the more general problem of insertion of biological and other molecules into lipid and surfactant layers.
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Affiliation(s)
- Piotr Popov
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
| | - Daniel J Lacks
- Department of Chemical Engineering, Case Western Reserve University, Cleveland, Ohio 44106, USA
| | - Antal Jákli
- Liquid Crystal Institute, Kent State University, Kent, Ohio 44242-0001, USA
| | - Elizabeth K Mann
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
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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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Xiang Y, Liu YK, Buka Á, Éber N, Zhang ZY, Xu MY, Wang E. Electric-field-induced patterns and their temperature dependence in a bent-core liquid crystal. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2014; 89:012502. [PMID: 24580241 DOI: 10.1103/physreve.89.012502] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2013] [Indexed: 06/03/2023]
Abstract
Two kinds of electroconvection patterns in an ether-bridged bent-core nematic liquid crystal material (BCN), which appear in different frequency ranges, are examined and compared. One is a longitudinal pattern with the stripes parallel to the orientation of the BCN and with a periodicity of approximately the cell thickness, occurring in the high-frequency range of several hundreds Hz; the other one is oblique stripes, which results in a zigzag pattern, and appears in the low-frequency range of several tens Hz. In addition, within an intermediate-frequency range, transformations from oblique to longitudinal and then to normal stripes occur at increased ac voltages. In particular, we investigated the temperature behavior of longitudinal and oblique stripes: When the temperature T increases and approaches the clearing temperature Tc, the contrast of the domains is enhanced and the frequency range of existence becomes wider, while the onset voltages increase only moderately instead of diverging, thus suggesting an isotropic mechanism of pattern formation.
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Affiliation(s)
- Ying Xiang
- School of Information Engineering, Guangdong University of Technology, Guangzhou 510006, People's Republic of China
| | - Yi-Kun Liu
- State Key Laboratory of Optoelectronic Materials and Technologies, Sun Yat-sen University, Guangzhou 510275, People's Republic of China
| | - Ágnes Buka
- Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, Konkoly Thege Miklós út 29-33, H-1121 Budapest, Hungary
| | - Nándor Éber
- Institute for Solid State Physics and Optics, Wigner Research Centre for Physics, Hungarian Academy of Sciences, Konkoly Thege Miklós út 29-33, H-1121 Budapest, Hungary
| | - Zhi-Yong Zhang
- Department of Chemistry and Environmental Engineering, Wuhan Polytechnic University, Wuhan 430023, People's Republic of China
| | - Ming-Ya Xu
- School of Information Engineering, Guangdong University of Technology, Guangzhou 510006, People's Republic of China
| | - Everett Wang
- School of Information Engineering, Guangdong University of Technology, Guangzhou 510006, People's Republic of China
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Shanker G, Prehm M, Tschierske C. Laterally connected bent-core dimers and bent-core-rod couples with nematic liquid crystalline phases. ACTA ACUST UNITED AC 2012. [DOI: 10.1039/c1jm13649f] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Wang Y, Yoon HG, Bisoyi HK, Kumar S, Li Q. Hybrid rod-like and bent-core liquid crystal dimers exhibiting biaxial smectic A and nematic phases. ACTA ACUST UNITED AC 2012. [DOI: 10.1039/c2jm34315k] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Kaur S, Belaissaoui A, Goodby JW, Görtz V, Gleeson HF. Nonstandard electroconvection in a bent-core oxadiazole material. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2011; 83:041704. [PMID: 21599183 DOI: 10.1103/physreve.83.041704] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/09/2010] [Revised: 01/20/2011] [Indexed: 05/30/2023]
Abstract
Electroconvection (EC) phenomena have been investigated in the nematic phase of a bent-core oxadiazole material with negative dielectric anisotropy and a frequency dependent conductivity anisotropy. The formation of longitudinal roll (LR) patterns is one of the predominant features observed in the complete frequency and voltage range studied. At voltages much above the LR threshold, various complex patterns such as the "crisscrossed" pattern, bimodal varicose, and turbulence are observed. Unusually, the nonstandard EC (ns-EC) instability in this material, is observed in a regime in which we measure the dielectric and conductivity anisotropies to be negative and positive respectively. A further significant observation is that the EC displays distinct features in the high and low temperature regimes of the nematic phase, supporting an earlier report that EC patterns could distinguish between regions that have been reported as uniaxial and biaxial nematic phases.
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Affiliation(s)
- S Kaur
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom
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Yoon HG, Kang SW, Dong RY, Marini A, Suresh KA, Srinivasarao M, Kumar S. Nematic biaxiality in a bent-core material. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 81:051706. [PMID: 20866246 DOI: 10.1103/physreve.81.051706] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/18/2009] [Revised: 02/21/2010] [Indexed: 05/29/2023]
Abstract
The results of a recent investigation of the nematic biaxiality in a bent-core mesogen (A131) are in apparent disagreement with earlier claims. Samples of mesogen A131 used in the two studies were investigated with polarized optical microscopy, conoscopy, carbon-13 NMR, and crossover frequency measurements. The results demonstrate that textural changes associated with the growth of biaxial nematic order appear at ∼149 °C. The Maltese cross observed in the conoscopic figure gradually splits into two isogyres at lower temperatures indicating phase biaxiality. Presence of the uniaxial to biaxial nematic phase transition is further confirmed by temperature trends of local order parameters based on 13C chemical shifts in NMR experiments. Frequency switching measurements also clearly reveal a transition at 149 °C. Differences between the two reports appear to be related to the presence of solvent, impurities, and/or adsorbed gases in samples of A131 used in the study of Van Le [Phys. Rev. E 79, 030701 (2009)].
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Affiliation(s)
- Hyung Guen Yoon
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
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Tadapatri P, Hiremath US, Yelamaggad CV, Krishnamurthy KS. Patterned Electroconvective States in a Bent-Core Nematic Liquid Crystal. J Phys Chem B 2009; 114:10-21. [DOI: 10.1021/jp9058802] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Pramod Tadapatri
- Centre for Liquid Crystal Research, P.O. Box 1329, Jalahalli, Bangalore 560 013, India
| | - Uma S. Hiremath
- Centre for Liquid Crystal Research, P.O. Box 1329, Jalahalli, Bangalore 560 013, India
| | - C. V. Yelamaggad
- Centre for Liquid Crystal Research, P.O. Box 1329, Jalahalli, Bangalore 560 013, India
| | - K. S. Krishnamurthy
- Centre for Liquid Crystal Research, P.O. Box 1329, Jalahalli, Bangalore 560 013, India
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Tanaka S, Takezoe H, Eber N, Fodor-Csorba K, Vajda A, Buka A. Electroconvection in nematic mixtures of bent-core and calamitic molecules. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 80:021702. [PMID: 19792141 DOI: 10.1103/physreve.80.021702] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/16/2009] [Indexed: 05/28/2023]
Abstract
The onset of electroconvection in binary mixtures of a bent-core and a rodlike nematic has been characterized by measuring the threshold voltage U(c) and the critical wave number of the pattern in a wide range of frequencies f. In the mixtures rich in bent-core molecules, a "conductive-prewavy2-patternless-prewavy1" morphological sequence has been detected with an unusual negative slope of U(c)(f) at high frequencies. This latter scenario seems to be related to the bent-core component, as it disappears with increasing the concentration of rodlike molecules. In addition, one of the parameters most relevant for electroconvection, the electrical conductivity, has also been varied by ionic salt doping. It has been found that the above effect of the banana-shaped molecules on the electroconvection scenarios can be suppressed by the conductivity.
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Affiliation(s)
- Shingo Tanaka
- Department of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-12-1 S8-Ookayama, Meguro-Ku, Tokyo 152-8552, Japan
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Kumar P, Marinov YG, Hinov HP, Hiremath US, Yelamaggad CV, Krishnamurthy KS, Petrov AG. Converse Flexoelectric Effect in Bent-Core Nematic Liquid Crystals. J Phys Chem B 2009; 113:9168-74. [DOI: 10.1021/jp903241z] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Pramoda Kumar
- Centre for Liquid Crystal Research, P.O. Box 1329, Jalahalli, Bangalore 560 013, India, and Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, Sofia 1784, Bulgaria
| | - Y. G. Marinov
- Centre for Liquid Crystal Research, P.O. Box 1329, Jalahalli, Bangalore 560 013, India, and Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, Sofia 1784, Bulgaria
| | - H. P. Hinov
- Centre for Liquid Crystal Research, P.O. Box 1329, Jalahalli, Bangalore 560 013, India, and Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, Sofia 1784, Bulgaria
| | - Uma S. Hiremath
- Centre for Liquid Crystal Research, P.O. Box 1329, Jalahalli, Bangalore 560 013, India, and Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, Sofia 1784, Bulgaria
| | - C. V. Yelamaggad
- Centre for Liquid Crystal Research, P.O. Box 1329, Jalahalli, Bangalore 560 013, India, and Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, Sofia 1784, Bulgaria
| | - K. S. Krishnamurthy
- Centre for Liquid Crystal Research, P.O. Box 1329, Jalahalli, Bangalore 560 013, India, and Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, Sofia 1784, Bulgaria
| | - A. G. Petrov
- Centre for Liquid Crystal Research, P.O. Box 1329, Jalahalli, Bangalore 560 013, India, and Institute of Solid State Physics, Bulgarian Academy of Sciences, 72 Tzarigradsko Chaussee, Sofia 1784, Bulgaria
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