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Brumby PE, Kowaguchi A, Nozawa T, Yasuoka K, Wensink HH. Pre-Smectic Ordering and the Unwinding Helix in Monte Carlo Simulations of Cholesteric Liquid-Crystals. J Phys Chem B 2023; 127:7194-7204. [PMID: 37540189 DOI: 10.1021/acs.jpcb.3c02018] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 08/05/2023]
Abstract
In this paper, molecular chirality is studied for liquid-crystal fluids represented by hard rods with the addition of an attractive chiral dispersion term. Chiral forces between molecular pairs are assumed to be long-ranged and are described in terms of the pseudotensor of Goossens [W. J. A. Goossens, Mol. Cryst. Liq. Cryst. 1971, 12, 237-244]. Following Varga and Jackson [S. Varga and G. Jackson, Chem. Phys. Lett. 2003, 377, 6-12], this is combined with a hard-spherocylinder core. We investigate the relationship between molecular chirality and the helical pitch of the system, which occurs in the absence of full three-dimensional periodic boundary conditions. The dependence of the wavenumber of this pitch on the thermodynamic variables, temperature, and density is measured. We also explore the use of a novel surface boundary interaction model. As a result of this approach, we are able to lower the temperature of the system without the occurrence of nematic droplets, which would interfere with the formation of a uniaxial pitch. Regarding the theoretical predictions of Wensink and Jackson [H. H. Wensink and G. Jackson, J. Chem. Phys. 2009, 130, 234911], on the one hand, we have qualitative agreement with the observed non-monotonic density dependence of the wavenumber. Initially increasing with density, the wavenumber reaches a maximum, before falling as the density moves toward the point of phase transition from cholesteric to smectic. However, further analysis for shorter rods, in the presence of novel boundary conditions, reveals some disagreement with the theory, at least in this case; the unwinding of the cholesteric helix in the cholesteric phase occurs simultaneously with subtle increases in smectic ordering. These pre-smectic fluctuations have not been accounted for so far in theories on cholesterics but turn out to play a key role in controlling the pitch of cholesteric phases of rod-shaped mesogens with a small to moderate aspect ratio.
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Affiliation(s)
- Paul E Brumby
- Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
| | - Akie Kowaguchi
- Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
| | - Takuma Nozawa
- Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
| | - Kenji Yasuoka
- Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku, Yokohama 223-8522, Japan
| | - Henricus H Wensink
- Laboratoire de Physique des Solides─UMR 8502, Université Paris-Saclay & CNRS, Orsay 91405, France
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Molecular Simulation Approaches to the Study of Thermotropic and Lyotropic Liquid Crystals. CRYSTALS 2022. [DOI: 10.3390/cryst12050685] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Over the last decade, the availability of computer time, together with new algorithms capable of exploiting parallel computer architectures, has opened up many possibilities in molecularly modelling liquid crystalline systems. This perspective article points to recent progress in modelling both thermotropic and lyotropic systems. For thermotropic nematics, the advent of improved molecular force fields can provide predictions for nematic clearing temperatures within a 10 K range. Such studies also provide valuable insights into the structure of more complex phases, where molecular organisation may be challenging to probe experimentally. Developments in coarse-grained models for thermotropics are discussed in the context of understanding the complex interplay of molecular packing, microphase separation and local interactions, and in developing methods for the calculation of material properties for thermotropics. We discuss progress towards the calculation of elastic constants, rotational viscosity coefficients, flexoelectric coefficients and helical twisting powers. The article also covers developments in modelling micelles, conventional lyotropic phases, lyotropic phase diagrams, and chromonic liquid crystals. For the latter, atomistic simulations have been particularly productive in clarifying the nature of the self-assembled aggregates in dilute solution. The development of effective coarse-grained models for chromonics is discussed in detail, including models that have demonstrated the formation of the chromonic N and M phases.
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Affiliation(s)
- Michael P. Allen
- Department of Physics, University of Warwick, Coventry, UK
- H. H. Wills Physics Laboratory, Royal Fort, Bristol, UK
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Růžička Š, Wensink HH. Simulating the pitch sensitivity of twisted nematics of patchy rods. SOFT MATTER 2016; 12:5205-5213. [PMID: 27184814 DOI: 10.1039/c6sm00727a] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Stiff, elongated biomolecules such as filamentous viruses, DNA or cellulose nanocrystals are known to form liquid crystals often exhibiting a helical supramolecular organization. Little is known about the microscopic origin, size and handedness of the helical pitch in these, so-called cholesteric phases. Experimental observations in chiral lyotropics suggest that long-ranged chiral forces of electrostatic origin acting between the mesogens are responsible for such organization. Using large-scale computer simulation we study the sensitivity of the pitch imparted by soft microscopic helices and confirm that the helical sense is sensitive to a change of packing fraction, magnitude of the molecular pitch and amplitude of the chiral interactions. In particular, we find evidence that the cholesteric helix sense may change spontaneously upon variation of particle density, at fixed molecular chirality. These pitch inversions have been reported in recent theoretical studies but simulation evidence remains elusive. We rationalize these sudden changes in the supramolecular helical symmetry on the basis of detailed measurements of the mean-torque generated by the twisting of the helices. The simulation methodology employed does not require confining the twisted nematic in a slab geometry and allows for a simultaneous measurement of the pitch and the twist elastic constant. We find that the twist elastic constant increases almost linearly with density suggesting that twisted nematic shows no signs of anomalous stiffening due to pre-smectic fluctuations at higher packing fraction.
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Affiliation(s)
- Štěpán Růžička
- Laboratoire de Physique des Solides, CNRS, Université Paris-Sud, Université Paris-Saclay, UMR 8502 - 91405 Orsay Cedex, France.
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Affiliation(s)
- Michael P. Allen
- Department of Physics, University of Warwick, Coventry, UK
- H. H. Wills Physics Laboratory, Bristol, UK
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Dussi S, Belli S, van Roij R, Dijkstra M. Cholesterics of colloidal helices: Predicting the macroscopic pitch from the particle shape and thermodynamic state. J Chem Phys 2015; 142:074905. [DOI: 10.1063/1.4908162] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Affiliation(s)
- Simone Dussi
- Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands
| | - Simone Belli
- Institute for Theoretical Physics, Center for Extreme Matter and Emergent Phenomena, Utrecht University, Leuvenlaan 4, 3584 CE Utrecht, The Netherlands
| | - René van Roij
- Institute for Theoretical Physics, Center for Extreme Matter and Emergent Phenomena, Utrecht University, Leuvenlaan 4, 3584 CE Utrecht, The Netherlands
| | - Marjolein Dijkstra
- Soft Condensed Matter, Debye Institute for Nanomaterials Science, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands
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Matsuyama A. Theory of polymer-dispersed cholesteric liquid crystals. J Chem Phys 2013; 139:174906. [DOI: 10.1063/1.4828940] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Yoshida J, Watanabe G, Kakizawa K, Kawabata Y, Yuge H. Tris(β-diketonato) Ru(III) Complexes as Chiral Dopants for Nematic Liquid Crystals: the Effect of the Molecular Structure on the Helical Twisting Power. Inorg Chem 2013; 52:11042-50. [DOI: 10.1021/ic401240f] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Jun Yoshida
- Department
of Chemistry and ‡Department of Physics, School of Science, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan
| | - Go Watanabe
- Department
of Chemistry and ‡Department of Physics, School of Science, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan
| | - Kaori Kakizawa
- Department
of Chemistry and ‡Department of Physics, School of Science, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan
| | - Yasuhiro Kawabata
- Department
of Chemistry and ‡Department of Physics, School of Science, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan
| | - Hidetaka Yuge
- Department
of Chemistry and ‡Department of Physics, School of Science, Kitasato University, 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan
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Varga S, Jackson G. A study of steric chirality: the chiral nematic phase of a system of chiral two-site HGO molecules. Mol Phys 2011. [DOI: 10.1080/00268976.2011.556577] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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CAMP BPHILIPJ. RESEARCH NOTE On the helical twisting power of chiral dopants in liquid crystals. Mol Phys 2010. [DOI: 10.1080/002689797171670] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/16/2022]
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MEMMER R, KUBALL HG. Computer simulation of chiral liquid crystal phases III. A cholesteric phase formed by chiral Gay-Berne atropisomers. Mol Phys 2010. [DOI: 10.1080/002689796172977] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
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Ferrarini A, Pieraccini S, Masiero S, Spada GP. Chiral amplification in a cyanobiphenyl nematic liquid crystal doped with helicene-like derivatives. Beilstein J Org Chem 2009; 5:50. [PMID: 19936270 PMCID: PMC2779693 DOI: 10.3762/bjoc.5.50] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2009] [Accepted: 10/02/2009] [Indexed: 11/23/2022] Open
Abstract
The addition of a chiral non-racemic dopant to a nematic liquid crystal (LC) has the effect of transferring the molecular chirality to the phase organization and a chiral nematic phase is formed. This molecular chirality amplification in the LC provides a unique possibility for investigating the relationship between molecular structure, intermolecular interactions, and mesoscale organization. It is known that axially chiral or helical-shaped molecules with reduced conformational disorder are good candidates for high helical twisting power derivatives. In particular, biaryl derivatives are known to be efficient chiral inducers in biaryl nematic mesophases. In this paper, we focus on a new series of helicene-like molecules of known absolute configuration. We have integrated cholesteric pitch measurements with geometry optimization by DFT calculations and analysis of the twisting ability by the Surface Chirality model to shed light on the structural features responsible for the analogies and differences exhibited by these derivatives. The investigation of these dopants with well-defined geometry, by virtue of the low conformational freedom, and the substituents variously distributed around the core, allows us to extend our knowledge of the molecular origin of the chirality amplification in liquid crystals and to confirm the simple relationship “molecular P-helicity” → “cholesteric P-handedness” for helical-shaped helicene-like derivatives.
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Affiliation(s)
- Alberta Ferrarini
- Dipartimento di Scienze Chimiche, Università di Padova, 35131 Padova, Italy.
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Yoshizawa A, Nishiyama I. Interlayer Correlation in Smectic Phases Induced by Chiral Twin Molecules. ACTA ACUST UNITED AC 2006. [DOI: 10.1080/10587259508038714] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Kamberaj H, Low RJ, Neal MP. Correlation between molecular chirality and helical twisting power: a computer simulation study. Mol Phys 2006. [DOI: 10.1080/00268970500350898] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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Earl DJ, Wilson MR. Calculations of helical twisting powers from intermolecular torques. J Chem Phys 2004; 120:9679-83. [PMID: 15267981 DOI: 10.1063/1.1718122] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
We present a Monte Carlo molecular simulation method that calculates the helical twisting power of a chiral molecule by sampling intermolecular torques. The approach is applied to an achiral nematic liquid crystalline system, composed of Gay-Berne particles, that is doped with chiral molecules. Calculations are presented for six chiral dopant molecules and the results show a good correlation with the sign and magnitude of experimentally determined helical twisting powers.
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Affiliation(s)
- David J Earl
- Department of Bioengineering MS142, Rice University, Houston, Texas 77005-1892, USA.
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Germano G, Allen MP, Masters AJ. Simultaneous calculation of the helical pitch and the twist elastic constant in chiral liquid crystals from intermolecular torques. J Chem Phys 2002. [DOI: 10.1063/1.1475747] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Cook MJ, Wilson MR. Calculation of helical twisting power for liquid crystal chiral dopants. J Chem Phys 2000. [DOI: 10.1063/1.480703] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Abstract
A short review is given of recent progress in the computer simulation of liquid crystal phases using hard particles. Emphasis is placed on the richness of phase behaviour that may result from the effects of molecular size and shape alone, and on the role of simulations in testing modern theories of liquid crystal phase transitions, structure and dynamics. Two specific examples are treated in detail: the simulation of twisted nematic liquid crystals, allowing a direct calculation of the twist elastic constant and the helical twisting power of chiral dopant molecules; and the recent quantitative explanation of diffusive behaviour in isotropic and nematic liquids using kinetic theory.
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Ferrarini A, Moro GJ, Nordio PL. Simple molecular model for induced cholesteric phases. PHYSICAL REVIEW. E, STATISTICAL PHYSICS, PLASMAS, FLUIDS, AND RELATED INTERDISCIPLINARY TOPICS 1996; 53:681-688. [PMID: 9964299 DOI: 10.1103/physreve.53.681] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
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Komolkin AV, Maliniak A. Local structure in anisotropic systems determined by molecular dynamics simulation. Mol Phys 1995. [DOI: 10.1080/00268979500100851] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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