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Zavvou EE, Welch C, Mehl GH, Vanakaras AG, Karahaliou PK. Comparative Study of the Optical and Dielectric Anisotropy of a Difluoroterphenyl Dimer and Trimer Forming Two Nematic Phases. MATERIALS (BASEL, SWITZERLAND) 2024; 17:2555. [PMID: 38893819 PMCID: PMC11173927 DOI: 10.3390/ma17112555] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/26/2024] [Revised: 05/22/2024] [Accepted: 05/23/2024] [Indexed: 06/21/2024]
Abstract
We present a comparative study of the optical and dielectric anisotropy of a laterally fluorinated liquid crystal dimer and its homologous trimer, both exhibiting two nematic phases. In the high-temperature nematic phase, both oligomers exhibit positive optical anisotropy with similar magnitude, which, however, is lower in comparison with the optical anisotropy of the monomer. In the same temperature range, the dielectric permittivity along and perpendicular to the nematic director, measured on magnetically aligned samples, reveals negative dielectric anisotropy for both oligomers, which saturates as the temperature approaches the N-N phase transition temperature. Comparison of the dielectric anisotropies of the oligomers with the corresponding anisotropy of the monomer indicates a systematic variation of its magnitude with the number of the linked mesogenic units. Results are compared with the corresponding anisotropies of the cyanobiphenyl dimers, the archetypal compounds with two nematic phases, and are discussed in terms of the dipolar structure of the mesogens and the dipolar correlations in their nematic phases.
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Affiliation(s)
| | - Chris Welch
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK; (C.W.); (G.H.M.)
| | - Georg H. Mehl
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK; (C.W.); (G.H.M.)
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Kocot A, Czarnecka M, Arakawa Y, Merkel K. Dielectric Study of Liquid Crystal Dimers: Probing the Orientational Order and Molecular Interactions in Nematic and Twist-Bend Nematic Phases. J Phys Chem B 2023; 127:7082-7090. [PMID: 37526147 PMCID: PMC10424235 DOI: 10.1021/acs.jpcb.3c03496] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2023] [Revised: 07/02/2023] [Indexed: 08/02/2023]
Abstract
Dielectric spectroscopy in frequencies that range from 10 Hz to 1 GHz has been used to study the molecular orientational dynamics of the two types of dimers that form the twist-bend nematic phase over a wide range of temperatures for both nematic and twist-bend nematic phases. The symmetrical and asymmetrical liquid crystal dimers with the cyanobiphenyl mesogenic groups were investigated. The results were analyzed within the framework of the molecular theory of dielectric permittivity for nematogens. The two molecular processes can be assigned to the reorientation of the monomeric unit: the high frequency one to the precessional rotation of the longitudinal components of the cyanobiphenyl groups (CN) and the second (low frequency) to the end-over-end rotation of the CN dipole around the short molecular axis. The precession mode, which is determined by the local order and is almost unaffected by the phase transition from the nematic to the twist-bend phase, while the end-over-end rotation clearly slowed down at the transition, as it is affected by the growth of the intermolecular interactions. The latter corresponds well to the fact revealed by IR spectroscopy about the longitudinal correlation of the molecular dipoles.
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Affiliation(s)
- Antoni Kocot
- Institute
of Materials Engineering, Faculty of Science and Technology, University of Silesia, 75 Pułku Piechoty 1a, Chorzów 41-500, Poland
| | - Małgorzata Czarnecka
- Faculty
of Electrical Engineering, Automatics, Computer Science and Biomedical
Engineering, AGH University of Science and
Technology, al. Adama Mickiewicza 30, Cracow 30-059, Poland
| | - Yuki Arakawa
- Department
of Applied Chemistry and Life Science, Graduate School of Engineering, Toyohashi University of Technology, Toyohashi 441-8580, Japan
| | - Katarzyna Merkel
- Institute
of Materials Engineering, Faculty of Science and Technology, University of Silesia, 75 Pułku Piechoty 1a, Chorzów 41-500, Poland
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Thioether-Linked Liquid Crystal Trimers: Odd-Even Effects of Spacers and the Influence of Thioether Bonds on Phase Behavior. MATERIALS 2022; 15:ma15051709. [PMID: 35268942 PMCID: PMC8911043 DOI: 10.3390/ma15051709] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 02/18/2022] [Accepted: 02/20/2022] [Indexed: 02/04/2023]
Abstract
We report the synthesis, phase-transition behavior, and mesophase structures of the first homologous series of thioether-linked liquid crystal (LC) trimers, 4,4′-bis[ω-(4-cyanobiphenyl-4′-ylthio)alkoxy]biphenyls (CBSnOBOnSCB with a wide range of spacer carbon numbers, n = 3–11). All CBSnOBOnSCB homologs exhibited LC phases. Interestingly, even-n and odd-n homologs showed monotropic layered smectic A (SmA) and pseudo-layered twist-bend nematic (NTB) phases, respectively, below a nematic (N) phase. This alternate formation, which depends on spacer chain parity, is attributed to different average molecular shapes, which are associated with the relative orientations of the biphenyl moieties: linear and bent shapes for even-n and odd-n homologs, respectively. In addition, X-ray diffraction analysis indicated a strong cybotactic N phase tendency, with a triply intercalated structure. The phase-transition behavior and LC phase structures of thioether-linked CBSnOBOnSCB were compared with those of the all-ether-linked classic LC trimers CBOnOBOnOCB. Overall, thioether linkages endowed CBSnOBOnSCB with a monotropic LC tendency and lowered phase-transition temperatures, compared to those of CBOnOBOnOCB, for the same n. This is attributed to enhanced flexibility and bending (less molecular anisotropy) of the molecules, caused by the greater bond flexibility and smaller inner bond angles of the C–S–C bonds, compared to those of the C–O–C bonds.
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Arakawa Y, Ishida Y, Komatsu K, Arai Y, Tsuji H. Thioether-linked benzylideneaniline-based twist-bend nematic liquid crystal dimers: Insights into spacer lengths, mesogenic arm structures, and linkage types. Tetrahedron 2021. [DOI: 10.1016/j.tet.2021.132351] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Arakawa Y, Komatsu K, Shiba T, Tsuji H. Phase behaviors of classic liquid crystal dimers and trimers: Alternate induction of smectic and twist-bend nematic phases depending on spacer parity for liquid crystal trimers. J Mol Liq 2021. [DOI: 10.1016/j.molliq.2021.115319] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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6
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Arakawa Y, Komatsu K, Ishida Y, Igawa K, Tsuji H. Carbonyl- and thioether-linked cyanobiphenyl-based liquid crystal dimers exhibiting twist-bend nematic phases. Tetrahedron 2021. [DOI: 10.1016/j.tet.2020.131870] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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Pocock EE, Mandle RJ, Goodby JW. Experimental and Computational Study of a Liquid Crystalline Dimesogen Exhibiting Nematic, Twist-Bend Nematic, Intercalated Smectic, and Soft Crystalline Mesophases. Molecules 2021; 26:532. [PMID: 33498518 PMCID: PMC7864162 DOI: 10.3390/molecules26030532] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Revised: 01/18/2021] [Accepted: 01/19/2021] [Indexed: 11/16/2022] Open
Abstract
Liquid crystalline dimers and dimesogens have attracted significant attention due to their tendency to exhibit twist-bend modulated nematic (NTB) phases. While the features that give rise to NTB phase formation are now somewhat understood, a comparable structure-property relationship governing the formation of layered (smectic) phases from the NTB phase is absent. In this present work, we find that by selecting mesogenic units with differing polarities and aspect ratios and selecting an appropriately bent central spacer we obtain a material that exhibits both NTB and intercalated smectic phases. The higher temperature smectic phase is assigned as SmCA based on its optical textures and X-ray scattering patterns. A detailed study of the lower temperature smectic ''X'' phase by optical microscopy and SAXS/WAXS demonstrates this phase to be smectic, with an in-plane orthorhombic or monoclinic packing and long (>100 nm) out of plane correlation lengths. This phase, which has been observed in a handful of materials to date, is a soft-crystal phase with an anticlinic layer organisation. We suggest that mismatching the polarities, conjugation and aspect ratios of mesogenic units is a useful method for generating smectic forming dimesogens.
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Affiliation(s)
- Emily E. Pocock
- Department of Chemistry, University of York, Heslington, York YO10 5DD, UK;
| | - Richard J. Mandle
- Department of Chemistry, University of York, Heslington, York YO10 5DD, UK;
- School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK
| | - John W. Goodby
- Department of Chemistry, University of York, Heslington, York YO10 5DD, UK;
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Chiral Photoresponsive Liquid Crystalline Materials Derived from Cyanoazobenzene Central Core: Effect of UV Light Illumination on Mesomorphic Behavior. CRYSTALS 2020. [DOI: 10.3390/cryst10121161] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
One of the most frequently utilized liquid crystalline (LC) materials is a rod-like (calamitic) compound 4-cyano-4′-pentylbiphenyl (5-CB). The main objective of this work is to enhance its functionality by introducing a photoresponsive diazenyl spacer in the aromatic core and replace the non-chiral pentyl chain with various chiral alkyl carboxylate units. The mesomorphic properties of the prepared materials have been studied using polarizing optical microscopy and differential scanning calorimetry. It has been found that materials with an extended aromatic system possess the liquid crystalline behavior. The studied LC materials have shown mesophases at lower temperatures than previously reported analogous substances. Furthermore, one of them exhibits a chiral orthogonal frustrated twist grain boundary smectic phase, which has not been previously observed for this structural type of materials. We also investigated photoresponse of the mesophases under illumination with UV-light (365 nm) using a polarizing optical microscope. A non-conventional photoresponse of the prepared materials in a crystalline phase is presented and discussed.
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Al-Janabi A, Mandle RJ. Utilising Saturated Hydrocarbon Isosteres of para Benzene in the Design of Twist-Bend Nematic Liquid Crystals. Chemphyschem 2020; 21:697-701. [PMID: 32078227 DOI: 10.1002/cphc.202000130] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2020] [Indexed: 11/09/2022]
Abstract
The nematic twist-bend (NTB ) liquid crystal phase possesses a local helical structure with a pitch length of a few nanometres and is the first example of spontaneous symmetry breaking in a fluid system. All known examples of the NTB phase occur in materials whose constituent mesogenic units are aromatic hydrocarbons. It is not clear if this is due to synthetic convenience or a bona fide structural requirement for a material to exhibit this phase of matter. In this work we demonstrate that materials consisting largely of saturated hydrocarbons can also give rise to this mesophase.
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Affiliation(s)
| | - Richard J Mandle
- Department of Chemistry, University of York, York, UK.,School of Physics and Astronomy, University of Leeds, Leeds, UK
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10
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Arakawa Y, Ishida Y, Tsuji H. Ether- and Thioether-Linked Naphthalene-Based Liquid-Crystal Dimers: Influence of Chalcogen Linkage and Mesogenic-Arm Symmetry on the Incidence and Stability of the Twist-Bend Nematic Phase. Chemistry 2020; 26:3767-3775. [PMID: 31825562 DOI: 10.1002/chem.201905208] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2019] [Revised: 12/05/2019] [Indexed: 11/11/2022]
Abstract
The twist-bend nematic (NTB ) phase with a heliconical nanostructure of the local director generating symmetry breaking by achiral bent-shaped molecules is a hot topic of current liquid-crystal science. As opposed to the most common methylene-linked dimers, this study demonstrates chalcogen ether- and/or thioether-linked 6-(4-cyanophenyl)-2-naphthyl-based liquid-crystal dimers with symmetric and asymmetric π-conjugated mesogenic-arm structures that exhibit the NTB phase. Although the symmetric bis(ether)-linked dimer exhibits only the conventional nematic (N) phase, the asymmetric bis(ether)-linked dimer can form the NTB phase. All thioether-linked dimers form the NTB phase, wherein the dimers with asymmetric arms vitrify in the NTB phase on cooling to room temperature. The phase transitions are discussed in terms of the chalcogen linkage combination, mesogenic-arm symmetry, and spacer length. It is revealed that thioether-linked dimers based on asymmetric π-conjugated mesogenic arms with terminal cyano groups are highly beneficial for the realization of materials that form a wide range of NTB phases and glassy NTB states at room temperature.
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Affiliation(s)
- Yuki Arakawa
- Department of Applied Chemistry and Life Science, Graduate School of Engineering, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi, Aichi, 441-8580, Japan
| | - Yuko Ishida
- Department of Applied Chemistry and Life Science, Graduate School of Engineering, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi, Aichi, 441-8580, Japan
| | - Hideto Tsuji
- Department of Applied Chemistry and Life Science, Graduate School of Engineering, Toyohashi University of Technology, 1-1 Hibarigaoka, Tempaku-cho, Toyohashi, Aichi, 441-8580, Japan
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12
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13
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Koo J, Lim SI, Lee SH, Kim JS, Yu YT, Lee CR, Kim DY, Jeong KU. Polarized Light Emission from Uniaxially Oriented and Polymer-Stabilized AIE Luminogen Thin Films. Macromolecules 2019. [DOI: 10.1021/acs.macromol.8b02513] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
| | | | | | | | | | | | - Dae-Yoon Kim
- Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States
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14
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Arakawa Y, Komatsu K, Tsuji H. Twist-bend nematic liquid crystals based on thioether linkage. NEW J CHEM 2019. [DOI: 10.1039/c8nj06456c] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
“Thioether”-based twist-bend nematogens.
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Affiliation(s)
- Yuki Arakawa
- Department of Applied Chemistry and Life Science
- Graduate School of Engineering
- Toyohashi University of Technology
- Toyohashi
- Japan
| | - Kenta Komatsu
- Department of Applied Chemistry and Life Science
- Graduate School of Engineering
- Toyohashi University of Technology
- Toyohashi
- Japan
| | - Hideto Tsuji
- Department of Applied Chemistry and Life Science
- Graduate School of Engineering
- Toyohashi University of Technology
- Toyohashi
- Japan
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15
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KneŽević A, Sapunar M, Buljan A, Dokli I, Hameršak Z, Kontrec D, Lesac A. Fine-tuning the effect of π-π interactions on the stability of the N TB phase. SOFT MATTER 2018; 14:8466-8474. [PMID: 30324187 DOI: 10.1039/c8sm01569d] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
The synthesis and liquid-crystalline properties are reported for novel bent-shaped dimers in which a naphthyl group has been incorporated into the mesogenic cores. In addition to the nematic and twist-bend nematic phase, a new liquid-crystalline phase was observed. The combined experimental and computational study demonstrated how the interplay between the molecular geometry and π-π interactions affects the thermal stability of the twist-bend nematic and nematic phases. Correlation between mesomorphic properties and molecular geometry revealed that a greater conformational diversity leads to a broader distribution of bend-angles and destabilization of the NTB phase. Qualitative correlation between the thermal behaviour and electronic structure of the molecules of a similar geometry suggested that the transition temperatures of both nematic phases depend on the relative contribution of dispersion and electrostatic energies which determines the strength of the π-π interactions. These results provide an insight into how subtle changes in chemical structure can be exploited to tune the intermolecular interactions and influence the thermal stability of the liquid crystalline phase.
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16
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Krzyżewska K, Jaroch T, Maranda-Niedbała A, Pociecha D, Górecka E, Ahmed Z, Welch C, Mehl GH, Proń A, Nowakowski R. Supramolecular organization of liquid-crystal dimers - bis-cyanobiphenyl alkanes on HOPG by scanning tunneling microscopy. NANOSCALE 2018; 10:16201-16210. [PMID: 30123918 DOI: 10.1039/c8nr02069h] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
2D supramolecular organization of a series of six cyanobiphenyls bimesogens deposited on highly oriented pyrolytic graphite (HOPG) is studied by scanning tunneling microscopy (STM). The adsorbates are 1,ω-bis(4-cyanobiphenyl-4'-yl)alkanes (CBnCB) with different lengths of their flexible alkyl spacer (containing from 7 to 12 methylene groups). Microscopic investigations at the molecular resolution allow for detailed analysis of the effect of the alkyl spacer length on the type and the extent of the resulting 2D organization. It was demonstrated that bimesogens with shorter spacers (7 and 8 methylene units) organize in a similar manner characterized by the formation of two types of differently ordered monolayers: dense packed, wherein the molecules are oriented in one direction and ordered into parallel rows (layer structure), or less densely packed where they are organized into a chiral windmill-like structure. For derivatives with longer spacers (ranging from 9 to 12 methylene units) the additional effect of parity of carbon atoms in the spacer (even versus odd) is observed. In this range of the spacer lengths even membered bimesogens are also organized in a typical layer structure. However, odd-membered dimers exhibit a much more complex 2D supramolecular organization with a larger unit cell and a helical arrangement of the molecules. Careful comparison of this structure with the 3D structural data derived from the X-ray diffraction investigations of single crystals indicates that for these bimesogens a clear correlation exists between the observed complex 2D supramolecular organization in the monolayer and the organization in one of the crystallographic planes of the 3D nematic twist-bent phase.
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Affiliation(s)
- Klaudyna Krzyżewska
- Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, Warsaw 01-224, Poland.
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17
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Mandle RJ. Designing Liquid-Crystalline Oligomers to Exhibit Twist-Bend Modulated Nematic Phases. CHEM REC 2018; 18:1341-1349. [DOI: 10.1002/tcr.201800010] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2018] [Accepted: 04/09/2018] [Indexed: 01/28/2023]
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Mandle RJ. The Shape of Things To Come: The Formation of Modulated Nematic Mesophases at Various Length Scales. Chemistry 2017; 23:8771-8779. [PMID: 28453914 PMCID: PMC5518215 DOI: 10.1002/chem.201701167] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Indexed: 11/22/2022]
Abstract
The twist-bend nematic (NTB ) phase is a recently discovered liquid-crystalline phase that exhibits macroscopic chirality even when formed from achiral materials, and as such presents a unique testbed for studies concerning the spontaneous breaking of mirror symmetry in soft matter. It is primarily exhibited by materials for which the molecular structure is composed of two rigid aromatic units (such as biphenyl connected by a flexible spacer). The local structure of the NTB phase is nematic-like-with molecules having an average orientational order but no positional order-with a nanoscale helix in which the pitch (i.e., the repeat distance of the helix) is of the order of several nanometres. A helix is chiral, and so the bulk NTB phase-in the absence of a biasing chiral environment-spontaneously separates into macroscopic domains of opposite handedness. After discussing the structure of this mesophase and its elucidation, this concept article presents the molecular factors that determine its incidence. The apparent dependency primarily on molecular shape and bend angle rather than particular functional group combinations manifests in this mesophase being exhibited on length scales far beyond those of simple liquid-crystalline dimers, not only in oligomers and polymers, but also in aqueous suspensions of micron sized helical particles.
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Mandle RJ, Goodby JW. Does Topology Dictate the Incidence of the Twist-Bend Phase? Insights Gained from Novel Unsymmetrical Bimesogens. Chemistry 2016; 22:18456-18464. [PMID: 27706844 PMCID: PMC5217080 DOI: 10.1002/chem.201604030] [Citation(s) in RCA: 45] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Indexed: 11/21/2022]
Abstract
We prepared a significant number of unsymmetrical liquid-crystalline dimers that exhibit the twist-bend nematic phase; a state of matter that exhibits spontaneous breaking of mirror symmetry and, for some materials, a microsecond electrooptic response. A number of novel unsymmetrical bimesogens were synthesized and in comparing their thermal behaviour to previous literature examples, we have uncovered an unexpected relationship between the thermal stability of the nematic and NTB phases. This relationship demonstrates that molecular shape dictates the incidence of this fascinating phase of matter and leads us to speculate as to the existence of "twist-bend nematic phases" on length scales beyond those of the molecule.
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Tomczyk W, Pająk G, Longa L. Twist-bend nematic phases of bent-shaped biaxial molecules. SOFT MATTER 2016; 12:7445-7452. [PMID: 27604824 DOI: 10.1039/c6sm01197g] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
How can a change in molecular structure affect the relative stability and structural properties of the twist-bend nematic phase (NTB)? Here we extend the mean-field model(1) (C. Greco, G. R. Luckhurst and A. Ferrarini, Soft Matter, 2014, 10, 9318) for bent-shaped achiral molecules, to study the influence of arm molecular biaxiality and the value of the molecule's bend angle on the relative stability of NTB. In particular we show that by controlling the biaxiality of the molecule's arms, up to four ordered phases can become stable. They involve local uniaxial and biaxial variants of NTB, together with uniaxial and biaxial nematic phases. However, a V-shaped molecule shows a stronger ability to form stable NTB than a biaxial nematic phase, where the latter phase appears in the phase diagram only for bend angles greater than 140° and for large biaxiality of the two arms.
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Affiliation(s)
- Wojciech Tomczyk
- Marian Smoluchowski Institute of Physics, Department of Statistical Physics, Jagiellonian University, prof. S. Łojasiewicza 11, 30-348 Kraków, Poland.
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21
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Mandle RJ. The dependency of twist-bend nematic liquid crystals on molecular structure: a progression from dimers to trimers, oligomers and polymers. SOFT MATTER 2016; 12:7883-7901. [PMID: 27722733 DOI: 10.1039/c6sm01772j] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
This article gives an overview on recent developments concerning the twist-bend nematic phase. The twist-bend nematic phase has been discussed as the missing link between the uniaxial nematic mesophase (N) and the helical chiral nematic phase (N*). After an introduction discussing the key physical properties of the NTB phase and the methods used to identify the twist-bend nematic mesophase this review focuses on structure property relationships and molecular features that govern the incidence of this phase.
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Affiliation(s)
- Richard J Mandle
- Department of Chemistry, University of York, York, YO10 5DD, UK.
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22
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Robles-Hernández B, Sebastián N, Salud J, Diez-Berart S, Dunmur DA, Luckhurst GR, López DO, de la Fuente MR. Molecular dynamics of a binary mixture of twist-bend nematic liquid crystal dimers studied by dielectric spectroscopy. Phys Rev E 2016; 93:062705. [PMID: 27415332 DOI: 10.1103/physreve.93.062705] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2016] [Indexed: 06/06/2023]
Abstract
We report a comprehensive dielectric characterization of a liquid crystalline binary mixture composed of the symmetric mesogenic dimer CB7CB and the nonsymmetric mesogenic dimer FFO9OCB. In addition to the high-temperature nematic phase, such a binary mixture shows a twist-bend nematic phase at room temperature which readily vitrifies on slow cooling. Changes in the conformational distribution of the dimers are reflected in the dielectric permittivity and successfully analyzed by means of an appropriate theoretical model. It is shown that the dielectric spectra of the mixture reflect the different molecular dipole properties of the components, resembling in the present case the characteristic dielectric spectra of nonsymmetric dimers. Comparison of the nematic and twist-bend nematic phases reveals that molecular dynamics are similar despite the difference in the molecular environment.
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Affiliation(s)
- Beatriz Robles-Hernández
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain
| | - Nerea Sebastián
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain
- Otto-von-Guericke Universitat Magdeburg, Institute for Experimental Physics, ANP, 39106 Magdeburg, Germany
| | - Josep Salud
- Grup de Propietas Físiques dels Materials (GRPFM), Departament de Física, E.T.S.E.I.B. Universitat Politècnica de Catalunya, Diagonal 647, E-08028 Barcelona, Spain
| | - Sergio Diez-Berart
- Grup de Propietas Físiques dels Materials (GRPFM), Departament de Física, E.T.S.E.I.B. Universitat Politècnica de Catalunya, Diagonal 647, E-08028 Barcelona, Spain
| | - David A Dunmur
- School of Physics and Astronomy, University of Manchester, Manchester M13 9PL, United Kingdom
| | - Geoffrey R Luckhurst
- Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, United Kingdom
| | - David O López
- Grup de Propietas Físiques dels Materials (GRPFM), Departament de Física, E.T.S.E.I.B. Universitat Politècnica de Catalunya, Diagonal 647, E-08028 Barcelona, Spain
| | - M Rosario de la Fuente
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain
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Pardaev SA, Shamid SM, Tamba MG, Welch C, Mehl GH, Gleeson JT, Allender DW, Selinger JV, Ellman B, Jakli A, Sprunt S. Second harmonic light scattering induced by defects in the twist-bend nematic phase of liquid crystal dimers. SOFT MATTER 2016; 12:4472-4482. [PMID: 27089236 DOI: 10.1039/c6sm00585c] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The nematic twist-bend (NTB) phase, exhibited by certain thermotropic liquid crystalline (LC) dimers, represents a new orientationally ordered mesophase - the first distinct nematic variant discovered in many years. The NTB phase is distinguished by a heliconical winding of the average molecular long axis (director) with a remarkably short (nanoscale) pitch and, in systems of achiral dimers, with an equal probability to form right- and left-handed domains. The NTB structure thus provides another fascinating example of spontaneous chiral symmetry breaking in nature. The order parameter driving the formation of the heliconical state has been theoretically conjectured to be a polarization field, deriving from the bent conformation of the dimers, that rotates helically with the same nanoscale pitch as the director field. It therefore presents a significant challenge for experimental detection. Here we report a second harmonic light scattering (SHLS) study on two achiral, NTB-forming LCs, which is sensitive to the polarization field due to micron-scale distortion of the helical structure associated with naturally-occurring textural defects. These defects are parabolic focal conics of smectic-like "pseudo-layers", defined by planes of equivalent phase in a coarse-grained description of the NTB state. Our SHLS data are explained by a coarse-grained free energy density that combines a Landau-deGennes expansion of the polarization field, the elastic energy of a nematic, and a linear coupling between the two.
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Affiliation(s)
- Shokir A Pardaev
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
| | - S M Shamid
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
| | - M G Tamba
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK
| | - C Welch
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK
| | - G H Mehl
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK
| | - J T Gleeson
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
| | - D W Allender
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
| | - J V Selinger
- Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - B Ellman
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
| | - A Jakli
- Chemical Physics Interdisciplinary Program and Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - S Sprunt
- Department of Physics, Kent State University, Kent, Ohio 44242, USA.
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Ramou E, Ahmed Z, Welch C, Karahaliou PK, Mehl GH. The stabilisation of the Nx phase in mixtures. SOFT MATTER 2016; 12:888-899. [PMID: 26549345 DOI: 10.1039/c5sm01961c] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
The phase behaviour of mixtures between two symmetric dimers, CBC9CB and the ether-linked analogue CBOC9OCB was investigated by Polarizing Optical Microscopy (POM), Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) studies. The dimeric constituents are fully miscible and the construction of a temperature-composition phase diagram reveals a surprising amplification of the stability of the Nx phase in compositions of up to 37 wt% of CBOC9OCB in CBC9CB. The origin for this enhancement of stability is discussed and an explanation based on chiral recognition is developed.
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Affiliation(s)
- E Ramou
- Department of Chemistry, University of Hull, Hull HU6 7RX, UK.
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25
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Emsley JW, Lelli M, Joy H, Tamba MG, Mehl GH. Similarities and differences between molecular order in the nematic and twist-bend nematic phases of a symmetric liquid crystal dimer. Phys Chem Chem Phys 2016; 18:9419-30. [DOI: 10.1039/c5cp07304a] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Carbon-13 chemical shift anisotropies reveal an unusual temperature dependence of the order parameters, Szz, for the difluoroterphenyl groups in the normal nematic, N and the twist-bend nematic, NTB, phases.
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Affiliation(s)
- J. W. Emsley
- Department of Chemistry
- University of Southampton
- Southampton SO17 1BJ
- UK
| | - M. Lelli
- Institut des Sciences Analytiques
- Centre RMN à Très Hauts Champs (CRMN)
- 69100 Villeurbanne
- France
| | - H. Joy
- Department of Chemistry
- University of Hull
- Hull HU6 7RX
- UK
| | - M.-G. Tamba
- Department of Chemistry
- University of Hull
- Hull HU6 7RX
- UK
| | - G. H. Mehl
- Department of Chemistry
- University of Hull
- Hull HU6 7RX
- UK
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26
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Sebastián N, Tamba MG, Stannarius R, de la Fuente MR, Salamonczyk M, Cukrov G, Gleeson J, Sprunt S, Jákli A, Welch C, Ahmed Z, Mehl GH, Eremin A. Mesophase structure and behaviour in bulk and restricted geometry of a dimeric compound exhibiting a nematic–nematic transition. Phys Chem Chem Phys 2016; 18:19299-308. [DOI: 10.1039/c6cp03899a] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
We demonstrate a liquid crystal system exhibiting a variety of modulated structures on different length-scales: from helicoidal nematic to modulated smectic.
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Mandle RJ, Goodby JW. Intercalated soft-crystalline mesophase exhibited by an unsymmetrical twist-bend nematogen. CrystEngComm 2016. [DOI: 10.1039/c6ce02123a] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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