1
|
Barthakur A, Bag B, Shivaraja SJ, Karcz J, Kula P, Dhara S. Mixing twist-bend and ferroelectric nematic liquid crystals. Phys Rev E 2024; 109:024702. [PMID: 38491706 DOI: 10.1103/physreve.109.024702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2023] [Accepted: 01/12/2024] [Indexed: 03/18/2024]
Abstract
Twist-bend (N_{tb}) and ferroelectric (N_{F}) nematic liquid crystals exhibit several novel effects and new physical properties. Here, we report experimental studies on the phase diagram and some physical properties of binary mixtures of CB9CB and RM734 mesogens. Both N-N_{tb} and N-N_{F} phase transition temperatures and the corresponding enthalpies decrease significantly and, eventually, these transitions disappear at some intermediate compositions, stabilizing wide nematic phase (N). Temperature-dependent birefringence several degrees above the N-N_{tb} phase transition shows strong director tilt fluctuations. The critical range of the fluctuations increases with the nematic range and the critical exponent is consistent with the mean field. The spontaneous polarization of RM734 decreases drastically with the addition of CB9CB mesogen. The temperature dependence of the splay elastic constant of the mixtures' high-temperature nematic (N) phase strikingly differs from that of the pristine CB9CB and RM734 mesogens. The study shows that a small inclusion of either compound has a substantial effect on the phase diagram and physical properties.
Collapse
Affiliation(s)
| | - Bidisha Bag
- School of Physics, University of Hyderabad, Hyderabad 500046, India
| | | | - Jakub Karcz
- Institute of Chemistry, Faculty of Advanced Technologies and Chemistry, Military University of Technology, Warsaw 00-908, Poland
| | - Przemyslaw Kula
- Institute of Chemistry, Faculty of Advanced Technologies and Chemistry, Military University of Technology, Warsaw 00-908, Poland
| | - Surajit Dhara
- School of Physics, University of Hyderabad, Hyderabad 500046, India
| |
Collapse
|
2
|
Longa L, Cieśla M, Karbowniczek P, Chrzanowska A. Conformational degrees of freedom and stability of splay-bend ordering in the limit of a very strong planar anchoring. Phys Rev E 2023; 107:034707. [PMID: 37073017 DOI: 10.1103/physreve.107.034707] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2022] [Accepted: 03/09/2023] [Indexed: 04/20/2023]
Abstract
We study the self-organization in a monolayer (a two-dimensional system) of flexible planar trimer particles. The molecules are made up of two mesogenic units linked by a spacer, all of which are modeled as hard needles of the same length. Each molecule can dynamically adopt two conformational states: an achiral bent-shaped (cis-) and a chiral zigzag (trans-) one. Using constant pressure Monte Carlo simulations and Onsager-type density functional theory (DFT), we show that the system consisting of these molecules exhibits a rich spectrum of liquid crystalline phases. The most interesting observation is the identification of stable smectic splay-bend (S_{SB}) and chiral smectic-A (S_{A}^{*}) phases. The S_{SB} phase is also stable in the limit, where only cis- conformers are allowed. The second phase that occupies a considerable portion of the phase diagram is S_{A}^{*} with chiral layers, where the chirality of the neighboring layers is of opposite sign. The study of the average fractions of the trans- and cis- conformers in various phases shows that while in the isotropic phase all fractions are equally populated, the S_{A}^{*} phase is dominated by chiral conformers (zigzag), but the achiral conformers win in the smectic splay-bend phase. To clarify the possibility of stabilization of the nematic splay-bend (N_{SB}) phase for trimers, the free energy of the N_{SB} and S_{SB} phases is calculated within DFT for the cis- conformers, for densities where simulations show stable S_{SB}. It turns out that the N_{SB} phase is unstable away from the phase transition to the nematic phase, and its free energy is always higher than that of S_{SB}, down to the transition to the nematic phase, although the difference in free energies becomes extremely small when approaching the transition.
Collapse
Affiliation(s)
- Lech Longa
- Marian Smoluchowski Institute of Physics, Department of Statistical Physics and Mark Kac Center for Complex Systems Research, Jagiellonian University, ul. Łojasiewicza 11, 30-348 Kraków, Poland
| | - Michał Cieśla
- Marian Smoluchowski Institute of Physics, Department of Statistical Physics and Mark Kac Center for Complex Systems Research, Jagiellonian University, ul. Łojasiewicza 11, 30-348 Kraków, Poland
| | - Paweł Karbowniczek
- Faculty of Materials Engineering and Physics, Cracow University of Technology, ul. Podchorążych 1, 30-084, Kraków, Poland
| | - Agnieszka Chrzanowska
- Faculty of Materials Engineering and Physics, Cracow University of Technology, ul. Podchorążych 1, 30-084, Kraków, Poland
| |
Collapse
|
3
|
Sellarès J, Diego JA, López DO, Salud J, Robles-Hernández B, de la Fuente MR, Cañadas JC, Mudarra M, López de Rioja V, Levit R, Diez-Berart S. Comparative dielectric and thermally stimulated-depolarization-current studies of the liquid crystal dimers 1″,9″-bis(4-cyanobiphenyl-4'-yl) nonane and heptane and a binary mixture between them, close to the glass transition. Phys Rev E 2022; 106:054702. [PMID: 36559473 DOI: 10.1103/physreve.106.054702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Accepted: 10/27/2022] [Indexed: 06/17/2023]
Abstract
We have performed dielectric spectroscopy and thermally stimulated-depolarization-current experiments to study the molecular dynamics of the twist-bend nematic phase close to the glass transition of two members of the 1″,7'-bis(4-cyanobiphenyl-4'-yl)alkane homologous series (CBnCB): the liquid crystal (LC) dimers CB9CB and CB7CB, as well as a binary mixture of both. By doping CB9CB with a small quantity of CB7CB, the crystallization is inhibited when cooling the sample down, while the bulk properties of CB9CB are retained and we can investigate the supercooled behavior close to the glass transition. The study reveals that the inter- and intramolecular interactions of the mixture are similar to those of pure CB9CB and confirms that there is a single glass transition in symmetric LC dimers.
Collapse
Affiliation(s)
- Jordi Sellarès
- DILAB, Departament de Física, E.S.E.I.A.A.T. Universitat Politècnica de Catalunya, Colom 11, 08222 Terrassa, Spain
| | - José Antonio Diego
- DILAB, Departament de Física, E.S.E.I.A.A.T. Universitat Politècnica de Catalunya, Colom 11, 08222 Terrassa, Spain
| | - David O López
- Grup de les Propietas Físiques del Materials (GRPFM), Departament de Física, E.T.S.E.I.B. Universitat Politècnica de Catalunya, Avinguda Diagonal, 647, 08028 Barcelona, Spain
| | - Josep Salud
- Grup de les Propietas Físiques del Materials (GRPFM), Departament de Física, E.T.S.E.I.B. Universitat Politècnica de Catalunya, Avinguda Diagonal, 647, 08028 Barcelona, Spain
| | - Beatriz Robles-Hernández
- Donostia International Physics Center, Manuel Lardizabal Ibilbidea 4, 20018 Donostia, Spain
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain
| | - María Rosario de la Fuente
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain
| | - Juan Carlos Cañadas
- DILAB, Departament de Física, E.S.E.I.A.A.T. Universitat Politècnica de Catalunya, Colom 11, 08222 Terrassa, Spain
| | - Miguel Mudarra
- DILAB, Departament de Física, E.S.E.I.A.A.T. Universitat Politècnica de Catalunya, Colom 11, 08222 Terrassa, Spain
| | - Victor López de Rioja
- Grup de les Propietas Físiques del Materials (GRPFM), Departament de Física, E.T.S.E.I.B. Universitat Politècnica de Catalunya, Avinguda Diagonal, 647, 08028 Barcelona, Spain
| | - Rafael Levit
- Caracterització Elèctrica dels Materials i Dispositius (CEMAD), Departament de Física, E.T.S.E.I.B. Universitat Politècnica de Catalunya, Avinguda Diagonal, 647, 08028 Barcelona, Spain
| | - Sergio Diez-Berart
- Grup de les Propietas Físiques del Materials (GRPFM), Departament de Física, E.T.S.E.I.B. Universitat Politècnica de Catalunya, Avinguda Diagonal, 647, 08028 Barcelona, Spain
| |
Collapse
|
4
|
Chemical-Physical Characterization of a Binary Mixture of a Twist Bend Nematic Liquid Crystal with a Smectogen. CRYSTALS 2020. [DOI: 10.3390/cryst10121110] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Nematic twist-bend phases (NTB) are new types of nematic liquid crystalline phases with attractive properties for future electro-optic applications. However, most of these states are monotropic or are stable only in a narrow high temperature range. They are often destabilized under moderate cooling, and only a few single compounds have shown to give room temperature NTB phases. Mixtures of twist-bend nematic liquid crystals with simple nematogens have shown to strongly lower the nematic to NTB phase transition temperature. Here, we examined the behaviour of new types of mixtures with the dimeric liquid crystal [4′,4′-(heptane-1,7-diyl)bis(([1′,1″-biphenyl]4″-carbo-nitrile))] (CB7CB). This now well-known twist-bend nematic liquid crystal presents a nematic twist-bend phase below T ≈ 104 °C. Mixtures with other monomeric alkyl or alkoxy -biphenylcarbonitriles liquid crystals that display a smectic A (SmA) phase also strongly reduce this temperature. The most interesting smectogen is 4′-Octyl-4-biphenylcarbonitrile (8CB), for which a long-term metastable NTB phase is found at room and lower temperatures. This paper presents the complete phase diagram of the corresponding binary system and a detailed investigation of its thermal, optical, dielectric, and elastic properties.
Collapse
|
5
|
Shi J, Sidky H, Whitmer JK. Novel elastic response in twist-bend nematic models. SOFT MATTER 2019; 15:8219-8226. [PMID: 31495852 DOI: 10.1039/c9sm01395d] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Bent-shaped liquid crystals have attracted significant attention recently due to their novel mesostructure and the intriguing behavior of their elastic constants, which are strongly anisotropic and have an unusual temperature dependence. Though theories explain the onset of the twist-bend nematic phase (NTB) through spontaneous symmetry breaking concomitant with transition to a negative bend (K3) elastic constant, this has not been observed as yet in experiments. There, the small bend elastic constant has a strongly non-monotonic temperature dependence, which first increases after crossing the isotropic (I)-nematic (N) transition, then dips near the nematic (N)-twist-bend (NTB) transition before it increases again as the transition is crossed. The molecular mechanisms responsible for this exotic behavior are unclear. Here, we utilize density of states algorithms in Monte Carlo simulation applied to a variant of the Lebwohl-Lasher model which includes bent-shaped-like interactions to analyze the mechanism behind elastic response in this novel mesostructure and understand the temperature dependence of its Frank-Oseen elastic constants.
Collapse
Affiliation(s)
- Jiale Shi
- Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, USA.
| | | | | |
Collapse
|
6
|
Abstract
The response of the nematic twist-bend ([Formula: see text]) phase to an applied field can provide important insight into the structure of this liquid and may bring us closer to understanding mechanisms generating mirror symmetry breaking in a fluid of achiral molecules. Here we investigate theoretically how an external uniform field can affect structural properties and the stability of [Formula: see text] Assuming that the driving force responsible for the formation of this phase is packing entropy, we show, within Landau-de Gennes theory, that [Formula: see text] can undergo a rich sequence of structural changes with the field. For the systems with positive anisotropy of permittivity, we first observe a decrease of the tilt angle of [Formula: see text] until it transforms through a field-induced phase transition to the ordinary prolate uniaxial nematic phase (N). Then, at very high fields, this nematic phase develops polarization perpendicular to the field ([Formula: see text]). For systems with negative anisotropy of permittivity, the results reveal new modulated structures. Even an infinitesimally small field transforms [Formula: see text] to its elliptical counterpart ([Formula: see text]), where the circular base of the cone of the main director becomes elliptic. With stronger fields, the ellipse degenerates to a line, giving rise to a nonchiral periodic structure, the nematic splay-bend ([Formula: see text]), where the two nematic directors are restricted to a plane. The three structures-[Formula: see text], [Formula: see text], and [Formula: see text]-with a modulated polar order are globally nonpolar. But further increase of the field induces phase transitions into globally polar structures with nonvanishing polarization along the field's direction. We found two such structures, one of which is a polar and chiral modification of [Formula: see text], where splay and bend deformations are accompanied by weak twist deformations ([Formula: see text]). Further increase of the field unwinds this structure into a polar nematic ([Formula: see text]) of polarization parallel to the field.
Collapse
|
7
|
Knežević A, Dokli I, Sapunar M, Šegota S, Baumeister U, Lesac A. Induced smectic phase in binary mixtures of twist-bend nematogens. BEILSTEIN JOURNAL OF NANOTECHNOLOGY 2018; 9:1297-1307. [PMID: 29765808 PMCID: PMC5942249 DOI: 10.3762/bjnano.9.122] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2017] [Accepted: 03/22/2018] [Indexed: 05/28/2023]
Abstract
The investigation of liquid crystal (LC) mixtures is of great interest in tailoring material properties for specific applications. The recent discovery of the twist-bend nematic phase (NTB) has sparked great interest in the scientific community, not only from a fundamental viewpoint, but also due to its potential for innovative applications. Here we report on the unexpected phase behaviour of a binary mixture of twist-bend nematogens. A binary phase diagram for mixtures of imino-linked cyanobiphenyl (CBI) dimer and imino-linked benzoyloxy-benzylidene (BB) dimer shows two distinct domains. While mixtures containing less than 35 mol % of BB possess a wide temperature range twist-bend nematic phase, the mixtures containing 55-80 mol % of BB exhibit a smectic phase despite that both pure compounds display a Iso-N-NTB-Cr phase sequence. The phase diagram shows that the addition of BB of up to 30 mol % significantly extends the temperature range of the NTB phase, maintaining the temperature range of the nematic phase. The periodicity, obtained by atomic force microscopy (AFM) imaging, is in the range of 6-7 nm. The induction of the smectic phase in the mixtures containing 55-80 mol % of BB was confirmed using polarising optical microscopy (POM), differential scanning calorimetry (DSC) and X-ray diffraction. The origin of the intercalated smectic phase was unravelled by combined spectroscopic and computational methods and can be traced to conformational disorder of the terminal chains. These results show the importance of understanding the phase behaviour of binary mixtures, not only in targeting a wide temperature range but also in controlling the self-organizing processes.
Collapse
Affiliation(s)
- Anamarija Knežević
- Division of Organic Chemistry and Biochemistry, Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia
| | - Irena Dokli
- Division of Organic Chemistry and Biochemistry, Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia
| | - Marin Sapunar
- Division of Physical Chemistry, Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia
| | - Suzana Šegota
- Division of Physical Chemistry, Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia
| | - Ute Baumeister
- Institute of Chemistry, Physical Chemistry, Martin Luther University Halle-Wittenberg, von-Danckelmann-Platz 4, 06120 Halle, Germany
| | - Andreja Lesac
- Division of Organic Chemistry and Biochemistry, Ruđer Bošković Institute, Bijenička cesta 54, 10000 Zagreb, Croatia
| |
Collapse
|
8
|
López DO, Salud J, de la Fuente MR, Sebastián N, Diez-Berart S. Cooperative behavior of molecular motions giving rise to two glass transitions in the same supercooled mesophase of a smectogenic liquid crystal dimer. Phys Rev E 2018; 97:012704. [PMID: 29448339 DOI: 10.1103/physreve.97.012704] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2017] [Indexed: 06/08/2023]
Abstract
In the present work, a detailed analysis of the glassy behavior and the relaxation dynamics of the liquid crystal dimer α-(4-cyanobiphenyl-4'-yloxy)-ω-(1-pyrenimine-benzylidene-4'-oxy) heptane (CBO7O.Py) throughout both nematic and smectic-A mesophases by means of broadband dielectric spectroscopy has been performed. CBO7O.Py shows three different dielectric relaxation modes and two glass transition (T_{g}) temperatures: The higher T_{g} is due to the freezing of the molecular motions responsible for the relaxation mode with the lowest frequency (μ_{1L}); the lower T_{g} is due to the motions responsible for the two relaxation modes with highest frequencies (μ_{1H} and μ_{2}), which converge just at their corresponding T_{g}. It is shown how the three modes follow a critical-like description via the dynamic scaling model. The two modes with lowest frequencies (μ_{1L} and μ_{1H}) are cooperative in the whole range of the mesophases, whereas the highest frequency mode (μ_{2}) is cooperative just below some crossover temperature. In terms of fragility, at the glass transition, the ensemble (μ_{1H}+μ_{2}) presents a value of the steepness index and μ_{1L} a different one, meaning that fragility is a property intrinsic to the molecular motion itself. Finally, the steepness index seems to have a universal behavior with temperature for the dielectric relaxation modes of liquid crystal dimers, being almost constant at high temperatures and increasing drastically when cooling the compound down to the glass transition from a temperature about 3/4T_{NI}.
Collapse
Affiliation(s)
- 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
| | - 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
| | - María Rosario de la Fuente
- Departamento de Física Aplicada II, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, E-48080 Bilbao, Spain
| | - Nerea Sebastián
- Jožef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, Slovenia
| | - 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
| |
Collapse
|
9
|
Stevenson WD, Zou HX, Zeng XB, Welch C, Ungar G, Mehl GH. Dynamic calorimetry and XRD studies of the nematic and twist-bend nematic phase transitions in a series of dimers with increasing spacer length. Phys Chem Chem Phys 2018; 20:25268-25274. [DOI: 10.1039/c8cp05744c] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
A modulated DSC study of bent dimesogens with (CH2)n spacers n = 5–11 showed that the enthalpy of the ordinary nematic is lowest for n = 11 due to the lowest C–C torsion energy needed to straighten the dimer, causing near disappearance of twist-bend-nematic to nematic transition enthalpy.
Collapse
Affiliation(s)
- Warren D. Stevenson
- Department of Physics
- Zhejiang Sci-Tech University
- Hangzhou 310018
- China
- Department of Materials Science and Engineering
| | - Heng-xing Zou
- Department of Physics
- Zhejiang Sci-Tech University
- Hangzhou 310018
- China
| | - Xiang-bing Zeng
- Department of Materials Science and Engineering
- University of Sheffield
- Sheffield S1 3JD
- UK
| | | | - Goran Ungar
- Department of Physics
- Zhejiang Sci-Tech University
- Hangzhou 310018
- China
- Department of Materials Science and Engineering
| | - Georg H. Mehl
- Department of Chemistry
- University of Hull
- Hull HU6 7RX
- UK
| |
Collapse
|
10
|
Emsley JW, Lelli M, Luckhurst GR, Zimmermann H. ^{13}C NMR study of the director distribution adopted by the modulated nematic phases formed by liquid-crystal dimers with odd numbers of atoms in their spacers. Phys Rev E 2017; 96:062702. [PMID: 29347294 DOI: 10.1103/physreve.96.062702] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Indexed: 11/07/2022]
Abstract
The orientational order of the molecules in the bent mesogen CB6OCB has been studied throughout the range of temperature stability of both the N_{U} and N_{TB} liquid-crystal phases by ^{13}C NMR spectroscopy. These spectra provide local order parameters for the para axes of both of the nonequivalent cyanobiphenyl groups and show how they change on entering the twist-bend nematic phase. A key feature of the order parameters is a weak, but clear maximum in the temperature variation of the order parameter prior to the N_{TB} phase. This suggests that the directors in both the N_{U} and N_{TB} phases are tilted with respect to the magnetic field of the spectrometer. Significantly the conformational states of the spacer are comparable in both phases, although the low temperature nematic is chiral but not that at high temperature. It is proposed that the higher temperature, tilted phase could be the splay-bend nematic phase.
Collapse
Affiliation(s)
- J W Emsley
- Chemistry, University of Southampton, Highfield, Southampton, SO17 1BJ, United Kingdom
| | - M Lelli
- Department of Chemistry, Center for Magnetic Resonance, University of Florence, Sesto Fiorentino (FI) 50019, Italy
| | - G R Luckhurst
- Chemistry, University of Southampton, Highfield, Southampton, SO17 1BJ, United Kingdom
| | - H Zimmermann
- Max-Planck-Institut für Medizinische Forschung, Department of Biomolecular Mechanisms, D-69120 Heidelberg, Germany
| |
Collapse
|
11
|
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.
Collapse
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
| |
Collapse
|
12
|
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.
Collapse
Affiliation(s)
- Richard J Mandle
- Department of Chemistry, University of York, York, YO10 5DD, UK.
| |
Collapse
|
13
|
Paterson DA, Gao M, Kim YK, Jamali A, Finley KL, Robles-Hernández B, Diez-Berart S, Salud J, de la Fuente MR, Timimi BA, Zimmermann H, Greco C, Ferrarini A, Storey JMD, López DO, Lavrentovich OD, Luckhurst GR, Imrie CT. Understanding the twist-bend nematic phase: the characterisation of 1-(4-cyanobiphenyl-4'-yloxy)-6-(4-cyanobiphenyl-4'-yl)hexane (CB6OCB) and comparison with CB7CB. SOFT MATTER 2016; 12:6827-6840. [PMID: 27447288 DOI: 10.1039/c6sm00537c] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
The synthesis and characterisation of the nonsymmetric liquid crystal dimer, 1-(4-cyanobiphenyl-4'-yloxy)-6-(4-cyanobiphenyl-4'-yl)hexane (CB6OCB) is reported. An enantiotropic nematic (N)-twist-bend nematic (NTB) phase transition is observed at 109 °C and a nematic-isotropic phase transition at 153 °C. The NTB phase assignment has been confirmed using polarised light microscopy, freeze fracture transmission electron microscopy (FFTEM), (2)H-NMR spectroscopy, and X-ray diffraction. The effective molecular length in both the NTB and N phases indicates a locally intercalated arrangement of the molecules, and the helicoidal pitch length in the NTB phase is estimated to be 8.9 nm. The surface anchoring properties of CB6OCB on a number of aligning layers is reported. A Landau model is applied to describe high-resolution heat capacity measurements in the vicinity of the NTB-N phase transition. Both the theory and heat capacity measurements agree with a very weak first-order phase transition. A complementary extended molecular field theory was found to be in suggestive accord with the (2)H-NMR studies of CB6OCB-d2, and those already known for CB7CB-d4. These include the reduced transition temperature, TNTBN/TNI, the order parameter of the mesogenic arms in the N phase close to the NTB-N transition, and the order parameter with respect to the helix axis which is related to the conical angle for the NTB phase.
Collapse
Affiliation(s)
- Daniel A Paterson
- Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Meston Building, Aberdeen, AB24 3UE, UK.
| | - Min Gao
- Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, OH 44242, USA
| | - Young-Ki Kim
- Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, OH 44242, USA
| | - Afsoon Jamali
- Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, OH 44242, USA
| | - Kirsten L Finley
- Department of Physics, Polytechnic University of Catalonia, Barcelona, Spain
| | | | - Sergio Diez-Berart
- Department of Physics, Polytechnic University of Catalonia, Barcelona, Spain
| | - Josep Salud
- Department of Physics, Polytechnic University of Catalonia, Barcelona, Spain
| | - M Rosario de la Fuente
- Department of Applied Physics II, University of the Basque Country, E-48080 Bilbao, Spain
| | - Bakir A Timimi
- Chemistry, University of Southampton, Highfield, Southampton, SO17 1BJ, UK
| | - Herbert Zimmermann
- Max-Planck-Institut für Medizinische Förschung, D-69120 Heidelberg, Germany
| | - Cristina Greco
- Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, 35121 Padova, Italy
| | - Alberta Ferrarini
- Dipartimento di Scienze Chimiche, Università di Padova, via Marzolo 1, 35121 Padova, Italy
| | - John M D Storey
- Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Meston Building, Aberdeen, AB24 3UE, UK.
| | - David O López
- Department of Physics, Polytechnic University of Catalonia, Barcelona, Spain
| | - Oleg D Lavrentovich
- Liquid Crystal Institute and Chemical Physics Interdisciplinary Program, Kent State University, Kent, OH 44242, USA
| | | | - Corrie T Imrie
- Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Meston Building, Aberdeen, AB24 3UE, UK.
| |
Collapse
|
14
|
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.
Collapse
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
| |
Collapse
|