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Krishnamurthy KS, Shankar Rao DS, Khatavi SY, Yelamaggad CV. Twist-bend nematic drops as colloidal particles: Electric instabilities. Phys Rev E 2023; 107:044703. [PMID: 37198758 DOI: 10.1103/physreve.107.044703] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2023] [Accepted: 04/10/2023] [Indexed: 05/19/2023]
Abstract
The mesogen 1,''7''-bis(4-cyanobiphenyl-4'-yl)heptane (CB7CB), doped with a small quantity of an amphiphilic compound, is examined in its biphasic state in which twist-bend nematic (N_{TB}) drops are dispersed in the isotropic fluid. Various flexoelectric and electrokinetic responses of small drops in their escaped-radial-like (ER) geometry, and also of larger ones with parabolic focal conic defects, are discussed. A pair of confocal parabolas with their axes along the applied low-frequency electric field undergo periodic dimensional changes so as to contribute flexoelectrically to free-energy reduction. In an ER droplet, the same result is achieved by periodic relocations of the hedgehog core. Sine-wave fields of low frequency and high voltage excite patterned states near zero-voltage crossings and homeotropic alignment at peak voltages. ER drops also exhibit electrohydrodynamic effects; in relatively weak fields, they undergo translatory motion with a velocity that is a quadratic in the field strength; the drift, which occurs over a very wide frequency range, extending from dc to MHz region, is enabled by radial symmetry breaking that their off-centered geometry entails; and the drift direction reverses across a critical frequency. In high fields, vortical flows occurring within an ER N_{TB} drop become discernible. The hydrodynamic effects are discussed based on the Taylor-Melcher leaky dielectric model.
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Affiliation(s)
- K S Krishnamurthy
- Centre for Nano and Soft Matter Sciences, Survey No. 7, Shivanapura, Bangalore 562162, India
| | - D S Shankar Rao
- Centre for Nano and Soft Matter Sciences, Survey No. 7, Shivanapura, Bangalore 562162, India
| | - Santosh Y Khatavi
- Centre for Nano and Soft Matter Sciences, Survey No. 7, Shivanapura, Bangalore 562162, India
| | - Channabasaveshwar V Yelamaggad
- Centre for Nano and Soft Matter Sciences, Survey No. 7, Shivanapura, Bangalore 562162, India
- Manipal Academy of Higher Education, Madhav Nagar, Manipal 576104, India
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2
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Aya S, Tang W, Kong X, Arakawa Y, Komatsu K, Tsuji H. Nontrivial ultraslow dynamics under electric-field in nematics of bent-shaped molecules. Phys Chem Chem Phys 2022; 25:297-303. [PMID: 36477024 DOI: 10.1039/d2cp02407a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
For over decades, nematic liquid crystals have been recognized as highly fluidic materials that respond to electric field on the millisecond scale. In contrast to traditional nematics with fast responsivity, we herein report nontrivial ultraslow electric-driven dynamics in bent-shaped nematic materials. Varying the alkyl chain spacers of bent-shaped cyanobiphenyl dimers (COOm and OCOm) shows a 'transition' in the dynamics behavior between the bent-dimeric and bent-core materials. Interestingly, with short alkyl chain spacers, COO2 exhibits unexpected ultra-slow dynamic pathways, i.e., "quasi-static" electrohydrodynamic convection. A significant observation is that the on/off-electro-switching time of COO2 is 10 000 times higher than that of typical nematic materials, which is the largest value reported ever in the kilo-second range. In addition, the threshold voltage for inducing the reorientation of the nematic director for COO2 is higher than 5 V, which is uncommon in traditional N materials. These properties are distinct from those of traditional nematic materials and discussed in terms of dielectric constants and electrohydrodynamic convection.
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Affiliation(s)
- Satoshi Aya
- South China Advanced Institute for Soft Matter Science and Technology (AISMST), School of Emergent Soft Matter, South China University of Technology, Guangzhou 510640, China. .,Guangdong Provincial Key Laboratory of Functional and Intelligent Hybrid Materials and Devices, South China University of Technology, Guangzhou 510640, China
| | - Wentao Tang
- South China Advanced Institute for Soft Matter Science and Technology (AISMST), School of Emergent Soft Matter, South China University of Technology, Guangzhou 510640, China.
| | - Xian Kong
- South China Advanced Institute for Soft Matter Science and Technology (AISMST), School of Emergent Soft Matter, South China University of Technology, Guangzhou 510640, China.
| | - Yuki Arakawa
- Department of Applied Chemistry and Life Science, Graduate School of Engineering, Toyohashi University of Technology, Toyohashi, 441-8580, Japan.
| | - Kenta Komatsu
- Department of Applied Chemistry and Life Science, Graduate School of Engineering, Toyohashi University of Technology, Toyohashi, 441-8580, Japan.
| | - Hideto Tsuji
- Department of Applied Chemistry and Life Science, Graduate School of Engineering, Toyohashi University of Technology, Toyohashi, 441-8580, Japan.
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Imrie CT, Paterson DA, Storey JMD, Chamignon C, Lelli M, Emsley JW, Luckhurst GR. Phase transitions in a high magnetic field of an odd, symmetric liquid crystal dimer having two nematic phases, N_{U} and N_{TB}, studied by NMR spectroscopy. Phys Rev E 2020; 102:042706. [PMID: 33212702 DOI: 10.1103/physreve.102.042706] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Accepted: 07/31/2020] [Indexed: 11/07/2022]
Abstract
Both ^{1}H and ^{13}C NMR spectra have been obtained in a static magnetic field of 23.5 T on a bent-shaped dimer molecule, 1^{''},7^{''}-bis(4-cyanobiphenyl-4'-yl) nonane (CB9CB), which shows the sequence of liquid crystal phases twist-bend nematic, N_{TB}, and uniaxial nematic, N_{U}, before entering the isotropic phase. The ^{1}H spectra are used to locate the temperature at which the sample melts to form a twist-bend nematic, T_{CrN_{TB}}, and then T_{N_{U}I} when the isotropic phase is entered, both in a magnetic field of 23.5 T, and to compare these with those measured at the Earth's field. The differences between these transition temperatures are found to be zero within the error in their measurement, in stark contrast to previous measurements by Salili et al. [Phys. Rev. Lett. 116, 217801 (2016)10.1103/PhysRevLett.116.217801]. In the isotropic phase in the presence of the field the sample exists in a paranematic phase in which the molecules of CB9CB are partially ordered. The ^{1}H and ^{13}C NMR spectra in the paranematic phase are used to measure the critical temperature T* below which this phase is unstable. The spectra are also used to study the structure, molecular orientational order, and distribution of molecular conformations in the paranematic phase.
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Affiliation(s)
- C T Imrie
- Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Aberdeen AB24 3FX, United Kingdom
| | - D A Paterson
- Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Aberdeen AB24 3FX, United Kingdom
| | - J M D Storey
- Department of Chemistry, School of Natural and Computing Sciences, University of Aberdeen, Aberdeen AB24 3FX, United Kingdom
| | - C Chamignon
- Centre de RMN à Très Hauts Champs de Lyon (FRE 2034-CNRS, UCB Lyon 1, ENS Lyon), 5 rue de la Doua, 69100 Villeurbanne, France
| | - M Lelli
- Department of Chemistry "Ugo Schiff," Center for Magnetic Resonance, University of Florence, Sesto Fiorentino (FI) 50019, Italy
| | - J W Emsley
- School of Chemistry, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton SO17 1BJ, United Kingdom
| | - G R Luckhurst
- School of Chemistry, Faculty of Engineering and Physical Sciences, University of Southampton, Southampton SO17 1BJ, United Kingdom
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Aluculesei A, Cachitas H, Carvalho J, Vaca Chavez F, Figueirinhas JL, Sebastião PJ, Cruz C, Tamba MG, Kohlmeier A, Mehl GH. 1H NMR study of molecular order and dynamics in the liquid crystal CB-C9-CB. Phys Chem Chem Phys 2019; 21:4523-4537. [PMID: 30735227 DOI: 10.1039/c8cp06868b] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Molecular order and dynamics of the CB-C9-CB liquid crystalline dimer exhibiting the nematic (N) and the twist bend nematic (Ntb) phases were investigated by proton NMR spectroscopy, using fields of 0.78 T and 7.04 T, and relaxometry. The first relaxometry experiments for a very wide Larmor frequency domain (8 kHz-300 MHz) on this system, using a combination of standard and fast field cycling NMR techniques, were performed. The spectroscopy results in the Ntb phase allowed us to probe the local molecular orientation relative to the Ntb helix axis. The relaxation data were analyzed considering order director fluctuations (ODF), molecular self-diffusion (SD) and local molecular rotations/reorientations (R) relaxation mechanisms. Global fits of theoretical relaxation models, as a function of temperature and Larmor frequency, for the phases under investigation, allowed for the determination of rotational correlation times, diffusion coefficients, viscoelastic parameters, correlation lengths and activation energies (in the case of thermally activated mechanisms). A clear difference between the structures of the N and Ntb phases was detected from the results of proton spin-lattice relaxation through distinct temperature and frequency dependencies' signatures of the collective modes. Significant pre-transitional effects were observed at the N-Ntb phase transition both from relaxometry and spectroscopy data. The experimental results correlate to data and models for comparable liquid crystalline systems.
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Affiliation(s)
- Alina Aluculesei
- Centro de Física e Engenharia de Materiais Avançados, Dept. of Physics, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais, 1049-001 Lisbon, Portugal.
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Carvalho J, Cruz C, Figueirinhas JL, Tamba MG, Kohlmeier A, Mehl GH. Proton and Deuterium NMR Study of the CBC9CB Dimer System. J Phys Chem B 2019; 123:1442-1451. [DOI: 10.1021/acs.jpcb.8b11526] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- J. Carvalho
- Department of Physics, and CeFEMA, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
| | - C. Cruz
- Department of Physics, and CeFEMA, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
| | - J. L. Figueirinhas
- Department of Physics, and CeFEMA, Instituto Superior Técnico, Universidade de Lisboa, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
| | - M. G. Tamba
- Department of Chemistry, University of Hull, Hull HU6 7RX, United Kingdom
| | - A. Kohlmeier
- Department of Chemistry, University of Hull, Hull HU6 7RX, United Kingdom
| | - G. H. Mehl
- Department of Chemistry, University of Hull, Hull HU6 7RX, United Kingdom
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Merkel K, Kocot A, Welch C, Mehl GH. Soft modes of the dielectric response in the twist–bend nematic phase and identification of the transition to a nematic splay bend phase in the CBC7CB dimer. Phys Chem Chem Phys 2019; 21:22839-22848. [DOI: 10.1039/c9cp04952e] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Two collective processes resulting from distortion of the heliconical structure of the twist–bend nematic phase of an achiral dimer: one tilt mode due to distortions of the conical angle and second related to long range fluctuation of the cone phase.
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Affiliation(s)
- K. Merkel
- Faculty of Computer Science and Material Science
- Institute of Technology and Mechatronics
- University of Silesia in Katowice
- Poland
| | - A. Kocot
- Faculty of Computer Science and Material Science
- Institute of Technology and Mechatronics
- University of Silesia in Katowice
- Poland
| | - 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
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7
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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.
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8
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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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9
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Krishnamurthy KS, Kanakala MB, Yelamaggad CV, Kleman M. Instabilities in the electric Freedericksz state of the twist-bend nematic liquid crystal CB7CB. SOFT MATTER 2018; 14:5393-5406. [PMID: 29930998 DOI: 10.1039/c8sm00554k] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
We report on the instabilities in the Freedericksz state of the twist-bend nematic (NTB) liquid crystal 1'',7''-bis(4-cyanobiphenyl-4'-yl)heptane (CB7CB). The quasi homeotropic NTB state, into which a planar (untwisted or 90°-twisted) nematic CB7CB layer transits under a strong electric field, is found to be unstable despite the material being dielectrically positive. Close to the NTB melting point, destabilization occurs through the formation of metastable toric focal conic domains (TFCDs) that, in time, transform into parabolic focal conic domains (PFCDs) with the confocal parabolae in vertical planes through the layer normal. This transformation occurs by a novel process of continued dissociation of TFCDs. We outline how the extended Volterra process could help in a general appreciation of focal conic defects in the NTB phase. At relatively lower temperatures, stripes develop competingly with TFCDs. Identifiable as oily streaks, they are both localized and polarity sensitive; they form close to the substrates; and in low frequency square wave fields, they get suppressed at the cathode and augmented at the anode at each polarity switch. The study also dwells on the N-NTB-N sandwich region, found between the N and NTB states under a small temperature gradient.
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10
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Exploring “Dormant” Opto-Mechanical Properties of the Isotropic Phase of Liquid Crystals and Revealing Hidden Elasticity of (Ordinary) Liquids. FLUIDS 2018. [DOI: 10.3390/fluids3020043] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
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11
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Bian Y, Ding W, Hu L, Ma Z, Cheng L, Zhang R, Zhu X, Tang X, Dai J, Bai J, Sun Y, Sheng Z. Acceleration of Kirkendall effect processes in silicon nanospheres using magnetic fields. CrystEngComm 2018. [DOI: 10.1039/c7ce01802a] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We show that a magnetic field can act as an independent parameter to accelerate the Kirkendall effect in a liquid reaction system.
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12
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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.
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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
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Mandle RJ, Cowling SJ, Goodby JW. Combined Microscopy, Calorimetry and X-ray Scattering Study of Fluorinated Dimesogens. Sci Rep 2017; 7:13323. [PMID: 29042568 PMCID: PMC5645320 DOI: 10.1038/s41598-017-12799-1] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2017] [Accepted: 09/15/2017] [Indexed: 11/09/2022] Open
Abstract
The material FDO11DFCB3 (compound 2 in this work) remains the only example of a liquid-crystalline material to exhibit a phase transition from the heliconical twist-bend phase into a lamellar smectic A mesophase, additionally this material exhibits a previously unidentified mesophase. We have prepared and characterised several homologues of this compound, with each material subjected to an in-depth analysis by optical microscopy, calorimetry and small angle X-ray scattering studies. Despite FDO11DFCB3 being similar in chemical structure to the novel materials presented herein its liquid-crystalline behaviour is rather different, indicating an unexpected sensitivity of the twist-bend phase to molecular structure.
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Affiliation(s)
- Richard J Mandle
- Department of Chemistry, University of York, Heslington, YO10 5DD, UK.
| | - Stephen J Cowling
- Department of Chemistry, University of York, Heslington, YO10 5DD, UK
| | - John W Goodby
- Department of Chemistry, University of York, Heslington, YO10 5DD, UK
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14
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Krishnamurthy KS, Palakurthy NB, Yelamaggad CV. Confined Electroconvective and Flexoelectric Instabilities Deep in the Freedericksz State of Nematic CB7CB. J Phys Chem B 2017; 121:5447-5454. [PMID: 28489383 DOI: 10.1021/acs.jpcb.7b03072] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
We report wormlike flexoelectric structures evolving deep in the Freedericksz state of a nematic layer of the liquid crystal cyanobiphenyl-(CH2)7-cyanobiphenyl. They form in the predominantly splay-bend thin boundary layers and are built up of solitary flexoelectric domains of the Bobylev-Pikin type. Their formation is possibly triggered by the gradient flexoelectric surface instability that remains optically discernible up to unusually high frequencies. The threshold voltage at which the worms form scales as square root of the frequency; in their extended state, worms often appear as labyrinthine structures on a section of loops that separate regions of opposite director deviation. Such asymmetric loops are also derived through pincement-like dissociation of ring-shaped walls. Formation of isolated domains of bulk electroconvection precedes the onset of surface instabilities. In essence, far above the Freedericksz threshold, the twisted nematic layer behaves as a combination of two orthogonally oriented planar half-layers destabilized by localized flexoelectric distortion.
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Affiliation(s)
| | - Nani Babu Palakurthy
- Centre for Nano and Soft Matter Sciences , P.O. Box 1329, Jalahalli, Bangalore 560013, India
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15
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The Dependency of Nematic and Twist-bend Mesophase Formation on Bend Angle. Sci Rep 2016; 6:36682. [PMID: 27819300 PMCID: PMC5098182 DOI: 10.1038/srep36682] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2016] [Accepted: 10/18/2016] [Indexed: 01/07/2023] Open
Abstract
We have prepared and studied a family of cyanobiphenyl dimers with varying linking groups with a view to exploring how molecular structure dictates the stability of the nematic and twist-bend nematic mesophases. Using molecular modelling and 1D 1H NOESY NMR spectroscopy, we determine the angle between the two aromatic core units for each dimer and find a strong dependency of the stability of both the nematic and twist-bend mesophases upon this angle, thereby satisfying earlier theoretical models.
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16
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Salili SM, Xiang J, Wang H, Li Q, Paterson DA, Storey JMD, Imrie CT, Lavrentovich OD, Sprunt SN, Gleeson JT, Jákli A. Magnetically tunable selective reflection of light by heliconical cholesterics. Phys Rev E 2016; 94:042705. [PMID: 27841485 DOI: 10.1103/physreve.94.042705] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Indexed: 06/06/2023]
Abstract
We present studies of chiral nematic liquid crystals composed of flexible dimer molecules subject to large dc magnetic fields between 0 and 31 T. We observe that these fields lead to selective reflection of light depending on temperature and magnetic field. The band of reflected wavelengths can be tuned from ultraviolet to beyond the IR-C band. A similar effect induced by electric fields has been presented previously, and was explained by a field-induced oblique-heliconical director deformation in accordance with early theoretical predictions. The use of magnetic field here instead of electric field allows precise measurements of some material constants and holds promise for wireless tuning of selective reflection.
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Affiliation(s)
- S M Salili
- Chemical Physics Interdisciplinary Program & Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - J Xiang
- Chemical Physics Interdisciplinary Program & Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - H Wang
- Chemical Physics Interdisciplinary Program & Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - Q Li
- Chemical Physics Interdisciplinary Program & Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - D A Paterson
- Department of Chemistry, University of Aberdeen, AB24 3UE Scotland, United Kingdom
| | - J M D Storey
- Department of Chemistry, University of Aberdeen, AB24 3UE Scotland, United Kingdom
| | - C T Imrie
- Department of Chemistry, University of Aberdeen, AB24 3UE Scotland, United Kingdom
| | - O D Lavrentovich
- Chemical Physics Interdisciplinary Program & Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
| | - S N Sprunt
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
| | - J T Gleeson
- Department of Physics, Kent State University, Kent, Ohio 44242, USA
| | - A Jákli
- Chemical Physics Interdisciplinary Program & Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
- Complex Fluid Group, Wigner Research Centre, Budapest, Hungary
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17
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Deuteron and proton NMR study of D2, p-dichlorobenzene and 1,3,5-trichlorobenzene in bimesogenic liquid crystals with two nematic phases. Chem Phys Lett 2016. [DOI: 10.1016/j.cplett.2016.07.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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18
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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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