Theory of chiral periodic mesophases formed from an achiral liquid of bent-core molecules

Lorman, Vladimir; Mettout, B.

doi:10.1103/physreve.69.061710

Cited by 37 publications

(36 citation statements)

References 48 publications

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“…Later the same idea was pursued by Lorman and Mettout, 9 who proposed a theoretical Landau model based on local ferroelectric polarisation for the nematic-nematic transition, 10 which was further developed by others. 11,12 In 2001, Dozov 13 developed a purely elastic Landau theoretical model for achiral bent-core molecules in which elastic distortions induce local spontaneous bend in the nematic director, resulting in structural deviation from the uniformlyaligned nematic phase.…”

Section: Introductionmentioning

confidence: 99%

Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the N_TB–N phase transition

López

Robles‐Hernández

Salud

et al. 2016

Phys. Chem. Chem. Phys.

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Section: Introductionmentioning

confidence: 99%

Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the N_TB–N phase transition

López

Robles‐Hernández

Salud

et al. 2016

Phys. Chem. Chem. Phys.

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“…The linear electric field terms are canceled out in the symmetric geometry used. A spontaneous symmetry breaking with a formation of domains with right-and left-handed helices has already been theoretically discussed 13 and experimentally reported 14 in bent-core materials. This leads us to consider ULH as one of the potential explanations together with the formation of chiral domains.…”

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confidence: 96%

Microsecond linear optical response in the unusual nematic phase of achiral bimesogens

Панов¹,

Balachandran²,

Nagaraj³

et al. 2011

Applied Physics Letters

147

146

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Some hydrocarbon linked mesogenic dimers are known to exhibit an additional nematic phase (N x ) below a conventional uniaxial nematic (N u ) phase. Although composed of non-chiral molecules, the N x phase is found to exhibit linear (polar) switching under applied electric field. This switching has remarkably low response time of the order of a few microseconds. Two chiral domains with opposite handedness and consequently opposite responses are found in planar cells. Uniformly lying helix, electroclinic, and flexoelectric effects are given as possible causes for this intriguing phenomenon. A change in the direction of the optical axis by a moderate electric field is the basis of the use of liquid crystals (LCs) in contemporary display technologies. However, further exploitation of this property in optical telecommunication technologies is hindered by the limited speed of the optical axis switching. Amongst the fastest electro-optic effects in LCs are surface stabilized ferroelectric smectic LCs, 1 uniformly lying helix (ULH) geometry in flexoelectric cholesteric LCs, 2 electro-optic effect in blue phases, 3 and the electroclinic effect 4 found in both chiral smectic and cholesteric LCs. These switching modes are defined by the asymmetry of the chiral molecules forming the corresponding LC phases.Meanwhile, non-chiral dimers of mesogenic molecules linked with a flexible hydrocarbon chain with odd number of alkyl units have recently attracted attention due to the presence of an unusual liquid crystalline phase (currently designated as N x ) in the temperature range below the classical nematic phase (N u ). [5][6][7] Although identified as a nematic phase by x-ray diffraction studies, the phase exhibits clearly different patterns in polarised optical microscopy (POM) observations as well as a difference in the enthalpy from N u measured by the differential scanning calorimetry. 5 The ability of this class of materials to spontaneously form unusual stripe patterns with periodicity defined by the gap between containing surfaces is promising for applications in photonics. A theoretical explanation connecting the molecular properties to the macroscopic self-assembly properties is still to be developed.In this Letter, we report one more intriguing property of the N x phase: it exhibits polar switching with remarkably low switching time under electric field in a similar manner as the above mentioned materials involving chirality.The molecular structures of materials under investigation are shown in Fig. 1. We have investigated both pure dimers (M1-3) and mixtures of M4 with 4-4 0 pentyl-cyano-biphenyl (5CB) (70/30% w/w) and of M2 with its monomer (65/35% w/w). A number of cells with cell gaps varying from 2 to 25 lm and with different alignment layers have been used. These include anti-parallel planar commercial cells (EHC. Co., KSRP-XX-A2 jj P1NSS), homemade planar cells (planar aligning agent RN1175, Nissan Chemicals, Japan), and homemade hybrid aligned cells (homeotropic aligning agent AL60702 JSR, Korea). The experim...

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“…Thus, the N -TB N transformation is the phase transition between two orientationally ordered phases, achiral N and chiral TB N . Although the microscopical mechanisms leading to longrange nematic-like but heliconical (and therefore chiral) order in the TB N phase are to a large extent unknown, a number of phenomenological theoretical models have been proposed in the literature [13][14][15][16][17][18][19][20][21][22]. Aiming to contribute into the special issue of the Low Temperature Physics Journal devoted to I.M.…”

Section: Introductionmentioning

confidence: 99%

Spontaneous chiral symmetry breaking in liquid crystals

Kats

2017

Low Temperature Physics

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Motivated by new experimental observations we generalize the Landau-like approach to include the direct phase transition between isotropic liquid (I) and heliconical nematic liquid crystal (N TB ) structure. We show that depending on the Landau expansion coefficients, our model allows either direct I-N TB transition, or the sequence of the phases I-N-N TB with the classical nematic liquid crystal (N) sandwiched between the isotropic liquid and heliconical nematic liquid crystal. Which of these two situations is realized depends on how strong is the first order phase transition from the isotropic liquid. If it is strong enough the system undergoes I-N-N TB sequence, and for the very weak first order phase transition I-N TB transformation occurs. Furthermore in the latter case the N TB structure can be biaxial heliconical nematic liquid crystal.PACS: 61.30.Cz Molecular and microscopic models and theories of liquid crystal structure; 61.30.Gd Orientational order of liquid crystals; electric and magnetic field effects on order; 84.37.+q Measurements in electric variables (including voltage, current, resistance, capacitance, inductance, impedance, and admittance, etc.).

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Theory of chiral periodic mesophases formed from an achiral liquid of bent-core molecules

Cited by 37 publications

References 48 publications

Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the N_TB–N phase transition

Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the N_TB–N phase transition

Microsecond linear optical response in the unusual nematic phase of achiral bimesogens

Spontaneous chiral symmetry breaking in liquid crystals

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Theory of chiral periodic mesophases formed from an achiral liquid of bent-core molecules

Cited by 37 publications

References 48 publications

Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the NTB–N phase transition

Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the NTB–N phase transition

Microsecond linear optical response in the unusual nematic phase of achiral bimesogens

Spontaneous chiral symmetry breaking in liquid crystals

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Resources

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Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the N_TB–N phase transition

Miscibility studies of two twist-bend nematic liquid crystal dimers with different average molecular curvatures. A comparison between experimental data and predictions of a Landau mean-field theory for the N_TB–N phase transition