Methylene-linked liquid crystal dimers and the twist-bend nematic phase

Henderson, Peter A.; Imrie, Corrie T.

doi:10.1080/02678292.2011.624368

Cited by 278 publications

(194 citation statements)

References 24 publications

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“…The twist-bend nematic phase has been observed in molecules of various architecture, including dimers [4,20,21] and bent-core liquid crystals [22,23]. Dimeric liquid crystals consist of two mesogenic units linked together via a flexible spacer.…”

Section: Figurementioning

confidence: 99%

Dielectric properties of liquid crystalline dimer mixtures exhibiting the nematic and twist-bend nematic phases

2017

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© 2017 American Physical Society. This is an author produced version of a paper published in Physical Review E. Uploaded in accordance with the publisher's self-archiving policy.eprints@whiterose.ac.uk https://eprints.whiterose.ac.uk/ Reuse Unless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. A detailed investigation of the thermal and dielectric properties of a series of binary mixtures exhibiting the nematic (N) and twist-bend nematic (NTB) liquid crystal phases is presented. The mixtures consist of an achiral, dimeric liquid crystal CB7CB, which forms the nematic and twist-bend nematic phases, and a calamitic liquid crystal 5CB, which shows the nematic phase. As the concentration of the calamitic liquid crystal is increased, the transition temperatures decrease linearly, and the width of the nematic phase increases. The enthalpies of phase transitions obtained from DSC measurements show that on increasing the concentration of 5CB in the binary mixtures, the enthalpy associated with the N to NTB phase transitions reduces considerably compared to a clear first order N-NTB transition in pure CB7CB. The real and imaginary parts of the dielectric permittivity are measured as a function of frequency from 100 Hz to 2 MHz in the nematic and twist-bend nematic phases in planar and homeotropic devices. A significant decrease in the average dielectric permittivity as a function of temperature for mixtures forming the NTB phase is observed. Measurements of the imaginary part of the dielectric permittivity show a relaxation peak in the measured frequency window for all of the mixtures exhibiting the NTB phase. The activation energy associated with this relaxation process is calculated and is shown to remain constant irrespective of the composition of the mixtures.2

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Section: Figurementioning

confidence: 99%

Dielectric properties of liquid crystalline dimer mixtures exhibiting the nematic and twist-bend nematic phases

2017

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“…A number of reviews concerning the twist-bend phase have been published recently [18][19][20]. A relatively large number of dimeric liquid crystals are known to exhibit this state of matter [1,3,8,9,11,12,[21][22][23][24][25][26][27][28][29][30], and there is a growing number of liquid-crystalline oligomers known to exhibit the twist-bend phase [18,[31][32][33][34]. Additionally, this phase has been observed in a phenylpiperazine derived bent-core liquid crystal [4].…”

Section: Introductionmentioning

confidence: 99%

“…The discovery of the twist-bend phase (N TB ) has given fresh impetus to the study of dimeric liquid crystals [1][2][3][4][5][6][7][8][9][10][11][12][13]. First predicted by Dozov [13], this liquid-crystalline state of matter has a locally helical structure with a pitch measured to be on the order of 10 nm [4,14], with this phase displaying a number of unusual and unique optical textures [15].…”

Section: Introductionmentioning

confidence: 99%

Conformational landscapes of bimesogenic compounds and their implications for the formation of modulated nematic phases

et al. 2017

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The twist-bend phase (N TB ) is most commonly observed in materials with a gross-bent shape: dimers; bent-cores; bent-oligomers. We had suggested previously that the bend-angle of such systems effectively dictates the relative thermal stability of the N TB phase. However, our earlier paper relied on the use of a single energy-minimum conformer and so failed to capture any information about flexibility and conformational distribution. In the present work, we revisit our hypothesis and examine a second set of dimers with varying linking groups and spacer composition. We have improved on our earlier work by studying the conformational landscape of each material, allowing average bend-angles to be determined as well as the conformer distribution. We observe that the stability of the N TB phase exhibits a strong dependence not only on the Boltzmann-weighted average bend-angle (rather than just a static conformer), but also on the distribution of conformers. To a lesser extent, the flexibility of the spacer appears important. Ultimately, this work satisfies both theoretical treatments and our initial experimental study and demonstrates the importance of molecular bend to the N TB phase. ARTICLE HISTORY

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“…Recently, the twist-bend nematic (N TB ) phase, a fundamentally new type of nematic ground state of achiral molecules, exhibiting layer-free, helical liquid crystal ordering of nanoscale pitch, has been structurally identified and characterized [1,2]. The twist-bend nematic phase was initially suggested as a theoretical possibility by Meyer over 40 years ago [3] and discussed in 2000 by Dozov [4] and Memmer [5], who suggested that the tendency for local bend curvature in the director field of bent molecules (for example, Figure 1a [6,7] having nematic characteristics, spontaneous chirality [8,9], and smectic textural features [10,11] but no smectic-like lamellar x-ray diffraction peaks [12] have been interpreted in terms of the N TB structure [4]. The N TB phase is in general polar and structurally chiral despite being formed from achiral molecules.…”

Section: Introductionmentioning

confidence: 99%

Twist-bend heliconical chiral nematic liquid crystal phase of an achiral rigid bent-core mesogen

et al. 2014

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The chiral, heliconical (twist-bend) nematic ground state is reported in an achiral, rigid, bent-core mesogen (UD68). Similar to the nematic twist-bend (N TB ) phase observed in bent molecular dimers, the N TB phase of UD68 forms macroscopic, smectic-like focal-conic textures and exhibits nanoscale, periodic modulation with no associated modulation of the electron density, i.e., without a detectable lamellar x-ray reflection peak. The N TB helical pitch is p TB ~ 14 nm. When an electric field is applied normal to the helix axis, a weak electroclinic effect is observed, revealing 50 µm -scale left-and right-handed domains in a chiral conglomerate.2

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Methylene-linked liquid crystal dimers and the twist-bend nematic phase

Cited by 278 publications

References 24 publications

Dielectric properties of liquid crystalline dimer mixtures exhibiting the nematic and twist-bend nematic phases

Dielectric properties of liquid crystalline dimer mixtures exhibiting the nematic and twist-bend nematic phases

Conformational landscapes of bimesogenic compounds and their implications for the formation of modulated nematic phases

Twist-bend heliconical chiral nematic liquid crystal phase of an achiral rigid bent-core mesogen

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