The dependency of twist-bend nematic liquid crystals on molecular structure: a progression from dimers to trimers, oligomers and polymers

Mandle, Richard J.

doi:10.1039/c6sm01772j

Cited by 113 publications

(74 citation statements)

References 138 publications

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“…The pattern of the N TB phase differs from that of the N phase mainly by a certain loss of orientation (Fig. 3 and Figure S1, Supporting Information File 1 for additional data) as frequently found at the N–N TB transition [2,17,21]. The inner scattering is too weak to find the maximum but can be estimated to be near that of the N phase, which has its maxima at about 1.8 nm for the d value.…”

Section: Resultsmentioning

confidence: 94%

Induced smectic phase in binary mixtures of twist-bend nematogens

Knežević¹,

Dokli²,

Sapunar³

et al. 2018

Beilstein J. Nanotechnol.

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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.

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Section: Resultsmentioning

confidence: 94%

Induced smectic phase in binary mixtures of twist-bend nematogens

Knežević¹,

Dokli²,

Sapunar³

et al. 2018

Beilstein J. Nanotechnol.

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“…When the twist-bend phase is chiral, other 'nematiclike' mesophases have been reported whose structure is as yet unknown [5,16], whereas a nematic-to-nematic transition has also been recently reported for a polar rod-like compound [17]. 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].…”

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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“…Nematic-to-nematic phase transitions are currently topical due to the recent discovery of the twist-bend nematic (N TB ), [1][2][3] and as noted by Clark et al ''The appearance of new nematic liquid crystal (LC) equilibrium symmetry (ground state) is a rare and typically important event''. 4 Several other nematic or nematic-like liquid crystalline phases are known to exist (chiral nematic (N*), discotic nematic (N D ), 5 re-entrant nematic (N RE ), 6 biaxial nematic (N B ), 7,8 blue phases I, II, and III), whereas others are either predicted or contentious (cubatic nematic (N cub ), 9 splay-bend nematic (N SB ) 10,11 ).…”

Section: Introductionmentioning

confidence: 99%

A nematic to nematic transformation exhibited by a rod-like liquid crystal

Mandle

Cowling

Goodby

2017

Phys. Chem. Chem. Phys.

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177

145

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A novel, highly polar rod-like liquid crystal was found to exhibit two distinct nematic mesophases (N and N X ).When studied by microscopy and X-ray scattering experiments, and under applied electric fields, the nematic phases are practically identical. However, calorimetry experiments refute the possibility of an intervening smectic mesophase, and the transformation between the nematic phases was associated with a weak thermal event. Analysis of measured dielectric data, along with molecular properties obtained from DFT calculations, applying the Maier-Meier relationship allowed for the degree of antiparallel pairing of dipoles in both nematic phases to be quantified. Based on the results, we conclude that the onset of the lower temperature phase is driven by the formation of antiparallel molecular associations.

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The dependency of twist-bend nematic liquid crystals on molecular structure: a progression from dimers to trimers, oligomers and polymers

Cited by 113 publications

References 138 publications

Induced smectic phase in binary mixtures of twist-bend nematogens

Induced smectic phase in binary mixtures of twist-bend nematogens

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

A nematic to nematic transformation exhibited by a rod-like liquid crystal

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