Nano‐Segregation and Directed Self‐Assembly in the Formation of Functional Liquid Crystals

Phys. Chem. Chem. Phys.

Cowling

Goodby

2017

Self Cite

201

145

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.

Section: Discussionmentioning

confidence: 99%

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

Phys. Chem. Chem. Phys.

Cowling

Goodby

2017

Self Cite

201

145

“…The N TB phase becomes less stable in comparison to intercalated smectic phases (both SmC A and SmB) as the proportionality of s to p-bonded structure is increased, mirroring the trends seen for conventional calamitic materials. 107 3.2. Dimers with other linking groups 3.2.1.…”

Section: Methylene Linked Dimersmentioning

confidence: 99%

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

2016

Soft Matter

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115

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 N 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.

“…By drawing structure-property correlationsn ew "N TB "m aterials can be obtained by rational design rather than chance discovery,w hile also allowing the impact of specific structural features upon bulk properties to be elucidated. [22] The most general structure-property correlation that exists for the N TB phase concerns the angle between the two mesogenic units. An overall bent shape is currently seen as ap rerequisite, with atomistic modelling showing that only dimers with odd spacerp arity possess as ufficiently bent geometry to exhibit this phase.…”

Section: Introductionmentioning

confidence: 99%

Apolar Bimesogens and the Incidence of the Twist–Bend Nematic Phase

Davis

Archbold

et al. 2015

Chemistry A European J

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102

113

The nematic twist-bend phase (NTB) was, until recently, only observed for polar mesogenic dimers, trimers or bent-core compounds. In this article, we report a comprehensive study on novel apolar materials that also exhibit NTB phases. The NTB phase was observed for materials containing phenyl, cyclohexyl or bicyclooctyl rings in their rigid-core units. However, for materials with long (>C7) terminal chains or mesogenic core units comprising three ring units, the NTB phase was not observed and instead the materials exhibited smectic phases. One compound was found to exhibit a transition from the NTB phase to an anticlinic smectic C phase; this is the first example of this polymorphism. Incorporation of lateral substitution with respect to the central core unit led to reductions in transition temperatures; however, the NTB phase was still found to occur. Conversely, utilising branched terminal groups rendered the materials non-mesogenic. Overall, it appears that it is the gross molecular topology that drives the incidence of the NTB phase rather than simple dipolar considerations. Furthermore, dimers lacking any polar groups, which were prepared to test this hypothesis, were found to be non mesogenic, indicating that at the extremes of polarity these effects can dominate over topology.