Chemically induced twist-bend nematic liquid crystals, liquid crystal dimers, and negative elastic constants
- 12 August 2013
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review E
- Vol. 88 (2), 022503
- https://doi.org/10.1103/physreve.88.022503
Abstract
Here we report the chemical induction of the twist-bend nematic phase in a nematic mixture of ether-linked liquid crystal dimers by the addition of a dimer with methylene links; all dimers have an odd number of groups in the spacer connecting the two mesogenic groups. The twist-bend phase has been identified from its optical texture and x-ray scattering pattern as well as NMR spectroscopy, which demonstrates the phase chirality. Theory predicts that the key macroscopic property required for the stability of this chiral phase formed from achiral molecules is for the bend elastic constant to tend to be negative; in addition the twist elastic constant should be smaller than half the splay elastic constant. To test these important aspects of the prediction we have measured the bend and splay elastic constants in the nematic phase preceding the twist-bend nematic using the classic Frederiks methodology and all three elastic constants employing the dynamic light scattering approach. Our results show that, unlike the splay, the bend elastic constant is small and decreases significantly as the transition to the induced twist-bend nematic phase is approached, but then exhibits unexpected behavior prior to the phase transition.Keywords
This publication has 29 references indexed in Scilit:
- Spontaneous Periodic Deformations in Nonchiral Planar-Aligned Bimesogens with a Nematic-Nematic Transition and a Negative Elastic ConstantPhysical Review Letters, 2010
- Unusual properties of a bent-core liquid-crystalline fluidSoft Matter, 2008
- Liquid crystals: a chemical physicist's viewLiquid Crystals, 2005
- Chiral ordering in the nematic and an optically isotropic mesophase of bent-core mesogens with a halogen substituent at the central coreLiquid Crystals, 2004
- Dynamics of the Nematic Phase Formed by Achiral Banana-shaped MaterialsMolecular Crystals and Liquid Crystals, 2004
- Spontaneous chiral ordering in the nematic phase of an achiral banana-shaped compoundJournal of Materials Chemistry, 2002
- On the spontaneous symmetry breaking in the mesophases of achiral banana-shaped moleculesEurophysics Letters, 2001
- Liquid crystal dimers and oligomers: Experiment and theoryMacromolecular Symposia, 1995
- An enhanced odd-even effect of liquid crystal dimers Orientational order in the α,ω-bis(4′-cyanobiphenyl-4-yl)alkanesLiquid Crystals, 1993
- On the relative propensities of ether and methylene linkages for liquid crystal formation in calamiticsLiquid Crystals, 1991