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Temperature dependence of bend elastic constant in oblique helicoidal cholesterics

Iadlovska, Olena S.; Babakhanova, Greta; Mehl, Georg H.; Welch, Christopher; Cruickshank, Ewan; Strachan, Grant J.; Storey, John M. D.; Imrie, Corrie T.; Shiyanovskii, Sergij V.; Lavrentovich, Oleg D.


Olena S. Iadlovska

Greta Babakhanova

Christopher Welch

Ewan Cruickshank

Grant J. Strachan

John M. D. Storey

Corrie T. Imrie

Sergij V. Shiyanovskii

Oleg D. Lavrentovich


Elastic moduli of liquid crystals, known as Frank constants, are of quintessential importance for understanding fundamental properties of these materials and for the design of their applications. Although there are many methods to measure the Frank constants in the nematic phase, little is known about the elastic constants of the chiral version of the nematic, the so-called cholesteric liquid crystal, since the helicoidal structure of the cholesteric renders these methods inadequate. Here we present a technique to measure the bend modulus of cholesterics that is based on the electrically tunable reflection of light at an oblique helicoidal ChOH cholesteric structure. is typically smaller than 0.6 pN, showing a non-monotonous temperature dependence with a slight increase near the transition to the twist-bend phase. depends strongly on the molecular composition. In particular, chiral mixtures that contain the flexible dimer 1′′,7′′ - bis(4-cyanobiphenyl-4′-yl) heptane (CB7CB) and rod-like molecules such as pentylcyanobiphenyl (5CB) show a value that is 5 times smaller than of pure CB7CB or of mixtures of CB7CB with chiral dopants. Furthermore, in CB11CB doped with a chiral agent is noticeably smaller than in a similarly doped CB7CB which is explained by the longer flexible link in CB11CB. The proposed technique allows a direct in-situ determination of how the molecular composition, molecular structure and molecular chirality affect the elastic properties of chiral liquid crystals.


Iadlovska, O. S., Babakhanova, G., Mehl, G. H., Welch, C., Cruickshank, E., Strachan, G. J., …Shiyanovskii, S. V. (2020). Temperature dependence of bend elastic constant in oblique helicoidal cholesterics. Physical Review Research, 2(1),

Journal Article Type Article
Acceptance Date Jan 26, 2020
Online Publication Date Mar 3, 2020
Publication Date Mar 3, 2020
Deposit Date Mar 6, 2020
Publicly Available Date Mar 9, 2020
Journal Physical Review Research
Publisher American Physical Society
Peer Reviewed Peer Reviewed
Volume 2
Issue 1
Article Number 013238
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Published by the American Physical Society under the terms of theCreative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s)and the published article’s title, journal citation, and DOI

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