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Characterization of large tilt-angle flexoelectro-optic switching in chiral nematic liquid crystal devices

Wang, Xiuze; Fells, Julian A. J.; Welch, Chris; Tamba, Maria-Gabriela; Mehl, Georg H.; Morris, Stephen M.; Elston, Steve J.


Xiuze Wang

Julian A. J. Fells

Chris Welch

Maria-Gabriela Tamba

Stephen M. Morris

Steve J. Elston


The “flexoelastic ratio”, which is the ratio of the effective flexoelectric coefficient to the elastic
coefficients, is commonly used to characterize the electro-optic behavior of chiral nematic liquid crystal
(LC) devices that exhibit flexoelectro-optic switching. In the uniform lying helix configuration, this
electro-optic effect is manifested as a rapid (~100 s) rotation of the macroscopic optic axis when an
electric field is applied perpendicular to the helix axis of the chiral nematic LC and is attractive for both
intensity and phase modulation devices. There has been renewed interest in this electro-effect as new
LC materials and mixtures have been developed that exhibit large tilt angles, , of the optic axis ( ≥
45°) whilst maintaining a fast response time. In this Letter, we consider the relevance of the flexoelastic
ratio when characterizing the performance of the devices and find that an alternative ratio is required to
characterize materials that can switch by  = ±45° when the pitch is constrained. We show that for large
tilt angles of the optic axis the values for the new and conventional flexoelastic ratios measurably
diverge. In addition, a simple way of determining this new characteristic ratio is presented that involves
determining the electric field amplitude at the point the transmission levels are the same for both
positive and negative electric field polarities.


Wang, X., Fells, J. A. J., Welch, C., Tamba, M., Mehl, G. H., Morris, S. M., & Elston, S. J. (2019). Characterization of large tilt-angle flexoelectro-optic switching in chiral nematic liquid crystal devices. Liquid crystals, 46(3), 408-414.

Journal Article Type Article
Acceptance Date Jul 17, 2018
Online Publication Date Jul 31, 2018
Publication Date 2019
Deposit Date Sep 5, 2018
Publicly Available Date Oct 27, 2022
Print ISSN 0267-8292
Electronic ISSN 1366-5855
Publisher Taylor and Francis
Peer Reviewed Peer Reviewed
Volume 46
Issue 3
Pages 408-414
Keywords Flexo-electro-optic switching, chiral nematic large tilt angle mixtures
Public URL
Publisher URL


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Copyright Statement
© 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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