Characterization of large tilt-angle flexoelectro-optic switching in chiral nematic liquid crystal devices |
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Authors: | Xiuze Wang Julian A J Fells Chris Welch Maria-Gabriela Tamba Georg H Mehl Stephen M Morris |
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Institution: | 1. Department of Engineering Science, University of Oxford, Oxford, UK;2. Department of Chemistry, University of Hull, Hull, UK |
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Abstract: | The ‘flexoelastic ratio’ is commonly used to characterise the electro-optic behaviour of chiral nematic liquid crystal (LC) devices that exhibit flexoelectro-optic switching. There has been renewed interest in this electro-optic effect of late as new LC materials and mixtures have been developed that exhibit large tilt angles, Ø, of the optic axis (Ø ≥ 45°) whilst maintaining a fast response time (< 1 ms). In this study, we compare the different flexoelastic ratios that are obtained for fixed and variable-pitch chiral nematic LCs for materials with a tilt of the optic axis as large as Ø = ± 45°. We show that for large tilt angles of the optic axis the values for the two different flexoelastic ratios measurably diverge. Of the two ratios, we propose that for large tilt-angle mixtures it is more appropriate to use the flexoelastic ratio that is derived for the case when the pitch of the helix is constrained. In addition, a simple way of determining the ‘pitch-constrained’ flexoelastic ratio is presented that involves identifying the electric field amplitude at the point for which the transmission levels are the same for both positive and negative electric field polarities. |
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Keywords: | Flexoelectro-optic switching chiral nematic large tilt-angle mixtures |
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