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Issue 47, 2012
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Increasing the flexoelastic ratio of liquid crystals using highly fluorinated ester-linked bimesogens

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Abstract

We present experimental results on the bulk flexoelectric coefficients e and effective elastic coefficients K of non-symmetric bimesogenic liquid crystals when the number of terminal and lateral fluoro substituents is increased. These coefficients are of importance because the flexoelastic ratio e/K governs the magnitude of flexoelectro-optic switching in chiral nematic liquid crystals. The study is carried out for two different types of linkage in the flexible spacer chain that connects the separate mesogenic units: these are either an ether or an ester unit. It is found that increasing the number of fluorine atoms on the mesogenic units typically leads to a small increase in e and a decrease in K, resulting in an enhancement of e/K. The most dramatic increase in e/K, however, is observed when the linking group is changed from ether to ester units, which can largely be attributed to an increase in e. Increasing the number of fluorine atoms does, however, increase the viscoelastic ratio and therefore leads to a concomitant increase in the response time. This is observed for both types of linkage, although the ester-linked compounds exhibit smaller viscoelastic ratios compared with their ether-linked counterparts. Highly fluorinated ester-linked compounds are also found to exhibit lower transition temperatures and dielectric anisotropies. As a result, these compounds are promising materials for use in electro-optic devices.

Graphical abstract: Increasing the flexoelastic ratio of liquid crystals using highly fluorinated ester-linked bimesogens

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Publication details

The article was received on 08 Oct 2012, accepted on 19 Oct 2012 and first published on 06 Nov 2012


Article type: Paper
DOI: 10.1039/C2CP43535G
Phys. Chem. Chem. Phys., 2012,14, 16377-16385

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    Increasing the flexoelastic ratio of liquid crystals using highly fluorinated ester-linked bimesogens

    K. L. Atkinson, S. M. Morris, M. M. Qasim, F. Castles, D. J. Gardiner, P. J. W. Hands, S. S. Choi, W. Kim and H. J. Coles, Phys. Chem. Chem. Phys., 2012, 14, 16377
    DOI: 10.1039/C2CP43535G

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