Lehmann rotatory power: a new concept in cholesteric liquid crystals |
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| Authors: | P. Oswald L. Jørgensen A. Żywociński |
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| Affiliation: | 1. Physics Laboratory, University of Lyon, Ecole Normale Supérieure de Lyon , UMR 5672 of the CNRS, 46 Allée d'Italie, 69364, Lyon, Cedex 07, France patrick.oswald@ens-lyon.fr;3. Physics Laboratory, University of Lyon, Ecole Normale Supérieure de Lyon , UMR 5672 of the CNRS, 46 Allée d'Italie, 69364, Lyon, Cedex 07, France;4. Physics Laboratory, University of Lyon, Ecole Normale Supérieure de Lyon , UMR 5672 of the CNRS, 46 Allée d'Italie, 69364, Lyon, Cedex 07, France;5. Institute of Physical Chemistry, Polish Academy of Sciences , Kasprzaka 44-52, PL-01224, Warsaw, Poland |
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| Abstract: | By doping a nematic phase with a chiral molecule one obtains a cholesteric phase. Each chiral molecule is characterised by its helical twisting power (HTP) which is defined as HTP?=?q/(2πC) where q is the equilibrium pitch of the cholesteric phase and C the concentration (in wt%) of chiral molecules. In a similar way, we define the Lehmann rotatory power (LRP) as LRP?=?v/(2πC) where v is the thermomechanical Lehmann coefficient. By making compensated mixtures, we measured the HTP and the LRP of five chiral molecules (R811, S2011, CC, CB15 and CE4) dissolved in an eutectic mixture 8CB/8OCB. We found that, although these quantities were different, their ratio R?=?LRP/HTP changed little from one molecule to another. This result shows that the Lehmann effect is closely, but not completely, related to the twist of the phase. |
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| Keywords: | liquid crystals cholesteric helical twisting power thermomechanical Lehmann effect compensated mixture |
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