Lehmann rotation of cholesteric droplets subjected to a temperature gradient: Role of the concentration of chiral molecules
Laboratoire de Physique, École Normale Supérieure de Lyon, UMR 5672 of the CNRS, 46 Allée d’Italie, 69364, Lyon, France
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Accepted: 21 January 2009
Published online: 24 March 2009
We present a systematic study of the Lehmann rotation of cholesteric droplets subjected to a temperature gradient when the concentration of chiral molecules is changed. The liquid crystal chosen is an eutectic mixture of 8CB and 8OCB doped with a small amount of the chiral molecule R811. The angular velocity of the droplets strongly depend on their size and on the concentration of chiral molecules. The Lehmann coefficient is estimated by using three different methods. Our results are consistent with a Lehmann coefficient proportional to the concentration of chiral molecules. We additionally show the existence of a critical size of the droplets below which they change texture and stop rotating.
PACS: 61.30.-v Liquid crystals – / 65.40.De Thermal expansion; thermomechanical effects – / 05.70.Ln Nonequilibrium and irreversible thermodynamics –
© EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg, 2009