Lehmann rotation of cholesteric droplets subjected to a temperature gradient: role of the concentration of chiral molecules

Patrick Oswald (1)

1 Phys-ENS - Laboratoire de Physique de l'ENS Lyon

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.

Keywords: Cholesteric liquid crystal; Thermomechanical Lehmann effect

Domains: Physics [physics]; Condensed Matter [cond-mat]; Soft Condensed Matter [cond-mat.soft]

Patrick Oswald. Lehmann rotation of cholesteric droplets subjected to a temperature gradient: role of the concentration of chiral molecules. European Physical Journal E: Soft matter and biological physics, 2009, 28 (4), pp.377-383. ⟨ensl-00507795⟩