ABSTRACT
We study the Lehmann rotation of the cholesteric helix in droplets of the liquid crystal N-(p-methoxybenzilidene)-p-butylaniline doped with a small amount of the chiral molecule R811 when they are subjected to a temperature gradient. We show that the helix rotates much faster when it is parallel to the temperature gradient than when it is perpendicular to it. The first configuration is obtained by submitting the droplets to an ac electric field parallel to the temperature gradient, whereas the second one is observed at zero field. We show that the rotation velocity of the helix strongly depends on the droplet radius, even when the helix is parallel to the temperature gradient. This observation supports the idea that the Leslie thermomechanical coupling cannot explain alone the Lehmann effect.
