Role of an oscillatory electric field on the Lehmann rotation of cholesteric droplets.

This paper deals with the Lehmann rotation of banded cholesteric droplets subjected to a temperature gradient when they coexist with their own isotropic liquid. I show that their angular rotation velocity increases --in absolute value-- when they are subjected to an additional AC electric field in the conducting regime. This velocity increase is correlated with a prolate distortion of the droplets and the probable presence of electrohydrodynamical toroidal circulation flows inside and outside the droplets. I propose that the coupling between these flows and the director field is responsible for the increase of the angular velocity of the texture. The origin of these flows is discussed qualitatively in the framework of the leaky dielectric model by taking into account the generation of charges both in the bulk via a Carr-Helfrich mechanism (Tarasov, Krekhow and Kramer model) and at the surface of the droplet (Taylor-Melcher model).