Direct Observation of Rigid-Body Rotation of Cholesteric Droplets Subjected to a Temperature Gradient

Abstract

Droplets of cholesteric liquid crystals exhibit unidirectional rotation of their stripe textures when subjected to a temperature gradient perpendicular to their helical axes. The phenomenon is well-known as a typical thermomechanical cross-coupling, however, there has been an argument whether the textural rotation is ascribed to rigid-body rotation of the droplets or pure director rotation. To distinguish the two possibilities, we dispersed micron-size particles in a cholesteric-isotropic coexisting sample and visualized the flow-field by tracing the particles. The result showed that the particles adhering onto the cholesteric droplets rotated at the same angular velocity as the droplets. This observation provided a clear evidence of the rigid-body rotation of the droplet and settled the argument.