Direct observation of rigid-body rotation of cholesteric droplets subjected to a temperature gradient

Droplets of cholesteric liquid crystals rotate their helical structure when subjected to a thermal gradient perpendicular to their helical axes. Concerning the interpretation of their dynamics, there has been an argument whether the textural rotation indicates rigid-body rotation of the droplets or pure director rotation. To clarify this, we dispersed micron-size particles in a cholesteric-isotropic coexisting sample and traced their motion, and found that the particles adhering onto a cholesteric droplet rotated together with the helix in phase. This observation provided clear evidence of the rigid-body rotation of the droplet, and we also revealed an unusual hydrodynamic flow in the coexisting phase.