Colloidal Micromotor in Smectic a Liquid Crystal Driven by DC Electric Field

Converting linear stimulus to rotation has endless examples in virtually all scales of the universe. One of the interesting examples is Quincke rotation, a spinning rotation of a dielectric sphere neutrally buoyant in an isotropic fluid caused by a unidirectional DC electric field. Recently Quincke rotation has been reported in liquid crystalline (LC) phases, and it was noted that spinning triggers a translational motion normal to the electric field and the rotation axis. In this work, we explain the translation of spinning spheres as a result of hydrodynamic interaction with the bounding walls. We also describe a unique orbiting motion: the spinning particles circumnavigate air inclusions in the liquid crystal. The effect is caused by an elastic entrapment of the spheres at tilted grain boundaries in the meniscus region in the smectic phase. This phenomenon can offer new types of microfluidic devices and micromotors.