Flows in parallelepiped cells of nematic liquid crystals

We identified three types of flow in a nematic liquid crystal parallelepiped cell subjected to an ac electric field at low frequency. Our observations show the existence of translational flow, backflow, and convection flow in parallelepiped cells. We measured the backflow velocity by introducing microparticles into the sample. The backflow velocity at the normalized voltage epsilon = 0.05 is approximately 0.1 mu m/s. It has the same order as the translational flow velocity at epsilon = 0.05. Furthermore, convection flow occurs earlier than translational flow.