Unidirectional collective transport of microspheres in nematic liquid crystal by electrically tunable reorientation

Manipulation of microparticles in dispersion medium has attracted a widespread attention, with applications ranging from microfluidic physics to engineering. At present, manipulating microparticles unidirectionally along the direction perpendicular to the electric field remains a challenge. In this work, we designed a liquid crystal cell with an opposite pretilt orientation to transport the silica spheres with diameters of several microns. We investigated the effect of field parameters on the transport velocity of microspheres, mechanism of the unidirectional collective transport, and motion behaviors in the case of collision. The results show that, depending on the field intensity and modulation frequency, the transport velocity varies from a few to more than 100 μm/s. The microspheres move to the opposite side of rubbing direction, and it can be adjusted by changing the alignment layer's orientation direction. The proposed cell structure is simple, and the microspheres do not require surface modifications. Both these factors facilitate the high-throughput transport of micro-cargoes.