Maneuvering superparamagnetic particles in a nematic liquid crystal by transverse electric and in-plane rotating magnetic fields

The transport of microparticles in fluids is of current interest and controlling their trajectories at will is of paramount importance for fundamental research and applications. Here, we demonstrate the effect of an ac electric field and a dc magnetic field on the orientation and electrophoretic propulsion of superparamagnetic microparticles in a nematic liquid crystal. The magnetic field changes the orientation of the elastic dipoles in the plane, and the competing effect of the elastic and magnetic torques is used to measure the induced magnetic moment of a single particle. In the absence of the magnetic field, the particles propel along the far-field director under the application of a low-frequency transverse electric field. The rotating magnetic field changes the direction of motion, facilitating remote control of the particle trajectories. Our study demonstrates the potentialities of orthogonal electric and magnetic fields for maneuvering microparticle trajectories, which are important for practical applications, ranging from targeted delivery and microfluidics to microrobotics.