Propulsion of microparticles in nonlinearly viscoelastic fluids through symmetry breaking*

Magnetic micro- and nanoparticles are being utilized in a variety of techniques including hyperthermia, drug delivery, and magnetic resonance imaging. However, the propulsion of spherical microparticles has been limited to a handful of techniques including catalytic propulsion, external magnetic gradients, and geometric functionalization. The research presented here will demonstrate microparticle propulsion through spontaneous symmetry breaking and their control using a combination of static and rotating magnetic fields. Nonlinearities in certain fluids create rod-climbing-like effects that allow rotating microparticles to experience symmetry broken propulsion along their rotation axes. This type of propulsion was demonstrated in several nonlinearly viscoelastic fluids including synthetic mucus and low concentration polyacrylamide. The propulsion direction along the rotation axes were altered by adjusting the magnitude and direction of an overlaid static magnetic field. Several studies were performed including velocity vs. rotational frequency, velocity vs. static magnetic field, particle image velocimetry, and selected 2D and 3D trajectories under both open loop and closed loop control.