Mobility dynamics of rotationally driven particles in a structured environment

Understanding how active particles migrate in a complex landscape is vital when designing micron-scale devices, targeted medicine, and controlled self-assembly. Recent work reveals that interactions with structure lead to rich and complex behavior such as fluctuation-induced particle trapping near cylindrical obstacles and geometry induced changes in mobility. Here, using both simulations and experiments, we study the mobility dynamics of rotationally driven micro-spheres and how these dynamics are altered due to hydrodynamic interactions with confined structures. Multi-photon lithography is used to create structures on the order of the particle size to experimentally investigate how mobility dynamics are altered under strong confinement. Here we explore single-particle dynamics, and how they are altered by flow-structure interactions, as well as how collective interactions in dense suspensions alter them. Lubrication corrected Brownian dynamics simulations are used in tandem with experiments to fully understand the mechanism behind geometry-induced mobility changes. We find that individual particle velocity is strongly controlled by spatial confinement and moreover in dense suspensions, emergent structures tend to compete with mobility and can completely arrest suspension flows.