Microrollers maneuvering complex geometries

As we move towards development of more realistic and applications-driven active matter systems, we must understand how active particles interact with complex and crowded environments. We study this problem experimentally using a system which consists of weakly magnetic colloids suspended in water, and driven by a rotating magnetic field. These colloids are heavy and sedimented near the bottom of the sample chamber; hydrodynamic coupling between the particles and the floor induces propulsion. This results in a model system for driven colloids where the dominant force is hydrodynamics. Here we use microscopy and particle tracking to observe and characterize what happens when these rolling particles encounter various types of three-dimensional obstacles. We explore how variables such as roller angular velocity and obstacle geometry influence individual roller trajectories as well as collective interactions, measuring the effect of these parameters on roller movement. Additionally, we explore whether the hydrodynamic trapping effects seen in other active systems appear here, and how this trapping may be influenced by obstacle geometry.