When microrollers meet anisotropy

Driven colloidal particles can display an array of collective effects. Here we study a system in which these collective interactions are largely driven by hydrodynamics: microrollers. Microrollers can be experimentally realized by driving (weakly) magnetic colloidal particles suspended in a liquid above a wall with a rotating magnetic field. Using fluorescence microscopy and particle tracking we can study their response to the field, as well as their collective interactions. Here, we study how anisotropy in the shape of the rollers alters their dynamics. We explore the collective response of rod-shaped hematite-silica microrollers and how this response is modified by adjusting their concentration and shape. Additionally, we study the role of the alignment of the magnetic moment of the rollers with respect to the anisotropic axis of the rollers themselves. Finally, we will show how these microrollers interact with passive obstacles.