Abstract

Confining active particles has two intertwined consequences: it changes the local arrangement of particles, and particles exert forces onto the confining boundary. I will present recent and ongoing work to characterize the behavior of active particles under confinement combining experiments using colloidal particles with simulations and dynamic mean-field theory. First, I will discuss how active particles modulate forces between a hard wall and a trapped probe particle, opening strategies for microrheological investigations of active media. In contrast to passive suspensions, such active depletants imply large repulsive forces governed by a pronounced local structure. I will then discuss the behavior of active particles if confined to a channel or annulus by soft forces as relevant for many biological situations in which confinement is rather soft and flexible. Varying the propulsion speed and confinement strength, we observe the formation of dynamic clusters and a reentrant transition into a uniform gas-like phase. Finally, I will present some preliminary results on immersed bodies that undergo cyclic shape changes.