Tuning surface aggregation of active particles.*

Collection of disk-like self-propelled particles, interacting via a short-range repulsive force is an effective model to understand the emergent properties in active matter. It is well known that for sufficiently high propulsion speed and density they aggregate to form clusters and at low density, they are in a homogeneous fluid state.

We study the aggregation properties of such particles on a rigid wall at a low density where they do not spontaneously form clusters in the bulk. Our numerical studies show that the cluster formation crucially depends on how the particles interact with the wall and the propulsion speed of the particles. We get two different type of clusters on the surface, as a function of the wall properties. For a range of wall parameters and particle mobility, the particles form a connected cluster all along the wall. For these parameters, we study the surface height fluctuations and compare with studies made on passive particle deposition. For a different range of wall parameters, we observe that the connected cluster becomes unstable and it breaks into smaller clusters. We study the growth dynamics of these clusters and their dependence on wall parameters and particle propulsion speed.