  Self-propelled particles can spontaneously form dense phases from a dilute
suspension in a process referred to as motility-induced phase separation. The
properties of the out-of-equilibrium structures that are formed are governed by
the specifics of the particle interactions and the strength of the activity.
Thus far, most studies into the formation of these structures have focused on
spherical colloids, dumbbells, and rod-like particles endowed with various
interaction potentials. Only a few studies have examined the collective
behavior of more complex particle shapes. Here, we increase the geometric
complexity and use Molecular Dynamics simulations to consider the structures
formed by triangular self-propelled particles with surface roughness. These
triangles either move towards their apex or towards their base, i.e., they
possess a polarity. We find that apex-directed triangles cluster more readily,
more stably, and have a smoother cluster interface than their base-directed
counterparts. A difference between the two polarities is in line with the
results of [H.H. Wensink, et al., Phys. Rev. E 89, 010302(R) (2014)], however,
we obtain the reversed result when it comes to clustering, namely that
apex-directed particles cluster more readily. We further show that reducing the
surface roughness negatively impacts the stability of the base-directed
structures, suggesting that their formation is in large part due to surface
roughness. Our results lay a solid foundation for future experimental and
computational studies into the effect of roughness on the collective dynamics
of swimmers.
