  Frictional forces affect the rheology of hard-sphere colloids, at high shear
rate. Here we demonstrate, via numerical simulations, that they also affect the
dynamics of active Brownian particles, and their motility induced phase
separation. Frictional forces increase the angular diffusivity of the
particles, in the dilute phase, and prevent colliding particles from resolving
their collision by sliding one past to the other. This leads to qualitatively
changes of motility-induced phase diagram in the volume-fraction motility
plane. While frictionless systems become unstable towards phase separation as
the motility increases only if their volume fraction overcomes a threshold,
frictional system become unstable regardless of their volume fraction. These
results suggest the possibility of controlling the motility induced phase
diagram by tuning the roughness of the particles.
