Competing chemical and hydrodynamic effects in autophoretic colloidal suspensions.

At the surfaces of autophoretic colloids, slip velocities arise from local chemical gradients that are many-body functions of particle configuration and activity. For rapid chemical diffusion, coupled with slip-induced hydrodynamic interactions, we deduce the chemohydrodynamic forces and torques between colloids. Near a no-slip wall, the forces can be expressed as gradients of a non-equilibrium potential which, by tuning the type of activity, can be varied from repulsive to attractive. When this potential has a barrier, we find arrested phase separation with a mean cluster size set by competing chemical and hydrodynamic forces. These are controlled in turn by the monopolar and dipolar contributions to the active chemical surface fluxes.