Rheological properties of a dilute suspension of self-propelled particles

With a detailed microscopic model for a self-propelled swimmer, we derive the rheological properties of a dilute suspension of such particles at small Peclet number. It is shown that, in addition to Einstein's like contribution to the effective viscosity, that is proportional to the volume fraction of the swimmers, a contribution due to the activity of self-propelled particles influences the viscosity. As a result of the activity of swimmers, the effective viscosity would be lower (higher) than the viscosity of the suspending medium when the particles are pusher (puller). Such activity-dependent contribution will also result a non-Newtonian behavior of the suspension in the form of normal stress differences. Copyright (C) EPLA, 2015