A Possible Instability Mechanism for Plug Formation in a Sheared Suspension Flow

The viscosity of a suspension depends on its concentration. Moreover, a particle subject to an inhomogeneous shear is subject to a transverse lift force. If the latter has the appropriate sign (towards regions of low shear), we show that a first-order phase separation occurs past a critical shear, thereby leading to plug formation. We describe the phase diagram and we briefly discuss the origin of the lift force, which remains largely open.