title: Microfluidic rheology of active particle suspensions: Kinetic theory.
abstract: We analyze the effective rheology of a dilute suspension of self-propelled slender particles confined between two infinite parallel plates and subject to a pressure-driven flow. We use a continuum kinetic model to describe the configuration of the particles in the system, in which the disturbance flows induced by the swimmers are taken into account, and use it to calculate estimates of the suspension viscosity for a range of channel widths and flow strengths typical of microfluidic experiments. Our results are in agreement with previous bulk models, and in particular, demonstrate that the effect of activity is strongest at low flow rates, where pushers tend to decrease the suspension viscosity whereas pullers enhance it. In stronger flows, dissipative stresses overcome the effects of activity leading to increased viscosities followed by shear-thinning. The effects of confinement and number density are also analyzed, and our results confirm the apparent transition to superfluidity reported in recent experiments on pusher suspensions at intermediate densities. We also derive an approximate analytical expression for the effective viscosity in the limit of weak flows and wide channels, and demonstrate good agreement between theory and numerical calculations.
authors.affiliation: Department of Mechanical and Aerospace Engineering, University of California San Diego , 9500 Gilman Drive, La Jolla, California 92093, USA.
authors.forename: Roberto
authors.identifier: 0000-0003-0869-9269
authors.initials: R
authors.lastname: Alonso-Matilla
authors.affiliation: Department of Mechanical and Aerospace Engineering, University of California San Diego , 9500 Gilman Drive, La Jolla, California 92093, USA.
authors.forename: Barath
authors.initials: B
authors.lastname: Ezhilan
authors.affiliation: Department of Mechanical and Aerospace Engineering, University of California San Diego , 9500 Gilman Drive, La Jolla, California 92093, USA.
authors.forename: David
authors.initials: D
authors.lastname: Saintillan