Self-organisation of phoretic suspensions in shear flows*

Janus phoretic particles exploit chemical energy to self-propel at microscopic scale, and respond to their hydrodynamic and chemical environment. As a result, they are able to interact both hydro-dynamically and chemically with other particles, like chemotactic biological microswimmers (e.g., bacteria, algea), or with an external flow or chemical signal, leading to non-trivial collective behaviour (e.g., phoretic particles clustering or bacterial swarming). Recent experiments and analysis have demonstrated that the response of sheared active suspensions can in fact lead to significant reduction in viscosity due to the injection of energy at the microscopic scale.

Using a continuum kinetic model, we analyse numerically the response to simple shear flow of a dilute and confined phoretic suspension, focusing specifically on the dual influence of confinement and shear strength. Depending on the relative intensity of these effects to the particles’ chemotaxis and self-propulsion, different steady and unsteady regimes are observed and analysed, together with their impact on the suspension’s effective viscosity.