Collective dynamics and rheology of confined phoretic suspensions

TL;DR

This paper investigates how confinement and flow influence the collective behavior and viscosity of active suspensions of chemically-active Janus particles, revealing new regimes and effects of chemotactic aggregation.

Contribution

It introduces a kinetic model analyzing the interplay of flow, chemotaxis, and confinement in active suspensions, highlighting the inversion of hydrodynamic effects on viscosity due to aggregation.

Findings

Identification of four dynamic regimes under varying flow strength.

Chemotactic aggregation alters the effective viscosity, reversing hydrodynamic effects.

Flow and chemical interactions compete to determine collective behavior.

Abstract

Similarly to their biological counterparts, suspensions of chemically-active autophoretic swimmers exhibit nontrivial dynamics involving self-organization processes as a result of inter-particle interactions. Using a kinetic model for a dilute suspension of autochemotactic Janus particles, we analyse the effect of a confined pressure-driven flow on these collective behaviours and the impact of chemotactic aggregation on the effective viscosity of the active fluid. Four dynamic regimes are identified when increasing the strength of the imposed pressure-driven flow, each associated with a different collective behaviour resulting from the competition of flow- and chemically-induced reorientation of the swimmers together with the constraints of confinement. Interestingly, we observe that the effect of the pusher (resp. puller) hydrodynamic signature, which is known to reduce (resp. increase) the effective viscosity of a sheared suspension, is inverted upon the emergence of autochemotactic aggregation. Our results provide new insights on the role of collective dynamics in complex environments, which are relevant to synthetic as well as biological systems.