Exact Phoretic Interaction of Two Chemically Active Particles.

Babak Nasouri,Ramin Golestanian

doi:10.1103/physrevlett.124.168003

Abstract

We study the nonequilibrium interaction of two isotropic chemically active particles taking into account the exact near-field chemical interactions as well as hydrodynamic interactions. We identify regions in the parameter space wherein the dynamical system describing the two particles can have a fixed point-a phenomenon that cannot be captured under the far-field approximation. We find that, due to near-field effects, the particles may reach a stable equilibrium at a nonzero gap size or make a complex that can dissociate in the presence of sufficiently strong noise. We explicitly show that the near-field effects originate from a self-generated neighbor-reflected chemical gradient, similar to interactions of a self-propelling phoretic particle and a flat substrate.

Highlights

Nonequilibrium interfacial transport processes known as phoretic mechanisms [1,2] have been key to the development of the field of active matter [3]
We study the nonequilibrium interaction of two isotropic chemically active particles taking into account the exact near-field chemical interactions as well as hydrodynamic interactions
We explicitly show that the near-field effects originate from a self-generated neighbor-reflected chemical gradient, similar to interactions of a selfpropelling phoretic particle and a flat substrate

Summary

Exact Phoretic Interaction of Two Chemically Active Particles

We study the nonequilibrium interaction of two isotropic chemically active particles taking into account the exact near-field chemical interactions as well as hydrodynamic interactions. Studies of phoretic interactions in many-particle systems have led to a number of nontrivial scenarios for selforganization that gives rise to emergent swimming of clusters of isotropic particles [22,23,24,25,26] or cometlike propulsion of large swarms [27,28] These self-organized structures typically involve active colloids in close proximity, where near-field effects play a dominant role. It will be important to study the exact nonequilibrium interaction between two phoretically active particles, resolving the near-field effects of the chemical activity as well as the hydrodynamic interactions. This is the task we set out to do here. In this system, the nonequilibrium activity manifests itself as broken actionreaction symmetry [22,23,28]

Published by the American Physical Society

Note that regimes III and IV are located between regimes