Disorder-mediated crowd control in an active matter system.

Erçağ Pinçe,Sylvain Gigan,Giorgio Volpe,Agnese Callegari,Parviz Elahi,Giovanni Volpe,Sabareesh K P Velu

doi:10.1038/ncomms10907

Abstract

Living active matter systems such as bacterial colonies, schools of fish and human crowds, display a wealth of emerging collective and dynamic behaviours as a result of far-from-equilibrium interactions. The dynamics of these systems are better understood and controlled considering their interaction with the environment, which for realistic systems is often highly heterogeneous and disordered. Here, we demonstrate that the presence of spatial disorder can alter the long-term dynamics in a colloidal active matter system, making it switch between gathering and dispersal of individuals. At equilibrium, colloidal particles always gather at the bottom of any attractive potential; however, under non-equilibrium driving forces in a bacterial bath, the colloids disperse if disorder is added to the potential. The depth of the local roughness in the environment regulates the transition between gathering and dispersal of individuals in the active matter system, thus inspiring novel routes for controlling emerging behaviours far from equilibrium.

Highlights

Living active matter systems such as bacterial colonies, schools of fish and human crowds, display a wealth of emerging collective and dynamic behaviours as a result of far-fromequilibrium interactions
The colloidal particles are driven far from thermal equilibrium by an active bath of motile Escherichia coli (E. coli) bacteria (Methods section)[17], which are self-propelling microorganisms whose motion proceeds as an alternation of running and tumbling events[18]; because of random collisions with the bacteria in the solution, the colloids are driven far from equilibrium, and, in a homogenous environment, their motion features a crossover at a characteristic time in the order of a few seconds from ballistic motion at short times to enhanced diffusion at long times with an effective diffusion coefficient that is higher for higher concentrations of bacteria[17]
From a system at equilibrium, our results show that the presence of spatial disorder in an external attractive potential alters the long-term dynamics of the colloidal active matter system: in particular, the depth of the local roughness in the environment regulates the transition between individuals gathering in and dispersing from the attractive potential, inspiring novel routes for controlling emerging behaviours far from equilibrium

Summary

Introduction

Living active matter systems such as bacterial colonies, schools of fish and human crowds, display a wealth of emerging collective and dynamic behaviours as a result of far-fromequilibrium interactions The dynamics of these systems are better understood and controlled considering their interaction with the environment, which for realistic systems is often highly heterogeneous and disordered. From a system at equilibrium, our results show that the presence of spatial disorder in an external attractive potential alters the long-term dynamics of the colloidal active matter system: in particular, the depth of the local roughness in the environment regulates the transition between individuals gathering in and dispersing from the attractive potential, inspiring novel routes for controlling emerging behaviours far from equilibrium

Methods

Results

Conclusion