Abstract
Following the goal of using active particles as targeted cargo carriers aimed, for example, to deliver drugs towards cancer cells, the quest for the control of individual active particles with external fields is among the most explored topics in active matter. Here, we provide a scheme allowing to control collective behaviour in active matter, focusing on the fluctuating band patterns naturally occurring e.g. in the Vicsek model. We show that exposing these patterns to a travelling wave potential tames them, yet in a remarkably nontrivial way: the bands, which initially pin to the potential and comove with it, upon subsequent collisions, self-organize into a macroband, featuring a predictable transport against the direction of motion of the travelling potential. Our results provide a route to simultaneously control transport and structure, i.e. micro- versus macrophase separation, in polar active matter.
Highlights
Active matter contains self-propelled particles like bacteria, algae, or synthetic autophoretic Janus colloids whose properties can be designed on demand [1–3]
While single particle guidance with external fields is among the most explored problems in active matter [5, 30–37] and there is a moderate knowledge on interacting particles in external fields [38–43] and their control [44–48], surprisingly little is known about the controllability of polar active particles and band patterns they naturally form
We apply a “traveling wave potential” to the Vicsek model. We find that such an external field does allow to control the late time direction of motion of particle ensembles in polar active matter, yet, in a remarkably nontrivial way
Summary
Active matter contains self-propelled particles like bacteria, algae, or synthetic autophoretic Janus colloids whose properties can be designed on demand [1–3]. The phase transition from the disordered phase which occurs for strong noise to the long-range ordered TonerTu phase is known to be discontinuous [27] and features a remarkably large coexistence region [28, 29] where high-density bands of comoving polarized particles spontaneously emerge and traverse through a background of a low-density disordered gas-like phase These bands behave highly randomly; they merge when colliding with each other and split up frequently, rendering an irregular pattern of sharply localized and strongly polarized moving bands. We apply a “traveling wave potential” ( called travelling potential ratchet [49]) to the Vicsek model We find that such an external field does allow to control the late time direction of motion of particle ensembles in polar active matter, yet, in a remarkably nontrivial way.
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