Diversity of self-propulsion speeds reduces motility-induced clustering in confined active matter

Abstract

Self-propelled swimmers such as bacteria agglomerate into clusters as a result of their persistent motion. In 1D, those clusters do not coalesce macroscopically and the stationary cluster size distribution (CSD) takes an exponential form. We develop a minimal lattice model for active particles in narrow channels to study how clustering is affected by the interplay between \textit{self-propulsion speed diversity} and confinement. A mixture of run-and-tumble particles with a distribution of self-propulsion speeds is simulated in 1D. Particles can swap positions at rates proportional to their relative self-propulsion speed. Without swapping, we find that the average cluster size $L_\text{c}$ \textit{decreases} with diversity and follows a non-arithmetic power mean of the single-component $L_\text{c}$'s, unlike the case of tumbling-rate diversity previously studied. Effectively, the mixture is thus equivalent to a system of identical particles whose self-propulsion speed is the \textit{harmonic} mean self-propulsion speed of the mixture. With swapping, particles escape more quickly from clusters. As a consequence, $L_\text{c}$ decreases with swapping rates and depends less strongly on diversity. We derive a dynamical equilibrium theory for the CSDs of binary and fully polydisperse systems. Similarly to the clustering behaviour of one-component models, our qualitative results for mixtures are expected to be universal across active matter. Using literature experimental values for the self-propulsion speed diversity of unicellular swimmers known as choanoflagellates, which naturally differentiate into slower and faster cells, we predict that the error in estimating their $L_\text{c}$ via one-component models which use the conventional arithmetic mean self-propulsion speed is around $30\%$.

Article information

Article type
Paper
Submitted
08 Jul 2021
Accepted
12 Oct 2021
First published
14 Oct 2021

Soft Matter, 2021, Accepted Manuscript

Diversity of self-propulsion speeds reduces motility-induced clustering in confined active matter

P. de Castro, F. M. Rocha, S. Diles, R. Soto and P. Sollich, Soft Matter, 2021, Accepted Manuscript , DOI: 10.1039/D1SM01009C

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements