Active particles in periodic lattices

TL;DR

This paper explores how spherical micro-swimmers move within a complex, periodic lattice environment, revealing different trajectory behaviors based on swimming strength and lattice density through simulations and hydrodynamic theory.

Contribution

It introduces a numerical and theoretical study of micro-swimmer dynamics in a 3D periodic lattice, highlighting the influence of swimmer type and environment on motion.

Findings

Identified phase diagram of swimmer trajectories based on actuation strength and packing density.

Hydrodynamic theory explains how swimmer type affects behavior at high volume fractions.

Demonstrated the importance of far-field swimmer characteristics in complex environments.

Abstract

Both natural and artificial small-scale swimmers may often self-propel in environments subject to complex geometrical constraints. While most past theoretical work on low-Reynolds number locomotion addressed idealised geometrical situations, not much is known on the motion of swimmers in heterogeneous environments. As a first theoretical model, we investigate numerically the behaviour of a single spherical micro-swimmer located in an infinite, periodic body-centred cubic lattice consisting of rigid inert spheres of the same size as the swimmer. Running a large number of simulations we uncover the phase diagram of possible trajectories as a function of the strength of the swimming actuation and the packing density of the lattice. We then use hydrodynamic theory to rationalise our computational results and show in particular how the far-field nature of the swimmer (pusher vs. puller) governs even the behaviour at high volume fractions.