Dynamics of microswimmers near a soft penetrable interface

TL;DR

This study uses numerical simulations to explore how microswimmers interact with deformable, penetrable fluid interfaces, revealing behaviors like penetration, parallel swimming, or bouncing, depending on swimmer type and incident angle.

Contribution

The paper introduces a numerical model of microswimmer dynamics near deformable interfaces, highlighting different behaviors based on swimmer type and interface properties.

Findings

Pullers can penetrate or swim parallel to the interface.

Pushers tend to bounce between interfaces.

Behavior depends on swimmer type and incident angle.

Abstract

Few simulations exist for microswimmers near deformable interfaces. Here, we present numerical simulations of the hydrodynamic flows associated with a single microswimmer embedded in a binary fluid mixture. The two fluids demix, separated by a penetrable and deformable interface that we assume to be initially prepared in its planar ground-state. We find that the microswimmer can either penetrate the interface, move parallel to it or bounce back off it. We analyze how the trajectory depends on the swimmer type (pusher/puller) and the angle of incidence with respect to the interface. Our simulations are performed in a system with periodic boundary conditions, corresponding to an infinite array of fluid interfaces. A puller reaches a steady state in which it either swims parallel to the interface or selects a perpendicular orientation, repeatedly penetrating through the interface. In contrast, a pusher follows a bouncing trajectory between two interfaces. We discuss several examples in biology in which swimmers penetrate soft interfaces. Our work can be seen as a highly simplified model of such processes.