Filament actuation by an active colloid at low Reynolds number

TL;DR

This paper demonstrates how an active colloid attached to a semi-flexible filament can induce actuation and transport, revealing buckling instabilities and stable curved states useful for micro-machine design at low Reynolds number.

Contribution

It introduces a novel method of actuating passive filaments using active colloids and analyzes the resulting elastic instabilities and stable configurations.

Findings

Active colloids can induce buckling in attached filaments.

Stable non-zero curvature states are achievable through activity parameters.

The assembly's behavior is mapped in a parameter space of activity measures.

Abstract

Active colloids and externally actuated semi-flexible filaments provide basic building blocks for designing autonomously motile micro-machines. Here, we show that a passive semi-flexible filament can be actuated and transported by attaching an active colloid to its terminus. We study the dynamics of this assembly when it is free, tethered, or clamped using overdamped equations of motion that explicitly account for active fluid flow and the forces it mediates. Linear states are destabilized by buckling instabilities to produce stable states of non-zero curvature and writhe. We demarcate boundaries of these states in the two-dimensional parameter space representing dimensionless measures of polar and apolar activity. Our proposed assembly can be used as a novel component in the design of micro-machines at low Reynolds number and to study elastic instabilities driven by "follower" forces.