Activity induced collapse and re-expansion of rigid polymers

TL;DR

This study investigates how rigid polymers behave in active particle baths, revealing a non-monotonic response with collapse and re-expansion driven by activity levels, akin to polyelectrolyte behavior in salt solutions.

Contribution

It uncovers the activity-induced collapse and re-expansion phenomena in rigid polymers, a novel insight into their elastic response in active environments.

Findings

Rigid filaments soften at moderate activity levels.

Filaments collapse into metastable hairpins at intermediate activity.

Re-expansion occurs at high activity levels.

Abstract

We study the elastic properties of a rigid filament in a bath of self-propelled particles. We find that while fully flexible filaments swell monotonically upon increasing the strength of the propelling force, rigid filaments soften for moderate activities, collapse into metastable hairpins for intermediate strengths, and eventually re-expand when the strength of the activity of the surrounding fluid is large. This collapse and re-expansion of the filament with the bath activity is reminiscent of the behavior observed in polyelectrolytes in the presence of different concentrations of multivalent salt.