Sorting motile rods by activity

TL;DR

This paper demonstrates how active, geometrically polar granular rods exhibit a collective trapping phase transition near V-shaped obstacles, with potential applications in sorting particles by activity levels.

Contribution

It introduces a new mechanism explaining the trapping transition in active rods and utilizes this phenomenon for activity-based particle sorting.

Findings

Trapping occurs below a critical V-shape angle.

Transition is driven by cooperative noise reduction.

Sorting based on activity persistence is effective.

Abstract

We show, through experiments and simulations, that geometrically polar granular rods, rendered active by the transduction of vertical vibration, undergo a collective trapping phase transition in the presence of a V-shaped obstacle when the opening angle drops below a threshold value. We propose a mechanism that accounts qualitatively for the transition, based on the cooperative reduction of angular noise with increasing area fraction. We exploit the sensitivity of trapping to the persistence of directed motion to sort particles based on the statistical properties of their activity.