Trapping and sorting active particles: Motility-induced condensation and smectic defects.

Area of Science:

• Soft Matter Physics
• Granular Materials
• Active Matter Physics

Background:

• Collective phenomena in active matter systems are crucial for understanding emergent behaviors.
• Phase transitions, such as trapping, are fundamental to controlling particle dynamics.
• Polar granular rods exhibit complex behaviors due to their motility and orientational order.

Purpose of the Study:

• To experimentally realize and investigate the collective trapping phase transition in motile polar granular rods.
• To develop a theoretical framework explaining the trapping mechanism based on motility-induced condensation and liquid-crystalline ordering.
• To explore the potential for particle sorting based on activity-dependent trapping.

Main Methods:

• Experimental realization of trapping using motile polar granular rods and a V-shaped obstacle.
• Theoretical modeling incorporating motility-induced condensation and liquid-crystalline ordering.
• Numerical simulations to investigate the effect of rotational noise on the trapping transition.
• Exploitation of trapping sensitivity for particle sorting.

Main Results:

• Experimental observation of a collective trapping phase transition.
• A critical trap angle (θc) was identified, below which trapping occurs and above which particles escape.
• The critical angle decreases with increasing rotational noise, as predicted by theory and simulations.
• Successful particle sorting based on statistical properties of directed motion.

Conclusions:

• The collective trapping phase transition is governed by the balance between particle influx and defect expulsion.
• The system's behavior is sensitive to the trap geometry and rotational noise, offering control over particle dynamics.
• This work demonstrates a novel method for sorting active particles by exploiting their persistent motion.