Transverse Self-Propulsion Enhances the Aggregation of Active Dumbbells.

Area of Science:

• Soft matter physics
• Statistical mechanics
• Active matter systems

Background:

• Active matter systems, such as self-propelled particles, exhibit unique collective behaviors.
• Brownian dumbbells are a fundamental model for studying self-propelled entities.
• Understanding phase behavior and emergent dynamics is crucial in active matter research.

Purpose of the Study:

• To investigate the phase behavior of a 2D system of active Brownian dumbbells with transverse propulsion.
• To characterize the structural and dynamic properties of emergent clusters.
• To compare the behavior with axially self-propelled dumbbells and develop a theoretical model.

Main Methods:

• Molecular dynamics simulations of a two-dimensional system of active Brownian dumbbells.
• Analysis of phase separation, cluster formation, and local polarization.
• Characterization of cluster rotation dynamics and development of an analytical model.

Main Results:

• The system undergoes phase separation into dilute and dense phases across all activity levels.
• The dense phase exhibits hexatic order, with increased local polarization at higher activities.
• Transversely propelled dumbbells show enlarged binodal regions, enhanced cluster nucleation, and suppressed escape rates compared to axial propulsion.
• Clusters exhibit spontaneous rotation with angular velocity scaling as ω∼rg-2.

Conclusions:

• Transverse propulsion significantly alters the phase behavior and cluster dynamics of active Brownian dumbbells.
• The observed scaling of cluster rotation provides insights into the collective motion of these active systems.
• A simplified analytical model successfully rationalizes the observed rotational scaling behavior.