Interparticle torques suppress motility-induced phase separation for rodlike particles.

Area of Science:

• Soft Matter Physics
• Active Matter Systems
• Statistical Mechanics

Background:

• Motility-induced phase separation (MIPS) describes spontaneous pattern formation in systems of self-propelled particles.
• The influence of particle shape on MIPS is not fully understood, particularly the role of rotational dynamics.

Purpose of the Study:

• To investigate how particle shape, specifically elongation, affects motility-induced phase separation (MIPS).
• To explore the underlying mechanisms, including collision dynamics and rotational diffusion, that govern MIPS in anisotropic active matter.

Main Methods:

• Simulations of 2D and 3D active particles, ranging from isotropic disks/spheres to anisotropic rods.
• Phase diagram construction for various particle shapes.
• Stability analysis of the homogeneous isotropic phase using effective swimming speed and rotational diffusion.

Main Results:

• MIPS is suppressed as particle shape transitions from isotropic to anisotropic (rod-like).
• A quantitative prediction for the onset of MIPS was developed based on particle properties.
• Collision duration was identified as a key factor suppressing MIPS in elongated particles.

Conclusions:

• Particle elongation significantly suppresses MIPS, contrary to some existing models.
• The proposed collision-based mechanism explains MIPS suppression in rods and potential enhancement in other systems (e.g., Vicsek models).
• Findings provide insights into the design and behavior of active materials with specific shape characteristics.