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A minimal mechanism for flocking in phoretically interacting active particles.

Arvin Gopal Subramaniam1, Sagarika Adhikary1, Rajesh Singh1

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Active colloidal particles can exhibit flocking behavior driven solely by repulsive torques. This study reveals a new mechanism for collective motion in active matter, leading to crystalline or liquid flock phases.

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Area of Science:

  • Physics
  • Soft Matter Physics
  • Colloidal Science

Background:

  • Coherent collective motion is a hallmark of active matter systems.
  • Understanding flocking transitions is crucial for active matter research.

Purpose of the Study:

  • To investigate a novel flocking transition mechanism in chemically interacting active colloidal particles.
  • To identify the fundamental requirements for global polar order in such systems.

Main Methods:

  • Particle-based simulations of active colloidal particles.
  • Analysis of chemo-repulsive and chemo-attractive inter-particle forces.
  • Stability analysis of a complementary hydrodynamic model.

Main Results:

  • A flocking transition mechanism driven purely by chemo-repulsive torques was identified at low to medium densities.
  • Excluded volume repulsions and long-ranged repulsive torques are essential for global polar order.
  • Translational repulsive forces induce a crystalline flock structure, while chemo-attractive forces lead to liquid flocks.
  • Hydrodynamic model analysis confirmed the destabilization transition of the flocking state.

Conclusions:

  • Chemically interacting active colloids can achieve flocking through torque-driven mechanisms.
  • The system exhibits distinct crystalline and liquid flock phases depending on inter-particle forces.
  • The findings provide insights into the fundamental principles governing collective motion in active matter.