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Re-entrant phase separation in nematically aligning active polar particles.

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Active polar particles exhibit complex phase behavior. Increasing activity leads to a re-entrant fluid-phase separation-fluid transition, driven by flocking and sub-cluster dynamics.

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Area of Science:

  • Soft Matter Physics
  • Active Matter Systems
  • Statistical Mechanics

Background:

  • Understanding the collective behavior of self-propelled particles is crucial in active matter.
  • Polar particles with nematic alignment exhibit rich phase behaviors.
  • Controlling active matter systems requires understanding the interplay of activity and noise.

Purpose of the Study:

  • To numerically investigate the phase behavior of repulsively interacting active polar particles.
  • To explore the influence of active velocity amplitude and orientational noise on system dynamics.
  • To elucidate the mechanisms behind transitions between fluid, phase-separated, and re-entrant fluid states.

Main Methods:

  • Numerical simulations of active polar particle systems.
  • Analysis of phase transitions, including nematic-isotropic and phase separation.
  • Characterization of cluster formation, collective motion, and sub-cluster dynamics.

Main Results:

  • High orientational noise induces a continuous nematic-isotropic transition.
  • Lower noise strengths lead to active phase separation with hexatic cluster formation.
  • Increasing activity causes a re-entrant fluid-phase separation-fluid transition.
  • Low activity phase coexistence is explained by motility-induced phase separation.
  • High activity features flocking, sliding, jamming, and fragmentation mediating remelting.

Conclusions:

  • The phase behavior is sensitive to activity and orientational noise.
  • Motility-induced phase separation governs low-activity coexistence.
  • Flocking and complex sub-cluster dynamics drive high-activity transitions and remelting.
  • The study reveals a rich phase diagram for active polar particles.