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Spinodal decomposition and phase separation in polar active matter.
1Department of Physics and Institute for Fundamental Science, University of Oregon, Eugene, Oregon 97403, USA.
Physical Review. E
|April 18, 2024
Summary
Strong autochemotaxis in flocks creates density bands, unlike typical flocking instabilities. This leads to phase separation, forming distinct high- and low-density regions, similar to ant trails.
Area of Science:
- Collective behavior
- Active matter physics
- Theoretical biology
Background:
- Flocking describes coordinated motion in self-propelled entities.
- Autochemotaxis involves entities emitting substances that attract others.
- Existing theories like Keller-Segel and Toner-Tu model these phenomena separately.
Purpose of the Study:
- To develop and study a hydrodynamic theory of flocking with autochemotaxis.
- To investigate the emergent collective behaviors and phase transitions in such systems.
- To compare the observed instabilities with known flocking and phase separation phenomena.
Main Methods:
- Combined features of the Keller-Segel model (autochemotaxis) and Toner-Tu theory (flocking).
- Developed a hydrodynamic theory to describe the system's collective dynamics.
- Employed numerical simulations to validate the analytic theory.
Main Results:
- Identified a novel instability driven by strong autochemotaxis, leading to density bands moving parallel to the flock velocity.
- Observed that these bands coarsen over time into a phase-separated state with distinct high- and low-density regions.
- Demonstrated that this instability mechanism is general and applies to other flocking systems with strong attractive interactions.
Conclusions:
- Autochemotaxis can induce unique phase separation dynamics in flocks, distinct from equilibrium or motility-induced phase separation.
- The resulting steady-state densities are determined by an 'uncommon tangent construction'.
- The developed theory accurately predicts simulation results, providing a robust framework for studying active matter systems.
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