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Re-entrant percolation in active Brownian hard disks
David Evans1, José Martín-Roca2,3, Nathan J Harmer1
1Department of Chemistry, Durham University, South Road, Durham DH1 3LE, UK. m.a.miller@durham.ac.uk.
Soft Matter
|September 12, 2024
Summary
Active matter clustering and percolation show complex behavior. Increased activity initially aids cluster formation but later causes breakup, leading to non-monotonic percolation thresholds before phase separation.
Area of Science:
- Physics
- Statistical Mechanics
- Soft Matter Physics
Background:
- Active matter systems exhibit unique collective behaviors distinct from equilibrium systems.
- Motility-induced phase separation (MIPS) is a key phenomenon in active matter, driven by self-propulsion.
- Understanding non-equilibrium clustering and percolation is crucial for active matter dynamics.
Purpose of the Study:
- Investigate non-equilibrium clustering and percolation in a 2D active matter model.
- Analyze the influence of activity on cluster formation and percolation thresholds.
- Explore the transition from single-phase to motility-induced phase separation.
Main Methods:
- Dynamic simulations of self-propelled Brownian repulsive particles.
- Analysis of the single-phase region before MIPS.
- Application of iterative Boltzmann inversion to derive effective potentials.
- Comparison with Monte Carlo simulations of passive systems.
Main Results:
- Weak activity enhances cluster formation and lowers percolation thresholds.
- Higher activity levels lead to re-entrant percolation due to competing attraction and cluster breakup.
- A minimum critical density for system-spanning clusters is observed.
- Differences in higher-order structural correlations, not radial distribution functions, dictate percolation sensitivity.
Conclusions:
- Active matter exhibits non-monotonic percolation behavior in the pre-MIPS regime.
- Activity-driven forces create complex structures not fully captured by equilibrium models.
- Higher-order correlations are critical for understanding percolation in active systems.
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