Active Matter: Run-Tumble Phase Separation
MIPS — motility-induced phase separation • self-propelled particles • steric interactions
Particle Parameters
Run speed v₀
3.0
Tumble rate λ
0.05
Packing fraction φ
0.35
Interaction range
12
ṙᵢ = v₀ êᵢ + Σ Fᵢⱼ
θᵢ: Poisson tumbles (rate λ)
MIPS criterion:
∂μ/∂ρ < 0 ↔ v₀/λ large
Péclet: Pe = v₀²/(Dλ)
Pe =
–
| φ_dense ≈
–
Reset Particles
Pause/Resume
Run-and-tumble bacteria (E. coli) spontaneously phase-separate at high speed/density: dense clusters form because fast particles pile up behind slow/stalled ones. No attractive interactions needed — purely kinetic.