Polar Patterns in Active Fluids

Abstract

We study the spatio-temporal dynamics of a model of polar active fluid in two dimensions. The system exhibits a transition from an isotropic to a polarized state as a function of density. The uniform polarized state is, however, unstable above a critical value of activity. Upon increasing activity, the active fluids displays increasingly complex patterns, including traveling bands, traveling vortices and chaotic behavior. The advection arising from the particles self-propulsion and unique to polar fluids yields qualitatively new behavior as compared to that obtain in active nematic, with traveling-wave structures. We show that the nonlinear hydrodynamic equations can be mapped onto a simplified diffusion-reaction-convection model, highlighting the connection between the complex dynamics of active system and that of excitable systems.

12 pages, 11 figures

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• Banding, Excitability and Chaos in Active Nematic Suspensions
• Confined active nematic flow in cylindrical capillaries
• A classical nucleation theory description of active colloid assembly
• Insensitivity of active nematic dynamics to topological constraints
• Swimmer suspensions on substrates: anomalous stability and long-range order
• Inertia drives a flocking phase transition in viscous active fluids
• Emergence of epithelial cell density waves
• Pinning of Diffusional Patterns by Non-Uniform Curvature
• Self-generated gradients stabilize the hydrodynamic instabilities in active suspensions
• Hydrodynamics of Active Polar Systems in a (Visco)Elastic Background
• Inertia drives concentration-wave turbulence in swimmer suspensions
• Defect turbulence in a dense suspension of polar, active swimmers
• Self-propulsion of an active polar drop
• Hydrodynamic bend instability of motile particles on a substrate
• Instabilities and turbulence in extensile swimmer suspensions