Irreversibility and Chaos in Active Particle Suspensions

Abstract

Active matter has been the object of huge amount of research in recent years for its important fundamental and applicative properties. In this paper we investigate active suspensions of micro-swimmers through direct numerical simulation, so that no approximation is made at the continuous level other than the numerical one. We consider both pusher and puller organisms, with a spherical or ellipsoidal shape. We analyse the velocity and the characteristic scales for an homogeneous two-dimensional suspension and the effective viscosity under shear. We bring evidences that the complex features displayed are related to a spontaneous breaking of the time-reversal symmetry. We show that chaos is not a key ingredient, whereas a large enough number of interacting particles and a non-spherical shape are needed to break the symmetry and are therefore at the basis of the phenomenology. Our numerical study also shows that pullers display some collective motion, though with different characteristics from pushers.

References in corpus (26)

• Novel type of phase transition in a system of self-driven particles
• Active Particles in Complex and Crowded Environments
• The hydrodynamics of swimming microorganisms
• The Mechanics and Statistics of Active Matter
• Athermal Phase Separation of Self-Propelled Particles with no Alignment
• Active Brownian Particles. From Individual to Collective Stochastic Dynamics
• Meso-scale turbulence in living fluids
• Fluid dynamics and noise in bacterial cell-cell and cell-surface scattering
• Fluid dynamics of bacterial turbulence
• Bacterial hydrodynamics
• Turning bacteria suspensions into a "superfluid"
• The Significance of Simple Invariant Solutions in Turbulent Flows
• Effective viscosity of microswimmer suspensions
• Brownian motion of a self-propelled particle
• Enhanced diffusion due to active swimmers at a solid surface
• Spontaneous velocity alignment in Motility-induced Phase Separation
• Transport powered by bacterial turbulence
• Long-range nematic order and anomalous fluctuations in suspensions of swimming filamentous bacteria
• The role of correlations in the collective behaviour of microswimmer suspensions
• Nonequilibrium and irreversibility
• Regularity issues in the problem of fluid structure interaction
• Velocity alignment promotes motility-induced phase separation
• Effective Viscosity of Dilute Bacterial Suspensions: A Two-Dimensional Model
• Particle-resolved lattice Boltzmann simulations of 3-dimensional active turbulence
• Symmetric mixtures of pusher and puller microswimmers behave as noninteracting suspensions
• The role of the number of degrees of freedom and chaos in macroscopic irreversibility