Phase-separation during sedimentation of dilute bacterial suspensions

Abstract

Numerous natural systems depend on the sedimentation of passive particles in presence of swimming microorganisms. Here, we investigate the dynamics of the sedimentation of spherical colloids at various E. coli concentration within the dilute regime. Results show the appearance of two sedimentation fronts, a spherical particle front and the bacteria front. We find that the bacteria front behave diffusive at short times, whereas at long times decays linearly. The sedimentation speed of passive particles decays at a constant speed and decreases as bacteria concentration (${\varphi }_b$) is increased. As ${\varphi }_b$ is increased further, the sedimentation speed becomes independent of ${\varphi }_b$. The timescales of the bacteria front is associated with the particle settling speeds. Remarkably, all experiments collapse onto a single master line by using the bacteria front timescale. A phenomenological model is proposed that captures the sedimentation of passive particles in active fluids.

References in corpus (18)

• The Mechanics and Statistics of Active Matter
• Statistical Mechanics of Interacting Run-and-Tumble Bacteria
• Sedimentation of active colloidal suspensions
• Turning bacteria suspensions into a "superfluid"
• Phase separation and rotor self-assembly in active particle suspensions
• Enhanced diffusion due to active swimmers at a solid surface
• Nonequilibrium equation of state in suspensions of active colloids
• Non-Newtonian viscosity of E-coli suspensions
• Fluctuations and Rheology in Active Bacterial Suspensions
• Run-and-tumble particles with hydrodynamics: sedimentation, trapping and upstream swimming
• Enhanced diffusion of nonswimmers in a three-dimensional bath of motile bacteria
• The colloidal nature of complex fluids leads to enhanced motility of flagellated bacteria
• Entrainment dominates the interaction of microalgae with micron-sized objects
• Particle diffusion in active fluids is non-monotonic in size
• Sedimentation of self-propelled Janus colloids: polarization and pressure
• Active ideal sedimentation: Exact two-dimensional steady states
• Bacterial activity hinders particle sedimentation
• The Hindered Settling Function at Low Re Has Two Branches

Cited by in corpus (1)

• Sedimentation dynamics of passive particles in dilute bacterial suspensions: emergence of bioconvection