Colloids in active fluids: Anomalous micro-rheology and negative drag

Abstract

We simulate an experiment in which a colloidal probe is pulled through an active nematic fluid. We find that the drag on the particle is non-Stokesian (not proportional to its radius). Strikingly, a large enough particle in contractile fluid (such as an actomyosin gel) can show negative viscous drag in steady state: the particle moves in the opposite direction to the externally applied force. We explain this, and the qualitative trends seen in our simulations, in terms of the disruption of orientational order around the probe particle and the resulting modifications to the active stress.

5 pages, 3 figures

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• Active Microrheology in Active Matter Systems: Mobility, Intermittency and Avalanches
• Mesoscopic Simulations of Active-Nematics
• Passive particle in an active bath: How can we tell it is out of equilibrium?
• Hydrodynamic coupling and rotational mobilities near planar elastic membranes
• Rheological properties of a dilute suspension of self-propelled particles
• Active turbulence and spontaneous phase separation in inhomogeneous extensile active gels
• Harvesting information to control non-equilibrium states of active matter
• Dynamics of a Passive Droplet in Active Turbulence
• Object Transport by a Confined Active Suspension
• A Cold Tracer in a Hot Bath: In and Out of Equilibrium
• Statistical mechanics of a cold tracer in a hot bath