Forced microrheology of active colloids
arXiv:2205.03715 · doi:10.1122/8.0000504
Abstract
Particle-tracking microrheology of dilute active (self-propelled) colloidal suspensions is studied by considering the external force required to maintain the steady motion of an immersed constant-velocity colloidal probe. If the probe speed is zero, the suspension microstructure is isotropic but exhibits a boundary accumulation of active bath particles at contact due to their self-propulsion. As the probe moves through the suspension, the microstructure is distorted from the nonequilibrium isotropic state, which allows us to define a microviscosity for the suspension using the Stokes drag law. For a slow probe, we show that active suspensions exhibit a swim-thinning behavior in which their microviscosity is gradually lowered from that of passive suspensions as the swim speed increases. When the probe speed is fast, the suspension activity is obscured by the rapid advection of the probe and the measured microviscosity is indistinguishable from that of passive suspensions. Generally for finite activity, the suspension exhibits a velocity-thinning behavior -- though with a zero-velocity plateau lower than passive suspensions -- as a function of the probe speed. These behaviors originate from the interplay between the suspension activity and the hard-sphere excluded-volume interaction between the probe and a bath particle.
19 pages, 12 figures
References in corpus (8)
- The hydrodynamics of swimming microorganisms
- Physics of Microswimmers - Single Particle Motion and Collective Behavior
- Turning bacteria suspensions into a "superfluid"
- Collective Chemotactic Dynamics in the Presence of Self-Generated Fluid Flows
- Active Microrheology in Active Matter Systems: Mobility, Intermittency and Avalanches
- The curved kinetic boundary layer of active matter
- Non-equilibrium fluctuations and nonlinear response of an active bath
- Activity-induced propulsion of a vesicle