Orientational dynamics and rheology of active suspensions in weakly viscoelastic flows

Abstract

Microswimmer suspensions in Newtonian fluids exhibit unusual macroscale properties, such as a superfluidic behavior, which can be harnessed to perform work at microscopic scales. Since most biological fluids are non-Newtonian, here we study the rheology of a microswimmer suspension in a weakly viscoelastic shear flow. At the individual level, we find that the viscoelastic stresses generated by activity substantially modify the Jeffery orbits well-known from Newtonian fluids. The orientational dynamics depends on the swimmer type; especially pushers can resist flow-induced rotation and align at an angle with the flow. To analyze its impact on bulk rheology, we study a dilute microswimmer suspension in the presence of random tumbling and rotational diffusion. Strikingly, swimmer activity and its elastic response in polymeric fluids alter the orientational distribution and substantially amplify the swimmer-induced viscosity. This suggests that pusher suspensions reach the superfluidic regime at lower volume fractions compared to a Newtonian fluid with identical viscosity.

Communications Physics 6, 163 (2023)

References in corpus (8)

• Physics of Microswimmers - Single Particle Motion and Collective Behavior
• Hydrodynamic attraction of swimming microorganisms by surfaces
• Hydrodynamics of self-propulsion near a boundary: predictions and accuracy of far-field approximations
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Cited by in corpus (2)

• Unified description of viscous, viscoelastic, or elastic thin active films on substrates
• Rheologically tuned modes of collective transport in active viscoelastic films