Microrheology of active suspensions

Area of Science:

• Soft Matter Physics
• Fluid Dynamics
• Biophysics

Background:

• Active suspensions exhibit complex rheological properties.
• Hydrodynamic interactions (HIs) play a crucial role in the collective behavior of microswimmers.
• Understanding microrheology is essential for characterizing fluid behavior at small scales.

Purpose of the Study:

• To investigate the microrheology of active suspensions using model pusher-like microswimmers.
• To quantify the effect of microswimmer hydrodynamic interactions on a probe particle's friction coefficient.
• To elucidate the mechanisms behind drag reduction in active suspensions.

Main Methods:

• Direct hydrodynamic simulations.
• Modeling of pusher-like microswimmers.
• Analysis of probe particle dynamics and interactions with microswimmers.

Main Results:

• Hydrodynamic interactions with microswimmers significantly reduce the probe particle's friction coefficient.
• A front-rear asymmetry in swimmer orientation around the probe generates a net driving force.
• The observed drag-reduction mechanism is distinct from bulk viscosity reduction.

Conclusions:

• Hydrodynamic interactions in active suspensions can lead to novel drag-reduction phenomena at the microscale.
• The findings provide fundamental insights into the behavior of active matter.
• This study clarifies differences between microrheology and macrorheology measurements.