Particle-scale statistical theory for hydrodynamically induced polar ordering in microswimmer suspensions

Area of Science:

• Physics
• Soft Matter Physics
• Fluid Dynamics

Background:

• Particle-based simulations show puller microswimmers (contractile) order more readily than pusher microswimmers (extensile).
• Understanding the emergence of spontaneous polar ordering in microswimmer suspensions is crucial for active matter physics.

Purpose of the Study:

• To evaluate a microscopic statistical theory for spontaneous polar ordering in microswimmer suspensions.
• To investigate the linear instability of disordered states leading to polar order.

Main Methods:

• Developed a microscopic statistical theory for active microswimmer systems.
• Utilized a heuristic variant of the Percus test-particle method for orientation-dependent pair-distribution functions.
• Analyzed linear instability of the disordered state.

Main Results:

• The theory predicts inherent polar order evolution in planar puller microswimmer systems.
• Hydrodynamic interactions and active rotation-translation coupling drive ordering in pullers.
• Pusher microswimmer suspensions remain linearly stable against polar ordering.

Conclusions:

• Microscopic theory explains spontaneous polar ordering in puller microswimmers.
• Actively induced hydrodynamic rotation-translation coupling is the key mechanism for puller ordering.
• Experimental verification in biological microswimmer systems is anticipated.