Active microrheology, Hall effect, and jamming in chiral fluids

Area of Science:

• Soft Matter Physics
• Active Matter Physics
• Fluid Dynamics

Background:

• Chiral active matter systems exhibit complex emergent behaviors.
• Understanding particle dynamics in such fluids is crucial for designing micro-machines and understanding biological systems.

Purpose of the Study:

• To investigate the motion of a probe particle in a chiral fluid of self-swimming disks.
• To analyze the factors influencing the probe particle's velocity and the resulting Hall angle.
• To explore the relationship between fluid properties, swimmer activity, and jamming transitions.

Main Methods:

• Simulating a probe particle driven through a fluid of circularly swimming disks.
• Analyzing the probe particle's velocity components (longitudinal and transverse).
• Varying parameters such as swimmer activity, density, and swimming frequency.

Main Results:

• The probe particle exhibits both longitudinal and transverse motion, creating a Hall angle.
• Probe particle velocity shows nonmonotonic behavior with increasing swimmer activity.
• The Hall angle is maximized at resonance between disk frequency and probe motion, and decreases with density, reaching zero at jamming.
• Jamming onset is dependent on chiral particle swimming frequency.

Conclusions:

• The study reveals a rich dynamic response of a probe particle in chiral active fluids.
• Resonance and jamming are key phenomena governing particle transport and system state.
• Swimmer activity, frequency, and density are critical control parameters for active matter systems.