Oscillatory active microrheology of active suspensions

Area of Science:

• Soft Matter Physics
• Statistical Mechanics
• Non-equilibrium Systems

Background:

• Understanding the dynamic properties of active matter is crucial for fields ranging from biology to materials science.
• Active suspensions exhibit complex behaviors not captured by equilibrium statistical mechanics.

Purpose of the Study:

• To investigate the dynamic properties of a 2D suspension of active disks at high Péclet numbers.
• To explore tracer particle motion under constant and oscillatory external forces using active microrheology.

Main Methods:

• Brownian dynamics simulations were employed.
• A tracer particle was subjected to constant and oscillatory external forces.
• Active microrheology techniques were utilized to probe dynamic properties.

Main Results:

• Tracer mobility decreased with increasing constant external force, then plateaued.
• Dynamic mobility under oscillatory force showed complex, nonlinear dependence on amplitude and frequency.
• No linear regime was observed within the studied force range.

Conclusions:

• The dynamic mobility of tracers in active disk suspensions is highly nonlinear.
• Simple linear stochastic models, even with memory kernels, are insufficient to describe tracer motion in these active media.
• These findings necessitate revised theoretical frameworks for active matter dynamics.