Oscillatory active microrheology of active suspensions

TL;DR

This paper investigates the dynamic response of active particle suspensions under oscillatory and constant forces using Brownian dynamics simulations, revealing complex nonlinear behaviors that challenge simple phenomenological models.

Contribution

It introduces a detailed simulation study of active microrheology in active suspensions, highlighting nonlinear mobility responses under different forcing conditions.

Findings

Tracer mobility decreases then plateaus with increasing force

Mobility exhibits complex nonlinear behavior with oscillatory forcing

Linear stochastic models are insufficient to describe tracer dynamics

Abstract

Using the method of Brownian dynamics, we investigate the dynamic properties of a 2d suspension of active disks at high P\'eclet numbers using active microrheology. In our simulations the tracer particle is driven either by a constant or an oscillatory external force. In the first case, we find that the mobility of the tracer initially appreciably decreases with the external force and then becomes approximately constant for larger forces. For an oscillatory driving force we find that the dynamic mobility shows a quite complex behavior -- it displays a highly nonlinear behavior on both the amplitude and frequency of the driving force. This result is important because it reveals that a phenomenological description of tracer motion in active media in terms of a simple linear stochastic equation even with a memory-mobility kernel is not appropriate.