Oscillatory active microrheology of active suspensions

Miloš Knežević,Holger Stark,Luisa E Avilés Podgurski

doi:10.1038/s41598-021-02103-7

Miloš Knežević, Holger Stark + Show 1 more

Open Access

https://doi.org/10.1038/s41598-021-02103-7

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Journal: Scientific Reports	Publication Date: Nov 22, 2021
Citations: 10	License type: open-access

Affiliation: Technische Universität Berlin

Abstract

Using the method of Brownian dynamics, we investigate the dynamic properties of a 2d suspension of active disks at high Péclet 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. In the range of forces studied, we do not observe a linear regime. 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, in the general case.

Highlights

Using the method of Brownian dynamics, we investigate the dynamic properties of a 2d suspension of active disks at high Péclet numbers using active microrheology
In the first part of this section we present our results obtained for the tracer driven through a suspension of active disks by a constant external force, while the second part shows our findings for the tracer guided through the suspension by a harmonic force
Taking the average of Eq (8) from the Methods section, which describes the tracer dynamics, and using Eq (1), we find that the effective mobility of the tracer driven by a constant force is μ where the sum goes over all active disks in the bath and FiTx is the x-component of the force exerted on the tracer by the i-th disk

Summary

Introduction

Using the method of Brownian dynamics, we investigate the dynamic properties of a 2d suspension of active disks at high Péclet numbers using active microrheology. Our setup is depicted in Fig. 1: We study a tracer particle of radius R, immersed in a two dimensional suspension of active disks, and driven by an external force Fe(t) .

Results

Conclusion