Study of dynamic heterogeneity of an active particle system

Huai Ding, Huijun Jiang, and Zhonghuai Hou
Phys. Rev. E 95, 052608 – Published 24 May 2017

Abstract

We have studied spatial and temporal dynamic heterogeneity (DH) in a system of hard-sphere particles, subjected to active forces with constant amplitude and random direction determined by rotational diffusion with correlation time τ. We have used a variety of observables to characterize the DH behavior, including the deviation from standard Stokes-Einstein (SE) relation, a non-Gaussian parameter α2Δt for the distribution of particle displacement within a certain time interval Δt, a four-point susceptibility χ4Δt,ΔL for the correlation in dynamics between any two points in space separated by distance ΔL within some time window Δt, and a vector spatial-temporal correlation function SvecR,Δt for vector displacements within time interval Δt of particle pairs originally separated by R. By mapping the particle motion into a continuous-time random walk with constant jump length, we can obtain the average waiting time txDs1 and persistence time tpη, with Ds the self-diffusion coefficient and η the shear viscosity, such that the observable λ=tp/txDsη can be calculated as a function of the control parameter τ to show how it deviates from its SE value λ0. Interestingly, we find λ/λ0 shows a nonmonotonic behavior for large volume fraction φa, wherein λ/λ0 undergoes a minimum at a certain intermediate value of τ, indicating that both small and large particle activity may lead to strong DH. Such a reentrance phenomenon is further demonstrated in terms of the non-Gaussian parameters α2, four-point susceptibility χ4, and vector spatiotemporal correlation functions Svec, respectively. Detail analysis shows that it is the competition between the dual roles of particle activity, namely, activity-induced higher effective temperature and activity-induced clustering, that leads to such nontrivial nonmonotonic behaviors. In addition, we find that DH may also show a maximum level at an intermediate value of φa if τ is large enough, implying that a more crowded system may be less heterogeneous than a less crowded one for a system with high particle activity.

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  • Received 14 February 2017

DOI:https://doi.org/10.1103/PhysRevE.95.052608

©2017 American Physical Society

Physics Subject Headings (PhySH)

Polymers & Soft Matter

Authors & Affiliations

Huai Ding, Huijun Jiang, and Zhonghuai Hou*

  • Department of Chemical Physics and Hefei National Laboratory for Physical Sciences at Microscales, University of Science and Technology of China, Hefei, Anhui 230026, China

  • *Corresponding author: hzhlj@ustc.edu.cn

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Issue

Vol. 95, Iss. 5 — May 2017

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