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 . 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 for the distribution of particle displacement within a certain time interval , a four-point susceptibility for the correlation in dynamics between any two points in space separated by distance within some time window , and a vector spatial-temporal correlation function for vector displacements within time interval of particle pairs originally separated by . By mapping the particle motion into a continuous-time random walk with constant jump length, we can obtain the average waiting time and persistence time , with the self-diffusion coefficient and the shear viscosity, such that the observable can be calculated as a function of the control parameter to show how it deviates from its SE value . Interestingly, we find shows a nonmonotonic behavior for large volume fraction , wherein undergoes a minimum at a certain intermediate value of , 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 , four-point susceptibility , and vector spatiotemporal correlation functions , 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 if 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.
- Received 14 February 2017
DOI:https://doi.org/10.1103/PhysRevE.95.052608
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