Dai Chengyu, Bruss Isaac R, Glotzer Sharon C
Department of Physics, University of Michigan, Ann Arbor, Michigan 48109, USA.
Soft Matter. 2020 Mar 21;16(11):2847-2853. doi: 10.1039/c9sm01683j. Epub 2020 Feb 27.
Active matter systems are of great interest for their novel out-of-equilibrium collective behavior. Active Brownian particles (ABPs) are known to exhibit clustering and motility-induced phase separation, and there have been many studies revealing this rich behavior in the overdamped limit of Brownian motion, where inertial effects are insignificant. Here we simulate an Active Inertial Particle (AIP) model where we focus on the underdamped, rather than overdamped limit, to study the interplay between particle inertia and collective behavior, such as phase separation. We show that inertia reduces particle motility due to collisions and a longer time delay for particles to regain speed, thereby suppressing phase separation relative to that observed in the overdamped limit. Additionally, we observe interesting oscillatory behavior between a phase separated steady-state and a homogeneous fluid state that results from inertia-induced collective motion within active clusters due to momentum transfer. Such oscillatory behavior has been reported for ABP systems with particle shape anisotropy, where collective motion is mediated by particle shape anisotropy. Furthermore, we confirm that there is no single characteristic frequency for the oscillatory behavior. The power spectral density is a power law in the high frequency domain, with an exponent close to -2.5.
活性物质系统因其新颖的非平衡集体行为而备受关注。已知活性布朗粒子（ABP）会表现出聚集和运动诱导的相分离，并且有许多研究揭示了在布朗运动的过阻尼极限下这种丰富的行为，在该极限下惯性效应不显著。在此，我们模拟了一个活性惯性粒子（AIP）模型，其中我们关注欠阻尼而非过阻尼极限，以研究粒子惯性与集体行为（如相分离）之间的相互作用。我们表明，由于碰撞以及粒子恢复速度所需的更长时间延迟，惯性会降低粒子的运动性，从而相对于在过阻尼极限中观察到的情况抑制相分离。此外，我们观察到在相分离稳态和均匀流体状态之间存在有趣的振荡行为，这是由于动量传递在活性簇内由惯性诱导的集体运动导致的。对于具有粒子形状各向异性的ABP系统，已经报道了这种振荡行为，其中集体运动由粒子形状各向异性介导。此外，我们证实振荡行为不存在单一的特征频率。功率谱密度在高频域是幂律，指数接近 -2.5。
