Rebocho T C, Tasinkevych M, Dias C S
Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisbon, Portugal.
Centro de Física Teórica e Computacional, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisbon, Portugal.
Phys Rev E. 2022 Aug;106(2-1):024609. doi: 10.1103/PhysRevE.106.024609.
Active colloids belong to a class of nonequilibrium systems where energy uptake, conversion, and dissipation occur at the level of individual colloidal particles, which can lead to particles' self-propelled motion and surprising collective behavior. Examples include coexistence of vapor- and liquid-like steady states for active particles with repulsive interactions only, phenomena known as motility-induced phase transitions. Similarly to motile unicellular organisms, active colloids tend to accumulate at confining surfaces forming dense adsorbed films. In this work, we study the structure and dynamics of aggregates of self-propelled particles near confining solid surfaces, focusing on the effects of the particle anisotropic interactions. We performed Langevin dynamics simulations of two complementary models for active particles: ellipsoidal particles interacting through the Gay-Berne potential and rodlike particles composed of several repulsive Lennard-Jones beads. We observe a nonmonotonic behavior of the structure of clusters formed along the confining surface as a function of the particle aspect ratio, with a film spreading when particles are near-spherical, compact clusters with hedgehog-like particle orientation for more elongated active particles, and a complex dynamical behavior for an intermediate aspect ratio. The stabilization time of cluster formation along the confining surface also displays a nonmonotonic dependence on the aspect ratio, with a local minimum at intermediate values. Additionally, we demonstrate that the hedgehog-like aggregates formed by Gay-Berne ellipsoids exhibit higher structural stability as compared to the ones formed by purely repulsive active rods, which are stable due to the particle activity only.
活性胶体属于一类非平衡系统，在该系统中，能量的吸收、转换和耗散发生在单个胶体粒子层面，这可能导致粒子的自推进运动和令人惊讶的集体行为。例子包括仅具有排斥相互作用的活性粒子的气相和液相稳态共存，即所谓的运动诱导相变现象。与能动的单细胞生物类似，活性胶体倾向于在限制表面聚集形成致密的吸附膜。在这项工作中，我们研究了限制固体表面附近自推进粒子聚集体的结构和动力学，重点关注粒子各向异性相互作用的影响。我们对活性粒子的两个互补模型进行了朗之万动力学模拟：通过盖伊 - 伯恩势相互作用的椭球形粒子和由几个排斥性 Lennard - Jones 珠子组成的棒状粒子。我们观察到沿限制表面形成的团簇结构作为粒子纵横比的函数呈现非单调行为，当粒子接近球形时膜会铺展，对于更细长的活性粒子会形成具有刺猬状粒子取向的紧凑团簇，而对于中间纵横比则表现出复杂的动力学行为。沿限制表面形成团簇的稳定时间也显示出对纵横比的非单调依赖性，在中间值处有一个局部最小值。此外，我们证明，与仅由粒子活性而稳定的纯排斥性活性棒形成的团簇相比，由盖伊 - 伯恩椭球体形成的刺猬状聚集体表现出更高的结构稳定性。
