Controlling the transport of active matter in disordered lattices of asymmetrical obstacles

Abstract

We investigate the transport of active matter in the presence of a disordered square lattice of asymmetric obstacles, which is built by removing a fraction of them from the initial full lattice. We consider no external field. We observe a spontaneous inversion of the net particle current, compared to the usual sense of such a current reported in the literature, if the obstacle (half-circle) has the same diameter of the unit cell of the square lattice. If this diameter is smaller, there is no inversion. We show a calculation that reproduces our numerical results, based on the argument that such effects are a consequence of the imbalance of particles traveling in the positive and the negative directions due to traps formed by the obstacles: for positive travelers the traps are the spaces between neighboring obstacles, while for negative travelers, they are the flat side of the obstacles. PACS numbers: 87.80.Fe, 47.63.Gd, 87.15.hj, 05.40.-a f -0.02 0 0.02 0.04 0.06 0.08 J J x -φ = 0.732 J x -φ = 0.244 J y -φ = 0.732 J y -φ = 0.244 FIG. 4: The x and y components of the mean particle current, Jx and Jy, as a function of f for distinct values of the area fraction φ. We consider wedges as obstacles. The aperture angle of the wedges is 90 • .

Fast and slow self-propelled particles interacting with asymmetric obstacles: Wetting, segregation, rectification, and vorticity

“…The stationary average speed of the particles was found to be nonzero: instead, an effective rectification current emerges since particles traveling from the curved to the flat side of the obstacle spend less time trapped than those in the opposite direction. A similar behavior was observed for an irregular array of randomly-located obstacles oriented in the same fixed direction [19]. The sizes of the obstacles and accumulation layers directly affect the intensity of such rectification currents.…”

Residence time in presence of moving defects and obstacles

“…For instance, a careful design of the shape and the location of the obstacles in microfluidic channels was observed to enhance the mixing of fluid flows [6]. Moreover, crowding effects, generated by obstacles of different size and shape, turn out to significantly affect the transport properties by even altering the sign of the fluxes, as recently reported, e.g., in active matter numerical experiments [7,8].…”

Transport of closed ring containing chiral active particles under transversal temperature difference

“…性粒子主要集中在三个方面：群集和相分离 [8−17] ，不同手征性的混合粒子分离 [18−21] ，手征活性粒子的整 流 [22−27] 。研究手征活性物质的意义，一方面能从统计物理学的角度来揭示生命体系的运动和迁移，丰富 非平衡统计物理的相关规律；另一方面在智能材料与微纳米机器的设计，解决水资源及土壤污染等环境问 题，靶向药物输运和癌症检测等精准医疗领域有突出的应用前景。 手征活性粒子与障碍物之间的相互作用已经在理论、模拟及实验方面研究了很多。2007年Galajda研 究组 [28] 率先从实验上验证了大肠杆菌在放置了一组漏斗阵列的腔室中会发生整流现象。Potiguar等人提出 了在没有外场作用的情况下，不对称凸障碍物能诱导粒子的定向输运 [29] 。 McDermott等人研究了准一维 不对称衬底中活性粒子的集体棘轮效应和流的反转 [30] 。Ghosh课题组对Janus粒子的棘轮输运进行了研究， 发现其整流比普通热势棘轮强得多 [31] 。 此外，他们还研究了旋转微泳物的定向输运，发现在上下和左右 都不对称的通道能产生净离子流 [24] 。 Sandor 等人研究了在行波基片作用下，run-and-tumble主动圆盘的 输运情况，发现在这种输运过程中，圆盘与基片有一个明显的过渡，即磁盘只与基片部分耦合，形成相 分离的团簇状态 [32] 。 Reichhardt 课题组研究了随机或周期性障碍阵列以及漏斗阵列中的活性粒子输运行 为 [33−35] 。 Schakenraad研究组证明了地形梯度引入了对粒子持续性的空间调节，导致粒子向更高持久性 区域的定向运动 [36] 。 Kaiser等人 [37] 证明了在V形障碍物中运动的细菌会发生集体捕获现象，并于2019年 从实验上实现了这种捕获 [38] 。 2020 年，Ribeiro及其合作者 [39] 研究了不同噪声大小的活性物质在吸引的 周期背景势中的扩散机制和捕获行为。近期，Borba等人 [40] 发现活性物质在由不对称障碍物组成的无序晶 格中会发生定向输运。由于障碍物周围容易捕获粒子，造成活性粒子发生流反转。叶方富团队联合陈科团 队和郑宁课题组研究了手征活性流体的拓扑边界输运，证明了在奇粘度增强的耗尽力作用下，粒子能稳定 地位于系统边界，不受障碍物的影响沿边界单向运动 [41] 。 陈康教授研究了活性布朗粒子在二维结构中与 刷毛表面的相互作用，结果发现在大自驱动力下，链束振荡伴随着动态团簇的形成和解体 [42] 。 艾保全教 授课题组研究了由行进障碍阵列驱动的极性粒子的输运和对齐相互作用粒子的俘获行为 [43−44] 。 目前，大多数的活性系统研究中，活性粒子和障碍物之间并未相互约束，而在实际系统中，共同约束 在活性粒子的棘轮输运中起重要作用。 如施夏清课题组 [45] 研究了自驱动杆状粒子在半柔性弹性环中的集 体行为。 结果显示，不对称的粒子分布对弹性环整体迁移有重要贡献。 田文得课题组 [46] 研究了封闭圆环 内的活性粒子定向运动导致的柔软圆环的反常形变。此外，以往对手征活性粒子的研究主要集中在恒温方 面，平动和转动扩散系数被假定为不耦合。然而，温差环境更接近于真实系统。众所周知，平动和转动扩 散耦合且与温度有关。 温差对粒子输运行为有重要影响。 如艾保全教授课题组 [47] particles. The particles on average move to the right for t 1 > t 2 and the left for t 1 < t 2 .…”