Kelidou Maria, Fazelzadeh Mohammad, Parage Baptiste, van Dijk Marinde, Hooijschuur Twan, Jabbari-Farouji Sara
Institute of Theoretical Physics, University of Amsterdam, Amsterdam, The Netherlands.
J Chem Phys. 2024 Sep 14;161(10). doi: 10.1063/5.0215545.
Self-propelled particles possessing permanent magnetic dipole moments occur naturally in magnetotactic bacteria and can be built into man-made systems such as active colloids or micro-robots. Yet, the interplay between self-propulsion and anisotropic dipole-dipole interactions on dynamic self-assembly in three dimensions (3D) remains poorly understood. We conduct Brownian dynamics simulations of active dipolar particles in 3D, focusing on the low-density regime, where dipolar hard spheres tend to form chain-like aggregates and percolated networks with increasing dipolar coupling strength. We find that strong active forces override dipolar attractions, effectively inhibiting chain-like aggregation and network formation. Conversely, activating particles with low to moderate forces results in a fluid composed of active chains and rings. At strong dipolar coupling strengths, this active fluid transitions into an active gel, consisting of a percolated network of active chains. Although the overall structure of the active gel remains interconnected, the network experiences more frequent configurational rearrangements due to the reduced bond lifetime of active dipolar particles. Consequently, particles exhibit enhanced translational and rotational diffusion within the active fluid of strings and active gels compared to their passive counterparts. We quantify the influence of activity on aggregate topology as they transition from branched structures to unconnected chains and rings. Our findings are summarized in a state diagram, delineating the impact of dipolar coupling strength and active force magnitude on the system.
具有永久磁偶极矩的自驱动粒子天然存在于趋磁细菌中，也可以构建到人造系统中，如活性胶体或微型机器人。然而，在三维（3D）中，自推进与各向异性偶极 - 偶极相互作用对动态自组装的相互作用仍知之甚少。我们对3D中的活性偶极粒子进行布朗动力学模拟，重点关注低密度状态，在该状态下，偶极硬球随着偶极耦合强度的增加倾向于形成链状聚集体和渗流网络。我们发现，强大的活性力会克服偶极吸引力，有效抑制链状聚集和网络形成。相反，以低到中等强度的力激活粒子会产生一种由活性链和环组成的流体。在强偶极耦合强度下，这种活性流体转变为活性凝胶，由活性链的渗流网络组成。尽管活性凝胶的整体结构保持相互连接，但由于活性偶极粒子的键寿命缩短，网络经历更频繁的构型重排。因此，与被动粒子相比，粒子在弦状活性流体和活性凝胶中表现出增强的平动和转动扩散。当聚集体从分支结构转变为不相连的链和环时，我们量化了活性对聚集体拓扑结构的影响。我们的研究结果总结在一个状态图中，描绘了偶极耦合强度和活性力大小对系统的影响。
