2020/06/05 by Fabian R. Koessel, Sara Jabbari‐Farouji, Sara Jabbari-Farouji
Engineering · Physics and Astronomy · #Advanced Thermodynamics and Statistical Mechanics #Characterization and Applications of Magnetic Nanoparticles #Classical mechanics #Condensed matter physics #Field (mathematics) #Instability #Magnetic field #Magnetic moment #Magnetosphere particle motion #Mechanics #Mesoscopic physics #Micro and Nano Robotics #Physics #Polar #Quantum mechanics #Smoluchowski coagulation equation #cond-mat.soft #cond-mat.stat-mech #nlin.PS
paper · pdf · doi:10.1088/1367-2630/abb64d
22 pages, 22 figures
arxiv created 2020/06/05 · openalex publication_date 2020/09/08 · openalex created_date 2020/09/14 · arxiv updated 2020/10/28 · openalex updated_date 2026/08/06
Abstract We study collective self-organization of weakly magnetic active suspensions in a uniform external field by analyzing a mesoscopic continuum model that we have recently developed. Our model is based on a Smoluchowski equation for a particle probability density function in an alignment field coupled to a mean-field description of the flow arising from the activity and the alignment torque. Performing linear stability analysis of the Smoluchowski equation and the resulting orientational moment equations combined with non-linear 3D simulations, we provide a comprehensive picture of instability patterns as a function of strengths of activity and magnetic field. For sufficiently high activity and moderate magnetic field strengths, the competition between the activity-induced flow and external magnetic torque renders a homogeneous polar steady state unstable. As a result, four distinct dynamical patterns of collective motion emerge. The instability patterns for pushers include traveling sheets governed by bend-twist instabilities and dynamical aggregates. For pullers, finite-sized and system spanning pillar-like concentrated regions predominated by splay deformations emerge which migrate in the field direction. Notably, at very strong magnetic fields, we observe a reentrant hydrodynamic stability of the polar steady state.