Transport of Active Matter With Confining Geometries

Active matter describes systems with some form of self motility, which can arise in soft matter, biological, social, and robotic systems. In soft and biological systems, these can be particle like such as self-propelled colloids or filaments forming active nematics. In many cases, active matter systems can also be in some form of confinement. Here, we examine both particle-like active matter and active nematics in confining geometries such as walls, obstacle arrays, channels, and asymmetric potentials. For active disks moving through obstacle arrays, we find activity-induced clogging phases where the activity reduces the flow; however, for a strong biasing drive flow the particles can form 1D stripe-like solids that move easily through the arrays. For active nematics in circular confinement, we find that the topological defects form a spontaneous spiral flow [1], while without confinement, the mobile defects undergo isotropic flow, suggesting that confinement can be used to create controlled motion for topological devices. For active nematics in periodic obstacle arrays, the defects generate ferromagnetic or antiferromagnetic vortex lattices in square arrays and dynamically frustrated states in honeycomb arrays [2]. With an asymmetric array, the active nematics form a partially ordered vortex state, leading to a ratchet effect. For active nematics in channel arrays, we find that there is a coupling between the vortex states between channels as a function of both activity and channel spacing.

[1] Friction mediated phase transition in confined active nematics, C.D. Schimming, C.J.O. Reichhardt and C. Reichhardt, Phys. Rev. E 108, L012602 (2023).

[2] Vortex lattices in active nematics with periodic obstacle arrays, C.D. Schimming, C.J.O. Reichhardt and C. Reichhardt, Phys. Rev. Lett. 132, 018301 (2024).