Dancing disclinations in confined active nematics

Abstract

The spontaneous emergence of collective flows is a generic property of active fluids and often leads to chaotic flow patterns characterised by swirls, jets, and topological disclinations in their orientation field. However, the ability to achieve structured flows and ordered disclinations is of particular importance in the design and control of active systems. By confining an active nematic fluid within a channel, we find a regular motion of disclinations, in conjunction with a well defined and dynamic vortex lattice. As pairs of moving disclinations travel through the channel, they continually exchange partners producing a dynamic ordered state, reminiscent of Ceilidh dancing. We anticipate that this biomimetic ability to self-assemble organised topological disclinations and dynamically structured flow fields in engineered geometries will pave the road towards establishing new active topological microfluidic devices.

Reconfigurable flows and defect landscape of confined active nematics

“…Dynamically tion. A similar state had been predicted by simulations and was referred to as the dancing state [30]. However, contrary to the published simulations, the dancing state observed in our experiments is quite fragile, and vortex lattices are always transient and localised in space.…”

“…They preferentially align perpendicular to the walls and, due to their active self-propulsion [24,28,43], they move away from the walls into the bulk. On the contrary, because of their three-fold symmetric configuration, −1/2 defects have no self-propulsion and remain in the vicinity of the walls [30]. Eventually, the +1/2 defects reach the opposite wall and annihilate with negative defects residing close to it.…”

Active matter invasion

“…In addition to the bulk dynamics, the interaction with walls or obstacles of different shape can add further complexity. Theoretically, using the active nematohydrodynamics framework, a transition to spontaneous flows in channels has been predicted [49,50], as well as more complex states with intricate interplay of defects and vortices, and a transition to active turbulence [51,52,53].…”

“…The activity-induced length-scale Λ ζ = K Q /ζ emerges from the competition between the activity driving the dynamics and the elastic resistance against deformations in the director field [28,61,62], while the capillary width d imposes an upper limit for hydrodynamic interactions across the capillary. The activity number A relates these two length-scales [51,52].…”

“…3C; right panel). Corresponding to the characteristic selfmotility of +1/2-topological defects [63,51,35], the interface on this side continues to move backwards relative to the mean interface-position stretching out the interface until the defect detaches from the interface and moves into the active phase.…”