Influence of flow structures on defect dynamics in 3D active nematics

Active nematics are orientationally ordered materials that convert energy from their surroundings to exert mechanical forces that drive the material out of equilibrium. Through the feedback between orientational order and active flows, macroscopic features emerge, such as coherent flow structures and a steady-state population of topological defects. Recently, experiments and simulations in two-dimensions have uncovered a mesoscopic bridge between topological structures in the coupled orientation and flow field: motile +1/2 defects move along isolines where strain-rate and vorticity balance, termed viscometric surfaces [1]. In this work, we explore the relationship between topological defects and flow structures in three-dimensions, where defect lines continuously vary their winding character and undergo complex morphological behaviours. We present the nature of the flow patterns generated by disclination profiles and demonstrate how the tight coupling between defects and viscometric surfaces is maintained in simulations of three-dimensional bulk active turbulence and confined geometries. Our results highlight the importance of flow structures as paths for defect dynamics which could provide insight into how to control their complex behaviours.

[1] Head, L.C. et al. Spontaneous self-constraint in active nematic flows. Nat. Phys. 20, 492–500 (2024).