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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 42: Active Matter IV (joint session BP/CPP/DY)

CPP 42.8: Vortrag

Freitag, 21. März 2025, 11:45–12:00, H44

A route to active turbulence in circular activity spots — •Arghavan Partovifard and Holger Stark — Institute of Theoretical Physics, Institut für Theoretische Physik, Technische Universität Berlin, Hardenbergstr. 36, 10623Berlin, Germany.

Active nematics exhibit distinctive behavior such as active turbulence and regular flow patterns under spatially varying activity [1]. Utilizing the Doi-Edwards theory supplemented by an active stress tensor [1], we investigate active nematics confined to a circular spot by switching off activity outside the spot. The open boundary allows topological defects to enter and leave the spot.

We calculate the total topological defect charge inside the spot using three approaches: counting all defects, measuring the rotation of the director field along the rim of the spot, and integrating the diffusive charge density. All methods agree that for spot radii just larger than the nematic coherence length, the system has a total topological charge of +1, where two +1/2 defects perform a regular swirling motion. As the radius increases, more defects enter and their motion becomes more and more chaotic. Ultimately, the charge per unit area saturates at the value characteristic of bulk active turbulence. For the range of radii where the total charge in the spot is +1, the nematic director exhibits shear-induced anchoring at an angle of 45^∘ with respect to the tangent at the spot rim. With increasing radius, when more defects enter, the anchoring angle deviates from 45^∘ but its distribution still peaks around this value.

[1] A. Partovifard et. al., Soft Matter 20, 1800 (2024)

Keywords: active turbulence; active nematics; topological defects; controlling active turbulence