Defect self-propulsion in active nematic films with spatially varying activity. Issue 2 (15th February 2023)

• Record Type: Journal Article
• Authors: Rønning, Jonas; Marchetti, M. Cristina; Angheluta, Luiza
• Is Part Of: Royal Society open science. Volume 10:Issue 2(2023)
• Publication Date: 2023-02-15
• Subjects: active nematics -- topological defects -- nematic liquid crystals -- hydrodynamics; Science -- Periodicals; 500
• DOI: 10.1098/rsos.221229
• Languages: English
• ISSNs: 2054-5703

Abstract

Abstract : We study the dynamics of topological defects in active nematic films with spatially varying activity and consider two set-ups: (i) a constant activity gradient and (ii) a sharp jump in activity. A constant gradient of extensile (contractile) activity endows the comet-like +1/2 defect with a finite vorticity that drives the defect to align its nose in the direction of decreasing (increasing) gradient. A constant gradient does not, however, affect the known self-propulsion of the +1/2 defect and has no effect on the −1/2 that remains a non-motile particle. A sharp jump in activity acts like a wall that traps the defects, affecting the translational and rotational motion of both charges. The +1/2 defect slows down as it approaches the interface and the net vorticity tends to reorient the defect polarization so that it becomes perpendicular to the interface. The −1/2 defect acquires a self-propulsion towards the activity interface, while the vorticity-induced active torque tends to align the defect to a preferred orientation. This effective attraction of the negative defects to the wall is consistent with the observation of an accumulation of negative topological charge at both active/passive interfaces and physical boundaries.