Flow around topological defects in active nematic films

Abstract

We study the active flow around isolated defects and the self-propulsion velocity of+1/2defects in an active nematic film with both viscous dissipation (with viscosityη) and frictional dampingΓwith a substrate. The interplay between these two dissipation mechanisms is controlled by the hydrodynamic dissipation lengthℓd=η/Γthat screens the flows. For an isolated defect, in the absence of screening from other defects, the size of the shear vorticity around the defect is controlled by the system sizeR. In the presence of friction that leads to a finite value ofℓd, the vorticity field decays to zero on the lengthscales larger thanℓd. We show that the self-propulsion velocity of+1/2defects grows withRin small systems whereR<ℓd, while in the infinite system limit or whenR≫ℓd, it approaches a constant value determined byℓd.