Stability of the interface of an isotropic active fluid

Abstract

We study the linear stability of an isotropic active fluid in three different geometries: a film of active fluid on a rigid substrate, a cylindrical thread of fluid, and a spherical fluid droplet. The active fluid is modeled by the hydrodynamic theory of an active nematic liquid crystal in the isotropic phase. In each geometry, we calculate the growth rate of sinusoidal modes of deformation of the interface. There are two distinct branches of growth rates; at long wavelength, one corresponds to the deformation of the interface, and one corresponds to the evolution of the liquid crystalline degrees of freedom. The passive cases of the film and the spherical droplet are always stable. For these geometries, a sufficiently large activity leads to instability. Activity also leads to propagating damped or growing modes. The passive cylindrical thread is unstable for perturbations with wavelength longer than the circumference. A sufficiently large activity can make any wavelength unstable, and again leads to propagating damped or growing modes.

12 pages, 12 figures

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Cited by in corpus (6)

• Dynamics of active liquid interfaces
• Activity-suppressed phase separation
• Asymmetric fluctuations and self-folding of active interfaces
• Traveling waves at the surface of active liquid crystals
• Active nematic response to a deformable body or boundary: elastic deformations and anchoring-induced flow
• Interfacial instability of confined 3D active droplets