Interfacial instability of confined 3D active droplets

Abstract

Instabilities of fluid-fluid interfaces are ubiquitous in passive soft matter. Adding activity to the interface or either fluid can dramatically change the stability of the interface. Using experiment and theory, we investigate the interfacial instability of a deformable 3D active nematic liquid crystal droplet in the isotropic phase surrounded by a passive fluid and confined between two parallel plates. Spontaneous active flows drive the growth of undulations along the active/passive interface, with the mode number of the fastest-growing mode increasing with droplet radius and decreasing with gap height. We apply the lubrication approximation to a minimal nematohydrodynamic model to determine the growth rates of all interfacial modes. The magnitude of the growth rate is determined by the active timescale and the relaxation timescales associated with liquid crystalline order, as well as capillary and viscous stresses. We find multiple points of agreement between experiment and theory, including the shape evolution of individual droplets, the growth rates of unstable modes averaged across many droplets, and the extensional shear flows observed within droplets.

References in corpus (26)

• Spontaneous motion in hierarchically assembled active matter
• Topology and Dynamics of Active Nematic Vesicles
• Fluid dynamics of bacterial turbulence
• Rheology of Active-Particle Suspensions
• Confinement Stabilizes a Bacterial Suspension into a Spiral Vortex
• Transition from turbulent to coherent flows in confined three-dimensional active fluids
• Active wetting of epithelial tissues
• Mechanics of active surfaces
• Biphasic, Lyotropic, Active Nematics
• Dynamics of active liquid interfaces
• Active Fingering Instability in Tissue Spreading
• Confinement controlled bend instability of three-dimensional active fluids
• Destabilization of a flow focused suspension of magnetotactic bacteria
• Mechanical Instabilities of Biological Tubes
• Extensile to contractile transition in active microtubule-actin composites generates layered asters with programmable lifetimes
• Confinement-induced Self-Pumping in 3D Active Fluids
• Morphology of active deformable 3D droplets
• Data-driven discovery of active nematic hydrodynamics
• Fingering Instability of Active Nematic Droplets
• Shear-induced gelation of self-yielding active networks
• Self-mixing in microtubule-kinesin active fluid from nonuniform to uniform distribution of activity
• Asymmetric fluctuations and self-folding of active interfaces
• Linear stability of an active fluid interface
• Traveling waves at the surface of active liquid crystals
• Stability of the interface of an isotropic active fluid
• Pure hydrodynamic instabilities in active jets of "puller" microalgae