Stability and tip streaming of a surfactant-loaded drop in an extensional flow. Influence of surface viscosity

We study numerically the nonlinear stationary states of a droplet covered with an insoluble surfactant in uniaxial extensional flow. calculate both eigenfunctions to reveal instability mechanism and time-dependent resulting from it, which provides coherent picture phenomenon. The transition is saddle-node type, without surfactant. flow becomes unstable under linear perturbations. Surfactant considerably reduces interval stable capillary numbers. Inertia increases deformation decreases critical number. In presence monolayer, neither nor stability significantly affected by viscosity. transient state fundamentally different for drops Tip streaming occurs only surfactants. eigenmode leading tip qualitatively same as that yielding central pinching mode clean interface, indicates small local scale characterizing set during deformation. viscous surface stress does not affect However, damping rate dominant Interestingly, shear alters arising supercritical regime, even very viscosities. stresses alter balance normal interfacial transport over stretched interface.