(343e) Breakup Behavior of Droplets with Interfacial Viscosity | AIChE

(343e) Breakup Behavior of Droplets with Interfacial Viscosity


Narsimhan, V. - Presenter, Purdue University
Lin, C., Purdue University
In this talk, we discuss the dynamics of droplets with a thin layer of viscous, insoluble surfactant whose mechanics are described by interfacial viscosity, i.e., a Boussinesq-Scriven constitutive law. We develop perturbation theories to quantify droplet shape under flow in the limit of weak deformation, to a sufficient level of approximation where one can extract information about non-linear rheology and droplet breakup. This talk will focus on the breakup behavior of droplets in linear flows. We characterize how shear and dilational surface viscosities alter the droplet shape and the critical capillary number (i.e., the flow rate above which the droplet stretches indefinitely). In the second half of the talk, we will perform boundary element simulations to compare these results to the perturbation theories, which are only valid up to second order in the capillary number. Our calculations indicate interfacial viscosity significantly alters the time scale and onset of breakup, and these results depend non-trivially on droplet deformation, as well as the flow type. We conclude our talk by developing simulations to characterize the droplet dynamics when interfacial viscosities depend non-uniformly with flow, which is common when surfactants and/or lipids are mobile on the droplet surface. We will conclude by discussing how to extend such simulations to viscoelastic membranes (which are commonly found in pickering emulsions and/or polymer films), as well as surface tension gradients.