Evaluating interfacial shear and strain stress during droplet deformation in micro-pores

Abstract

The formulation of high quality emulsions is a key challenge in many industrial applications. The premix emulsification process in porous membranes enables the generation of tailored emulsions with fine and narrow droplet size distributions under low shear and energy input. However, the droplet deformation and breakup process within porous structures is a complex mechanism and single breakup events are hard to relate to the local stress conditions and the pore geometry. This relation however is required for the proper design of membrane structures with specific emulsification behavior (i.e., avoidance of stress peaks). Thus, in this contribution, the stress residence time behavior of single droplets during deformation and breakup in idealized micro-pores is investigated for different Capillary numbers and droplet sizes. The interface stress induced droplet deformation and breakup process is to be analyzed in a generic flow configuration. The results show that interface stresses are applied by the wall interface (wall-droplet interface) and by the liquid-liquid (continuous-droplet interface) interface and that both stress contributions have to be considered separately in order to understand the droplet deformation and breakup process. Only at the liquid-liquid interface, stress induced deformation is possible. The analysis of the stress conditions delivers a correlation between the stress residence time behavior and the interface deformation, which can be directly related to the pore geometry. As a result, main deformation and breakup trends are derived. This enables better opportunities for proper membrane design and handling of shear sensitive media in the premix emulsification process.