Rheology And Possible Oriented Transition Of Multiple-emulsion Globules In Micro-channels

Currently, most research on the rheology of soft particals are limited on thesimple emulsion without sub-droplet or core-shell multiple emulsion with a singlesub-droplet. All these simplified modes cannot describe the multiple emulsions withcomplex internal structures. Even though the production technology of multipleemulsion droplets has developed rapidly in recent years, the further experimentalresearch almost has no breakthrough because the multiple emulsion is different tocontrol. Thus, on the basis of the production technology, the numerical research ofmultiple emulsion globules is imperative. In this article, we use the recentlydeveloped spectral boundary element method to investigate the movement of multipleemulsion globules in different micro-pipeline and analyze the dynamicscharacteristics and further research the rheology of multiple emulsion.When a globule with a complete symmetry (such as simple spherical droplets andconcentric double emulsions) is transiting in a constriction tube, there is only onepattern of the transition. However, for a multiple-emulsion globule with asymmetricinternal structures, there are many possible patterns with different pressure drops Pdue to various initial orientations of the inner droplets. In this paper, the Spectralboundary integral method developed recently is employed to investigate numericallythe possible oriented transition of a serious of globules with different internalstructures in an axisymmetric constricted capillary. The transition is driven by anaxisymmetric Poiseuille flow with a fixed volume flow rate, and the rheologicalbehaviors of the globule are observed carefully. When the big inner droplet is initiallylocated in the front of the globule, the maximum pressure drop during the transition isalways lower than that when it is initially placed in the rear. Thus, atropism—whereby a globule more easily gets through the constriction when its biggerinner droplet locates in its front initially—might exist, in which the orientatingstimulus is the required pressure drops. The physical explanation of this phenomenonand the influence factors on the tropism have also been analyzed in this paper.Meanwhile, in view of the dual-core multiple emulsions is one of the most widelyused multiple emulsions, as well as one of the most basic structures, they has anirreplaceable role in the microreactor, micro-mixing and other fields.In this paper, boundary integral method has been developed, to investigate the rheology ofdual-core multiple emulsions under an extensional flow in a cross-slot at lowReynolds number. The drop behavior such as deformation, burst, and breakup as wellas the coalescence of the cores will be summarized. Also, the phenomenon is alsofurther discussed from the viewpoint of fluid dynamics. The research will be animportant theoretical and experimental guidance on the multiple emulsion rheologyand controlled behavior of multiple droplets, such as internal chemical reactions andcontrolled release and breakup of droplets.