Rheological Behaviors Investigation Of Asymmetric Double-emulsion Globules In Extensional Flows

Micro-fluidic techniques based on multiple emulsions have broad potentials in drug delivery,cosmetics and food industries.The hydrophobic and hydrophilic ingredients could be wrapped in oil droplets and water droplets of multiple emulsions,respectively.However,these complex globules are usually stored and delivered in liquid phases,and they always deform under the action of the flow shear.Thus,it is natural and important to study their rheological behaviors carefully.In this paper,asymmetric rheological behaviors of double-emulsion globules with asymmetric internal structures in modest extensional flows are investigated through the spectral boundary element method.The effects of the asymmetry of the internal structures and the capillary number on their movement are specially studied.In order to disclose the mechanical mechanism of their rheological behaviors,the external drag force,interface curvature and internal pressure distribution are calculated and analyzed successfully.All numerical methods are programmed by Fortran language,and compiled and run in Compaq Visual Fortran 6.The study to asymmetric double-emulsion globules with two unequal inner droplets is to investigate the oriented shift of the globules which could be realized by controlling the size ratio and the location ratio of the two inner droplets.However,the variation of the capillary number could inverse the shift direction.Thus,the shift direction is determined not only by the internal asymmetry of the globules,but also by the capillary number.In addition,through many careful numerical calculations,this paper also investigates the pseudo-stable state of the asymmetric double emulsions in extensional flows,and presents the relation between the critical capillary number of the shift inverse and the size ratio and the location ratio.In order to completely analyze the phenomenon of the oriented shift of the asymmetric globules,the physical mechanism of the shift and inverse of eccentric globules in extensional flows has been investigated.The asymmetric layout of the daughter droplet leads to the asymmetric drags from the continuous phase and the asymmetric deformation of the globule with different interface curvatures.This curvature difference results in the asymmetric pressure distribution and circulation inside the globule.Eventually,the interaction of the inner driving force(pressure differences)and the outer drags causes the oriented shift and inverse of the globule.The shift direction is affected not only by the structural asymmetry parameter ?(eccentricity),but also by some flow features such as the capillary number.The most important new result of this paper is: when the eccentricity and capillary number are relatively small,the shift of the globules is determined by the interface curvature differences;when the eccentricity and capillary number are relatively large,the shift of the globules is determined by the external drag.This result may enlighten us to realize the movement of soft particles driven by interface curvatures.