Shifting Behavior Investigation Of Unsymmetric Multiple Emulsions In Microfluidic Devices

The size-controllable, multi-layered and multi-chambered multiple emulsions,can be prepared by the micro-fluid technology, and the hydrophobic and hydrophilic drugs are respectively wrapped in oil droplets and water droplets of multiple emulsions to control the drug release through different methods, which has drawn much attention recently. However,the rheological behavior of these complex particles is mostly unknown, especially,in the case of multiple emulsions with the internal unsymmetric droplets. In this paper, a triple emulsions containing one or two unequal unsymmetric grand-daughter droplets (GDD) is chosen to numerically study the complex hydrodynamic problems.In this paper, the spectral boundary element methods are employed to investigate the oriented shift of the daughter droplet of the unsymmetric multiple emulsions in an axisymmetric cross-like microfluidic device. In order to disclose the mechanism which causes the shift and determines the shift direction, the boundary integral equation to solve the pressure distribution in the multiple emulsions is derived, and the boundary integral equation is translated to algorithm which is programmed and debugged successfully on Compaq Visual Fortran 6.The boundary integral methods are employed to numerically simulate the rheology of multiple emulsions in the symmetric extensional flow. It is discovered that the unsymmetry of grand-daughter droplets would result in aymmetric circulations and pressure fields inside and outside the daughter droplet, which makes it shift in some specific direction, and finally would cause the oriented touching with the mother droplet and breakup of the multiple-emulsion globule. This phenomenon could be applied for the controlled release of the globule insertion by a hydrodynamic approach. The shift direction might be upward or downward, which is not only controlled by the unsymmetry of GDDs but also by other parameters such as physical parameters and parameters describing flow features. Futhermore, the interface dynamics of unsymmetric mutiple emulsion is in-depth studied by comparing with concentric emulsion. It is discovered that the unsymmetric distribution of innermost unsymmetric droplets (GDD) causes unsymmetric deformation of the upper and lower partial interface of the droplet DD, and then results in the different pressure distribution of the inside of droplet DD. Thus, the droplet DD is driven to shift by pressure difference. Finally, the reason that capillary number and unsymmetric parameter cause the droplet (DD) move in opposite directions is essentially revealed through the evolution of the curvature and the pressure with time combining with streamline of different time. Meanwhile, the false symmetric phenomenon is also disclosed that the droplet (DD) in the unsymmetric multiple emulsions is almost immobile under the condition of the critical parameters.The unsymmetry of the mutiple emulsion is determined by two factors: the volume of the droplets (GDDs) and eccentricity. The effect of the only volume and the only position of the unsymmetric emulsion on the droplet DD shift are studied by variable-controlling appraoch. Finally, the complete unsymmetric multiple emulsions(both volume and location of droplets GDDs are different) is investigated, and the influence of factors such as the capillary number, unsymmetric parameter and viscosity ratio on the shifting of the droplet DD are analyzed. Meanwhile, The conclusion in this paper is verified that internal unsymmetric structure affects the deformation of the droplet DD, and further affects the pressure distribution of upper and lower part of the droplet DD, and finally the pressure difference of the upper and lower part of the droplet DD drives it shift.