Rheology Investigation Of Multiple Emulsions In Microfluidic Devices

Droplet-based microfluidics is a multidisciplinary subject involving physics,chemistry, biology, and engineering that deals with droplets constrained inmicrochannels of crosssectional dimensions on the order of10to100μm. It hasdefined a new experimental platform for a diverse range of biological and chemicalprocesses. Various droplet-based microfluidic devices have been designed andmonodisperse multiple emulsion droplets are generated and manipulated inmicrofluidics devices through shearing between immiscible phases in microchannels.Investigating the rheology of the multiple emulsion droplets in microchannels throughdroplet-based microfluidics helps learn the behaviours of the multiple emulsiondroplets, such as the deformation, collision, transition. What’s more, the targetedrelease of the core can be controlled by microfluidic dynamics. Thus, droplet-basedmicrofluidics has potential application in microcapsules of targeted drug deliverysystem and biological cell assays.Multiple emulsions (ME) are nested liquid systems, which have highly orderedinternal structures consisting of multiple layers and probably containing one or moresmaller engulfed droplets.(The particle itself is the first layer; its direct daughterdroplets belong to the second layer; and the droplets of the i th layer have directmother droplets belonging to the (i-1) th layer.) In this paper, a two-dimensionalboundary integral method is developed to investigate the rheology of the ME globules.The two-dimensional spectral boundary element method exploits all the benefits ofthe spectral methods in exponential convergence and numerical stability and boundaryelement methods in flexibility in describing geometry.In this paper, our numerical simulation methods were translated into Fortranprogram. The program was debugged and executed in the Compaq Visual Fortran6.Employing the compiled program, we can obtain the computational results of therheology of ME droplets in the cross-slot, the deformation and transition of ME in thecontraction.The rheology of several types of ME (i.e., concentric ME with multiple layers,double emulsions containing multiple inner droplets and ME with asymmetric internal structures), under low Reynolds number flow in a cross-slot is studied numerically.The displacement, deformation and collision of inner droplets will generate resistanceof different strengths to inner circulations in the shell of double emulsions, which willcause the difference of the outer shear subjected by the globules with various internalstructures and vary their viscosities. In addition, the coalescence or release of innerdroplets changes the internal structure of the multiple emulsion particles.Compared with the shell deformation and core collision of ME in the stagnantpoint of the cross-slot, droplets in a contraction can be used to deal with thedeformation and collision while the ME is moving. The rheology of ME droplets inthe contraction is critical to the transport and release of their inclusion, which haspromising applications in targeted drug delivery and controlled release ofco-encapsulating incompatible actives in microcapsules.