Droplet formation and fission in shear-thinning/Newtonian multiphase system using bilayer bifurcating microchannel

With a novel platform of bilayer polydimethylsiloxane microchannel formed by bifurcating junction, we aim to investigate droplet formation and fission in a multiphase system with complex three-dimensional (3D) structure and understand the variations in mechanism associated with droplet formation and fission in the microstructure between shearthinning/ Newtonian system versus Newtonian/Newtonian system. The investigation concentrates on shear-thinning fluid because it is one of the most ubiquitous rheological properties of non-Newtonian fluids. Sodium carboxymethyl cellulose (CMC) solution and silicone oil have been used as model fluids and numerical model has been established to characterize the shear-thinning effect in formation of CMC-in-oil emulsions, as well as breakup dynamics when droplets flow through 3D bifurcating junction. The droplet volume and generation rate have been compared between two systems at the same Weber number and capillary number. Variation in droplet fission has been found between two systems, demonstrating that the shear-thinning property and confining geometric boundaries significantly affect the deformation and breakup of each mother droplet into two daughter droplets at bifurcating junction. The understanding of the droplet fission in the novel microstructure will enable more versatile control over the emulsion formation and fission when non-Newtonian fluids are involved. The model systems in the study can be further developed to investigate the mechanical property of emulsion templated particles such as drug encapsulated microcapsules when they flow through complex media structures, such as blood capillaries or the porous tissue structure, which feature with bifurcating junction.