Controlling the Orientation of Droplets in Ellipsoid-Filled Polymeric Emulsions with Particle Parameters and Flow Conditions

The effect of particle parameters [aspect ratio (AR) and concentration] and flow conditions (gap spacing and shear rate) on droplet orientation deformation behavior in polystyrene (PS) particle-filled binary polymeric emulsions is investigated by using a rheo-optical technique and confocal microscopy. Interesting vorticity orientation behavior is achieved by tailoring experimental conditions to yield rigid anisotropic droplets during slow confined shear flow. PS ellipsoids with a high AR are found to reside both at the fluid interface in a monolayer side-on state and inside droplets, leading to the formation of rigid anisotropic droplets because of the interfacial/bulk jamming effect at appropriate particle concentrations. In unconfined bulk samples, droplets with a vorticity orientation can also be observed under the wall migration effect and confinement effect arising from nearby droplets. However, the overly strong wall confinement effect remarkably facilitates the coalescence of vorticity-aligned droplets during slow shear, eventually leading to the formation of a long stringlike phase aligning along the flow direction. High shear rates generate refined droplets with lower particle coverage and weak rigidity, which restrain the formation of anisotropic droplets and thus suppress the droplet vorticity orientation.