In most applications, multiphase flow behavior in microscale is governed by the balance between capillary and viscous, or viscoelastic in case of polymer solutions, forces. Fundamental understanding of capillary hydrodynamics may lead to important technology development in different areas, including the manufacturing of optical and specialty films, printed electronics, biological sensors, CO2 sequestration and enhance oil recovery. We discuss two examples of capillary hydrodynamic flows. The first one is related to the manufacturing of functional films by slot coating process. The coated film must have a particular microstructure in order to function as designed. In many applications, such as solar panels, printed electronics and batteries, the coating liquid is a suspension of particles. The rheology of these systems may be quite complex and depends on the particle concentration and orientation with respect to the flow. Moreover, particles can migrate driven by different mechanisms leading to a non-uniform particle distribution in the flow. The fundamental understanding of this problem and its impact on the coating process are not well understood. We analyze slot coating flows of particle suspensions, investigating particle distribution and orientation and how process parameters may affect the final structure of the coated layer.
The second example is associated with flows of complex liquids in porous media, with application in oil recovery. A porous media can be thought as a 3D network of constricted micro channels, e.g. a very complex microfluidic device. We study the effect of complex dispersions (oil-water emulsions and soft microcapsules suspensions) and polymer solutions in the pore scale. Visualization of the flow of complex fluids through a transparent network of micro-channels, which serves as a model of a porous media, reveals how the pore blocking by the dispersed phase improves pore-level displacement efficiency, leading to lower residual oil saturation. In the case of soft capsule dispersions, the degree of pore level mobility reduction is controlled by the elastic properties of the capsule shell, which are fabricated using capillary microfluidic devices.