Segmented flows of viscous threads and droplets in microchannels*

Segmented flows of droplets and highly viscous oils are focused with low-viscosity oils to examine dynamic interactions between lubricating and recirculating flows and enhance mixing between fluids having large viscosity contrasts in microfluidic channels. A variety of complex flow regimes are analyzed based on initial droplet sizes and concentrations as well as ratio between low- and high-viscosity fluids. Focus is on the formation and stability of viscous threads (i.e., viscous core-annular flows) between droplets in square microchannels.