Deformation and breakup of high-viscosity droplets with symmetric microfluidic cross flows.

The dynamic response of highly viscous droplets to a sharp increase in the surrounding liquid velocity is experimentally investigated in a square microchannel junction. The local injection of the continuous phase from symmetric side channels onto a train of droplets produces a large velocity contrast between the front and the rear of droplets, yielding a broad range of time-dependent deformation and breakup. In particular, due to microscale confinement, the system displays a nonlinear behavior with the initial droplet size. Deformations, relaxation times, and fragmentation processes are examined as a function of flow parameters and fluids properties with emphasis on the formation of slender viscous structures such as spoon-shaped droplets, i.e., asymmetrical droplets.