Dynamics and Inner Mixing of a Droplet in a Stokes Trap

Recently, a flow-based, particle-trapping mechanism called the Stokes trap was developed to allow for trapping and control of small particles in microchannels in the intersection of multiple branches in a microfluidic channel [1]. The motion of such particles can then be controlled by changing the flow rates in the branches. For droplets, in contrast to rigid particles, the Stokes trap allows for extra features such as enhancement of inner mixing and shape control, which can be used in microreactors and fabrication processes. In this work, we analyze the motion and stability of a deformable droplet in a Stokes trap. To this end, the droplet dynamics are analyzed using boundary-integral simulations, which we use to explore the influence of physical parameters such as capillary number and viscosity ratio on drop dynamics and internal mixing. For low values of viscosity ratio and capillary number, there is a steady-state drop configuration, which can be unstable depending on the choice of parameters. Changes in the inlet and outlet flow rates result in changes in equilibrium configurations, allowing for shape control and manipulation of flow pattern inside the droplet, enhancing internal mixing.

[1] Shenoy, A., Kumar, D., Hilgenfeldt, S., & Schroeder, C. M. (2019). Phys. Rev. Appl.