Using Dissipative Particle Dynamics, we simulate an immiscible oil droplet on a polymer brush under a channel flow. Above a critical flow velocity, the droplet slides on the brush surface with contact angle hysteresis. Interestingly, we found the critical sliding velocity to be constant across droplet sizes and interphase interactions. Further increase in flow velocity results in droplet detachment and lift-off from the brush surface. Under poor solvent conditions, large droplets may deform into an airfoil shape, increasing the critical lift-off velocity. On an oleophilic brush, the droplet desorbs and spreads, instead of lift-off. Together, our results show surprisingly rich dynamics coupling three-way interactions between either soft or liquid phases. The present study has implications on the design of polymer brushes as well as the removal of droplets from soft surfaces using hydrodynamics.
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The computational work for this article was (fully/partially) performed on resources of the National Supercomputing Centre, Singapore (https://www.nscc.sg). This research was supported by A*STAR under the Pharos “Advanced Surfaces” Program (Award No. 152 37 00103).