Abstract
Active fluid droplets surrounded by oil can spontaneously develop circulatory flows. However, the dynamics of the surrounding oil and their influence on the active fluid remain poorly understood. To investigate interactions between the active fluid and the passive oil across their interface, kinesin-driven microtubule-based active fluid droplets were immersed in oil and compressed into a cylinder-like shape. The droplet geometry supported intradroplet circulatory flows, but the circulation was suppressed when the thickness of the oil layer surrounding the droplet decreased. Experiments with tracers and network structure analyses and continuum models based on the dynamics of self-elongating rods demonstrated that the flow transition resulted from flow coupling across the interface between active fluid and oil, with a millimeter–scale coupling length. In addition, two novel millifluidic devices were developed that could trigger and suppress intradroplet circulatory flows in real time: one by changing the thickness of the surrounding oil layer and the other by locally deforming the droplet. This work highlights the role of interfacial dynamics in the active fluid droplet system and shows that circulatory flows within droplets can be affected by millimeter–scale flow coupling across the interface between the active fluid and the oil.
Highlights
Active fluid droplets surrounded by oil can spontaneously develop circulatory flows
To gain deeper insight into our experimental results, we developed a continuum complex fluid simulation based on established active fluid models[26] and explored methods of directing active fluid flows with novel millifluidic devices that can manipulate interfacial dynamics and droplet shapes in real time
For a droplet immersed in a thicker oil layer (Δ = 2.4 mm), the directors were mostly aligned with the fluid flow and the nematic order parameter decreased with distance from the interface (Fig. 4e, f)
Summary
Active fluid droplets surrounded by oil can spontaneously develop circulatory flows. the dynamics of the surrounding oil and their influence on the active fluid remain poorly understood. Two novel millifluidic devices were developed that could trigger and suppress intradroplet circulatory flows in real time: one by changing the thickness of the surrounding oil layer and the other by locally deforming the droplet. We confined an active fluid in a water-in-oil droplet that was compressed into a cylinder-like s hape[32] and characterized the flow coupling between active fluid and oil (passive fluid) near water–oil interface. To gain deeper insight into our experimental results, we developed a continuum complex fluid simulation based on established active fluid models[26] and explored methods of directing active fluid flows with novel millifluidic devices that can manipulate interfacial dynamics and droplet shapes in real time
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