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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.
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Microfluidic elongation of viscous droplets at vanishing interfacial tension
The microflow behavior of liquid-liquid dispersions is experimentally investigated in the presence of miscible fluid additives. Original microfluidic methods are developed to characterize the dynamic response of mobile droplets to a local change of interfacial tension with the external phase using sequential injections and stratified flows. Various oil-alcohol combinations are examined to unravel out-of-equilibrium fluid interactions at short timescales and clarify the role of flow rates and fluid properties on individual droplet deformations. Functional relationships are developed to characterize the initial droplet strain as well as rates of elongation during immersion and submersion stages in hydrodynamic focusing junctions. It is shown, in particular, that the droplet deformation process is highly nonlinear with the initial droplet size and that droplet growth coefficients remain constant for fluid additives having ultralow interfacial tension. Overall, this study shows the possibility to manipulate the morphology of strongly elongated droplets to enhance oil interfacial area in miscible organic solvents using microchannels.
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- Award ID(s):
- 2223988
- PAR ID:
- 10537262
- Publisher / Repository:
- American Physical Society
- Date Published:
- Journal Name:
- Physical Review Fluids
- Volume:
- 8
- Issue:
- 10
- ISSN:
- 2469-990X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1103/PhysRevFluids.8.104201
