  Interfaces mediate fluid-fluid interactions among different immiscible
liquids. Here, we demonstrated that active fluids can induce oil flows across
water-oil interfaces and that the oil flows can, in return, alter the
self-organization of the active fluid. We created interface by immersing an
active fluid in a compressed water-in-oil droplet. The droplet geometry
supported the formation of intra-droplet circulatory flows, but the flows
turned chaotic when the thickness of the oil layer surrounding the droplet was
decreased. We showed that the flow transition was due to active fluid-oil flow
coupling across the interface, with a millimeter-scale coupling length. These
results were reproduced with a continuum active fluid simulation. Finally, we
developed two milli-fluidic devices that could trigger or suppress
intra-droplet circulatory flows in real time. One device achieved such control
by locally deforming the droplet; the other by decreasing the surrounding oil
layer thickness without contacting the droplet.
