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Abstract:
Self-propelled droplets are a special kind of self-propelled
matter that are easily fabricated by standard microfluidic tools and
locomote for a certain time without external sources of energy. The
typical driving mechanism is a Marangoni flow due to gradients in
the interfacial energy on the droplet interface. In this article we review
the hydrodynamic prerequisites for self-sustained locomotion and
present two examples to realize those conditions for emulsion droplets,
i.e. droplets stabilized by a surfactant layer in a surrounding immiscible
liquid. One possibility to achieve self-propelled motion relies on chemical
reactions affecting the surface active properties of the surfactant
molecules. The other relies on micellar solubilization of the droplet
phase into the surrounding liquid phase. Remarkable cruising ranges
can be achieved in both cases and the relative insensitivity to their
own ’exhausts’ allows to additionally study collective phenomena.
