Geometry of Fluid Interfaces
AG Prof. Dr. Ralf Seemann

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Self-propelled droplet driven by Marangoni Flow and its application

We developed a new class of self-propelled droplet, which is made of water/ethanol dispersed in squalane/monoolein. During the propulsion, spontaneous phase separation of the droplet phase occurs due to the release of ethanol and the uptake of monoolein. This phase separation can lead to the formation of a Janus droplet consisting of a water-rich phase and an ethanol-rich phase. The droplet moves as a pusher, which is determined by µPIV, before the phase separation and as a neutral squirmer after phase separation.

Depending on salt concentration in the droplet, added DNA or RNA can be controlled to accumulate either in the water-rich or in the ethanol-rich phase as a ’cargo’. This ’cargo’ can be selectively delivered to a target controlled by hydrodynamic interaction and wettability.

The same water/ethanol droplet in an ethanol-saturated squalane shows chemotaxic attraction. The droplet takes up ethanol from squalane and droplets are attracted to each other. Large numbers of droplets can form patterns with different shapes, which is controlled by number density and vertical confinement.

Fig.1:Self-propelling droplets are formed from a water/ethanol mixture in monoolein containing squalene. a), b) Show images and sketches of the droplet evolution for different ethanol concentration. C) Displays the velocity evolution of a droplet during the three stages. D) Ternary phase diagram clarifying the different demixing behavior for different initial ethanol concentrations in the water/ethanol droplet.

Group members on this project: Dr. Menglin Li, Mahmoud Hosseinzadeh, Dr. Martin Brinkmann, Dr. Jean-Baptiste Fleury, Prof. Dr. Ralf Seemann

External collaborations: Ignacio Pagonabarraga,

Funding: DFG-SPP1726