Experiments with Active Emulsions

author: Stephan Herminghaus, Dynamics of Complex Fluids Department, Max Planck Institute for Dynamics and Self-Organization (MPIDS), Max Planck Institute
published: June 13, 2012,   recorded: June 2012,   views: 4788


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Experiments are presented with emulsions showing various types of 'active' collective behavior. Ensembles of aqueous droplets containing Belouzov-Zhabotinski (BZ) oscillators are shown to exhibit coupling patterns depending on the formation of lipid bilayers between them. We observe target waves, quorum sensing, and spiral waves in two-dimensional rafts of mono-disperse emulsions. As the volume fraction of the dispersed phase (i.e., the droplets) is reduced, we observe self-propelled motion of the droplets, which can be controlled by the BZ reaction if desired. We propose a simple mechanism based on Marangoni stresses which accounts for this motion. Swarming is shown to exhibit pronounced correlation features which depend strongly on the raft density. While the bromine release provides the energy source for this type of self-propulsion, we present an alternative system based on liquid crystals which shows similar collective behaviour, but whose motion has a longer lifetime and is fuelled by the spontaneous formation of a microemulsion. Based on the meso-structure of the liquid crystal, it enables, aside from simple droplet motion, much more complex patterns to evolve, the details of which are yet far from understood.

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