Wed June 19th 2019
16:00 – 17:00
Seminar Clustering of coated micro droplets at channel ex- pansions: experiments and kinematic model
Kerstin Schirrmann


Micro droplets and coated micro droplets serve as well defined tiny reaction chambers or basis for capsules in chemistry and microbiology. However, the initially separated droplets tend to form clusters (or coalesce) whenever geometrical defects occur in the channel. By introducing a defined perturbation in form of a sudden channel expansion, we can study this cluster formation systematically. Our micro droplets (diameters around 300 ┬Ám) consist of glycerol, water and dye, have a liquid coating of fluorinated oil with a surfactant and flow in silicone oil within micro channels made from polydimethylsilicone (pdms). We observe very regular trains of coated micro droplets turning into well defined clusters at the expansion. We get up to 6 droplets enclosed in a combined coating for a channel expansion of factor 2. For smaller expansions (factor 1.7 and 1.5) the experimentally observed maximal number of droplets per cluster is smaller (4 and 3). Using a purely kinematic model we can predict, how many droplets will join a cluster, depending on initial distance, length and coating thickness of the droplets. Thus, an initially undesired effect is turned into a well defined phenomenon.
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The 10th Complex Motion in Fluids 2021
Max Planck Gesellschaft
Centre for Scientific Computing