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Dancing Droplets (Marangoni Self-Contracted Self-Lubricated Volatile Droplets)
When deposited on a clean glass slide, droplets of a mixture of propylene glycol and water of various concentrations enter a chaotic ballet for minutes, hence the name “dancing droplets”. Looking at one isolated droplet is already a surprise, as the mixture that should spread is instead stabilized by a gradient of surface tension due to evaporation that induces a Marangoni flow. It gives those droplets remarkable properties, such as an absence of pinning force, and even more surprisingly a long-range attraction between droplets. I will discuss the stabilization mechanism, the drag force such droplets feel and the long-range attraction mechanism. I’ll then present various microfluidic devices taking advantage of these properties. I’ll eventually show that these properties can be obtained with a large number of two-components mixtures, and tricks to increase the range of attraction.