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The uncertain fate of a colloid inside a vanishing droplet

By: Alvaro Marin
From: Physics of Fluids, University of Twente, Enschede, The Netherlands
At: Online - Zoom (https://videoconf-colibri.zoom.us/j/86529940183)
[2021-03-25] 10:00

The spontaneous evaporation of a droplet typically leads to certain internal motion. The intensity and structure of such flow is very sensitive to the environmental conditions and the content of the vanishing droplet, but in most cases, this spontaneously generated evanescent flow can have dramatic consequences for its (non-volatile) content. Such flows can drag along suspended particles, and in some situations, they can dictate their final position. Sometimes such flows can even determine in which fashion these particles will aggregate. But in general, the fate of a colloidal particle in an evaporating droplet is rather uncertain: the interaction with the soft and hard boundaries, that the droplet and solid substrate respectively impose, will be most decisive in its final position.  In this talk, I will give a very personal overview mainly based on careful experiments, and on some computational fluid dynamics simulations, of the very different scenarios one can find depending on the conditions in which the droplet finds itself in its last instants (content of the droplet, type of substrates and external conditions), but also depending on the type of colloidal particles contained inside the droplet.  Apart from the enormous interest that these phenomena have for their potential and actual applications (printing, coating, analytical chemistry, nanotechnology, etc), I will show you that they are more present in our daily lives than we typically think.