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Physics of Living Matter Seminar:
Watching paint dry: Structure formation in drying films and droplets

Arash Nikoubashman

Institute of Physics

Johannes Gutenberg University of Mainz

15.04.2021 11:00 Uhr
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Drying complex liquids are encountered in many technologies, including painting, manufacturing polymer LED displays, and spraying pesticides. Here, colloids and/or polymers are typically initially dispersed in a solvent such as water, which then evaporates, leaving behind a dried residue. Our recent simulations and experiments of drying bidisperse suspensions revealed that sufficiently fast evaporation could induce spatial segregation of the two species, with the smaller ones accumulating at the liquid-air interface followed by a homogeneously mixed region of small and big particles.

Theoretical Physics Copyright: Arash Nikoubashman

To understand this counterintuitive behavior, we conducted particle-based simulations and dynamic density functional theory calculations, with and without hydrodynamic interactions. According to our model calculations, this drying-induced segregation occurs due to a local increase of the solute concentration near the film-air interface, resulting in a chemical potential gradient for both species; typically, this gradient is steeper for the larger particles, leading to a stronger force pushing them away from the liquid-air interface.

Segregation then occurs if the mobility of the larger particles decreases slower than the driving force increases. Comparing the various simulations and experiments, we found that including hydrodynamics can decrease or even completely suppress the segregation.


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