Marangoni-driven flower-like patterning of an evaporating drop spreading on a liquid substrate | Nature Communications
▻https://www.nature.com/articles/s41467-018-03201-3
▻https://static-content.springer.com/esm/art%3A10.1038%2Fs41467-018-03201-3/MediaObjects/41467_2018_3201_MOESM4_ESM.mp4
Experiment described in the article. A 5.6 µl dichloromethane drop is deposited onto a 25 ml aqueous phase filling a 7cm Petri dish. A cationic surfactant, cetyltrimethylammonium bromide (CTAB), is initially present in both phases with the same concentration (0.5 mmol.L-1 ). The sequence is slowed down 20 times.
Abstract
Drop motility at liquid surfaces is attracting growing interest because of its potential applications in microfluidics and artificial cell design. Here we report the unique highly ordered pattern that sets in when a millimeter-size drop of dichloromethane spreads on an aqueous substrate under the influence of surface tension, both phases containing a surfactant. Evaporation induces a Marangoni flow that forces the development of a marked rim at the periphery of the spreading film. At some point this rim breaks up, giving rise to a ring of droplets, which modifies the aqueous phase properties in such a way that the film recoils. The process repeats itself, yielding regular large-amplitude pulsations. Wrinkles form at the film surface due to an evaporative instability. During the dewetting stage, they emit equally spaced radial strings of droplets which, combined with those previously expelled from the rim, make the top view of the system resemble a flower.
via Pour la Science, n°486, avril 2018
