An evaporating liquid drop containing solutes or particulates leaves a deposit whose form is determined by the flow field and interactions between suspended particles and a solid substrate, which are crucial for coating processes. We discover that a whisky drop creates a relatively uniform pattern after drying, in contrast to the well-known "coffee-ring stain". Based on measurements of the flow field, we show there are two key features to produce the uniform deposit pattern: First, spontaneous multiple sequential Marangoni flows continuously mix suspended materials and prevent non-uniform coating. Second, surface-adsorbable macromolecules in whisky contribute to a uniform deposit of the suspended materials. From this understanding of the pattern formation, we design a model liquid to achieve a nearly uniform surface deposit, which offers a new physicochemical avenue for control of coatings.
H. Kim, F. Boulogne, E. Um, I. Jacobi, E. Button, and H.A. Stone, "Controlled uniform coating induced by multiple Marangoni flows and surface-adsorbable macromolecules," Phys. Rev. Lett. 116, 124501 (2016)
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