Complex Fluids

 

We study about complex fluids including binary mixtures, partially miscible mixtures, emulsion liquids, and non-newtonian fluids. Using flow visualization techniques, we try to discover new features from the fluid mechanics point of view. We endeavor to achieve real applications using these complex fluids.

 

 

 
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)
(selected as a PRL cover and PRL Editors' Suggestion and highlighted in Physics and Nature physics)