Capillary flow as the cause of ring stains from dried liquid drops

Robert D. Deegan (), Olgica Bakajin, Todd F. Dupont, Greb Huber, Sidney R. Nagel and Thomas A. Witten
Additional contact information
Robert D. Deegan: James Franck Institute
Olgica Bakajin: James Franck Institute
Todd F. Dupont: University of Chicago
Greb Huber: James Franck Institute
Sidney R. Nagel: James Franck Institute
Thomas A. Witten: James Franck Institute

Nature, 1997, vol. 389, issue 6653, 827-829

Abstract: Abstract When a spilled drop of coffee dries on a solid surface, it leaves a dense, ring-like deposit along the perimeter (Fig. 1a). The coffee—initially dispersed over the entire drop—becomes concentrated into a tiny fraction of it. Such ring deposits are common wherever drops containing dispersed solids evaporate on a surface, and they influence processes such as printing, washing and coating1,2,3,4,5. Ring deposits also provide a potential means to write or deposit a fine pattern onto a surface. Here we ascribe the characteristic pattern of the deposition to a form of capillary flow in which pinning of the contact line of the drying drop ensures that liquid evaporating from the edge is replenished by liquid from the interior. The resulting outward flow can carry virtually all the dispersed material to the edge. This mechanism predicts a distinctive power-law growth of the ring mass with time—a law independent of the particular substrate, carrier fluid or deposited solids. We have verified this law by microscopic observations of colloidal fluids. Figure 1 A ring stain and a demonstration of the physical processes involved in production of such a stain. a, A 2-cm-diameter drop of coffee containing 1 wt% solids has dried to form a perimeter ring, accentuated in regions of high curvature. b, Spheres in water during evaporation, as described in the text. Multiple exposures are superimposed to indicate the motion of the microspheres.

Date: 1997
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DOI: 10.1038/39827

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