Robust fadeout profile of an evaporation stainT. A. Witten
James Franck Institute, University of Chicago - Chicago IL 60637 USA
received 27 March 2009; accepted in final form 27 May 2009; published June 2009
published online 10 July 2009
We propose an explanation for the commonly seen fading in the density of a stain remaining after a droplet has dried on a surface. The density decreases as a power p of the distance from the edge. For thin, dilute drops of general shape this power is determined by a flow stagnation point in the distant interior of the drop. The power p depends on the local evaporation rate J(0) at the stagnation point and the liquid depth h(0) there: , where and are averages over the drop surface.
47.57.ef - Sedimentation and migration.
02.40.Xx - Singularity theory.
47.55.D- - Drops and bubbles.
© EPLA 2009