The Black Sheep Pub
247 S. 17th Street
Philadelphia, PA 19103
Physics & Astronomy, University of Pennsylvania
In this talk, I will discuss the science needed to understand a drying drop of coffee. We will see that even this very simple effect depends on many factors, ranging from water evaporation and fluid convection within the drop, to tension at the air-water surface and pinning of the liquid-solid contact line onto the counter-top. This rich phenomenology is also important for practical applications related to coatings, printing, painting, and even genotyping. I will describe a series simple drying experiments, on increasingly more complex fluids, that reveal the zoology of physics ideas underlying this everyday occurrence.