Coffee ring
A coffee ring is the ring-shaped stain left by a drop of coffee drink on a smooth surface after it has dried. Analogously, the term is also applied to soiling caused by red wine and other liquids as well as in technology , for example in the development of paints, varnishes and inks. The coffee ring is not to be confused with the coffee rim, which is created by the shape of the cup base when spilled coffee flows under a cup.
If a drop of coffee dries on a smooth surface, the most intense soiling and coloring caused by the coffee is on the edges and not in the center of the area covered by the coffee drop. The coffee ring is created because the edges of the drop remain stable due to the surface tension even during evaporation . If the volume of the liquid decreases due to evaporation, liquid flows from the center to the edges. This also moves the particles contained in the drop from the center to the edge, where they gradually accumulate. Once the liquid has completely evaporated, the pollution caused by substances previously dissolved or suspended in the coffee is ring-shaped. The coffee ring has already prompted numerous scientific researches. It has now been found that the shape of the suspended particles plays an essential role. If the coloring particles are not round, as in coffee, but elliptical, this reduces or prevents the coffee ring effect. According to the research of the team of physicists at the University of Pennsylvania , the coffee ring effect can be interrupted by changing the shape of the dissolved particles.
Individual evidence
- ↑ The secret of the coffee rings. orf.at (08/18/2011), accessed on February 22, 2012 .
- ↑ The mystery of the “coffee ring effect” has been unveiled. diepresse.com (08/17/2011), accessed on February 22, 2012 .
- ↑ astropage.eu. Retrieved February 22, 2012 .