Coffee ring

Coffee is known as the ring of the annular patch, a drop of the coffee beverage leaves on a smooth surface after drying. Analogously, the term is applied to caused by red wine and other liquids, as well as contamination in the art, for example in the development of paints, varnishes and inks. The coffee ring is not to be confused with the coffee edge, caused by the shape of the cup floor when spilled coffee flows under a cup.

If a drop of coffee placed on a smooth surface and let it dry, then there is the most intense, caused by the pollution and coffee stain, the stain, do not end up in the middle of the previously covered by the coffee drop surface, but at its edge. The coffee ring arises because the edges of the drop and remain stable during the evaporation. The volume of the liquid by evaporation from, liquid flows from the center to the edges. This also dissolved particles are moved from the center to the edge, where they accumulate gradually. If the liquid is then evaporated completely, the pollution caused by previously dissolved substances in coffee is annular. The coffee ring led already to a number of scientific research. It was now found that the form of suspended particles plays an important role. Are the colored particles do not like in the coffee round but elliptical, reduces or prevents the coffee ring effect. According to the research of the physics team at the University of Pennsylvania, the coffee ring effect can be interrupted by changing the shape of the solute particles.