An experimental study of the coffee ring pattern 咖啡環圖案之實驗探究

洪啟鈞 楊宗于、陳妍伊、吳敏綺
The coffee ring effect is a general phenomenon in our daily life, in which a denser stain is formed at the outer region while a coffee drop is completely dried. The physical origin is that, to balance the higher evaporation rate at the outer region, the pinned contact line induces an outward capillary flow transporting the coffee particle outward. In this study, we explore the influence of varying evaporation rates on the formation of coffee ring patterns by analyzing the changes in the ring's brightness. We provide a quantitative investigation into how these patterns evolve in response to different evaporation rates. Furthermore, we examine how the interplay between evaporation and Marangoni stress impacts pattern formation in coffee rings.