COFFEE-RING EFFECT

About:

• For about two decades now, the ‘coffee ring effect’ has been known as when a drop of spilt coffee dries up, the outermost edge of the dried drop is a little darker than the centre, forming a darker ‘ring’.
• This is caused by the outward drift of suspended coffee particles from the centre, causing a denser, darkened rim.
• Now, researchers from Indian Institute of Technology, Madras, have shown that after reaching the rim, as the drop dries, some of the particles undergo an inward drift too.
• This research has applications in agriculture, forensic science and even disease diagnosis. The present work has been published in the journal, Soft Matter.