Some physics inside drying droplets.

Droplets are of great scientific interest because studying their formation and dynamics is important in many technologies such as in microfluidics [1, 2]. Evaporation of droplets is another interesting aspect that has caught much scientific attention. An example of an evaporating droplet is a coffee droplet spilled on a table. After evaporation the coffee droplet leaves a ring-like stain called a coffee ring or coffee stain [3]. This phenomenon, known as the 'coffee ring effect', occurs not only with coffee droplets but also with all droplets containing non-volatile solutes. There are a number of interesting physical processes going on within the droplets during evaporation to form the 'coffee stains'. In this article, we will see what they are. [ABSTRACT FROM AUTHOR]