Coffee Stain Effect

When a solution or a particle containing suspension droplet dries, the solute is often distributed on the substrate in an interesting ring pattern, usually in the vicinity of a (pinned) contact line. Higher rate of evaporation near the periphery of the drop causes a flow of liquid along with the particles or solute towards the contact line or periphery. As a result the solute concentration rises near the periphery and deposit there first. Most of the solute deposits near the periphery of the drop. ‘Coffee stain effect’ phenomenon is a result of complex interplay of marangoni flow, thermo-capillary flow, Rayleigh-Bennard convection, osmotic pressure driven flow and stick-slip flow (pinning depinning of contact line).