Contact line deposits in an evaporating drop

Abstract

Solids dispersed in an evaporating drop migrates to the drop edge and form a solid ring, leaving ringlike stains on the surface. An outward flow within the drop is identified, which is driven by solvent loss by evaporation and geometrical constraint that the drop maintain an equilibrium droplet shape with a fixed boundary. This flow is shown to be responsible for the migration. A theory that predicts the flow velocity, the ring growth rate, and the distribution of solute within the drop is proposed.