Modeling of Redistribution of Particles Arising from the Nonuniform Evaporation of a Thin Droplet

When a colloidal droplet with pinned contact line evaporates on a substrate, surface tension produce a fluid flow. Usually the flow directs to the contact line and the solute in the drop is dragged by this flow, where it accumulates. The deposit remains on the edge of the drop and forms a solid ring after complete evaporation of the liquid. The conditions of evaporation and solution properties affect on deposit structure. We propose simple model of sessile thin drop desiccation under nonuniform evaporation. The model is based on mass conservation and has numerical solution. If the droplet is covered by a ”mask” with hole, evaporation primarily occurs under the hole so that surface tension drives a flow of liquid to replenish this loss. In the proposed physical model a radial flow velocity was studed and the redistribution of component in the droplet arising from the nonuniform evaporation under a mask was predicted. The effect of diffusion and hole radius on the component redistribution was studed too.

sessile drop, evaporation, mass conservation, flow, diffusion