Control of spreading and drying of a polymer solution from Marangoni flows

We studied the drying process of polymer solution drops put on a wettable substrate. Three stages can be identified. First, the droplet spreads until a maximum radius where evaporation becomes dominant. The second phase is characterized by a constant radius due to competition between spreading and evaporation of the solvent. Finally, the contact line recedes until complete evaporation of the solvent. We show that, for complex fluids (highly viscous polymer), the morphology is not determined by the evaporation process, the "coffee stain" effect but essentially by the capillary instabilities. Using the appropriate couple of polymer/solvent, we were able to obtain a outward, inward or a lack of Marangoni flow in the droplets, leading to the formation of a rim, a drop or a uniform film, respectively. Copyright (c) EPLA, 2007.