Paradoxical Coffee-Stain Effect Driven by the Marangoni Flow Observed on Oil-Infused Surfaces

Formation of coffee stain deposits under evaporation of droplets containing aqueous solution of salts placed on silicone-oil impregnated substrates was observed. The formation of ring-like deposits was registered for various molar concentrations of salts for the droplets of 5-300 microlitres in volume. The effect occurred when the contact line was de-pinned, and the evaporation from the edge of a droplet was stopped by the silicone oil. The formation of the coffee stain deposit is related to the soluto-capillary Marangoni flow; the influence of the thermo-capillary flow taking place in parallel is negligible.