  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.
