Particle deposition after droplet evaporation on ultra-hydrophobic micro-textured surfaces

International audienceWe study the size and shape of the final deposit obtained when a drop with colloidal particles has driedon a ultra-hydrophobic surface made of micro-posts. As expected, most of the particles lie inside acircular area, whose radius roughly corresponds to the Laplace pressure threshold for liquidimpalement inside the structure (Cassie–Wenzel transition), inducing a coffee-stain deposit due tocontact-line pinning. Less expected is the observation of tiny deposits on top of posts in the areaexternal to the main ring, despite the low macroscopic liquid/solid friction. Experiments are carried outvarying the concentration in particles and initial volume of drops, in order to determine the influence ofthese parameters on the size distribution of deposits. A microscopic insight of the tiny deposits isproposed, based on recent experiments of non-volatile liquid sliding drops