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International audience; We report on the observation of thin salt shells that form at the periphery of evaporating pure water drops on salt. Shell shapes range from rings of inclined walls to hollow toroidal rims. We interpret this phenomenon as a consequence of a molecular coffee-stain effect by which the dissolved salt is advected toward the pinned contact line where an increased evaporation takes place. The subsequent salt supersaturation in the vicinity of the triple line drives the crystallization of the shell at the liquid-air interface. This interpretation is supported by a simple model for shell growth.

Most of the studies of drop evaporation focus on the liquid behavior and on the influence of the environment. The substrate always plays a role on the evaporation, through heat exchange and via its wetting properties, but most of the time it is chosen as inert. This chapter focuses on drops deposited on soluble substrates. After a short introduction of the dissolution reactions and of the coupling between dissolution and evaporation kinetics, a study of the effect of saline Rayleigh convection on an evaporating drop on a nonsoluble substrate is presented. The wettability in the case of a water drop deposited on a soluble-polymer-coated silicon substrate is then described, and followed by the description of a numerical study of evaporating nanometer-sized drops on nonsoluble and on soluble surfaces. An example of dissolution-induced watermarks during evaporation in the context of microelectronics is then given, illustrating how much the modification of the evaporation dynamics and of the substrate integrity during the evaporation process can be common. Finally, preliminary results on the evaporation of pure water drops on NaCl soluble single crystals show a strong coupling between the substrate dissolution and the evaporation process.