The evaporation of a droplet in well, and effect of the spatial variation of the evaporative flux on the deposition from a sessile droplet*

The evaporation of sessile droplets occurs in numerous physical contexts, with applications in nature, industry and biology, including nano-fabrication, chemical decontamination, and ink-jet printing. As a consequence of the wide variety of everyday applications, the evolution of and deposition from an evaporating droplet has been subject to extensive investigation in recent years, with particular interest in different evaporation modes, the prediction of lifetimes, and the ring-like deposit (the ``coffee-ring'') that often forms at the contact line of a pinned evaporating droplet. In this talk we describe some recent developments in the study of evaporating droplets. We first formulate and analyse a mathematical model for the evolution and lifetime of an evaporating droplet in a well of rather general shape and validate the model by comparing the theoretical predictions with experimental results for the special case of cylindrical wells. We then investigate the effect of the spatial variation in the evaporative flux on the deposition from an evaporating droplet, determining the flow velocity, concentration of particles within the droplet, and the evolution of the deposit for a one-parameter family of evaporative fluxes.