Evolution of and deposition from an evaporating 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 sessile 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") which often forms at the contact line of a pinned evaporating droplet. In this talk we report on some of the recent developments in the study of evaporating droplets at the University of Strathclyde. 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. (This part of the work was done in collaboration with Durham University, and further details of it can be found in the recent paper by D'Ambrosio et al. J. Fluid Mech. 927 A43 (2021).) We then investigate the effect of the spatial variation in the local evaporative flux on the deposition from an evaporating droplet, determining the flow velocity, concentration of solute within the droplet, and the evolution of the deposit for a one-parameter family of evaporative fluxes. Finally we discuss more recent work exploring the effect of gravity on the shape and evolution of evaporating sessile and pendant droplets, and the effect of particle adsorption on the deposition from an evaporating sessile droplet.