Recent advances in droplet wetting and evaporation.

The wetting of solid surfaces using liquid droplets has been studied since the early 1800s. Thomas Young and Pierre-Simon Laplace investigated the wetting properties, as well as the role of the contact angle and the coupling of a liquid and solid, on the contact angle formation. The geometry of a sessile droplet is relatively simple. However, it is sufficiently complex to be applied for solving and prediction of real-life situations (for example, metallic inks for inkjet printing, the spreading of pesticides on leaves, the dropping of whole blood, the spreading of blood serum, and drying for medical applications). Moreover, when taking into account both wetting and evaporation, a simple droplet becomes a very complex problem, and has been investigated by a number of researchers worldwide. The complexity is mainly due to the physics involved, the full coupling with the substrate upon which the drop is deposited, the atmosphere surrounding the droplet, and the nature of the fluid (pure fluid, bi- or multi-phase mixtures, or even fluids containing colloids and/or nano-particles). This review presents the physics involved during droplet wetting and evaporation by focusing on the evaporation dynamics, the flow motion, the vapour behaviour, the surface tension, and the wetting properties.