Wetting and evaporation of multicomponent droplets

Wetting and evaporation of sessile droplets are ubiquitous in nature and of importance to many industrial and everyday processes. While most of the research on sessile droplets has been constraint to single component droplets, complex multicomponent droplets are in fact the most common systems in natural and industrial fields. Multicomponent droplets show diverse behaviors as the concentration of the different components varies in both the liquid and the gas phases. The nonuniform distribution of different components leads to surface tension gradient and affects the wetting dynamics. Additionally, some ubiquitous behaviors can be induced by the preferential evaporation of more volatile components, and by actively tuning the vapor field by adjacent droplets or via external vapor sources. In this paper, we review the underlying physical and physicochemical mechanisms of multicomponent droplets during wetting and spreading, induced by evaporation and/or mediated by the vapor field. Especially we focus on volatile multicomponent droplets and exclude the colloidal or nanofluids droplets which have been reviewed in existing papers. We overview the droplet wetting dynamics, the interfacial mass flux, the droplet lifetime and the flow patterns of these complex droplets. The available experimental and numerical methodologies to date are also summarized, including the application conditions, accuracy, resolution and limitations from the experimental aspect; as well as the main assumptions, mathematical methods and corresponding reliability from the numerical aspect. Last we discuss the significance of exploiting the interacting mechanisms with complex droplets, and point out the innovation potentials in cutting-edge applications including 3D printing, self-cleaning, digital microfluidics, cellular sorting and biomedical diagnosis, amongst others.