ADVANCES AND CHALLENGES IN DROPLETS WETTING AND EVAPORATION
The wetting and evaporation of sessile droplets resting on solid substrates has been of interest to a wide range of disciplines. Ranging from engineering, biomedical to atmospheric science. The topic of droplets evaporation exhibits a fundamental importance to these areas. In this paper, we review some of the recent advances on this subject, including the influence of substrate thermal properties and flexibility, thermal instabilities driven by evaporation, patterns from dried droplets, progress in modelling these phenomena and predicting lifetimes. The challenges facing researchers in the field are highlighted aiming at providing some outlooks on this topic. The thermal properties of underlying substrate can indeed significantly affect the evaporation kinetics and hence lifetimes of volatile droplets. Equally thermal instabilities driven by evaporation is an interesting observation which still represents many unraveled aspects. The role of these latter in evaporation and their effect on phase change remains to be fully elucidated. Attempts to predict life times of droplets has been restricted to mainly mathematical models. Evaporation and drying of complex fluid droplets is another topic which presents many challenges to researchers. Understanding and predicting the patterns formed from dried complex fluid droplets remain of practical interest and challenging. The area of superhydrophic substrates and how evaporation of droplets proceeds on these new materials requires more experimental investigations. Many challenges on the modelling front are also highlighted. This includes the multiscale nature of the three-phase contact line region as well as non-symmetrical geometries and the three dimensional nature of droplets.