Variations of the contact line kinetics during the evaporation of a water droplet on solid surface

Droplet evaporation plays a vital role in various engineering fields, such as air/fuel-premixing, crystal growth, painting, inkjet printing and the applications of biology and drug discovery. Despite much research, the mechanism of the contact line kinetics in droplet evaporation is still not well understood. The main problem in understanding the drop kinetics concern to description of the contact line movement on the solid surface, where condition of hydrodynamic no-slip is contradicted. In this study, a physical justification is presented for the contact line slip in which the origin of the slip, using the molecular model of the flow near to a wall, is attributed to induced momentum gradient between the liquid / gas interface. As a result of that, approaching toward the liquid phase, the slip is reduced and the classical boundary condition of the no-slip is dominated. Using the slip/no-slip process in the contact line, a physical model for the second stage of evaporation of droplets on solid surfaces is proposed, where the droplet volume is reduced in constant contact angle and its validity is confirmed by comparison with experimental data.