Evolution of the interfacial shape in dissolutive wetting: Coupling of wetting and dissolution

Abstract Interface evolution of a droplet on a dissolvable substrate is controlled by coupling of wetting and dissolution, which makes dissolutive wetting more complicated than wetting on inert substrate. In our experiments, xylene and polystyrene are used as solvent and solute, respectively. We record the continuous evolution of interfacial shape and measure change of geometrical parameters. Then, a model is built based on the Noyes-Whitney equation. The evolution mechanisms of interface and solute concentration under the combined actions of wetting and dissolution are analyzed. There are two stages in dissolutive wetting. The two stages are identified by the speed ratio of wetting and dissolution, which reflects the coupling between wetting and dissolution. The model can recover the evolution of the interfacial shape observed in the experiment. Our work may help to predict change of interfacial shape in dissolutive wetting, and the results provide a better understanding of dissolutive wetting which is a process that occurs in many important application areas.