Dynamics of dissolutive wetting: Physical mechanics investigations

Dissolutive wetting, i.e. droplet wets and simultaneously dissolves its solid substrates, is of great significance in both academic research and practical applications. The diffusion interface at the moving contact line is one of the answers to the Huh-Scriven paradox. Besides, dissolutive wetting is the bottleneck problem in many practical fields, such as metal alloy processes, shale gas exploitation, drug release, etc. Furthermore, dissolutive wetting involves complex physical processes, i.e. wetting, diffusion and convection. The coupling transport of mass and momentum as well as the internal convection in the droplet increases the difficulty in studying dissolutive wetting. Even though previous works have been done on metal/metal, metal/ceramic systems, there has been no experimental observation on the flow details in droplets and changes of the solid-liquid interface due to the opacity of the materials in dissolutive wetting. Thus, the physical mechanism of dissolutive wetting is still far from being well understood. Based on the problems mentioned above, in this paper, dynamics of dissolutive wetting of droplets on solid surfaces is investigated by physical mechanics. From a new perspective, we carry out the molecular dynamic simulations of glucose and water dissolution pairs. we match the parameters that dominate the dissolutive wetting in our simulations with real experimental parameters. By this method, the simulation systems are simplified and the glucose molecules can be regarded as Lennard Jones particles. Experiments are also designed to show the in situ real time measurement of the dissolutive wetting. In order to obtain the flow details in the droplet, we select three pairs of high transparent materials. Beyond that, we built a dimensionless number space that divides the dissolutive wetting into two types. For small Pelect number, the convection effect is ignored. But when Pelect number is greater than one, the convection effect that leads to the uniform of the solute distribution must be considered. Morever, we obtain that the droplet follows different scaling laws in different dissolutive wetting stages. In the early stage, the surface tension dominates and the scaling law satisfies the Tanner law. Whereas scaling law in dissolutive wetting changes while diffusion and convection effect are more obvious with the dissolution of solutes. Compared with the non-convective process, the internal convection increases the energy dissipation within the dissolution pairs in our experiments and inhibits the spreading of the droplets to a certain extent. We also find that the coupling effect of dissolution and wetting process will have important influences on the molecular structure of the droplet. Overall, we establish multiscale dissolutive wetting model and reveal the scaling laws of droplet spreading in dissolutive wetting by physical mechanics. Our findings may help to further understand the mechanisms of dissolutive wetting and provide theoretical guidance of practical applications that involve dissolutive wetting.