Droplet impacting dynamics on wettable, rough and slippery oil-infuse surfaces

In this study, we investigated droplet impact dynamics offalling water drops (D₀ ~ 2.3 mm) on slippery oil-infused surfaces and compared them to other features of the surfaces, to elucidate the wettability- and roughness-controlled characteristics. We prepared transparent substrates with the designed characteristics, so it would be feasible to visualize the droplet impact dynamics in detail. A wide range of impact kinetics (We ~ 800 (=ρD₀V_i ²/σ_w)) was covered, which gave rise to several types of droplet-impact: gentle spreading, wavy (undulated fingers of spreading edges), droplet break-up, and splashing with small secondary droplets. The basic parameters of the droplet-solid interactions were measured, and events were mapped with respect to the sample surface and impact kinetic conditions. We found that, generally, surface wettability has a major influence on the triple line shape and instability during the impact and retraction process, and thus determines events in of the framework of the dynamic wetting-failure model. Furthermore, while rough conditions promote instability of the impacted droplet, slippery lubricant-infused features tend to dampen perturbations of the spreading/retracting edge.