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- Influence of wetting behavior on the morphology of droplet impacts onto dry smooth surfacesPublication . Foltyn, Patrick; Ribeiro, Daniela; Silva, André; Lamanna, Grazia; Weigand, BernhardThe influence of wettability on the morphology of droplet impacts onto dry surfaces is often neglected in the literature, despite its significant effect on the resulting morphology. In this work, the role of wettability is investigated systematically by considering droplet impact processes on smooth dry surfaces of two different materials. The wetting behavior is varied not only by employing two different fluids, but most importantly by varying the surface properties by plasma activation and polymerization. Overall, this leads to four different wetting behaviors for each surface. The changes in impact morphology are visualized by means of a three-perspective experimental facility. In particular, the bottom view employs a total internal reflection-configuration for visualizing the exact droplet contact area and contact time. This enables us to characterize the main features of the different wetting behaviors. Overall, we found that surface wettability mainly influences the receding phase, resulting in higher receding rates with decreasing wettability but also the maximum spreading diameter.
- Effect of Surface Wettability on the Droplet Impact Morphologies on Dry Smooth Polycarbonate SurfacesPublication . Foltyn, Patrick; Ribeiro, Daniela; Silva, André; Lamanna, Grazia; Weigand, BernhardThe surface wettability has a significant influence on the morphology and spreading behaviorduring droplet impacts on dry smooth walls. On the way for predicting spreading diameters independency of the wetting behavior, the experimental database was extended by an experi-mental study in which distilled water and isopropanol droplets have impacted onto dry smoothLexan®(Polycarbonate) surfaces at four different impact velocities. The range of Reynoldsnumbers was set between1,135and12,240and for the Weber number between80and1,165.The surface material, and thus also the characteristic surface roughness, were kept constant,while the wetting behavior was modified using plasma activation and plasma polymerizationprocesses. Different contact angles have been investigated in a range from full wetting to non-wetting for water and from full wetting to partial wetting for isopropanol. The experiments havebeen conducted on a newly designed test rig. High-speed diffuse backlight images at20 kHzfrom the top and the lateral perspective are acquired on a shared CMOS-sensor simultane-ously. A bottom perspective in a total internal reflection configuration is acquiring the footprintof the droplet impact. This enables to better define the maximum spreading diameter and todistinguish between wetted and non-wetted areas.