Ground spreading dynamics during single droplet impact onto a free-standing cubic surface element

In many technical applications the impact of a single droplet onto a dry, structured surface plays an important role. Hereby, the impact dynamics are often affected also by the wettability of the respective surface. In order to gain a better understanding of the complex interplay between surface structure and wettability, the basic process of single droplet impact onto a free-standing cubic surface element with varying surface wettability is investigated experimentally. High-speed visualization of the impact process is performed with the multi-perspective experimental facility in our laboratory [1]. The experimental parameter range covers cubic pillars with varying edge length (between 1 mm and 2.4 mm) and different surface wettabilities, multiple droplet diameters, impact velocities and two fluids, namely water and isopropanol. The focus of this work is on the effects of surface wettability and drop-pillar ratio L¯D on the evolution of the spreading factor d∗ = ds/Dd over the duration of the impact process.