ISBN 9783843952286

978-3-8439-5228-6, Reihe Thermodynamik

Patrick Foltyn
Droplet collisions with dry solid surfaces with variable wettability and topography

237 Seiten, Dissertation Universität Stuttgart (2022), Softcover, A5

Zusammenfassung / Abstract

Droplet-wall interactions are present in manifold technical and natural processes. In this doctoral thesis, the focus is set on the evaluation of the influence of different surface wettabilities and topographies on the respective physical phenomena during static droplets phenomena and dynamic droplet impacts. The smooth and structured surfaces were treated by plasma activation and plasma polymerization processes in order to alter the wettability with respect to the natural contact angles.

Static apparent contact angle measurements could show a contact angle hysteresis with respect to the azimuthal angle due to pinning. With finer surface structures, this hysteresis decreased significantly.

High-speed images of droplet impacts were acquired on a newly designed experimental test rig with four perspectives. A systematic parameter study investigated the splashing tendency and other physical behaviors on smooth and structured surfaces. The morphologies for impacts onto structured surfaces were by far more complex and the interdependency between surface topography and wettability was shown. With the help of the newly developed Laser Pattern Shift Method (LPSM), it could be shown that an increase in impact energy, and wettability, or a decrease in liquid viscosity results in a thinner droplet lamella. The influence of the surface material was negligible for the used parameter space. Furthermore, heterogeneous wetting states were observable when structured surfaces were used.

In summary, it was found that for droplet-wall interactions, the wettability and topography need to be considered not only for the capillary-driven regime, but also during the inertia-driven regime of droplet impacts.