The wetting of micro- and nanostructured surfaces is an intensively researched scientific field. In particular, the Cassie-Baxter wetting state has aroused great interest, in which flow losses are reduced by trapping a volume of gas between the liquid and the surface. A higher stability of this state can be achieved if a low-viscosity liquid (infusion) is used instead of a gas. This can reduce flow losses when flowing over such surfaces, which is of great technical interest. However, the disadvantage of these structures is that the infusion process discussed so far can only be insufficiently controlled from the outside.

For this reason, substrate-free structures (Fig. 1) are to be investigated for their wetting properties in this project. By removing the substrate, it is possible to directly influence the liquid/gas interface and thus actively control the slip length of the flow. As a first step in this direction, we have implemented thin silicon structures by ICP RIE etching and in a parallel process stainless steel sheets by laser ablation (Photonics Center Kaiserslautern) in such a way that parallel rectangular slits are created in a thin flat substrate. It is known that the rolling behavior along such structures is characterized by a small wetting hysteresis (Movie 1). Since the menisci are accessible from below, they can be modified by varying the pressure.