How Triangular Ridged Textures Affect the Impact Forces of Water Drops on Superhydrophobic Surfaces

The impact of drops on solid surfaces is a common occurrence in natural systems, with a particular focus on reducing contact time during impingement for applications such as deicing and condensation heat transfer. While studies have reported that superhydrophobic single-ridge and some crossed-ridge textures can effectively reduce contact time, the effect of the ridge structure on the force between impinging drops and substrates remains unexplored. In this study, we employ high-precision force measurements to directly measure the dynamic forces during drop impact on superhydrophobic surfaces featuring a single-ridge structure. Temporal evolution profiles of impact forces reveal double peaks corresponding to the spreading and retraction processes. At lower Weber numbers within a specific range, a propagating surface wave from the bottom to the top of the drop is observed, resulting in intricate force-time profiles. We reveal that the spreading process of the drop is primarily influenced by decelerating inertia upon surface contact with capillary forces becoming more prominent at lower Weber numbers. Moreover, the second peak force is attributed to the momentum transfer of the liquid from the ridge-aligned horizontal direction to the vertical direction. Notably, the second peak force on ridged surfaces is significantly reduced compared to that on flat surfaces due to the reduced liquid volume involved in the retraction process. The study offers valuable insights into the potential regulation of impact forces.