Effect of the surface peak-valley features on droplet splash dynamics

In this study, we fabricated two types of functional surfaces with the same roughness (Sa) but entirely opposite surface morphological features, which are defined as the positively skewed surface filled with protruding cylinder array (Ssk > 0) and the negatively skewed surface filled with circular pit array (Ssk < 0). The effect of surface morphology peak-valley features on droplet splash is analyzed, and the formation mechanism of the prompt splash and corona splash is also indicated based on the Kelvin-Helmholtz instability. Our results demonstrate that, under the same roughness conditions of Sa, the interaction between the liquid lamellae and the thin air layer is much stronger on the negatively skewed surface, which would inhibit droplet spreading and promote the generation of droplet splash. Increasing the depth of microstructures, resulting in more pronounced peak-valley features, has been found to facilitate both prompt and corona splash phenomena to some extent. Additionally, it is found that the ease of splash formation on each surface is related to the initial spreading speed variation, with the degree of reduction in the initial spreading speed indirectly reflecting the instability of the liquid lamellae. The findings from our study contribute to the development of advanced surface engineering strategies for controlling droplet splash and enhancing the performance of various industrial applications.