How surface roughness promotes or suppresses drop splash

This work presents an experimental study on the splashing behaviors of drops impinging on rough solid surfaces. Most prior studies have shown the increase in surface roughness can promote the occurrence of a drop splash. Interestingly, we found two opposite effects of surface roughness on the drop splash that the increase in surface roughness can promote splash of low-viscosity drops but suppress splash of high-viscosity drops. According to the wetting state of the spreading lamella on rough surfaces, the splash regime can be classified into two modes: corona splash and prompt splash. It is found that the increase in surface roughness can promote the prompt splash but suppress the corona splash. The increase in surface roughness could provide wide channels for air to escape and suppress the corona splash. Meanwhile, the larger surface roughness could also disrupt the expanding lamella and promote the prompt splash. The dimensionless parameter Ohr can be used to distinguish two splash regimes, and the critical value Ohrc is obtained from experimental results, at which the splash regime changes from the prompt to corona splash. Emphatically, we obtain the splash criteria in two regions, which could reflect the opposite effects of surface roughness on the drop splash and successfully characterize the splashing behaviors in this work and previous studies. The results of this work are expected to provide valuable insights to control the drop splash in industrial applications.