(343d) Shock Wave and Hole Formation on a Spreading Liquid Drop

Many biological surfaces (e.g. Bird feathers, insect wings, and plant leaves) are super-hydrophobic with physical morphology at different scales. However, it is not well understood how a raindrop impacts natural super-hydrophobic surfaces, and its significance of biological functions. In this present study, we found that a spreading drop at a high speed can generate shock waves on a spreading liquid in the presence of surface morphology at the micro scale. Furthermore, the spreading drop is suddenly ruptured by growing holes followed by the shock waves, which leads to a decrease in contact time more than 50%. As a result, heat and momentum transfers are reduced by raindrops, which may lower the hypothermia risk of animals or less affect the stability of insect flights. Additionally, we revealed that the drop fragmentation sheds smaller satellite droplets, which play a crucial role in promoting wet pathogenic dispersal by carrying pathogenic spores along. Therefore, our results shed light on multi-functional aspects of biological super-hydrophobic surfaces.