Drop Impact on Heated Nanostructures

Drop impact on a heated surface not only displays intriguing flow motion but also plays a crucial role in various applications and processes. We examine the impact dynamics of a water drop on both heated flat and nanostructured surfaces, with a wide range of impact velocity (<i>V</i>) and surface temperature (<i>T</i>_s) values. Via high-speed imaging and temperature measurements, we construct phase diagrams of different impact outcomes on these heated surfaces. Like those on the heated flat surface, water drops can deposit, spread, rebound, or break-up with atomizing on the heated nanostructures as <i>V</i> and <i>T</i>_s are increased. We find a significant influence of nanostructures on the impact dynamics by generating particular events in specific parameter ranges. For example, events of splashing, gentle central jetting, and violent central jetting are observed on and thus triggered by the heated nanostructures. The heated nanotextures with high roughness can easily trigger the splashing and the central jetting. Our data of the normalized maximum spreading diameter for the heated surfaces display distinct trends at low and high Weber number (<i>We</i>) ranges, where <i>We</i> compares the kinetic to surface energy of the impacting droplet. Finally, compared with the flat surface, the dynamic Leidenfrost temperature (<i>T</i>_L^D) for <i>We</i> ≈ 10 is decreased (by ≈60 °C) by the high-roughness nanotextures. In addition, our experimental data of <i>T</i>_L^D is consistent with a model prediction proposed by balancing the droplet dynamic and vapor pressure.