Influence of Surface Roughness on Supercooled Droplet Impacts

This study investigates how surface roughness influences the dynamics and nucleation characteristics of supercooled large water droplets upon impact. To conduct controlled droplet-impact experiments, an ultra-low temperature freezer was repurposed and fabricated into a custom environmental chamber, enabling precise control of droplet temperature, velocity, and environmental conditions. Droplet impact dynamics were previously characterized at ambient conditions across a variety of rough and superhydrophobic surfaces. Systematically varying droplet temperature, velocity, and substrate roughness, the spreading behavior and dynamic contact angle evolution of droplets at ambient temperature and at various supercooled temperatures are compared. The onset of ice nucleation and droplet spreading reveal the influence roughness has on the hydrodynamics and initial freezing, specifically during the Cassie‑Baxter or Wenzel wetting states. This study links roughness to inertial spreading, changes in surface wetting, and ice nucleation. The results reveal practical guidelines for designing icephobic coatings and supply crucial benchmark data for multiphase CFD models that must accurately resolve the Cassie‑to‑Wenzel wetting transition.