The influence of chemical surface patterning on the freezing behaviour of impacting supercooled water droplets

• Supercooled droplet impact was studied on polymer substrates patterned with hydrophilic stripes • Hydrophilic patterning can influence droplet receding, exposing dry voids between the stripes • Dry voids occurred more often at higher patterning density and higher droplet impact velocity • A higher wettability difference was connected to lower freezing probability and nucleation rate Impacting supercooled water droplets commonly cause in-flight ice accumulation on aircraft surfaces. Ice accretion can lead to dangerous situations such as disturbance of airflow around the aircraft wings, breakdown of vital antennae, or even malfunction of the engines. The adverse effects of aircraft icing could be avoided by designing passive anti-icing surfaces that either delay ice nucleation after droplet impact and/or reduce ice adhesion to promote its shedding. Among potential passive anti-icing strategies, smooth surfaces with patterned hydrophilic and hydrophobic regions have shown good potential to control local frost formation. In this study, we investigate how hydrophilic 150µm wide stripes influence the impact and freezing of supercooled water droplets on two polymeric substrates (Polyvinylchloride and Polypropylene). In addition to varying the wettability difference between the stripes and the substrate, the distance between the stripes (1.25—10 mm) and the impact velocity of the water droplet (4.1—6.5 m/s) were varied. High-speed video analysis of the impacting droplets shows that the presence of the hydrophilic patterns can lower ice nucleation rates and direct the shape of the droplet spreading after impact. However, a low wettability difference between the substrate and the patterns can lead to the opposite scenario with higher nucleation rates.