Supercooled Water Droplets Impacting at High Speed on Superhydrophobic Surfaces: Open Questions Related to Icephobicity

It is posited that impact ice adhesion strength on superhydrophobic surfaces is related to droplet impalement. Several gaps still exist in the understanding of how different types of textured surfaces resist the impalement of high‐speed impacting droplets (<10 2 μm diameter at 10 2 –10 3 m s −1 ). A previous study reveals that a pressure balance calculation can predict the wetting state of an impacting drop (≈10 3 μm diameter at ≈10 1 m s −1 ). However, the ability of this model to predict the wetting state of small droplets impacting at high speed or of droplets in a supercooled state has not been reported. To better understand supercooled microdroplet impalement, and to verify the hypothesis that droplet impalement is directly related to ice adhesion strength, herein, the impact behavior of microdroplets in a cold airflow onto surfaces of varying topography and wettability in an icing wind tunnel with support of high‐speed video images are investigated. Although the results do not allow for validating the above hypothesis about impalements and ice adhesion, they show that the difference between supercooled droplet spreading and retraction can be a predictor of ice adhesion strength. However, this relation must be validated with a greater body of data from samples with very diverse surface properties.