Passive Anti-Icing Performances of the Same Superhydrophobic Surfaces under Static Freezing, Dynamic Supercooled-Droplet Impinging, and Icing Wind Tunnel Tests

Overcoming ice accretion on external aircraft wing surfaces plays a crucial role in aviation, and developing environmentally friendly passive anti-icing surfaces is considered to be a promising strategy. Superhydrophobic surfaces (SHSs) have attracted increasing attention due to their potential advantages of keeping the airframe dry without causing additional aerodynamic losses. However, the passive anti-icing performances of SHSs reported to date varied a lot under different icing test conditions. Therefore, a systematic investigation is necessary to elucidate the icing conditions where SHSs can remain effective and pave the way for SHSs toward practical anti-icing applications. Herein, we designed and fabricated a typical type of SHS featuring dual-scale hierarchical structures with arrayed micromountains (with both spacings and heights of tens of micrometers) covered by single-scale sandy-corrugation-like periodic structures (with both spacings and heights of only several micrometers) (termed SS1). Its anti-icing performances under three representative icing conditions, including static water freezing, dynamic supercooled-droplet impinging, and icing wind tunnel conditions, were comparatively investigated. The SS1 SHS maintained a lower static ice-adhesion strength (<60 kPa even after 50 deicing cycles at temperatures as low as −25 °C), which was attributed to a cumulative cracking effect facilitating the ice detachment. Within the laboratory dynamic icing tests, the SS1 SHSs with micromountain heights of 20–30 μm performed optimally in the antiadhesion of supercooled droplets (at an impinging velocity of 3.4 m/s and temperatures of −5 to −25 °C). In spite of the significant anti-icing performances of the SS1 SHSs in both static and dynamic laboratory tests, they could hardly sustain reliable passive anti-icing performances in harsher icing wind tunnel tests with supercooled droplets impinging their surfaces at velocities of up to 50 m/s at a temperature of −5 °C for 10 min. This study can inspire the development of improved SHSs for achieving satisfactory anti-icing performances in real-aviation conditions.