Impinging Drops on Superhydrophobic Surfaces at Icing Conditions

Due to their excellent water repellent characteristics, superhydrophobic surfaces have been hypothesized to be icephobic. This is based on the premise that water droplets will be repelled from the surface before ice nucleation can occur. The icephobic nature of these surfaces provides an attractive solution to current icing problems that can occur in aerospace applications. However, significant challenges remain before anti-wetting coatings could be implemented as an effective ice mitigation tool. For example, the majority of current synthetic superhydrophobic surfaces are fragile and unable to withstand the harsh environmental conditions that are encountered by aerospace applications. In addition, their static and dynamic wettability at varying temperatures and humidity, as well as their ice-shedding performance under the impact of a super-cooled icing cloud, are not well understood. Therefore, in this dissertation, fabrication techniques for a previously developed nanocomposite surface were improved so that coatings of consistent anti-wetting performance and durability could be produced. The icephobicity of this nanocomposite coating was then systematically investigated. First, an experiment was conducted to study the wettability of a water drop on the coating for a full temperature cycle (20˚C to -3˚C and back to 20°C) and at varying humidity levels. The investigation was then extended to study the impact and rebound dynamics of a drop on an inclined coating, at different fluid viscosities and at various temperatures (50°C to -8°C). This was followed by a study of ice adhesion strength of the coatings created under the impingement of 20 µm super-cooled water droplets. The receding contact angle was discovered from these experiments to be a key parameter in controlling superhydrophobic wettability and ice adhesion. Therefore, the receding angle depinning dynamics from a superhydrophobic surface were also studied in detail at micron length scales and at microsecond temporal scales. In summary, results from this dissertation revealed the crucial parameters that govern the icing performance of a nanocomposite superhydrophobic surface.