Ice Adhesion Strength on Hydrophobic and Superhydrophobic Coatings

Abstract

Superhydrophobic coatings have shown promise in reducing both ice accretion and accumulation on a surface. However, recent studies revealed conflicting reports of ice adhesion strength on superhydrophobic surfaces. Therefore, a comprehensive experiment was conducted to measure the ice adhesion strength of a variety of hydrophobic and superhydrophobic coatings by subjecting test substrates to a super-cooled spray consisting of 20 μm droplets in a walk-in cold chamber, and at an air temperature of -20°C. The accreted ice was then removed by pressurized air in a tensile direction for a mode-1 fracture. The relationships between surface wettability, roughness parameters and ice adhesion were then studied in detail. Results showed that for hydrophobic surfaces, a high contact angle and receding contact angle resulted in a lower ice adhesion strength. However, ice adhesion strength for superhydrophobic surfaces correlated weakly with receding contact angle. It was discovered that low surface autocorrelation lengths for superhydrophobic surfaces would result in low ice adhesion strength. This is due to the fact that closely spaced surface features create a high capillary pressure between the surface asperities to resist the penetration of impacting super-cooled droplets to result in ice formation at a Cassie wetting state. However, if the surface asperities are infiltrated with water droplets, the ice adhesion strength can be affected by secondary surface roughness parameters such as arithmetic mean roughness, kurtosis and skewness.