Effect of Cassie-Baxter versus Wenzel states on ice adhesion: A fracture toughness approach

Ice adhesion to superhydrophobic surfaces is most of the time studied regarding their wetting properties, in attempts to predict the best candidates to promote low ice adhesion. However, no clear correlation between water repellency and ice adhesion has yet been defined, thus limiting the development of low ice adhesion superhydrophobic surfaces to empirical testing. The present study puts forward a mechanical based approach (usually used for bonded joints) to rationalize the role of the surface structure on ice adhesion. Experimental observations on a single microtextured substrate form the basis for the development of a fracture toughness analysis. Compared to a smooth aluminum substrate, shear ice adhesion measurements show that adhesion increased by 30% when ice penetrated the surface structure microgrooves (Wenzel ice) or decreases by 36% when air remained trapped beneath the ice (Cassie ice). Post-mortem observations of the fracture surfaces were performed using a replica technique. Formulas were derived to compute the interfacial fracture toughness of Cassie and Wenzel ice, depending on the geometry of the microtexture. The fracture toughness was then used as an input parameter into a finite element model comprising a cohesive zone layer to model the interface. This semi-analytical approach gave values in good agreement with experimental results, thus showing the relevance of the present toughness analysis.