Back to the basics: Wettability, icing and ice adhesion

Icing in the wet growth regime is caused by water drops on a surface, the dynamics of which are determined by external forces, such a gravity and wind drag. However, the drop dynamics also depend on the wetting characteristics of the surface material. The static contact angle determines the area of a drop that is in contact with the solid, and the difference between the advancing contactangle and receding contact angle, i.e., the contact angle hysteresis, determines the critical external force at which the drop begins to slide. Many studies have been made on the contact angles and their relation to runback icing andice adhesion, but no quantitative theory for the contact angle hysteresis exists. Here, the contact angle hysteresis is explained by a first principles theory, and good quantitative agreement between the theory and experimental data isfound. The implications of the theory to icing and ice adhesion are outlined.