Do Self-cleaning Surfaces Repel Ice?

Abstract

The effects of nano- and micro-roughness as well as the chemical composition of surface treatments on self-cleaning properties and their suitability for ice repellency were investigated. In the first part of the study, the thermodynamics of water wettability of coated surfaces was evaluated both theoretically and experimentally. Accordingly, relationships were derived between the interfacial adhesion strength of a liquid drop to a polymer surface of a given composition, the mass of the drop, the measured contact angles, and the sliding angle. To verify the proposed model various hydrophobic coatings having different surface nanoand micro-roughnesses were prepared using polycarbonate as a substrate. The surface treatment was based on fluoroalkylsilane. Roughness was introduced by means of silica (microparticle) and POSS — Polyhedral Oligomeric Sil Sesquioxane (hybrid inorganic-organic nanoparticle) using a two tier topography. Using optimal compositions and processing conditions transparent ultrahydrophobic (superhydrophobic) characteristics were obtained. In these cases the contact angle was above 160° and the sliding angle was below 5°. In the second part of the investigation, the relationship between water wettability and ice repellency represented by ice adhesion to the coated surfaces was studied. Consequently, the surfaces were tailored using nanotechnology approach for their chemistry as well as their nanostructure in order to obtain fully wetting (hydrophilic) having a contact angle close to zero and the fully dewetting (ultrahydrophobic) (self-cleaning) surfaces where the contact angle approaches 180°. Ice adhesion test results have shown that the lower the surface energy the lower is the ice adhesion. The lowest adhesion values were obtained where ultra-hydrophobicity was present, with a combination of very low sliding angle with very high contact angle. These novel ultra-hydrophobic surface coatings and the associated model were used to develop and design surfaces for a variety of applications such as self-cleaning, glazing and anti-icing surfaces.