Quantification of ice adhesion strength and the effect of ion implantation on icephobicity

Abstract

The adhesion of ice onto surfaces can lead to many problems in the engineering world, creating hazards and economic losses. Recently, passive icephobic surfaces have been developed that can prevent ice build-up on a surface, but the mechanism of ice adhesion to a surface is still not well understood. For research purposes, the icephobicity of a material can be characterised by its ice adhesion strength, mainly affected by the surface topography and chemistry of the material. This study aims to improve the understanding of the mechanism of ice adhesion to metallic surfaces. In order to do this, two novel quantitative characterisation methods were developed to measure ice adhesion strength in two different length scales. The first method measures macro-scale tensile ice adhesion strength while the second method quantifies the micro-nano scale shear ice adhesion strength using a novel nanoscratch method to mechanically shear microscopic ice droplets. The samples for this study were made using ion implantation technique with Xe+ ions for surface topography modifications and CF+ ions for surface chemistry modifications on stainless steel substrates. A combination of both treatments on stainless steel were also investigated. The results of this study confirm the theory that the ice adhesion strength of a material is determined by the degree of interaction between ice and the material at the ice-solid interface. An ice droplet that penetrates into the space between asperities (Wenzel-type) shows higher ice adhesion strength than an ice droplet that sits on top of the asperities and microscopic air bubbles (Cassie-Baxter type). This conclusion was obtained by performing both quantification methods on the ion implanted stainless steels, and it was suggested that because hydrophobic substances were implanted near the base of the asperities, the transition of a Cassie-Baxter water droplet into a Wenzel type ice droplet during freezing was prevented. With the results of this study, the mechanism of ice adhesion to a metallic surface was better understood in an effort to achieve practical icephobicity for engineering applications.