Relationships between Water Wettability and Ice Adhesion

TLDR

Ice formation can impede critical infrastructure such as aircraft, power lines, and ships, yet the fundamentals of ice adhesion remain poorly understood and the design of icephobic surfaces is not well established. The study investigates how advancing and receding water contact angles relate to ice adhesion strength on bare steel and 21 thin polymer coatings. Contact angles were measured with a commercial goniometer and ice adhesion strengths were evaluated using a custom laboratory-scale apparatus on 200–300 nm thick coatings, including fluorinated POSS additives. Ice adhesion strength correlates strongly with the practical work of adhesion (1 + cos θrec) and can be reduced by up to 4.2× on fluorodecyl POSS-coated steel, but further reductions likely require textured surfaces since smooth materials have reached the minimum achievable receding angles.

Abstract

Ice formation and accretion may hinder the operation of many systems critical to national infrastructure, including airplanes, power lines, windmills, ships, and telecommunications equipment. Yet despite the pervasiveness of the icing problem, the fundamentals of ice adhesion have received relatively little attention in the scientific literature and it is not widely understood which attributes must be tuned to systematically design "icephobic" surfaces that are resistant to icing. Here we probe the relationships between advancing/receding water contact angles and the strength of ice adhesion to bare steel and twenty-one different test coatings (∼200−300 nm thick) applied to the nominally smooth steel discs. Contact angles are measured using a commercially available goniometer, whereas the average strengths of ice adhesion are evaluated with a custom-built laboratory-scale adhesion apparatus. The coatings investigated comprise commercially available polymers and fluorinated polyhedral oligomeric silsesquioxane (fluorodecyl POSS), a low-surface-energy additive known to enhance liquid repellency. Ice adhesion strength correlates strongly with the practical work of adhesion required to remove a liquid water drop from each test surface (i.e., with the quantity [1 + cos θrec]), and the average strength of ice adhesion was reduced by as much as a factor of 4.2 when bare steel discs were coated with fluorodecyl POSS-containing materials. We argue that any further appreciable reduction in ice adhesion strength will require textured surfaces, as no known materials exhibit receding water contact angles on smooth/flat surfaces that are significantly above those reported here (i.e., the values of [1 + cos θrec] reported here have essentially reached a minimum for known materials).