Development of Hydrophobic Surfaces for Anti-Icing Applications
Abstract
Prevention of ice formation is an important yet dicult task for many industries operatingunder freezing conditions, such as aeronautics and the oil industry. Ice accumulationcan severely limit the operational eciency, life-time, and safety of constructions andmaterials exposed to such conditions. Current techniques to combat ice accumulationare highly expensive with respect to both equipment and manpower. The developmentof hydrophobic surfaces with anti-icing properties, which hinders or limits ice accumulationfrom the outset by being highly water-repellent, is an appealing solution and is theapproach taken in this master's thesis. Such surfaces must have both a favorable surfacechemistry and a favorable surface topography.In this work, spherical silicon dioxide (silica) nanoparticles have been synthesized by asol-gel process to yield three dierent size distributions of 40 5 nm, 81 7 nm, and 221 8 nm. The nanoparticles have been deposited, by dip-coating, on silicon (100) wafersubstrates, as well as sandblasted 316-steel substrates, to achieve a hierarchical surfacestructure of both micro- and nanoroughness. When combined with a uorosilane-basedcoating, the substrates are shown to be hydrophobic by contact angle measurements. Thehighest contact angle achieved was 162.3 1.2 on a steel substrate with hierarchicalsurface structure, obtained by combining sandblasting with 221 nm silica nanoparticles.The contact angle hysteresis of this substrate was measured to be 19.9 2.9.The icing characteristics of the substrates were investigated by exposing them to supercooledwater, in the form of droplets, under freezing conditions (-20 C). Anti-icingproperties such as delay of ice formation and water droplet roll-o were observed. Thesubstrates with the best hydrophobic properties (i.e. highest contact angle and lowestcontact angle hysteresis) showed the best anti-icing properties, suggesting a correlationbetween the two. However, the hydrophobic properties of the substrates were observedto deteriorate under the freezing conditions, compared to room temperature, allowing supercooledwater to stick to the surfaces. This is attributed to a change in wetting state,and shows that further improvements must be made.