Development of Hydrophobic Surfaces for Anti-Icing Applications

Prevention of ice formation is an important yet dicult task for many industries operating under freezing conditions, such as aeronautics and the oil industry. Ice accumulation can severely limit the operational eciency, life-time, and safety of constructions and materials exposed to such conditions. Current techniques to combat ice accumulation are highly expensive with respect to both equipment and manpower. The development of hydrophobic surfaces with anti-icing properties, which hinders or limits ice accumulation from the outset by being highly water-repellent, is an appealing solution and is the approach taken in this master's thesis. Such surfaces must have both a favorable surface chemistry and a favorable surface topography. In this work, spherical silicon dioxide (silica) nanoparticles have been synthesized by a sol-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) wafer substrates, as well as sandblasted 316-steel substrates, to achieve a hierarchical surface structure of both micro- and nanoroughness. When combined with a uorosilane-based coating, the substrates are shown to be hydrophobic by contact angle measurements. The highest contact angle achieved was 162.3 1.2 on a steel substrate with hierarchical surface 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 supercooled water, in the form of droplets, under freezing conditions (-20 C). Anti-icing properties such as delay of ice formation and water droplet roll-o were observed. The substrates with the best hydrophobic properties (i.e. highest contact angle and lowest contact angle hysteresis) showed the best anti-icing properties, suggesting a correlation between the two. However, the hydrophobic properties of the substrates were observed to deteriorate under the freezing conditions, compared to room temperature, allowing supercooled water to stick to the surfaces. This is attributed to a change in wetting state, and shows that further improvements must be made.