Characterization method of hydrophobic anti-icing coatings

Abstract

For anti-icing, supercooled water should be removed before frozen onto the contact surface. We use a hydrophobic coating for anti-icing and introduce the static- and dynamic-evaluation methods. The methods describe the contact surface between the hydrophobic surface and a supercooled-water droplet. The former is based on the contact angle, and the latter is based on the sliding angle. The temperature factor is included in these models to evaluate the hydrophobic coating under the supercooled conditions. Four hydrophobic coatings are experimentally evaluated based on the static- and dynamic evaluation methods: C1-C3 (commercial fluorocarbon coatings), and Jaxa coating (original fluorocarbon coating). These are evaluated under the supercooled conditions of -10 to 0 °C. The static-evaluation shows variations in the temperature. However, change in the contact angle by the temperature is relatively small compared to that of the sliding angle for the dynamic evaluation. Only C3 and Jaxa coatings are tolerant to the sliding angle under the supercooled conditions tested. The dynamic evaluation shows that even if the coating is hydrophobic, the dynamic evaluation should be included to understand the characteristic of removal for a supercooled-water droplet.

Effect of PTFE Particle Size on Superhydrophobic Coating for Supercooled Water Prevention

“…All other external forces acting on the droplet can be included in net force, F. The contact angle, θ can be found by setting the net force acting on the droplet equal to 0. At the boundary points 1 and 2, where the gas, liquid, and solid phases exist, Equation (3) can be derived [14].…”

“…In this case, the contact angle at both edges of the droplet is the same and can be measured as a function of the work needed to remove the droplet, W, and the surface tension γ L , shown in Equation (4). The predicted measured contact angle, θ meas , is shown in Equation (5) [14] where W is the work of adhesion to the surface, and A s is the area of interaction between the fluid and the solid surface.…”

“…Previous studies have shown that a microstructure comprised of spherical polytetrafluoroethylene (PTFE) nanoparticles is able to produce a superhydrophobic surface, with contact angles greater than 140 • [10,11] such as the surface shown in Figure 1. PTFE coatings can be applied to virtually any surface, including metals, wood, and plastics either by electrolytic coating or by mixing PTFE particles with a polymer [12][13][14][15].…”

“…Contact angle is not the only way to measure the hydrophobicity of a surface. Sliding angle measures the force required to remove a droplet from a surface [14]. This angle, regardless of wetting conditions, is a direct measure of the amount of energy required to remove a droplet from a surface, which can be influenced by the size of PTFE particles.…”

“…Because the properties of the liquid-gas interface, as well as water properties can be influenced by fluid temperature [14], it is necessary to evaluate the hydrophobicity of surfaces over a wide temperature range. Morita and Sakaue [14] have developed a method for the characterization of the hydrophobicity of a surface using both static and dynamic testing. The static test relies on the contact angle of a droplet, while the dynamic test relies on the sliding angle.…”