Polytetrafluoroethylene (PTFE) chemically repels water droplets due to the nature of fluorine substituents. This paper presents an experimental study on the impact of PTFE particle size and temperature on the hydrophobicity of a surface. The present study analyzes hydrophobicity due to both the chemical properties of PTFE and the microstructure created by PTFE particles. Herein, studies of the contact angle and the sliding angle of these surfaces are described in supercooled-water conditions ranging from −10 to 0 °C. From the equations governing the surface tension and sliding angle of a droplet on a superhydrophobic surface, it is found that particle size has a much greater effect on hydrophobicity than temperature. An increase in the PTFE particle size greatly reduces the sliding angle, which indicates a lower amount of energy required to remove the droplet from the surface.

Ice accretion is detrimental to numerous industries, including infrastructure, power generation, and aviation applications. Currently, some of the leading de-icing technologies utilize a heating source coupled with a superhydrophobic surface. This superhydrophobic surface reduces the power consumption by the heating element. Further power consumption reduction in these systems can be achieved through an increase in passive heat generation through absorption of solar radiation. In this work, a superhydrophobic surface with increased solar radiation absorption is proposed and characterized. An existing icephobic surface based on a polytetrafluoroethylene (PTFE) microstructure was modified through the addition of graphite microparticles. The proposed surface maintains hydrophobic performance nearly identical to the original superhydrophobic coating as demonstrated by contact and roll-off angles within 2.5% of the original. The proposed graphite coating also has an absorptivity coefficient under exposure to solar radiation 35% greater than typical PTFE-based coatings. The proposed coating was subsequently tested in an icing wind tunnel, and showed an 8.5% and 50% decrease in melting time for rime and glaze ice conditions, respectively.

View Video Presentation: https://doi.org/10.2514/6.2022-3370.vid A novel optical temperature sensor based on embedding 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium, also known as pyranine, within ice is developed. Pyranine, depending on solution conditions, emits light with peaks of both 440nm and 511nm. The ratio of intensities of these two peaks within ice is coupled with local ice temperature. The sensor is illuminated using 365nm illumination and the fluorescence intensity ratio of the 440nm and 511nm emission peaks of pyranine is studied as a function of temperature and phase change in the range 258-293K. By using this ratio, the temperature and phase changes within an ice block are measured in a temporally and spatially resolved manner. The temperature sensitivity within the ice phase is -9.2 ± .1%/K which is better than conventionally used fluorescence based temperature sensors. This sensor is used to capture dynamic changes in temperature and phase and can be applied to the study of aicraft icing and ablation studies. The pyranine sensor is a promising candidate for an optical temperature sensor with high sensitivity within bulk ice.