Surface roughness control of water-air dynamic contact angle hysteresis on metal substrates

Ice adhesion measurements for impact ice are critical for solving important aerospace challenges. Previous measurements have shown that the ice adhesion on surfaces of apparently identical materials differ significantly under similar measuring conditions. This striking observation indicates that surface properties, e.g. roughness, may significantly affect ice formationand its adhesion response. Roughness properties can regulate the water-air-substrate contact-line dynamics. In this work, we focus on water-air contact angle hysteresis on metal substrates of interest, e.g. aluminum, using a pendant-drop system over a frequency range 0.1-10 Hz. Surface roughness of metal substrates is measured using confocal microscope profilometry. To establish a quantitative correlation between roughness and contact angle hysteresis, we analyzed the spatial roughness correlation function, including its angular dependency. Contact angle hysteresis results reveal a weak dependency on frequency, but a strong function on anisotropy, spatial correlation and surface roughness. The effect depends highly on drop size, which might explain differences in ice accretion under atmospheric conditions.