Effect of Surfactants on Longevity of Submerged Superhydrophobic Surfaces

The gas trapped on a submerged superhydrophobic surface (SHS) could diffuse into the surrounding liquid, reducing the SHS longevity. Although surfactants are known to inhibit mass transfer between gas and liquid phases, their influence on SHS longevity remains unclear. In this work, we experimentally investigate the effect of surfactants on the mass transfer from the SHS to the surrounding liquid and the resulting SHS longevity. Four surfactants, 1-pentanol, Triton X-100, 2-propanol, and methanol, were tested over a range of concentrations and on three types of SHS texture geometries: microholes, microposts, and a randomly roughed texture. We found that at sufficiently high surfactant concentrations, the SHS longevity decreased significantly due to a sudden wetting transition triggered probably by surface energy minimization. In contrast, at low surfactant concentrations, the SHS longevity was larger than that in pure water and increased with an increasing surfactant concentration. This extended SHS longevity was observed for all four surfactants and across all three texture geometries. Our results demonstrate the universal role of surfactants in reducing the mass transfer coefficient and highlight the importance of accounting for surfactants when assessing the SHS longevity in real-world applications.