Colloidal Suppression of Droplet Jumping on Superhydrophobic Surfaces in Microgravity

Droplets resting on superhydrophobic substrates can spontaneously "jump" under microgravity as stored surface energy converts rapidly into kinetic energy during release. Introducing colloidal particles alters this dynamic by increasing viscous damping, modifying interfacial tension, and promoting contact line pinning. In this study, aluminum substrates coated with multilayer carbon soot (static contact angle ≈163° ± 1.5°) were used to investigate droplet rebound behavior in microgravity. Deionized and polystyrene colloidal droplets (100 nm and 1000 nm; 0.001 and 0.01 vol. fractions) were tested using NASA Glenn Research Center's 2.2-s drop tower. Of seven deionized tests, three exhibited successful capillary-driven jumping, while no colloidal droplets detached. Spectral analysis of inhibited droplets using discrete Fourier transforms revealed dominant oscillatory modes consistent with increased damping and interfacial energy loss. These findings indicate that even dilute colloidal suspensions can suppress droplet detachment through enhanced viscosity and particle-induced pinning. Continuing work will include quantifying receding contact angles, viscosity measurements, and performing controlled bounce experiments to determine the relative roles of dissipation, pinning, and surface tension modification.