F. Freese, A. Schwarzwälder, U. Janoske, A. Dittler

Separation and Purification Technology, 2025, Volume 376, Part 2, 133834, https://doi.org/10.1016/j.seppur.2025.133834

This study examines the interaction between single oil droplets and an oleophobic fiber subjected to sinusoidal mechanical excitation, with particular emphasis on the vibrational effects on the resulting droplet motion patterns. The research combines experiments providing high-speed images and CFD simulations, employing a dynamic overset grid technique, to explore various droplet motion patterns, such as pumping, swinging, vertical oscillation, rotation, and collapsing. A key finding is that fiber oscillation induces a lasting transformation, whereby clamshell-shaped droplets—typically seen on oleophobic fibers—permanently adopt a barrel shape, characteristic of oleophilic fibers, even after the excitation ceases. Despite differences in wettability, oil droplets exhibit similar motion patterns on both fiber types after their transition and prior to detachment. The results highlight the importance of droplet dynamics for optimizing coalescence and drainage in industrial settings.