Mechanisms of rebound suppression of oil-in-water emulsion droplet on superhydrophobic surface

Mitigating the rebounding of pesticide droplets on superhydrophobic leaf is of great significance for improving pesticide utilization. The purpose of this study is to elucidate the physical mechanism by which oil-in-water emulsions suppress rebounding, analyze the effects of emulsion concentration, impact velocity and droplet diameter on the impact process, identify the critical Weber number at which rebound ceases, and provide theoretical guidance for spray application.

Four distinct outcomes were observed for droplet impact on superhydrophobic surfaces: complete rebound, partial rebound, transition, and adhesion. With increasing emulsion concentration, impact velocity, and droplet diameter, droplets were more likely to adhere to the superhydrophobic surface. When adhesion occurred, splashing was typically observed during the spreading stage, accompanied by satellite droplets separation during the retraction stage. When the emulsion concentration is less than or equal to 0.6%, the droplet impact outcomes can be categorized by the Weber number; the critical Weber number for droplets adhering to the superhydrophobic surface is 279.

The suppression of droplet rebounding is governed by a wetting-induced energy dissipation mechanism. Surface wetting increases the contact area between the droplet and the surface, which enhances frictional resistance and energy dissipation. The maximum spreading velocity and coefficient of droplets increase with impact velocity and droplet diameter; accordingly, greater shear gradients and wetted areas lead to higher viscous dissipation and frictional energy loss. Furthermore, larger droplet diameter and higher impact velocity reduce the droplet's resistance to deformation and breakup, resulting in satellite droplets separation and therefore greater energy loss. © 2026 Society of Chemical Industry.