Droplet impact of emulsions on inclined microstructured surfaces
Abstract
Droplet impacts rarely occur on horizontal smooth surfaces, yet the combined influence of surface inclination, microstructure, and fluid composition remains poorly understood for emulsions. Here, we experimentally investigate the impact of 20% (v/v) silicone oil-in-water emulsion droplets on smooth glass and micropillar arrays with two interpillar spacings (50 and 100 μm) inclined at 55∘. The role of surface wettability is further examined using a superhydrophobic coating. High-speed imaging is employed to characterise the impact dynamics over a wide range of Weber numbers (18 ≤ We ≤ 565), while optical microscopy is used to quantify the residual wetted area after impact. Five impact regimes are identified: deposition, sliding, partial rebound, complete rebound, and splashing. Surface inclination introduces asymmetry in spreading and recoil, whereas microstructured substrates reduce adhesion and promote rebound by decreasing the liquid-solid contact area. In contrast to water, the emulsion exhibit enhanced deposition on smooth surfaces, increased sliding on uncoated microstructures, and earlier ligament formation and secondary breakup at high Weber numbers. The dispersed oil phase locally modifies wetting and lubrication, producing liquid bridges, heterogeneous recoil, and larger residual wetted areas on smooth substrates. On microstructured surfaces, however, capillary confinement within the texture limits the projected wetted area despite increased liquid retention inside the microstructure. These results demonstrate that the impact behaviour of emulsions cannot be predicted solely from conventional dimensionless groups, as local phase redistribution fundamentally alters energy dissipation, wetting, and fragmentation. The findings provide new insight into spray deposition on inclined textured surfaces relevant to agricultural spraying and coating technologies.
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BibTeX
@misc{rosalesgallegos2026droplet,
title = {{Droplet impact of emulsions on inclined microstructured surfaces}},
author = {Ulises Rosales-Gallegos and Laura Oropeza-Ramos and Francisco Manuel Sánchez-Arévalo and Miguel A. Quetzeri-Santiago},
howpublished = {arXiv},
year = {2026},
month = aug,
doi = {10.48550/arxiv.2608.29342},
eprint = {2608.29342},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.29342},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Droplet impact of emulsions on inclined microstructured surfaces
AU - Ulises Rosales-Gallegos
AU - Laura Oropeza-Ramos
AU - Francisco Manuel Sánchez-Arévalo
AU - Miguel A. Quetzeri-Santiago
PY - 2026
DA - 2026/08/29
PB - arXiv
DO - 10.48550/arxiv.2608.29342
UR - https://arxiv.org/abs/2608.29342
AB - Droplet impacts rarely occur on horizontal smooth surfaces, yet the combined influence of surface inclination, microstructure, and fluid composition remains poorly understood for emulsions. Here, we experimentally investigate the impact of 20% (v/v) silicone oil-in-water emulsion droplets on smooth glass and micropillar arrays with two interpillar spacings (50 and 100 μm) inclined at 55^∘. The role of surface wettability is further examined using a superhydrophobic coating. High-speed imaging is employed to characterise the impact dynamics over a wide range of Weber numbers (18 ≤ We ≤ 565), while optical microscopy is used to quantify the residual wetted area after impact. Five impact regimes are identified: deposition, sliding, partial rebound, complete rebound, and splashing. Surface inclination introduces asymmetry in spreading and recoil, whereas microstructured substrates reduce adhesion and promote rebound by decreasing the liquid-solid contact area. In contrast to water, the emulsion exhibit enhanced deposition on smooth surfaces, increased sliding on uncoated microstructures, and earlier ligament formation and secondary breakup at high Weber numbers. The dispersed oil phase locally modifies wetting and lubrication, producing liquid bridges, heterogeneous recoil, and larger residual wetted areas on smooth substrates. On microstructured surfaces, however, capillary confinement within the texture limits the projected wetted area despite increased liquid retention inside the microstructure. These results demonstrate that the impact behaviour of emulsions cannot be predicted solely from conventional dimensionless groups, as local phase redistribution fundamentally alters energy dissipation, wetting, and fragmentation. The findings provide new insight into spray deposition on inclined textured surfaces relevant to agricultural spraying and coating technologies.
ER -