On the (in)equality of droplet rebound dynamics at fixed Weber number

Berce, Jure (author), Golobič, Iztok (author)

The similarity of droplet impacts on nature-mimicking superhydrophobic surfaces is traditionally compared using the dimensionless Weber number. Yet, maintaining a constant We by decoupling droplet diameter and impact velocity influences secondary forces, challenging this assumption of similarity. In this work, we investigate water droplet impacts on a lotus-leaf-mimicking laser-textured superhydrophobic aluminum surface at two constant Weber number levels (25 and 50), varying droplet diameter from 2.1 to 4.15 mm. Our results confirm that maximum spreading depends on the Reynolds number at a fixed We, as smaller, faster droplets spread less due to increased relative viscous dissipation. We propose a modified empirical scaling model that describes our data with high accuracy and generalizes successfully to external datasets. Crucially, we demonstrate that the contact time of a droplet of a given size is not strictly velocity-independent, unveiling a Weber number-dependent inertia-capillary scaling. We show that this is driven by a shift in rebound dynamics, where the relative timescale of spreading increases over retraction for larger droplets. These findings demonstrate that We is insufficient to characterize droplet rebound across varying scales and that accounting for size-dependent deviations is critical for the precise design of technologies that leverage droplet-surface interactions.

• Language: English
• Keywords: droplet rebound, superhydrophobic surface, Weber number, rebound dynamics, maximum spreading coefficient, contact time
• Work type: Article
• Typology: 1.01 - Original Scientific Article
• Organization: FS - Faculty of Mechanical Engineering
• Publication status: Published
• Publication version: Version of Record
• Year: 2026
• Number of pages: 15 str.
• Numbering: Vol. 11, iss. 9, art. 640
• PID: 20.500.12556/RUL-186914
• UDC: 532.21:544.722.132
• ISSN on article: 2313-7673
• DOI: 10.3390/biomimetics11090640
• COBISS.SI-ID: 290161411
• Publication date in RUL: 07.09.2026

Record is a part of a journal

• Title: Biomimetics
• Shortened title: Biomimetics
• Publisher: MDPI
• ISSN: 2313-7673
• COBISS.SI-ID: 526328601

Licences

• License: CC BY 4.0, Creative Commons Attribution 4.0 International
• Link: http://creativecommons.org/licenses/by/4.0/
• Description: This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.

Secondary language

• Language: Slovenian
• Keywords: odboj kapljice, superhidrofobne površine, Webrovo število, dinamika odboja, maksimalni koeficient širjenja, kontaktni čas

Projects

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: P2-0223
• Name: Prenos toplote in snovi

• Funder: ARIS - Slovenian Research and Innovation Agency
• Project number: J2-50085
• Name: Raziskave medfaznih pojavov kapljic in mehurčkov na funkcionaliziranih površinah ob uporabi napredne diagnostike za razvoj okoljskih tehnologij prihodnosti in izboljšanega prenosa toplote (DroBFuSE)