2025-09-25 バース大学
Researchers found that it’s not just the surface or viscosity of droplets that determines their behaviour – they only bounce if they are at the right speed. (Credit: Jamie McLauchlan)
＜関連情報＞
- https://www.bath.ac.uk/announcements/why-tiny-droplets-stick-or-bounce-the-physics-of-speed-and-size/
- https://www.pnas.org/doi/10.1073/pnas.2507309122
疎水性表面上で跳ねる微小液滴 Bouncing microdroplets on hydrophobic surfaces
Jamie McLauchlan, Jim S. Walker, Vatsal Sanjay, +3 , and Anton Souslov
Proceedings of the National Academy of Sciences Published:September 4, 2025
DOI:https://doi.org/10.1073/pnas.2507309122
Significance
Microdroplets play a critical role in understanding disease transmission, industrial processes, and natural phenomena. We focus on microdroplet bouncing, which has been less explored compared to impingement of larger-scale drops. Using experiments and theory, we find a fundamental criterion that predicts whether a microdroplet will stick or bounce off a hydrophobic surface based on its incoming velocity. Our finding presents a fundamental limit to the deposition of fast-moving microdroplets and lays the groundwork for advances in aerosol and microfluidic technologies that leverage these dynamics.
Abstract
Intuitively, slow droplets stick to a surface and faster droplets splash or bounce. However, recent work suggests that on nonwetting surfaces, whether microdroplets stick or bounce depends only on their size and fluid properties, but not on the incoming velocity. Here, we show using theory and experiments that even poorly wetting surfaces have a velocity-dependent criterion for bouncing of aqueous droplets, which is as high as 6 m/s for diameters of 30 to 50 μm on hydrophobic surfaces such as Teflon. We quantify this criterion by analyzing the interplay of dissipation, surface adhesion, and incoming kinetic energy, and describe a wealth of associated phenomena, including air bubbles and satellite droplets. Our results on inertial microdroplets elucidate fundamental processes crucial to aerosol science and technology.
