78th Annual Meeting of the APS Division of Fluid Dynamics (Nov 23 — 25, 2025)

V056: Microbubbles entrapment in drop impact on thin liquid film

This video demonstrates that when drops impact thin liquid films, they generate radial trains of microbubbles-referred as large-area microbubbles (LAMs)-over regions comparable to the maximum spread of the impacting drop. By employing a thin viscous oil film, we immobilize the trapped bubbles and quantify their formation using high-speed imaging across a range of impact velocities and surface inclinations. This approach allows us to characterize microbubble entrainment, expressed as bubble density per unit area, in relation to drop inertia, visco-capillary interactions, and interfacial instabilities. The emergence of LAMs originates from the persistence of a thin intervening air layer and the onset of contact-line instabilities, reminiscent of classical coating processes. When wetting fails to initiate across the lubricating air film-for instance, during drop rebound-microbubble entrainment does not occur. Once a contact line is established, however, wetting instabilities generate slender air tubes that fragment via Rayleigh-type breakup, producing radial and azimuthal microbubble patterns beneath the thin air gap. Understanding of this work is essential for linking fundamental fluid mechanics to practical applications ranging from coating and printing processes to materials engineering.This work was published in Journal of Colloid and Interface Science.