Tran H, He Z, Pack M Y
Department of Mechanical Engineering, Baylor University, One Bear Place #97356, Waco, 76798, TX, United States.
Department of Chemical Engineering and Materials Science, University of Minnesota, 100 Church Street SE, 55455, Minneapolis, MN, United States.
J Colloid Interface Sci. 2025 Mar 15;682:915-923. doi: 10.1016/j.jcis.2024.11.236. Epub 2024 Dec 5.
This study reveals how drops impacting thin liquid films leave behind radial microbubble trains - here defined as large-area microbubbles (LAMs) - over a region comparable to the maximal surface coverage of the spreading phase. Using a thin, minimally compliant viscous oil film, the trapped bubbles are immobilized and quantified via high-speed imaging techniques across varying drop velocities and surface inclinations. The setup enables the characterization of microbubble entrainment (e.g., bubbles per unit area) as a function of the drop inertia, visco-capillary dynamics, and fluid instabilities. The formation of LAMs is driven by a thin intervening air gap and contact line instability, analogous to classic coating instabilities. Microbubble entrainment is absent if intermolecular forces fail to initiate wetting across the lubricating air layer (e.g., drop bouncing). Once the contact line forms, wetting instabilities induce air tubes to become unstable via the Rayleigh instability, leading to radial and azimuthal microbubble coverage under the thin air gap.
本研究揭示了液滴撞击薄液膜时如何在与铺展阶段最大表面覆盖率相当的区域留下径向微气泡序列——这里定义为大面积微气泡（LAMs）。使用薄的、顺应性极小的粘性油膜，通过高速成像技术在不同的液滴速度和表面倾斜度下对捕获的气泡进行固定和量化。该装置能够将微气泡夹带（例如单位面积的气泡数）表征为液滴惯性、粘毛细动力学和流体不稳定性的函数。LAMs的形成是由薄的中间气隙和接触线不稳定性驱动的，类似于经典的涂层不稳定性。如果分子间力未能引发跨越润滑空气层的润湿（例如液滴反弹），则不会发生微气泡夹带。一旦接触线形成，润湿不稳定性会通过瑞利不稳定性使空气管变得不稳定，从而在薄气隙下导致径向和方位向的微气泡覆盖。
