Yanagisawa Naoya, Tani Marie, Kurita Rei
Department of Physics, Tokyo Metropolitan University, 1-1 Minamioosawa, Hachiouji-Shi, Tokyo 192-0397, Japan.
Soft Matter. 2021 Feb 21;17(7):1738-1745. doi: 10.1039/d0sm02153a. Epub 2021 Feb 17.
Foams have unique properties that distinguish them from ordinary liquids and gases, and are ubiquitously observed in nature, both in biological systems and industrial products. Foams are known to eventually collapse over time; given their wide-range industrial application, understanding how bubbles in a foam collapse is an important aspect for product longevity and tailoring physical properties. Previously, it was shown that droplets are emitted during the collective bubble collapse, however the mechanism of the droplet emission in a foam is not yet clearly understood. It is directly related to the stability of the foam, thus we quantitatively investigate collapse dynamics in liquid films in a foam, and identify some unique features. When one film breaks, we see that the oscillation of the vertical Plateau border to which it is connected induces anomalous liquid transport from the edge of the border to the center. Once a crack appears near the border and a collapse front is formed, we find that the curvature of the front reverses as it migrates, followed by the emergence and emission of droplets. We elucidate the origins of this behavior and discuss the stability of foams, establishing how the characteristic time scales of the process relate to each other.
泡沫具有独特的性质，使其有别于普通液体和气体，并且在自然界中广泛存在，无论是在生物系统还是工业产品中。众所周知，泡沫最终会随着时间的推移而坍塌；鉴于其广泛的工业应用，了解泡沫中的气泡如何坍塌是影响产品寿命和定制物理性能的一个重要方面。此前，研究表明在气泡集体坍塌过程中会有液滴喷出，然而泡沫中液滴喷出的机制尚未完全清楚。这与泡沫的稳定性直接相关，因此我们定量研究了泡沫中液膜的坍塌动力学，并确定了一些独特的特征。当一层液膜破裂时，我们发现与之相连的垂直Plateau边界的振荡会引发从边界边缘到中心的异常液体传输。一旦在边界附近出现裂缝并形成坍塌前沿，我们发现前沿在迁移时曲率会反转，随后液滴出现并喷出。我们阐明了这种行为的起源，并讨论了泡沫的稳定性，确定了该过程的特征时间尺度之间的相互关系。
