Ryu Sangjin, Zhang Haipeng, Anuta Udochukwu John
Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588, USA.
Nebraska Center for Materials and Nanoscience, University of Nebraska-Lincoln, Lincoln, NE 68588, USA.
Micromachines (Basel). 2023 Oct 31;14(11):2046. doi: 10.3390/mi14112046.
The surface-tension-driven coalescence of drops has been extensively studied because of the omnipresence of the phenomenon and its significance in various natural and engineering systems. When two drops come into contact, a liquid bridge is formed between them and then grows in its lateral dimensions. As a result, the two drops merge to become a bigger drop. The growth dynamics of the bridge are governed by a balance between the driving force and the viscous and inertial resistances of involved liquids, and it is usually represented by power-law scaling relations on the temporal evolution of the bridge dimension. Such scaling laws have been well-characterized for the coalescence of unconfined or freely suspended drops. However, drops are often confined by solid or liquid surfaces and thus are a different shape from spheres, which affects their coalescence dynamics. As such, the coalescence of confined drops poses more complicated interfacial fluid dynamics challenges compared to that of unconfined drops. Although there have been several studies on the coalescence of confined drops, they have not been systematically reviewed in terms of the properties and geometry of the confining surface. Thus, we aim to review the current literature on the coalescence of confined drops in three categories: drop coalescence on a solid surface, drop coalescence on a deformable surface, and drop coalescence between two parallel surfaces with a small gap (i.e., Hele-Shaw cell), with a focus on power-law scaling relations, and to suggest challenges and outlooks for future research on the phenomena.
由于液滴表面张力驱动的聚并现象普遍存在且在各种自然和工程系统中具有重要意义，因此已得到广泛研究。当两个液滴接触时，它们之间会形成一个液桥，然后液桥的横向尺寸会增大。结果，两个液滴合并成一个更大的液滴。液桥的生长动力学受驱动力与相关液体的粘性和惯性阻力之间的平衡支配，通常用液桥尺寸随时间演化的幂律标度关系来表示。这种标度律已在无约束或自由悬浮液滴的聚并中得到很好的表征。然而，液滴常常受到固体或液体表面的限制，因此其形状与球体不同，这会影响它们的聚并动力学。因此，与无约束液滴相比，受限液滴的聚并带来了更复杂的界面流体动力学挑战。尽管已经有几项关于受限液滴聚并的研究，但尚未从约束表面的性质和几何形状方面进行系统综述。因此，我们旨在从三个类别综述当前关于受限液滴聚并的文献：固体表面上的液滴聚并、可变形表面上的液滴聚并以及两个具有小间隙的平行表面（即赫勒-肖细胞）之间的液滴聚并，重点关注幂律标度关系，并提出该现象未来研究的挑战和展望。
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