Xu Huadan, Wang Tianyou, Che Zhizhao
State Key Laboratory of Engines, Tianjin University, Tianjin 300350, China.
State Key Laboratory of Engines, Tianjin University, Tianjin 300350, China.
J Colloid Interface Sci. 2022 Dec 15;628(Pt A):869-877. doi: 10.1016/j.jcis.2022.08.013. Epub 2022 Aug 6.
Droplet coalescence is a common phenomenon and plays an important role in many applications. When two liquid droplets are brought into contact, a liquid bridge forms and expands quickly. Different from miscible droplets, an extra immiscible interface exists throughout the coalescence of immiscible droplets and is expected to affect the evolution of the liquid bridge, which has not been investigated. We hypothesized that the liquid bridge of immiscible droplets exhibits a different growth dynamics.
We experimentally study the coalescence dynamics of immiscible droplets. The evolution of the liquid bridge is measured and compared with miscible droplets. We also propose a theoretical model to analyze the effects of immiscibility.
We find that immiscibility plays different roles in the viscous-dominated and inertia-dominated regimes. In the initial viscous-dominated regime, the coalescence of immiscible droplets follows the linear evolution of the bridge radius as that of miscible droplets. However, in the later inertia-dominated regime, the coalescence of immiscible droplets is slower than that of miscible droplets due to the water-oil interface. By developing a theoretical model based on the force balance, we show that this slower motion is due to the immiscible interface and the extra interfacial tension. In addition, a modified Ohnesorge number is proposed to characterize the transition from the viscous-dominated regime to the inertia-dominated regime.
液滴聚并是一种常见现象，在许多应用中起着重要作用。当两个液滴接触时，会形成一个液桥并迅速扩展。与可混溶液滴不同，在不混溶液滴聚并的整个过程中存在一个额外的不混溶界面，预计该界面会影响液桥的演变，但尚未对此进行研究。我们假设不混溶液滴的液桥表现出不同的生长动力学。
我们通过实验研究不混溶液滴的聚并动力学。测量液桥的演变并与可混溶液滴进行比较。我们还提出了一个理论模型来分析不混溶性的影响。
我们发现不混溶性在粘性主导和惯性主导的区域中发挥着不同的作用。在初始粘性主导区域，不混溶液滴的聚并遵循与可混溶液滴相同的桥半径线性演变。然而，在后期惯性主导区域，由于水 - 油界面，不混溶液滴的聚并比可混溶液滴慢。通过基于力平衡建立一个理论模型，我们表明这种较慢的运动是由于不混溶界面和额外的界面张力。此外，还提出了一个修正的奥内佐格数来表征从粘性主导区域到惯性主导区域的转变。
