Impact of droplets onto surfactant-laden thin liquid films
Impact of droplets onto surfactant-laden thin liquid films
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DOI：
10.1017/jfm.2023.224
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发表时间：
2022-10
影响因子：
3.7
通讯作者：
C. Constante-Amores;L. Kahouadji;S. Shin;J. Chergui;D. Juric;J. Castrejón-Pita;O. Matar;A. A. Castrej
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文献类型：
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作者：
C. Constante-Amores;L. Kahouadji;S. Shin;J. Chergui;D. Juric;J. Castrejón-Pita;O. Matar;A. A. Castrej
摘要：考虑表面活性剂浓度梯度引起的表面活性剂诱导的Marangoni应力，采用界面跟踪/水平集混合方法，采用全三维直接数值模拟方法，研究了不溶性表面活性剂对无表面活性剂液滴对负载表面活性剂薄膜的影响。我们对无表面活性剂冠的时间演化的数值预测得到了Che和Matar （Langmuir, vol. 33, 2017, pp. 12140-12148）实验工作的验证。我们关注的是“冠状-飞溅状态”，我们观察到冠状动力学的发展经历了不同的阶段：从线性模式的增长（通过瑞利-高原不稳定）到非线性的发展，导致初级和次级破裂事件（通过末端挤压机制调节的液滴脱落）。我们表明，表面活性剂的添加不影响波的选择通过瑞利-高原不稳定性。然而，表面活性剂的存在在动力学的后期阶段起着关键作用，一旦韧带从边缘被赶出来。表面活性剂诱导的马兰戈尼应力延迟末端挤压机制，导致韧带在毛细血管奇点之前变长。我们的结果表明，马兰戈尼应力弥合相邻突出之间的间隙，促进相邻突出的碰撞和韧带融合。最后，我们证明了表面活性剂的加入会导致表面硬化，从而导致流动动力学的延迟。
Abstract We study the effect of insoluble surfactants on the impact of surfactant-free droplets onto surfactant-laden thin liquid films via a fully three-dimensional direct numerical simulation approach that employs a hybrid interface-tracking/level-set method, and by taking into account surfactant-induced Marangoni stresses due to gradients in interfacial surfactant concentration. Our numerical predictions for the temporal evolution of the surfactant-free crown are validated against the experimental work by Che & Matar (Langmuir, vol. 33, 2017, pp. 12140–12148). We focus on the ‘crown-splash regime’, and we observe that the crown dynamics evolves through various stages: from the growth of linear modes (through a Rayleigh–Plateau instability) to the development of nonlinearities leading to primary and secondary breakup events (through droplet shedding modulated by an end-pinching mechanism). We show that the addition of surfactants does not affect the wave selection via the Rayleigh–Plateau instability. However, the presence of surfactants plays a key role in the late stages of the dynamics as soon as the ligaments are driven out from the rim. Surfactant-induced Marangoni stresses delay the end-pinching mechanisms to result in longer ligaments prior to their capillary singularity. Our results indicate that Marangoni stresses bridge the gap between adjacent protrusions promoting the adjacent protrusions' collision and the merging of ligaments. Finally, we demonstrate that the addition of surfactants leads to surface rigidification and consequently to the retardation of the flow dynamics.