Abstract A thorough understanding of the collision motions and involved hydrodynamic behaviors of double emulsion droplets under the influence of an external flow is important for the design and fabrication of a core–shell structured chemical product via droplet-based fluidic processing. In this study, experimental observations are combined with numerical simulation to analyze the hydrodynamic binary collision between double emulsion droplets under shear. The passing-over motion of the colliding droplets is observed and quantitatively characterized by providing the motion trajectories and temporal droplet deformation. In particular, because of an additional interaction induced by the inner droplet, we demonstrate that the double emulsion droplets exhibit similar motion trajectories but different deformation development versus ordinary single-phase ones throughout the collision process. Additionally, the increase in confinement (i.e. the decrease in spacing gap between two parallel moving walls in the typical Couette shear geometry) is found to induce a higher shear rate and larger elongational components at the tips of the deformed double emulsion droplets, which produce further stretched colliding droplets.

中文翻译：

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双乳液滴在剪切作用下二元碰撞过程中的越过运动

摘要 彻底了解在外部流动影响下双乳液液滴的碰撞运动和相关流体动力学行为对于通过基于液滴的流体处理设计和制造核壳结构的化学产品非常重要。在这项研究中，实验观察与数值模拟相结合，分析了剪切作用下双乳液液滴之间的流体动力学二元碰撞。通过提供运动轨迹和时间液滴变形来观察碰撞液滴的通过运动并定量表征。特别是由于内部液滴引起的额外相互作用，我们证明了双乳液液滴在整个碰撞过程中表现出相似的运动轨迹，但与普通单相液滴相比，变形发展不同。此外，发现限制的增加（即典型的库埃特剪切几何中两个平行移动壁之间的间距减小）会在变形的双乳液液滴的尖端引起更高的剪切速率和更大的伸长分量，从而进一步产生拉伸碰撞液滴。