The utilization of T-junction microchannels with different lengths of branches is considered as the preferred method for asymmetric splitting to generate microdroplets with various sizes. In this study, a T-junction microfluidic chip with different-length branches is designed and an experimental platform is set up to visualize droplet asymmetric splitting in the chip, with a focus on elucidating microfluidic droplet asymmetric splitting behaviors. Through detailed analysis of the interface evolution and changing of the characteristic interface morphological parameters during the splitting process, the splitting flow patterns are clearly recognized and the underlying hydrodynamic mechanisms are revealed. Moreover, the influencing factors and their regulation rules on the asymmetric splitting volume ratios are also exposed. The results indicate that there are four types of flow patterns during droplet asymmetric splitting, i.e., splitting with obstruction and tunnel (SOT), splitting with tunnels and consequent droplets flowing in the opposite direction (ST-O), splitting with tunnels and consequent droplets flowing in the same direction (ST-S), and no splitting (NOS). A phase diagram of droplet splitting flow patterns is given. With the increasing initial droplet length for a given Capillary number, the splitting flow pattern experiences a transition from the NOS to the SOT through the ST-S and the ST-O. The splitting process comprises three distinct stages: the entering stage, the squeezing and splitting stage, and the post-splitting stage. During the squeezing and splitting stage, the competition of upstream continuous phase squeezing and interfacial tension causes asymmetric splitting by uneven shrinkage of the droplet neck. Additionally, it is found that the droplet final splitting volume ratio (Vl/Vs) increases with droplet length in the SOT flow pattern, while it decreases with droplet length in the ST-O and ST-S flow patterns. Importantly, the final Vl/Vs of the SOT pattern remains similar with increasing Ca for the same droplet length. However, the final Vl/Vs of the ST-O and ST-S pattern decreases with increasing Ca.

中文翻译：

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不同长度支管的液滴通过 T 型结的不对称分裂行为研究


利用具有不同分支长度的 T 型连接微通道被认为是不对称分裂产生各种大小的微液滴的首选方法。在本研究中，设计了具有不同长度分支的 T 型连接微流控芯片，并建立了一个实验平台来可视化芯片中的液滴不对称分裂，重点是阐明微流控液滴不对称分裂行为。通过对劈裂过程中界面演化和特征界面形态参数变化的详细分析，可以清晰地识别劈裂流模式，揭示潜在的水动力机制。此外，还揭示了影响不对称分裂体积比的因素及其调控规律。结果表明，液滴不对称分裂过程中存在四种类型的流型，即与障碍物和隧道一起分裂 （SOT）、与隧道和随之而来的液滴反向流动 （ST-O）、与隧道和随之而来的同向流动的液滴一起分裂 （ST-S） 和不分裂 （NOS）。给出了液滴分裂流型的相图。随着给定毛细管编号的初始液滴长度的增加，分流流型会通过 ST-S 和 ST-O 从 NOS 过渡到 SOT。劈裂过程包括三个不同的阶段：进入阶段、挤压和分裂阶段以及后分裂阶段。在挤压劈裂阶段，上游连续相挤压和界面张力的竞争导致液滴颈部收缩不均匀导致不对称分裂。 此外，研究发现，在 SOT 流型中，液滴最终分裂体积比 （V l/V s） 随液滴长度的增加而增加，而在 ST-O 和 ST-S 流型中，液滴最终分裂体积比 （V_l/V_s） 随液滴长度的增加而减小。重要的是，对于相同的液滴长度，SOT 模式的最终 V_l/V_s 与增加 Ca 保持相似。然而，ST-O 和 ST-S 模式的最终 V_l/V_s 随着 Ca 的增加而降低。