标题： 表面活性剂诱导的微流体限制中液滴横向迁移的滞缓效应 显示英文标题

标题： Surfactant-induced-retardation in lateral migration of droplets in a microfluidic confinement

摘要： 在本研究中，通过实验和理论方法研究了表面活性剂对液滴横向迁移的作用。 在实验分析中，向日葵油用作连续相，去离子水作为分散相，并与作为表面活性剂的Triton X-100混合。 在微通道中使用T型接头用于生成液滴。 施加的压力驱动流的存在导致液滴变形并破坏平衡，从而引起界面处的表面活性剂再分布。 这进一步在表面张力上产生梯度，从而产生马兰戈尼应力，显著改变液滴的动力学行为。 在后续的实验研究中发现，表面活性剂的存在会降低液滴的横向迁移速度。 此外，研究表明，在相同的时间范围内，与较小的液滴相比，较大的液滴在表面活性剂作用下其横向迁移的减少效果更为显著，前提是通道高度保持不变。 此外，发现较大的表面活性剂浓度会加剧液滴的横向迁移延迟，当液滴的初始横向位置更接近通道中心线时，这种影响会减弱。 本分析可以应用于各种基于液滴的微流控设备以及医学诊断设备，其中液滴轨迹的操控是一个主要问题。 在理论方面，采用渐近方法，在体相不溶性表面活性剂存在且假设流体惯性可忽略的情况下进行分析。 我们的理论预测与实验结果之间有很好的吻合。 显示英文摘要

摘要： In the present study, the role of surfactants on the cross-stream migration of droplets is investigated both experimentally and theoretically. For experimental analysis, sunflower oil is used as the carrier phase and DI water as the dispersed phase which is intermixed with Triton X-100 that acts as the surfactant. A T-junction is used in the microchannel for the purpose of droplet generation. Presence of an imposed pressure driven flow induces droplet deformation and disturbs the equilibrium that results in subsequent surfactant-redistribution along the interface. This further induces a gradient in the surface tension, thus generating a Marangoni stress that significantly alters the droplet dynamics. On subsequent experimental investigation, it is found that presence of surfactants reduces the cross-stream migration velocity of the droplet. Further, it is shown that the effect of surfactants in reducing the cross-stream migration is significantly enhanced for a larger droplet as compared to a smaller one within the same time span, provided the channel height is kept constant. In addition, a larger surfactant concentration is found to induce a greater retardation in cross-stream migration of the droplet, the effect of which is reduced when the initial transverse position of the droplet is shifted closer to the channel centerline. The present analysis can be applied to various droplet based microfluidic as well as medical diagnostic devices where manipulation of droplet trajectory is a major issue. For the theoretical counterpart, an asymptotic approach is adopted in the presence of bulk-insoluble surfactants and under the assumption of negligible fluid inertia. A good match between our theoretical prediction and the experimental results is obtained.