Cui Yongjin, Li Yankai, Wang Kai, Deng Jian, Luo Guangsheng
State Key Laboratory of Chemical Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China.
Langmuir. 2020 Nov 17;36(45):13633-13641. doi: 10.1021/acs.langmuir.0c02459. Epub 2020 Nov 4.
Liquid-liquid dispersion coupled with droplet formation and mass transfer of surfactants is one of the most typical phenomena in many chemical processes. As in every aspect of this process, the interfacial tension variation caused by the unsaturated adsorption of surfactants on the droplet surface plays an important role. This article focuses on microdroplet formation and the dynamic interfacial behavior of surfactants in the jetting regime. In a capillary embedded step T-junction device, controllable preparation of monodisperse droplets is achieved, and a correlation for predicting droplet sizes is established. A method for measuring the dynamic interfacial tension is provided. Mass transfer coefficients are then calculated for Tween 20 during the droplet formation process by a semiempirical correlation. The results indicate that dynamic interfacial tensions are lower than those obtained when the surfactant is adsorbed to equilibrium. Based on the tip-streaming phenomenon, mass transfer coefficients for Tween 20 can reach up to ∼10 m/s, higher than those obtained in coaxial microfluidic devices. All the preliminary results shed light on the nature of droplet formation and will be of significance for application in industrial apparatuses.
液-液分散以及液滴形成和表面活性剂的传质是许多化学过程中最典型的现象之一。在这个过程的各个方面，表面活性剂在液滴表面的不饱和吸附所引起的界面张力变化都起着重要作用。本文重点研究喷射模式下的微滴形成以及表面活性剂的动态界面行为。在毛细管嵌入式阶梯T型结装置中，实现了单分散液滴的可控制备，并建立了预测液滴尺寸的关联式。提供了一种测量动态界面张力的方法。然后通过半经验关联式计算吐温20在液滴形成过程中的传质系数。结果表明，动态界面张力低于表面活性剂吸附达到平衡时的界面张力。基于尖端流现象，吐温20的传质系数可达~10 m/s，高于在同轴微流控装置中获得的传质系数。所有这些初步结果揭示了液滴形成的本质，对工业设备中的应用具有重要意义。
