同轴流动下双乳液滴的生成机理及控比分裂特性研究

The droplet-based microfluidic technique has attracted widespread interest, attributed to the advantages such as a small volume of reagents consumed, the fast reaction and the independent control of each droplet. Among them, the unique core - shell structure of double emulsion droplets can effectively protect the reaction products in the core and provide an important carrier for the precise handling of multi-component droplets. The size and throughput of the emulsion droplets are important parameters in the application that are mainly regulated by the generation process at present, while the scope of manipulation is limited and the systematic analysis of the adjustment mechanism is lacked. In view of the double emulsion droplet generation and splitting during the flow process, the influence of the stress variation on the interfacial rupture and liquid flow state caused by the shear-induced surface evolution and the geometry confined unbalance will be studied by this project, based on the co-flow type of double emulsion droplet generation technology. The relationship between the flow field and the size of the droplets will be analyzed to obtain the critical conditions for different formation modes. The change of interfacial forces and the splitting conditions of the double emulsion droplets will be investigated in the symmetrical structure. The influencing factors of asymmetric splitting will be analyzed and the microfluidic chip with desired splitting ratio will be designed to achieve controllable and stable splitting of double-emulsion droplets, which can still play a stable role within a large range of flow rate. This project will deepen the theoretical study of the generation of double emulsion droplets, and expand the performance of controllability and application of the double emulsion droplets as well.

液滴微流控技术因其低耗、高效和封闭等优点被广泛关注，双乳液滴独特的核-壳结构能够有效保护内核中的反应物，也为多组分液滴的精准操控提供了重要载体。双乳液滴的尺寸和生成通量是应用中的重要参数，目前主要依靠生成过程进行调节，作用范围局限性大并且调节机理欠缺系统分析。本项目基于同轴流动型的双乳液滴生成技术，针对双乳液滴生成和流动中的分裂过程，研究界面剪切变形和几何受限不平衡所引起的受力变化对界面破裂和液体流动状态的影响。分析液体流场与双乳液滴生成尺寸之间的关系，得到双乳液滴不同生成模式的临界条件；探究对称结构中，双乳液滴对称分裂的界面受力变化过程以及分裂条件；分析不对称分裂的影响因素，设计分裂比可控的微流控芯片，实现双乳液滴的可控、稳定分裂，并且在较大流量范围内仍然能够稳定地发挥功能。本项目将深化双乳液滴生成的理论研究，扩大双乳液滴性能的可控性并提高其应用性能。

针对液滴微流控技术中双乳液滴尺寸和通量的精准调控问题，本项目利用显微粒子图像测速和显微高速摄像等实验方法以及基于N-S方程的VOF模型和基于LBM的颜色梯度模型等数值方法，结合界面动力学和微尺度流动理论研究双乳液滴的生成和分裂行为，分析多相流体流动与界面受力变化的相互作用，利用界面变形及其破裂规律探究双乳液滴尺寸的调控方法，实现对内外液滴尺寸的有效控制。.搭建了三重毛细管的双乳液滴制备与观测平台，探究了同轴流动微通道内双乳液滴的生成过程。根据两相界面受力推导临界液滴尺寸的控制方程，分析了通道几何结构、流动条件、液体物性参数和双乳液滴尺寸之间的关系，建立了双乳液滴不同生成模式的临界流动条件以及尺寸的预测模型。推导了内液滴周期生成的经验判定准则，确定了内液滴周期生成对外层射流界面破碎的影响规律，根据颈部尺寸与时间的标度率关系，确定了内液滴在射流颈部颈缩各阶段的作用特性，得到了复合射流不同界面断裂特性与剪切力、挤压力和界面张力的竞争机制。.探究了液滴内部流动行为，对两相流量、液滴大小和通道高宽比等变量进行解耦分析，确定了液滴内部流场与内部驱动力的关系。研究了双乳液滴在对称分岔结构中分裂特性，对比分析单乳和双乳液滴的分裂模式，基于毛细数和液滴长度之间的幂律关系标定了液滴分裂临界条件，建立了双乳液滴分裂模式的分布图。探究了内外液滴尺寸比对界面耦合效应的影响规律，分析不同分裂模式和分裂阶段中的液滴动力学特性，总结了界面耦合在各阶段的作用机制。分析了对称及非对称分岔结构处液滴的运动特性，结合两相界面的动态变化和流场特征，建立了不同液体体系下的界面受力模型。研究了局部缩颈结构、外加声场/电场等调控方式下的界面受力变化，进一步针对不同工程应用场景提出了预测液滴尺寸的修正模型。