含表面活性剂的微液滴生成机理及其新型混合计算方法

The technique of droplet formation using the manipulation of immiscible liquid-liquid flow in microchannels has received considerable attention due to its wide application prospect in the fields of biomedicine, chemical engineering, and energy etc. Surfactants are often used in the droplet formation process to control the droplet size, formation frequency and uniformity, and to stabilize the droplets against coalescence. Owing to the presence of surfactants, the droplet behavior in a microchannel is significantly different from that in the surfactant-free case. Nowadays, the mechanisms of droplet formation in the presence of surfactants are still poorly understood, greatly hindering the development of microfluidic technology. In this project, a novel hybrid method will be proposed to simulate two-phase flows with soluble surfactants and contact-line motion, in which the lattice Boltzmann color model and the finite difference method are used to solve the immiscible two-phase flow and the surfactant transport, respectively. The hybrid method will then be used to systematically study the droplet formation process with the addition of surfactants in microfluidic T-junctions, fully revealing the influence of the flow, fluid properties and channel geometry, as well as the surfactant concentration, solubility, elasticity and diffusion on the droplet formation process. Based on the numerical study, along with a combination of theoretical analysis and experimental measurement, a generalized scaling law will finally be established to predict the droplet size. This research will provide theoretical foundation for a deep understanding of droplet formation in the presence of surfactants, precise manipulation of micro-droplet behavior, and design and optimization of microfluidic devices.

利用微通道中液-液两相流操控方法生成微液滴的技术在生物医学、化工和能源等领域具有广泛应用前景。表面活性剂能够有效控制微液滴生成的几何尺寸、频率和均匀度，并且能够防止液滴间发生合并。在表面活性剂的影响下，微通道内的液滴动力学行为与干净液滴情况存在显著差异，对含表面活性剂液滴生成机理认知的不足已严重制约了微流控技术的发展。本项目通过格子玻尔兹曼颜色模型求解互不相溶的两相流动、有限差分法求解表面活性剂浓度分布，建立适合于含可溶表面活性剂和运动接触线的两相流动混合计算方法；在此基础上，对T型微通道内含表面活性剂的液滴生成过程进行系统深入的数值研究，全面揭示流动、物性、几何参数以及表面活性剂浓度、溶解性、弹性和扩散性对液滴生成过程的影响规律；结合理论分析和实验测量方法，建立预测液滴尺寸的普适关联式。项目为深刻认识含表面活性剂的液滴生成机制、精确操控微液滴行为、优化设计微流控设备提供理论基础。

利用微通道中液-液两相流操控方法生成微液滴的技术在生物医学、化工和能源等领域具有广泛应用前景。在微液滴操控过程中，添加表面活性剂既能降低两相间的界面张力，又能改变壁面的润湿性，已成为防止液滴间合并，控制液滴生成几何尺寸、频率和均匀度的重要手段。在表面活性剂的影响下，微通道内的液滴动力学行为与干净液滴情况存在显著差异，对含表面活性剂液滴动力学行为及其机理认知的不足已严重制约了微流控技术的发展。.本项目围绕微通道内含表面活性剂的液滴生成机理及其计算方法，发展了含不溶和可溶表面活性剂的两相流动格子玻尔兹曼-有限差分混合数值方法；提出了适用于任意复杂几何表面接触线动力学行为的建模方法；建立了动态接触角随表面活性剂浓度的变化关系，发展了能够同时模拟接触线动力学和表面活性剂动力学行为的高性能计算程序。研究了含表面活性剂的液滴在固体壁面的变形和破裂行为，发现在低、中等毛细数下表面活性剂的非均匀分布能够增加液滴的变形和运动速度，提升液滴的破裂，但高毛细数下表面活性剂的稀释作用能够阻止液滴的破裂。研究了不同流体粘性比下表面活性剂的存在对液滴破裂临界毛细数的影响规律，发现表面活性剂的存在减小液滴破裂的临界毛细数，但在低的粘性比时表面活性剂的影响更显著；对于无论是干净或含表面活性剂的液滴，随着粘性比的增加，临界毛细数先减小后增加；而且粘性比低时总是发生三次破裂，而粘性比高时发生二次破裂。此外，相比于不溶表面活性剂，含可溶表面活性剂的液滴变形有所增加，且随着毛细数的增大，可溶表面活性剂提升液滴变形的作用更加显著；同时，与不溶表面活性剂相比，可溶表面活性剂能够更大程度地提升液滴破裂。.项目研究为深刻认识含表面活性剂的液滴生成机制、精确操控微液滴行为、优化设计微流控设备提供理论基础。项目执行过程中共发表学术论文20篇，其中SCI论文18篇、EI论文2篇，培养从事相关工作的研究生2名。