光热作用下含表面活性剂的微液滴行为机理及多场耦合数值方法研究

Maniputaion of the droplet dynamics in microfluidics using laser heating technique has a broad application prospect. To stabilize the droplet interface, surfactants are usually added in microfluidics. However, due to the difficulty of measuring the surfactant concentration in experiments and developing the multi-field numerical model, most of the existing investigations have neglected the influence of surfactants. The dynamical behavior of the surfactant-laden droplet is significantly different from that of the clean droplet, and the outcomes of the heating control technique must be strongly influenced by the addition of surfactants. In this project, the color model is used to solve the two-phase flow, and the interface and bulk surfactant transport equations are introduced to describe the surfactant field. Combining with the temperature solver and wetting boundary condition for arbitrary solid surfaces, we establish a coupled multi-field numerical model for the simulation of surfactant-laden droplet. The method is used to systematically study the optical-thermal manipulation process of surfactant-laden droplet dynamics in microfluidics, fully revealing the influence of flow parameters, surfactant-related parameters and temperature parameters. Based on the numerical investigation, experimental measurement and theoretical analysis, a generalized relation will finally be established to predict the droplet size or migration velocity through theoretical analysis. The present project can not only provide a new coupled multi-field numerical method, but also be helpful in precise manipulation of micro-droplet behavior and the design and optimization of microfluidics.

利用光热效应实现微流控系统中液滴的控制具有广泛应用前景。为保证液滴界面稳定性，通常在微流控系统中添加表面活性剂。但是，由于实验测量表面活性剂浓度和数值模拟多场耦合求解等困难，现有研究大多忽略表面活性剂的作用，而含表面活性剂的微液滴动力学行为与干净液滴存在显著差异，势必影响光热操控的效果。本项目采用颜色模型求解两相流动，引入扩散界面形式的界面和体相活性剂浓度输运方程，结合温度场的求解和适用于任意表面的润湿边界条件，建立含可溶表面活性剂的全三维非等温两相流动多场耦合数值方法。在此基础上，系统研究微通道内光热效应下含表面活性剂的微液滴行为，全面揭示两相流、表面活性剂和温度参数对液滴生成、迁移、分拣等过程的影响规律；并结合实验测量和理论分析，建立预测液滴生成尺寸、迁移速度等参数的普适关联式。项目不仅提供了新型多场耦合计算方法，还为含表面活性剂液滴的精确操控技术、微流控设备的优化设计提供理论支撑。

微流控系统中，为保证液滴界面稳定性，通常在微流控系统中添加表面活性剂。但是，由于实验测量表面活性剂浓度和数值模拟多场耦合求解等困难，现有研究大多忽略表面活性剂的作用，而含表面活性剂的微液滴动力学行为与干净液滴存在显著差异，势必影响液滴控制的效果。本项目以格子玻尔兹曼（lattice Boltzmann，LB）方法为中心，逐步建立了能够模拟含可溶表面活性剂的非等温两相流动的格子玻尔兹曼-有限差分数值模型。针对剪切流作用下液滴变形及破裂行为开展了模拟，揭示了表面活性剂对液滴行为的影响机理。研究了T型通道内表面活性剂对液滴生成的影响情况，获得了毕渥数、吸附参数等对液滴生成的影响。对于微通道内光热控制的流动，开展了泊肃叶流动下含表面活性剂液滴热运动规律研究，并探索了光热控制下含表面活性剂液滴生成过程，揭示光斑位置及表面活性剂对液滴生成的影响规律，为微液滴内含表面活性剂液滴的光热控制理论研究打下了基础，为微液滴的精确操控提供理论依据和技术支持。