The initial motion of micro-oil droplets on substrates immersed in water is of great significance to study droplet motion. Here, microscopic experiments and mechanism analysis are used to establish a universal criterion and a mathematical model describing the critical conditions for the initial motion of droplets adhered on surfaces with different wettability in the laminar flow. We demonstrate a surface modification technique and analysis method in a microtest. Based on the force’s analysis on the three-phase contact points of two-dimensional oil droplets on the surfaces, the movement mechanism is also obtained when the oil droplets start to move. In addition, this work focuses on the coupling effects of oil droplet’s height, surface properties, and water flow velocity on the initial motion behaviors of oil droplets and obtains the critical shear water flow velocity required for the critical movement of oil droplets from different surfaces. We achieve a universal criterion and model for different application scenarios, which are of great scientific significance to improve theoretical systems of multiphase separation and guide the design and optimization of surface properties and flow field velocity.

中文翻译：

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粘附在层流中具有不同润湿性的表面上的液滴的临界运动的通用判据

微油滴在水中浸泡时的初始运动对研究油滴运动具有重要意义。在这里，使用微观实验和机理分析来建立通用标准和数学模型，该模型描述了粘附在层流中具有不同润湿性的表面上的液滴初始运动的临界条件。我们在微测试中演示了一种表面改性技术和分析方法。根据对二维油滴在表面上的三相接触点的力分析，还可以确定油滴开始移动时的移动机理。此外，这项工作着重于油滴高度，表面特性，以及水流速度对油滴的初始运动行为的影响，并获得了油滴从不同表面进行临界运动所需的临界剪切水流速。我们为不同的应用场景建立了通用的标准和模型，对于改进多相分离的理论体系并指导表面性能和流场速度的设计和优化具有重要的科学意义。