Universal Criterion for Critical Motion of Droplets Adhered on Surfaces with Different Wettability in Laminar Flow

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.