Numerical simulation study of self-driven microdroplet on locally restrictive discontinuous wetting gradient surface using front tracking method

The motion of droplet on surface with discontinuous wetting gradient is of great importance for understanding lab-on-achip systems and other microfluidic devices. Different wetting gradients are known to be the main influencing factor in the droplet self-driven process, but the effect of different wall structures on the droplet migration process also deserves further investigation. In this paper, we analyze the self-driven process of liquid droplets on a local wetting gradient surface under microgravity conditions using front tracking method. The effects of different driving stripe lengths LIIx, different restrictive stripe lengths LIIIy,and different surface wetting gradients Acos 0 on the droplet migration process and droplet morphology are analyzed. A theoretical formula that can predict the lateral spreading length of droplets is also proposed. The results show that different driving stripe length LIIx lengths and the wetting gradient Acos 0 have significant effects on the migration velocity of droplets, while different restrictive stripe length LIIIy lengths have very significant effects on the final morphological characteristics of droplets. When restrictive stripe length LIIIy >= 1, the hindering effect generated by the restrictive region has more and more significant effects on the morphological structure of droplets in the migration process. When the correction factor s = 0.735 in the prediction equation, the predicted value calculated by the theoretical equation has a good degree of similarity with the numerical simulation results.