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-a-chip 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 L_ΙΙx^*, different restrictive stripe lengths L_ΙΙΙy^*, and different surface wetting gradients ∆ cos⁡θ 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 L_ΙΙx^* lengths and the wetting gradient ∆ cos⁡θ have significant effects on the migration velocity of droplets, while different restrictive stripe length L_ΙΙΙy^* lengths have very significant effects on the final morphological characteristics of droplets. When restrictive stripe length L_ΙΙΙy^*≥1, the hindering effect generated by the restrictive region ΙΙΙ has more and more significant effects on the morphological structure of droplets in the migration process. When the correction factor ε=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.