Numerical Simulation Study of Self-driven Microdroplet on Locally Restrictive Discontinuous Wetting Gradient Surface Using Front Tracking Method

Abstract

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.