Effect of initial droplet position on coalescence-induced jumping on superhydrophobic surfaces with micropillar arrays

Coalescence-induced droplet jumping holds great potential for applications such as water harvesting, self-cleaning, and the thermal management of electronic devices. This study investigates the impact of the droplet's initial position on coalescence-induced jumping on superhydrophobic surfaces with micropillar arrays. Numerical simulations are conducted to examine the differences in droplet jumping at various initial positions with uniform and nonuniform micropillar distributions, and the effects of the droplet's initial position on its velocity and pressure distribution are analyzed. The findings indicate that altering the initial position produces an asymmetric distribution of the high-pressure region at the droplet's base and the pressure at the solid-liquid contact surface during the contraction of the liquid bridge. This asymmetry allows the droplet to jump away from the surface with both vertical and horizontal components of velocity, and to be transported in the horizontal direction. Furthermore, numerical simulations with various initial droplet positions and radii demonstrate that the direction of the horizontal jumping velocity is influenced by both the offset distance and the direction of the initial droplet position, and that the impact of the initial position decreases as the relative size of the droplet with respect to the micropillars increases. The droplet jumping velocity, direction, and horizontal transport distance can be controlled by adjusting the initial droplet position and size. This work reveals the mechanism of coalescence-induced droplet jumping on superhydrophobic surfaces with micropillar arrays and provides an important reference for practical applications.