Coalescence-Induced Self-Propulsion of Droplets on Superomniphobic Surfaces

We utilized superomniphobic surfaces to systematically investigate the different regimes of coalescence-induced self-propulsion of liquid droplets with a wide range of droplet radii, viscosities, and surface tensions. Our results indicate that the nondimensional jumping velocity V_j^* is nearly constant (V_j^* ≈ 0.2) in the inertial-capillary regime and decreases in the visco-capillary regime as the Ohnesorge number Oh increases, in agreement with prior work. Within the visco-capillary regime, decreasing the droplet radius R₀ results in a more rapid decrease in the nondimensional jumping velocity V_j^* compared to increasing the viscosity μ. This is because decreasing the droplet radius R₀ increases the inertial-capillary velocity V_ic in addition to increasing the Ohnesorge number Oh.