Regulation of Coalescence-Induced Droplet Jumping by Triangular Protrusions on Superhydrophobic Surfaces

Coalescence-induced droplet jumping provides a passive, spontaneous route to enhance condensation heat transfer, anti-icing, self-cleaning, and atmospheric water harvesting. However, conventional superhydrophobic surfaces are severely constrained by low energy conversion efficiency and uncontrolled jumping directions. Here, we fabricate a monolithic superhydrophobic surface featuring triangular protrusions via 3D printing and systematically investigate the effects of protrusion height (450-900 μm), apex angle (30°-150°), and droplet radius (0.75-1.20 mm) on coalescence-induced jumping dynamics using high-speed imaging. Compared with flat superhydrophobic surfaces, the triangular-protrusion architecture substantially enhances jumping height, dimensionless jumping velocity, and projected directional deflection of the merged droplets. Notably, the energy conversion efficiency, defined here as the experimentally accessible translational energy conversion fraction η_t, is increased by approximately 827% compared with that on the flat superhydrophobic surface. Parametric analyses reveal that taller protrusions promote directional jumping by suppressing nontarget lateral spreading. The apex-angle dependence exhibits a pronounced nonmonotonic trend, with the 60° geometry delivering optimal performance by balancing directional spreading capability and recoil recovery. Velocity-component decomposition demonstrates that the protrusions regulate droplet jumping primarily by redistributing horizontal and vertical velocity components at detachment. This work establishes a simple macroscopic geometric strategy that increases the experimentally accessible translational energy conversion fraction and improves the projected directional regulation of coalescence-induced droplet jumping, thereby offering design principles for next-generation functional interfaces.