Residue-Free Droplet Transport via a Two-Dimensional Water Droplet Pattern with Asymmetric Wettability

Directional droplet transport without external energy input has garnered considerable attention in the development of transportation systems. Introducing a wettability gradient or topography onto the surface has successfully harnessed the water to move directionally. However, classical capillary force requires complete wetting of the movement pathway, causing hydrodynamic dissipation and poor collection efficiency. Inspired by the water absorption of cactus spines and the droplet spreading of the pitcher plant, we designed hydrophobic water droplet patterns (WDPs) on a superhydrophobic background. Synergistic actuation of the sharp edge effect of the round end and the pinning effect of the pointed end enables the directional droplet transport with high flux (166.7 μL/s). Sharp edge effect on the hydrophobic surface enables water contact angle (WCA) to exceed 180°, achieving continuous cross-structural transport (transport speed: 11.67 mm/s). The nonwettability of the movement pathway reduces hydrodynamic dissipation. Through the patterning design of irrigation pathways, water could be delivered to the designed plant or crop to achieve precision fertilization or irrigation. Equipping the fertigation system with the WDP tracks will benefit experimental field cultivation and crop breeding. The functional surface features a simplified two-dimensional (2D) structure that provides more possibilities for the development of fluid delivery technologies.