Highly efficient fog harvesting system achieved on slippery micro-grooved cones

The directional transport of liquid droplets on asymmetrical one-dimensional surfaces has broad applicability, from fog harvesting and oil/water separation to desalination, sensing, and beyond. The balance between driving and hysteresis forces determines the performance of droplet motion. To improve droplet mobility, a common strategy is to increase driving forces by introducing multiple levels/types of asymmetries along the motion direction, or to decrease resistant forces by constructing a slippery surface. However, there have been few attempts to integrate enhanced driving forces and decreased resistance into one system, mainly because traditional lubricant surface is difficult to maintain stability on physically or chemically asymmetrical surfaces. In this study, we demonstrate a new approach by employing flexible polymer brush-enabled slippery technique on a micro-grooved cone structure. We show that this technique significantly enhances droplet motion performance compared to cones with pure micro-grooves or pure polymer brush modification. This improvement is achieved through the simultaneous increase in the Laplace driving force and the decrease in hysteresis. Our design, with its cooperative surface structure and chemical modification, provides new insights for developing smart surfaces to drive liquid droplets efficiently.