Bio-inspired composite surfaces based on rice leaves: Analysis of droplet flow characteristics

Inspired by the directional guidance exerted by rice leaves on liquid droplets, this paper employs a phase-field method to simulate the flow characteristics of droplets along various hydrophilic track structures. Simulation results indicate that droplet flow velocity on divergent tracks shows a 38.7% increase compared to that on parallel tracks (2.12 mm/s). Based on these findings, a superhydrophobic/bio-inspired linear hydrophilic track composite surface was prepared using laser processing and SiO2 nanoparticle deposition techniques. For divergent tracks, a spreading distance of droplets reaching 10.4 mm is achieved when a divergence angle Dα of 4° is used, representing an 8.33% improvement over parallel tracks. In contrast, in convergent tracks, the pinning effect of droplets is found to be significant, with a maximum droplet-spreading distance of only 7 mm. Both simulation and experimental results indicate that divergent tracks more effectively promote droplet flow. The driving force on droplets in parallel hydrophilic tracks is indicated through droplet flow mechanism analysis to be approximately 313 times greater than the resistance. Moreover, in divergent tracks, capillary forces induced by the wettability gradient of the surface tracks are also exerted on droplets, in addition to the aforementioned driving force, resulting in the farthest flow distance.