Droplet flow behavior on a biomimetic structure with a superhydrophobic gradient interface inspired by the Nepenthes pitcher plant

To address the challenge of lubricating oil creep loss in aerospace equipment, a biomimetic structure combining a wetting gradient with a geometric diversion pattern inspired by the peristome region of the Nepenthes pitcher plant is designed. A two-phase flow-field simulation is performed to investigate directional droplet transport on this biomimetic structure. Hydrothermal deposition and laser etching methods are then used to prepare surfaces incorporating this structure on a titanium substrate, and directional droplet transport is observed using high-speed photography. It is found that regions on this surface with a biomimetic structure region are superhydrophilic with a contact angle of 0°, while regions without any such structure are superhydrophobic with a contact angle of 159°. With increasing curvature of the biomimetic structural units, the self-actuation effect of the biomimetic structure on droplets decreases. The effects of the other structural parameters in the case of zero curvature is studied, and it is found that the droplet transport rate increases with increasing lateral spacing and longitudinal spacing between biomimetic structural units and decreases with increasing angle of inclination of these units and increasing droplet viscosity. The designed biomimetic structure is thus able to realize efficient directional transport of water and lubricating oil, with the transport rate being determined by the biomimetic structural parameters and the droplet viscosity.