Femtosecond laser constructed bioinspired gradient wedge-shaped surfaces for under-oil liquid self-transport

The spontaneous transport of liquids holds significant application potential in biomedicine, heat dissipation, microfluidic chips, and so forth. In particular, under-oil liquid self-transport is a significant pathway for manipulating volatile liquids. Although numerous functional surfaces have been developed to facilitate the directional self-transport of liquids (e.g., water, oil) in air, reports on the self-transport of liquids in oily environments remain scarce. Herein, inspired by lotus leaves and cactus spines, we propose a bionic superwetting gradient wedge-shaped surface (SGWS) for under-oil self-transport of liquids. The SGWS was fabricated through a combination of femtosecond laser texturing and hydrophobic modification. The as-prepared SGWS can achieve fast and continuous self-transport of a single droplet under-oil, exhibiting a maximal transport velocity of over 250 mm s^-1 and a transport distance of over 150 mm. The effect of the wedge-shaped angle, inclined angle, and surface tension on the self-transport behavior of a liquid on the SGWS was systematically investigated and the underlying mechanism was revealed. Furthermore, the potential applications of the SGWS in complex fluid manipulation, droplet microchemical reactions, cargo transport, and oil surface particle collection were explored in detail. This work offers a novel strategy for realizing under-oil liquid manipulation without energy input, showing promising applications in the industry.