The investigation of droplet directional self-transport ability on the slippery liquid-infused surface with anisotropic structure

Liquid directional transport on functional surfaces has promising application in society. Inspired by cactus spine and Nepenthes pitcher plant, a series of slippery liquid-infused microstructure surfaces (SLIMS) with uniform texture have been fabricated on T2 copper substrates by laser texturing technique. Such substrates show geometry-gradient shape with uniformly rough structure, which can successfully realize droplet directional self-transport behaviour. Combined with experimental findings, the mechanism of droplet self-transport is introduced based on the analyses of driven force induced by Laplace pressure and the adhesive force between droplet and surface. The experiment results indicate that the droplet displacement is well consistent with theoretical results on the SLIMS with uniform surface texture. Different from previous reports, we have particularly investigated the droplet self-transport property on SLIMS with rice-leaf-like anisotropic grooves. The results demonstrate significant difference between the parallel groove-patterned SLIMS (SLIMS//) and the perpendicular groovepatterned SLIMS (SLIMS perpendicular to). By considering both the adhesive force and droplet spreading ability, the variation of droplet transport distance is determined by synergistic effect of adhesive force in different directions (F-re(//) and F-re(perpendicular to)). We believe this work will provide novel insights to improve the droplet transport distance, which can widen liquid directional transport applications in both industrial and academic fields.