Mechanisms of metal wettability transition and fabrication of durable superwetting/superhydrophilic metal surfaces

Maintaining superhydrophilicity on metal surfaces is challenging due to the inevitable surface adsorption of airborne organics after exposure to ambient air. In this study, we aim to elucidate the mechanisms underlying the persistence of surface superhydrophilicity and propose a technique for the preparation of durable superwetting/superhydrophilic metal surfaces. The effects of atmospheric organic properties, including the type of functional groups and the length of the carbon chain, on the rate of wettability transition and the final surface wettability after the surface adsorption are first investigated. Molecular dynamics simulation is used to explain why long-chain organics can lead to more marked wettability transitions. The liquid wetting and organic diffusion on textured surfaces are then analyzed, which proves that conventional surface structures with only single-scale structural features are challenging to achieve long-lasting superhydrophilicity. Finally, an in-situ laser deposition technique is proposed to fabricate micro-nano composite porous structures, in which the microstructures promote liquid wetting and the nanostructures inhibit organic diffusion. The prepared surfaces exhibited a 54-fold enhancement in the duration of surface superhydrophilicity compared to conventional nanostructures. Our results help to understand the mechanisms of durable superhydrophilicity, which are beneficial for the practical applications of superwetting/superhydrophilic surfaces.