Expedited Transition in the Wettability Response of Metal Meshes Structured by Femtosecond Laser Pulses for Oil-Water Separation

Abstract

Oil-water separation using super-wetting and the selective permeability of membranes for oil or water has great ecological and economic significance. We report on the transition of wettability response, from superhydrophilic underwater-superoleophobic to superhydrophobic-superoleophilic state, by nanostructuring stainless steel and copper meshes using ultrashort femtosecond laser pulses. Our approach is environment-friendly, chemical free, and efficient as it exploits the benefit of aging the processed samples in a high vacuum environment. We optimized the laser scanning parameters, mesh pore size, and aging conditions to produce membranes exhibiting an extraordinary separation efficiency of 98% for the oil-water mixture. A variation in the water and oil contact angles for different meshes is presented as a function of the laser scanning speed. Stainless steel meshes with 150 μm pore size and copper meshes with 100 μm pore size have demonstrated an excellent wettability response for oil and water phases. Vacuum aging causes rapid chemisorption of hydrocarbons on laser-structured surfaces in the absence of water molecules, rapidly transforming the wetting state from superhydrophilic to superhydrophobic.

Ten Open Questions about Laser-Induced Periodic Surface Structures

“…However, previous work shows that the achieved contact angles cannot be described solely by topographical aspects, which is why the influence of surface chemistry has to be considered (see Question 5). During LIPSS generation in air environment, metals are subject to laser-induced oxide-layer formation, which favors the formation of a hydroxylated layer and is thus responsible for super-hydrophilic properties after laser processing [81].…”

Ultrasonic assisted rapid preparation of superhydrophobic stainless steel surface and its application in oil/water separation

“…Fig. 12 showed the separation efficiencies of superhydrophobic stainless steel surfaces obtained from different methods [48] , [52] , [53] , [54] . It was indicated that the separation efficiency of the as-prepared samples ranked among the highest values reported before.…”

Influence of gas media and low pressure on the dynamics of wetting transition of laser textured stainless steel meshes during air ageing

“…The role of low-pressure and vacuum ageing was also tested. Complex geometrical form and curved nature of meshes is crucial and not easy by itself and it was already demonstrated in [6]. In our work we focused on influence of processing atmosphere and subsequent long-term ageing on the wetting behaviour of laser treated meshes.…”

“…Stainless steel in form of meshes is a robust, durable and flexible construction material. Recently, controlling the wettability state of the metal meshes by femtosecond laser-induced structuring has found applications for efficient oil-water separation [5,6]. Wetting is the ability of a liquid medium to maintain contact with a solid medium due to intermolecular interaction when in contact with each other.…”