An aluminium alloy surface with a microgroove array was fabricated via laser processing, and exhibited superhydrophobicity. The as-prepared surface showed excellent anti-adhesion properties and potential self-cleaning behaviour. The wettability of the fabricated surface was investigated by measurement of the water contact angle. The surface morphology and chemical composition were characterised by scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The wettability of the surface was successfully modified from hydrophilicity to superhydrophobicity by the laser processing. The water contact angle was increased to 155°, and the sliding angle reduced to <5°, without any chemical modification. Water droplets on the surface existed in an almost perfectly suspended state, resembling a model Cassie state. The superhydrophobic surface showed excellent stability under conditions of external extrusion. This easy and inexpensive modification method is expected to play an important role in extending the applications of aluminium alloys.
The effect of the plating voltage on the surface roughness, morphology, chemical composition and wettability of the Ni coatings was investigated by means of Laser scanning confocal microscopy, scanning electronic microscope, X-ray diffraction, energy-dispersive spectroscopy, and water contact angle measurements. The results indicate that the evolution of surface morphology on Ni coatings prepared by brush-plating depends strongly on the variation of plating voltage. The microstructure characterization shows that the typical hierarchical cauliflower-like structures was formed uniformly on the as-prepared Ni coatings. The combination of the porous morphology and hierarchical cauliflower-like structures plays a crucial role in improving the hydrophobic property. In absence of surface chemical modification, the Ni coatings exhibit an excellent hydrophobicity and have a high contact angle of 141 degree. Based on the Cassie-Baxier models, the relationship of two dimensionless geometrical parameters and the wetting property of the Ni coatings were investigated. It was demonstrated that to obtain the stable Cassie hydrophobic state, the aspect ratio and the water contact angle on the basal surface should be as large as possible and the spacing factor should be limited within a specific range for given aspect ratio and water contact angle on the basal surface.
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