Wettability transition modes of aluminum surfaces with various micro/nanostructures produced by a femtosecond laser

The wettability transition of hierarchical micro/nanostructure metal surfaces over time shows huge potential to fabricate the superhydrophilic and superhydrophobic surfaces without chemical coating. Although a large number of studies have reported the transition phenomenon on structured metal surfaces, the knowledge of which kind of micro/nanostructure contributes significantly to the acceleration or inhabitation of transition processes is still limited. In this article, the authors fabricated three kinds of typical micro/nanostructures with different topography features on aluminum surfaces by a femtosecond laser. The authors then systematically studied the relationship between the micro/nanostructures and the transition modes in ambient air. The results show that all structured surfaces show superhydrophilic nature initially but then become hydrophobic even superhydrophobic over time. The surfaces with regular microstructures hybrid with nanoripples and a few nanoparticles can achieve superhydrophobicity quickly, 27–30 days. Especially, these structures can realize superhydrophobicity within only 2 h if the low temperature heat treatment is performed on them in ambient air. In addition, the surfaces with regular deep microstructures hybrid with nanoripples and abundant nanoparticles can maintain superhydrophilicity for the longest time and show slow wettability transition mode due to the slower adsorption processes. These results may provide an aid to further understanding the wettability transition modes of different micro/nanostructures in ambient air and fabricating stable superhydrophobic and superhydrophilic surfaces without adding chemical coating.