Femtosecond laser induced superhydrophobic transformation on metal surface

In general, a superhydrophobic surface refers to a surface with the water contact angle(CA) greater than 150° while the sliding angle(SA) smaller than 10°. It is expected to be widely used in numerous industries as well as in people's daily life in the coming future. Obtaining superhydrophobicity by microstructuring on material surfaces was exerted to an extensive research, but those former researches were mainly fastened on inorganic nonmetallic materials and polymeric materials. The methods used for microstructuring were mainly Chemical vapor deposition, anodic oxidation, phase separation, template synthesis, soft lithography, ion-beam lithography, electron-beam lithography and ultraviolet lithography, but only few were laser micro-machining technology. Although there are some studies about microstructuring on the surfaces of metals, most of them are focused on the mechanism of microstructure formation and the effects of process parameters on combination properties, or only the wetting properties on metal films. There is very little report on superhydrophobic metal-based substrate surfaces. We have constructed microstructures on metal surfaces, such as titanium and stainless steel, by using femtosecond laser induced microstructuring technology and preliminarily studying their wettability. We prove the feasibility of directly achieving steady superhydrophobicity on surfaces of metal-based materials, the maximal apparent contact angle of droplets on our titanium-based surfaces is up to 156.9° while the corresponding sliding angle is 4.7°, and the maximal apparent contact angle of droplets on our silanized stainless steel-based surfaces is up to 166.3° while the sliding angle is 4.2°. Our results are expected to provide guidance for designs of stable superhydrophobic metal surfaces.