Preparation of Superhydrophobic Surfaces Based on Rod-Shaped Micro-Structure Induced by Nanosecond Laser

Abstract

Solid–liquid frictional resistance is mainly attributed to the adhesion caused by the boundary layer effect. Superhydrophobic surfaces are expected to be an effective method to reduce frictional resistance. In this paper, a rod-shaped micro-structure was prepared on surfaces of Al alloy (5083) and Ti alloy (TC4) by line-by-line scanning with nanosecond laser. The inherent properties of the metal materials—such as their coefficient of thermal conductivity (CTC) and specific heat capacity (SHC)—had a major influence on the surface morphology and shape size of the rod-shaped micro-structure. Both two metals showed apparent oxidation on their surfaces during laser ablation, however, the degree of surface oxidation of the Al alloy was greater than that of the Ti alloy due to its more fragmentary rod-shaped micro-structure. The laser-treated surfaces could turn from hydrophilic to hydrophobic or even superhydrophobic after being left in the air for 20 days, which might be caused by the adsorption of low-surface energy matter in the air. In addition, the contact angle of the Al alloy was larger than that of the Ti alloy, which is due to the larger ratio of height to width of the micro–nano composite rod-shaped micro-structure on the surface of the Al alloy.