Fabrication of patterned surfaces that exhibit variable wettability ranging from superhydrophobicity to high hydrophilicity by laser irradiation

We present a simple method for fabricating patterned surfaces that exhibit different wettabilities in different areas using laser machining. This process can be extended to form complex and large patterns. The first step is the preparation of a superhydrophobic base surface on the aluminum specimen through formation of hierarchical micro- and nanostructures and coating of a self-assembled monolayer. This base surface is then patterned using a laser, which is moved along the surface using a computerized routing system. It was found that the surface hierarchical structures melted to a greater degree with an increase in the laser power used. However, with increases in the laser power, the degree of melting as well as the melted area increased, causing the wettability of the surface to change drastically and making the surface more hydrophilic. In addition, new crumb-like nanostructures were formed for high laser powers, which made the surface rougher and also increased its hydrophilicity. Further, when the rate at which the laser was moved across the machined surface was increased, the contact angle of the irradiated surface decreased for the same laser power. Finally, complex patterns, including stripes and circles, having different wettabilities in different area could be successfully fabricated.