Tuning the Wettability of a High-Strength Aluminum Alloy Using a Picosecond Laser and Stearic Acid Coating

Abstract

Imitating microstructures found in nature—such as lotus leaves and Namib beetles—is revolutionary in the field of surface science. Low-energy surfaces, when combined with different topographies, create different wetting states. Understanding the correlation between microstructure geometry and the behavior of water droplets is key to varying the contact angles on a low-energy surface. Here, a picosecond laser was used to modify the microtexture of aluminum alloy surfaces. Various microstructures were formed on the same surface, including the Laser-Induced Periodic Surface Structure (LIPSS), dual micro/nano hierarchical structures, and periodic arrays of a micropattern structure. Coating these microstructures with stearic acid was found to contribute to decreasing surface energy. The 92% fraction of the laser-machined to non-machined surface, when associated with different microgroove depths, created the capacity to form a superhydrophobic surface. Water droplets on a modified surface were transferred from hydrophilic at the Wenzel state to hydrophobic at the Cassie–Baxter state to a superhydrophobic state at microgroove depths ranging between 2.50 μm to 0.3 μm. The air pockets trapped in the microgrooves and nanocavities were found to subsidize the initiation of the composite interface underneath the water droplet.