Laser-Patterned Super-Hydrophobic Pure Metallic Substrates: Cassie to Wenzel Wetting Transitions

TLDR: In this article, a femtosecond laser was used to create microstructures on very pure metal surfaces and the irradiated samples initially showed super-hydrophilic behavior with time and exposure to ambient air.

Abstract: A femtosecond laser was used to create microstructures on very pure metal surfaces The irradiated samples initially showed super-hydrophilic behavior With time and exposure to ambient air the contact angle increased to about 160° with very low hysteresis The surfaces supported the Cassie and Wenzel wetting states, depending on the technique used to deposit the water droplets The created surface morphologies were idealized with a geometric model that is an assembly of densely packed cylindrical pillars with semispherical caps Using this geometric model for calculation of the surface roughness, a theoretical Young contact angle of about 99° was calculated for all samples from the Wenzel and Cassie–Baxter equations While the value of 99° significantly differs from the measured hydrophilic contact angles on the polished pure metallic samples, it indicates that a laser-induced surface reaction must be responsible for the evolution of contact angles to super-hydrophobic ones and that this phenomenon is in