Wettability modification of laser-fabricated hierarchical surface structures in Ti-6Al-4V titanium alloy

In the present work, a study of laser-based surface structuring of aerospace-grade titanium alloy (Ti-6Al-4V) with subsequent ageing by employing two different storage methods is undertaken. The titanium alloy samples were patterned using UV-ns and IR-fs pulsed lasers in a two-step process to fabricate bio-inspired hierarchical structures. The resulting surface structure consisted in regular periodic square-shaped micro-pillars covered by 810 nm-periodic LIPSS. After the laser processing the samples were kept in two different storage conditions: exposed to ambient air and inside polyethylene bags. The polyethylene bags were found to be beneficial for the surface ageing of laser fabricated titanium surfaces, increasing the ageing time when compared to ageing by exposure to ambient air. Hierarchical surface topographies exhibited higher water repellency when compared to non-hierarchical structures. Especially, hierarchical structures reached a hydrophobic state with water contact angle over 160° after 3 weeks storage in polyethylene bags. The micro-structured surfaces were characterized by using
confocal microscopy, scanning electron microscopy, static contact angle measurements and X-ray photoelectron spectroscopy.