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 degrees 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.