The surface wettability aging mechanism after ultrafast laser surface structuring

Ultrafast laser surface structuring offers a promising technique for controlling surface functionalities such as wettability, achieving a range from superhydrophilicity to superhydrophobicity on various materials. However, long-term storage in ambient air presents a stability challenge, as metals initially exhibiting superhydrophilicity tend to become hydrophobic or superhydrophobic over time after processing. Understanding the mechanisms behind this aging process and its impact on wettability is critical. This study investigates aging effects on metals structured with femtosecond lasers. It examines the roles of storage environments, surface chemistry, and morphology. A semi-quantitative model describing the aging process is proposed and aligns well with experimental observations, providing valuable insights into the interplay between surface characteristics and aging dynamics.