Effect of pH on wettability properties on aluminium alloy surfaces treated with direct laser writing

Nowadays, lightweight materials become more important in diverse industrial applications, such as automotive and aeronautics. Innovative surface features like superhydrophobicity enable further fields of applications. In this context, aluminium Al 2024-T351 alloy is structured using direct laser writing (DLW) to achieve a superhydrophobic surface. To address the effect of pH on the superhydrophobic behaviour, the static contact angle (SCA) is measured at different pH values (pH 1, 2, 4, 7, 9, 11 and 14), in comparison to a non-structured reference sample. The results show that superhydrophobic state in DLW samples is preserved in the pH range 2 - 9 with SCA between 151.1 ± 1.5° and 157.0 ± 0.5°. While stable hydrophobicity is still observed at pH 1, the samples exposed to pH 11 and 14 solutions exhibit collapse in the droplet and a fast chemical reaction, respectively. Concerning the non-structured samples, SCA is lower at pH 4, 11 and 14 than at neutral pH 7. This effect can be rationalized considering dealloying of Al2CuMg precipitates present in the surface of Al 2024-T351 alloy. Differences between non-structured and laser structured samples can be explained taking into account the change in present phases after laser ablation.