Generation of superhydrophobic surfaces and wettability gradients on metallic substrates by nanosecond laser irradiation

This work demonstrates superhydrophobic surfaces on copper and brass fabricated by a cost-effective and compact nanosecond fiber laser. The processing rate is particularly high, about two orders of magnitude faster than that using femtosecond lasers, which is favourable for large area processing. The laser processed copper and brass surfaces exhibit superhydrophilic behavior directly after fabrication but this changes to superhydrophobic (contact angle ∼152°) over time under ambient conditions. Applications of the superhydrophobic brass surfaces for chemical sensing, which is based on the decrease of contact angle with liquid concentration, are presented. Furthermore, a novel approach for making roughness gradients on brass surface is shown, thus enabling surfaces with wettability gradients. This approach could have potential applications for multi-sensitivity chemical sensors, liquid transportation and microfluidics.