Impact of laser texturing parameters and processing environment in the anti-wetting transition of nanosecond laser generated textures

Anti-wetting, or superhydrophobic surfaces have been a subject of significant interest in the engineering field for many years, particularly due to the potential to create self-cleaning surfaces. A droplet of water landing on a superhydrophobic surface will roll or slide away, whilst taking with it any surface debris. Such surfaces exist in nature, and there have been many reports where ultra-short pulsed lasers have been used to generate surfaces with similar feature sizes and hydrophobic performance. However it is also possible to produce superhydrophobic surfaces with short (nanosecond) laser pulses. In this paper we report our work in which flat sheets of SS304S15 were textured using a nanosecond pulsed fibre laser operating at 1064 nm. Quantitative analysis of the wettability of the laser structured surfaces was carried out by measuring the static contact angle of a droplet of deionized water with a volume in the microliter range. As with other reports, these surfaces are initially hydrophilic, and after a time delay of some days to weeks transition to hydrophobic, and in some cases to superhydrophobic. In order to realise a practical process, our work has concentrated in speeding up this transition from weeks to days, and to this end we have studied the role of the processing environment during laser texturing.