Wettability transition of femtosecond laser patterned nodular cast iron (NCI) substrate

Abstract This work focuses on the wettability transition of nodular cast iron (NCI) modified using a femtosecond laser-produced micro/nano-structure. Laser parameters such as laser fluences (0.10 to 3.18 J/cm2), and scan speed (0.2 to 1.0 mm/s) were varied to realize hierarchical or dual-phase structures. Raman spectroscopy was performed on samples treated at 0.10 to 0.63 J/cm2 to investigate the mechanism involved in the disappearance of the graphite nodule with increasing laser fluence. Just-after the laser treatment, surface was superhydrophilic in nature and progressively became superhydrophobic after cleaning and subsequent application of vacuum pressure for 8 h. In the present investigation, a static contact angle (SCA) of 164 ± 4° was measured. The temperature-dependent durability of the superhydrophobic surface was analyzed by heating at a temperature range from 80 °C to 240 °C. The results showed a stable superhydrophobic characteristic up to 120 °C even after five cycles of repetition. Scanning electron microscope (SEM) analysis was conducted to capture the micrograph of structures. Moreover, the chemisorption mechanism during the vacuum process and over the period was analyzed using X-ray photoelectron spectroscopy (XPS) that indicated a higher concentration of non-polar functional groups on the surface could effectively increase the SCA.