Effect of femtosecond laser irradiation on stainless steel's wettability

Abstract

Control of stainless steel (SS) variants’ surface wettability has attracted much attention due to their potential in the medical industry, particularly bio-implant applications. Surface modification via femtosecond laser irradiation is a promising technique due to its ability to create micro/nano-scale features with limited thermal effects. In this project, SS 316L were irradiated with ultra-short laser pulses in air at different laser processing parameters. The wettability was then characterized by static water contact angle (WCA) measurement. Surface morphology was obtained from optical images and surface roughness measurement was performed. Lastly, the irradiated samples were placed in four environments. The wettability properties and surface topography of irradiated SS surfaces under the various laser processing conditions were studied. This project showed that the SS samples initially displayed highly hydrophilic properties with WCA about 10 degrees. However, over time, the irradiated surfaces became highly hydrophobic with WCA saturating in the region of 130 degrees. The change in wettability properties was hypothesized to be due to a change in surface chemistry. The irradiated SS samples stored in different environments displayed changes in WCA measurement but did not pass from hydrophilic to hydrophobic. This re-affirmed the hypothesis that chemical changes on the irradiated surfaces are the underlying cause of changes in wettability.