Controlling the wettability of stainless steel by surface texturing using a high power femtosecond fiber laser

In this work, stainless steel samples have been textured by a simple and fast one-step laser process. The particularity of this process is the use of an ultrashort pulsed laser technology, combining a high power pulses at high repetition rate. An improved productivity can thus be considered. Successive ablations by IR laser pulses allow to generate dual-scale surface structures. Hierarchical structures, composed of micro-hills on which are superimposed periodic nano-ripples, have been produced at the repetition rate of 50 kHz, by a repeated irradiation of a crossed pattern of parallel lines. In order to increase the process throughput, repetition rates of 100, 250 and 500 kHz have been tested. After an adaptation of the process parameters, topographies with the same dimensions of structures have been created. The presence of these structures modifies the wetting properties of the material. Immediately after laser irradiation the surface becomes hydrophilic; however this wetting state evolves to become superhydrophobic with contact angles higher than 160° and water droplets unable to adhere to the surface. The temporal evolution of the wettability results from the combination of the surface roughness and the chemical composition of this surface. The modeling of the wetting behavior of water droplet, deposited on grooves structures, shows the enhancement of the initial wettability of the surface.In this work, stainless steel samples have been textured by a simple and fast one-step laser process. The particularity of this process is the use of an ultrashort pulsed laser technology, combining a high power pulses at high repetition rate. An improved productivity can thus be considered. Successive ablations by IR laser pulses allow to generate dual-scale surface structures. Hierarchical structures, composed of micro-hills on which are superimposed periodic nano-ripples, have been produced at the repetition rate of 50 kHz, by a repeated irradiation of a crossed pattern of parallel lines. In order to increase the process throughput, repetition rates of 100, 250 and 500 kHz have been tested. After an adaptation of the process parameters, topographies with the same dimensions of structures have been created. The presence of these structures modifies the wetting properties of the material. Immediately after laser irradiation the surface becomes hydrophilic; however this wetting state evolves to become sup...