Laser textured superhydrophobic surfaces and their applications for homogeneous spot deposition

This work reports the laser surface modification of 304S15 stainless steel to develop superhydrophobic properties and the subsequent application for homogeneous spot deposition. Superhydrophobic surfaces, with steady contact angle of ∼154° and contact angle hysteresis of ∼4°, are fabricated by direct laser texturing. In comparison with common pico-/femto-second lasers employed for this patterning, the nanosecond fiber laser used in this work is more cost-effective, compact and allows higher processing rates. The effect of laser power and scan line separation on surface wettability of textured surfaces are investigated and optimized fabrication parameters are given. Fluid flows and transportations of polystyrene (PS) nanoparticles suspension droplets on the processed surfaces and unprocessed wetting substrates are investigated. After evaporation is complete, the coffee-stain effect is observed on the untextured substrates but not on the superhydrophobic surfaces. Uniform deposition of PS particles on the laser textured surfaces is achieved and the deposited material is confined to smaller area

Nanosecond laser textured superhydrophobic metallic surfaces and their chemical sensing applications

tThis work demonstrates superhydrophobic behavior on nanosecond laser patterned copper and brasssurfaces. Compared with ultrafast laser systems previously used for such texturing, infrared nanosecondfiber lasers offer a lower cost and more robust system combined with potentially much higher processingrates. The wettability of the textured surfaces develops from hydrophilicity to superhydrophobicity overtime when exposed to ambient conditions. The change in the wetting property is attributed to the par-tial deoxidation of oxides on the surface induced during laser texturing. Textures exhibiting steady statecontact angles of up to ∼152◦with contact angle hysteresis of around 3–4◦have been achieved. Inter-estingly, the superhydrobobic surfaces have the self-cleaning ability and have potential for chemicalsensing applications. The principle of these novel chemical sensors is based on the change in contactangle with the concentration of methanol in a solution. To demonstrate the principle of operation ofsuch a sensor, it is found that the contact angle of methanol solution on the superhydrophobic surfacesexponentially decays with increasing concentration. A significant reduction, of 128◦, in contact angle onsuperhydrophobic brass is observed, which is one order of magnitude greater than that for the untreatedsurface (12◦), when percent composition of methanol reaches to 28%

Structuration multi-échelle d'alliages métalliques au moyen d'un laser Femtoseconde

Many industrial applications highlight the importance of the wetting properties of metallic surfaces related to their adhesion phenomena. Wenzel's (1936) and Cassie - Baxter's (1944) independent works showed that the wettability depended on both the surface tension of the solid but also on its surface topography. Thus the control and optimization of these properties require control of both aspects, like the lotus leaf whose superhydrophobic character lies in the presence of a hydrophobic wax and a multi-scale roughness. These observations are at the origin of the development of chemical etching techniques to produce surface texturing of materials and control their wettability. To overcome some limitations of these techniques and focus on a dry process, we considered the surface texturing of metal alloys of titanium, aluminum, and various stainless steels, using a femtosecond laser surface treatment. The analysis of the topography of the textured surfaces using different techniques (optical profilometry, AFM, SEM) showed the effectiveness of this method for generating multi-scale texturing. The different morphologies of textures can be associated with regimes transitions in the laser - matter interaction (ripples,spikes ...). The chemical and structural analysis (XRD, XPS) of the treated surfaces revealed microstructural changes due to thermal effects of laser, and a shift in the chemical state of the surface whose effects on the wettability are important. The hydrophobicity of metallic surfaces was significantly enhanced by laser treatment. These results may be used for various industrial applications, including the control of the surface state of plastic molds.De nombreuses applications industrielles mettent en évidence l'importance des propriétés de mouillage des surfaces métalliques que ce soit directement pour les propriétés d'écoulement de fluides sur ces surfaces ou indirectement pour leur lien avec les phénomènes d'adhésion. Les travaux de Wenzel (1936) et de Cassie -Baxter (1944) ont montré que cette mouillabilité dépendait à la fois de la tension superficielle du solide mais aussi de sa topographie de surface. Ainsi la maîtrise et l'optimisation de ces propriétés nécessitent le contrôle de ces deux aspects, à l'image de la feuille de lotus dont le caractère super-hydrophobe réside à la fois en la présence d'une cire hydrophobe et d'une rugosité multi-échelle. Ces observations sont à l'origine, cette dernière décennie, du développement des techniques de gravures chimiques pour réaliser des texturations superficielles de matériaux et contrôler leur mouillabilité. Afin de surmonter certaines limitations de ces techniques et privilégier un procédé par voie sèche, nous avons envisagé de structurer la surface d'alliages métalliques de titane, d'aluminium, et de différents aciers inoxydables, au moyen d'un traitement de surface par laser femtoseconde. L'analyse topographique de la surface des matériaux (profilométrie optique, AFM, MEB) en fonction des paramètres d'irradiation du laser comme la densité de puissance laser, le nombre d'impulsions et le décalage latéral du faisceau en configuration balayage, a montré l'efficacité de ce procédé pour générer des texturations multi-échelles. Les différentes morphologies de textures peuvent être associées à des transitions de régimes dans l'interaction laser - matière (ripples, spikes, ...). L'analyse chimique et structurale (DRX, XPS) des surfaces traitées a mis en évidence des modifications microstructurales dues aux effets thermiques du laser ainsi qu'une évolution de l'état chimique de la surface dont les effets sur la mouillabilité sont importants. L'hydrophobie des surfaces métalliques a été considérablement accentuée par le traitement laser. Ces résultats pourront être exploités pour différentes applications industrielles notamment comme moyen de contrôler l'état de surface des moules de plasturgie

Effect of stationary femtosecond laser irradiation on substructures' formation on a mold stainless steel surface

International audienceNano-scale and micro-scale laser-induced periodic surface structures (ripples), pores and splash-like structures with different formation thresholds fluence have been observed after stationary multiple linearly polarized femtosecond laser irradiations on a molding stainless steel. Nano-scale structures exhibit a formation threshold fluence lower than that of micro-scale ripples. When increasing both power density and number of pulses, nano-scale ripples are only sensitive to the latter, showing a 15% decrease of their spatial period in the range of used values. Micro-scale ripples respond to these two laser parameters by an increase followed by a decrease of their spatial period. The two types of ripples exhibit behavior differences that show that micro- and nano-scale ripples are the results of two distinct mechanisms

Time dependency of the hydrophilicity and hydrophobicity of metallic alloys subjected to femtosecond laser irradiations

International audienceSurfaces of metallic alloys were laser-processed with femtosecond laser pulses of 800 nm, with different power densities. The effect of time on the wettability of these surfaces was investigated. A multi-scale roughness made of undulations was created after the laser processing. This specific surface topography allowed the occurrence of a Wenzel's state. This state clearly explains the high hydrophilicity and hydrophobicity observed respectively one day after laser treatment and several days later. The change from hydrophilicity to hydrophobicity occurred over time and is due to surface chemistry modifications. The creation of new hydrophobic functional groups on aluminum alloy surface, for example, was proposed to be responsible for the hydrophobic behavior observed on these surfaces

Modifications of roughness and wettability properties of metals induced by femtosecond laser treatment

International audienceTopographic and wetting properties of AISI 316L stainless steel and Ti-6Al-V alloys were modified via linearly polarized femtosecond laser pulse irradiation. In order to induce a gradual evolution of the surface topography and wettability, four samples of each alloy were irradiated with different number of pulses. From the topographic point of view, a multi-scale morphology made of nano- and micro-periodic ripples was induced. The increase in the number of pulses led to the appearance of a third scale structure of waviness that is due to the laser scanning. The wettability of alloys was changed from a hydrophilic behavior to a hydrophobic one without lowering surface energies by chemical coatings. The apparent contact angle (CA) increased with increasing the number of pulses. A rise of about 50° of the apparent CA of the Ti-6Al-V was noticed

Cavitation erosion resistance of ultra high molecular weight polyethylene coatings

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