Award for Vittorio Vercillo at SAE conference

Last June, the SAE International Conference on Icing of Aircraft, Engines, and Structures took place in Minneapolis (USA). New trends, new knowledge, and new solutions were discussed in more than 160 oral presentations that dive into every aspect of icing. Vittorio Vercillo, an Early Stage Researcher (ESR) in the Laser4Fun project, was awarded of the Outstanding Oral Presentation Award, for his contribution “Icephobic Properties of Laser-Treated Superhydrophobic Surfaces”.

More info at: https://www.sae.org/participate/awards/sae-engineering-meetings-board-outstanding-oral-presentation-award

The Role of the Surface Nano-Roughness on the Wettability Performance of Microstructured Metallic Surface Using Direct Laser Interference Patterning

Results of the work in the Laser4Fun project has been published as:

Alfredo I. Aguilar-Morales, Sabri Alamri, Bogdan Voisiat, Tim Kunze and Andrés F. Lasagni. Nano-Roughness on the Wettability Performance of Microstructured Metallic Surface Using Direct Laser Interference Patterning. Materials 2019, 12(17), 2737.

Abstract

Superhydrophobic natural surfaces usually have multiple levels of structure hierarchy, particularly microstructures covered with nano-roughness. The multi-scale nature of such a surface reduces the wetting of water and oils, and supports self-cleaning properties. In this work, in order to broaden our understanding of the wetting properties of technical surfaces, biomimetic surface patterns were fabricated on stainless steel with single and multi-scale periodic structures using direct laser interference patterning (DLIP). Micropillars with a spatial period of 5.5 µm and a structural depth of 4.2 µm were fabricated and covered by a sub-micro roughness by using ultrashort laser pulses, thus obtaining a hierarchical geometry. In order to distinguish the influence of the different features on the wettability behavior, a nanosecond laser source was used to melt the nano-roughness, and thus to obtain single-scale patterns. Then, a systematic comparison between the single- and multi-scale structures was performed. Although, the treated surfaces showed hydrophilic behavior directly after the laser treatment, over time they reached a steady-state hydrophobic condition. However, the multi-scale structured metal showed a contact angle 31° higher than the single-scale geometry when the steady-state conditions were reached. Furthermore, the impact of the surface chemistry was investigated by energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analyses. Finally, a hydrophobizing agent was applied to the laser treated samples in order to further enhance the water contact angles and to determine the pure contribution of the surface topography. In the latter case, the multi-scale periodic microstructures reached static contact angles of 152° ± 2° and a contact angle hysteresis of only 4° ± 2°, while the single-scale structures did not show superhydrophobic behavior. These results definitely suggest that multi-scale DLIP structures in conjunction with a surface chemistry modification can promote a superhydrophobic regime.

Link

https://doi.org/10.3390/ma12172737

Avoiding Starvation in Tribocontact Through Active Lubricant Transport in Laser Textured Surfaces

Results of the work in the Laser4Fun project has been published as:

Tobias Stark , Thomas Kiedrowski, Holger Marschall and Andrés Fabián Lasagni. Avoiding Starvation in Tribocontact Through Active Lubricant Transport in Laser Textured Surfaces. Lubricants 2019, 7(6), 54.

Abstract

Laser texturing is a viable tool to enhance the tribological performance of surfaces. Especially textures created with Direct Laser Interference Patterning (DLIP) show outstanding improvement in terms of reduction of coefficient of friction (COF) as well as the extension of oil film lifetime. However, since DLIP textures have a limited depth, they can be quickly damaged, especially within the tribocontact area, where wear occurs. This study aims at elucidating the fluid dynamical behavior of the lubricant in the surroundings of the tribocontact where channel-like surface textures are left after the abrasion wear inside the tribocontact area. In a first step, numerical investigations of lubricant wetting phenomena are performed applying OpenFOAM. The results show that narrow channels (width of 10 μm) allow higher spreading than wide channels (width of 30 μm). In a second step, fluid transport inside DLIP textures is investigated experimentally. The results show an anisotropic spreading with the spreading velocity dependent on the period and depth of the laser textures. A mechanism is introduced for how lubricant can be transported out of the channels into the tribocontact. The main conclusion of this study is that active lubricant transport in laser textured surfaces can avoid starvation in the tribocontact.

Link(s)

How to Tailor Structural Colors for Extended Visibility and White Light Generation Employing Direct Laser Interference Patterning

Results of the work in the Laser4Fun project has been published as:

Storm, S., Alamri, S., Soldera, M., Kunze, T., Lasagni, A. F., How to Tailor Structural Colors for Extended Visibility and White Light Generation Employing Direct Laser Interference Patterning. Macromol. Chem. Phys. 2019, 1900205. 

Abstract

The appearance of a surface can be controlled by creating periodic microstructures designed to diffract light and produce structural colors. Nevertheless, since structural coloration is based on diffraction, the produced colors have a strong dependence on the viewing angle and absence of coloration takes place while tilting the samples. In this work direct laser interference patterning is used to firstly provide transparent polymer sheets a structural coloration with a high‐range observation angle, and secondly to demonstrate the combination of structural colors, producing a white coloring effect. The employed approaches are based on the fabrication of micro‐gratings with multiple periods in the same structured area and on the engineering of the diffraction orders of the diffraction spectrum. The patterned surfaces are characterized by confocal microscopy and angular spectrometry in reflection mode. The morphological characterization shows homogeneous surface patterns, while the spectral results demonstrate that combining four spatial periods on a single patterned surface, a white appearance is obtained over an angular observation range higher than 30°. The experimental results are supported by theoretical predictions by means of generalized formulas based on the diffraction of light.

Link(s)

Video: Hydrophobiticy of DLIP functionalized surface on stainless steel

The Direct Laser Interference Patterning (DLIP) technique has been used to create a functionalized surface on stainless steel (black area). In combination with an additional post-treatment, the metal surface has extremely water-repellent properties with contact angles of over 150 degrees. The microscopic surface exhibits “miniature mountains” that create a superhydrophobic surface, similar to its natural pendent on a lotus leaf. The sample was placed under water (no wetting of the structured areas is observed) to emphasize the water repellency. Consequently, even if the surface gets wet, it actually stays dry in the laser processed areas. Finally, DLIP allows for self-cleaning properties on technological surfaces at industrially-relevant throughput.

Durability of superhydrophobic laser-treated metal surfaces under icing conditions

Results of the work in the Laser4Fun project has been published as:

Vittorio Vercillo, José Tiago Cardoso, Daniel Huerta-Murillo, Simone Tonnicchia, Alexandre Laroche, Javier Alejandro Mayén Guillén, José Luis Ocaña, Andrés Fabián Lasagni, Elmar Bonaccurso. Durability of superhydrophobic laser-treated metal surfaces under icing conditions. Materials Letters: X 3 (2019) 100021.. 

Abstract

Ice accretion on external surfaces of aircraft due to the impingement of supercooled liquid water droplets can be tackled by the implementation of icephobic surfaces. Among these, superhydrophobic surfaces represent a promising solution, due to their water repellent nature. In the last decade, short/ultra-short pulsed laser technologies have been proposed as a one-step process to manufacture superhydrophobic surfaces. However, the effectiveness and durability of such surfaces in operational icing conditions has not yet been validated. In this work, we investigate ice adhesion strength and the chemical stability of metal alloys textured with a UV nanosecond laser via Direct Laser Writing.

Link(s)

PhD degree awarded to Jose Cardoso and Daniel Huerta Murillo

On April 11, Jose Cardoso and Daniel Huerta successfully defended their PhD thesis and were awarded the degree of PhD.

Jose Cardoso and Daniel Huerta Murillo were PhD candidates and Early Stage Researchers in the Laser4Fun project. They were the third and fourth (out of thirteen) PhD candidates from the Laser4Fun project to be awarded with the PhD degree.

The doctoral thesis were developed on the Laser Centre under the direction of Dr. José Luis Ocaña and the public defense of the doctoral thesis took place on April 11th 2019 at the School of Industrial Engineering of the Polytechnical University of Madrid (ETSII – UPM). The defense court was formed by Dr. Jesus de Vicente y Oliva as President, Dr. Henryk Fiedorowicz, Dr. Francisco Javier Ester Sola and Dr. Antonio Gimenez Fernandez as Vocals and Dr. Angel Garcia Beltran as Secretary.

20190411_133604

Positive effect of laser structured surfaces on tribological performance

Results of the work in the Laser4Fun project has been published as:

Tobias Stark, Sabri Alamri, Alfredo I. Aguilar-Morales, Thomas Kiedrowski, Andrés Fabián Lasagni. Positive Effect of Laser Structured Surfaces on Tribological Performance. Journal of Laser Micro/Nanoengineering Vol. 14, No. 1, 2019.

Abstract

In recent years laser surface structuring has emerged as a viable tool to enhance surface function-ality. In this study, an ultrashort pulsed laser is used to create advanced surface structures in order to improve the tribological properties of steels. The objective is to decrease friction and wear especially for the mixed lubrication regime in which body and counterbody are in contact. We state the hypoth-esis that the high flow resistance in small channels helps to hold the lubricant in the tribocontact and therefore separates contacting asperities. Direct Laser Writing and Direct Laser Interference Pattern-ing methods are used to create cross-like structures of different channel sizes. Tribological properties of these structures are evaluated by means of a ball-on-disc tribometer. The surface structures and the wear behavior are analyzed with confocal microscopy. The results show a decrease of the coefficient of friction depending on the size of the channels. This behavior is discussed and compared to the hypothesis stated above.

Link(s)