PhD degree awarded to Sabri Alamri

On September 4th, 2020, the Early Stage Researcher Sabri Alamri, from the Laser4Fun project, successfully defended his thesis for the degree of Doctor.

The work titled “Advanced microstructuring strategies of polymers using Direct Laser Interference Patterning” was carried out at Technical University Dresden and the Fraunhofer IWS, both in Germany, under the supervision of Professor Andres Lasagni.

We congratulate Sabri on his achievement!

PhD defense ceremony Marek Mezera on Oct. 16th 2020

Marek Mezera an Early Stage Researcher (ESR), will defend his PhD-thesis on October 16th, starting at 16:30 o’clock in room 4 of the Waaier building of the University of Twente in The Netherlands. Supervised by prof.dr.ir. Gert-willem Römer and Dr.ir. Dave Matthews, he carried out most of his work at the Chair of Laser Processing at the University of Twente. Below is a summary of the work and results of Marek.

Summary

The interaction of an object with its surroundings depends firstly on the object’s surface, which determines its surface properties due to its chemical properties and macro- and microscopic structures on the surface. Earth’s flora and fauna offers a vast collection of different specialized surface properties due to (hierarchical) micro- and nanostructures. These natural examples serve as a catalog for scientists and product designers who aim for replicating those properties. A one-step method to produce highly regular (hierarchical) nanostructures is to create Laser-induced Periodic Surface Structures (LIPSS). Although extensively studied in the last half century, LIPSS manufacturing did not emerge from an experimental status into industrial applications due to scientific and technical challenges. In this thesis, a picosecond pulsed laser source is evaluated for the potential of processing a large portfolio of LIPSS on different types of materials. Therefore, six research topics are addressed. First, the feasibility of processing LIPSS on polymers using a picosecond pulsed laser source was studied. It was found, that LIPSS can be indeed be processed on two most prominent polymers (polycarbonate and polystyrene) using picosecond pulsed laser sources. The wavelength range, at which LIPSS production was possible was found to be wider than for nanosecond pulsed laser sources, but not as wide as for femtosecond pulsed laser sources. However, the range of peak fluence levels and number of pulses impinging one spot needed to produce LIPSS are found to be similar for all laser pulse durations. Second, the influence of the bulk temperature of a thermoplastic polymer (polycarbonate) on the formation of LIPSS using a picosecond pulsed laser source was investigated. It was found that the peak fluence levels at which LIPSS form decrease with increasing bulk temperature. However, the bulk temperature did not influence the number of pulses impinging one spot necessary for LIPSS development. From this, it can be concluded, that the development of so-called Low Spatial Frequency LIPSS of type II (LSFL-II) is an accumulative process, depending on the number of pulses and that LIPSS formation is strongly affected by the local sample temperatures reached and by the involved strong variations of the polymer viscosity. Third, the formation of LIPSS on a pre-structured polymer (polycarbonate) was examined in order to achieve hierarchical micro-/nano-surface structures. It was found that LIPSS can be formed on top of various forms and sizes of micrometer-sized Direct Laser Interference Patterning (DLIP) structures (ridges) by selecting the laser beam polarization perpendicular to the pre-structured microscopic ridges. Since LIPSS only form in a narrow window of laser fluence levels, the growth of LIPSS only on top of the pre-structured microscopic ridges was limited by the non-normal angle of incidence of the laser radiation at the side walls of the microscopic ridges. Fourth, the feasibility of producing all types of LIPSS known to form on metals due to femtosecond laser pulses, by using a picosecond laser source, with different types of laser polarizations on a medical-grade cobalt-chrome-molybdenum alloy was explored. It was found that indeed all of LIPSS types which form due to femtosecond laser pulses on metals can be produced using picosecond laser pulses. Fifth, a mathematical model was developed to predict the homogeneity of large areas | i.e. larger than the area of a laser spot | of LIPSS depending on laser processing parameters and material constants. The model was validated by experiments on silicon. This model can also be used to optimize laser processing parameters to decrease the production time for large areas of LIPSS. It was concluded, that the model is a convenient tool, which can be exploited for determining the process parameters necessary for the production of large homogeneous areas of LIPSS at the shortest possible production time. Last, it was shown that the LIPSS production time for Low Spatial Frequency LIPSS of type I (LSFL-I) can be further decreased by defocused laser processing. That is, it was shown experimentally that LIPSS produced on silicon do not differ in periodicity and height when processing in focus, or below or above the focus of the laser beam. Hence, to further increase production rates of LIPSS, defocused laser processing is a viable approach.

LASER4FUN: the European Network on short pulsed laser micro/nanostructuring of surfaces

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

Antonio Ancona, Andrés Fabián Lasagni, Gert-willem R. B. E. Römer, Stefan Dimov, Rainer Kling, Thomas Kiedrowski, José Luis Ocaña, Elmar Bonaccurso, Carsten Werner, Andrés Escartín Barduzal. LASER4FUN: the European Network on short pulsed laser micro/nanostructuring of surfaces. 21st International Symposium on Laser Precision Microfabrication, 23 – 26 June 2020.

Abstract

Bio-inspired surface structures, containing features at the nanometer/micrometer scales, offer significant commercial potential for the creation of functionalized surfaces. To this extent, technologies to modify surfaces instead of creating composites or applying coatings on surfaces can offer new industrial opportunities. The aim of the LASER4FUN project was to structure surfaces embedding properties for industrial applications. The research programme resulted in insights and applications beyond the current state of the art through the development of new surface micro/nano-structuring/patterning methods by using emerging short pulsed and ultra-short pulsed laser technologies, i.e. Laser-Induced Periodic Surface Structures (LIPSS), Direct Laser Interference Patterning (DLIP), Direct Laser Writing (DLW) and two hybrid technologies. New laser-induced surface textures, and parameters to control these, were developed. Optimized laser-induced surface textures were developed for various surface functionalities for applications in the fields of e.g. tribology, aesthetics and wettability. In addition, methods, strategies and tools to allow production of these surface textured at high industrial production rates were developed. The project created an International Training Network (ITN) for Early Stage Researchers (ESRs) in the exciting field of laser-material processing, consisting of 14 doctoral students recruited by 10 international partners with wide experience in the field: 3 academic partners, i.e. Polytechnic University of Madrid (Spain), University of Birmingham (UK) and University of Twente (Netherlands), 4 research centers, i.e. Alphanov (France), Consiglio Nazionale delle Richerche (Italy), Fraunhofer Institute (Germany) and IPF-Leibniz-Institute fur Polymerforschung Dresden (Germany), and 3 industrial partners, i.e. Robert Bosch (Germany), Airbus (Germany), BSH Home Appliances (Spain). The close cooperation among multidisciplinary partners have fostered knowledge transfer to cross the Death Valley between science and the markets. Additionally, their participation in the LASER4FUN project have impacted highly the ESRs employability to knowledge-intensive companies/institutes that are the key for EU welfare. During the project duration more than 50 publications were prepared and more than 50 dissemination events (targeting both academica, industry and the general public) took place.

Link(s)

https://lpm2020.inventum.de

Design Rules for Laser‐Treated Icephobic Metallic Surfaces for Aeronautic Applications

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

Vittorio Vercillo, Simone Tonnicchia, Jean‐Michel Romano, Antonio García‐Girón, Alfredo I. Aguilar‐Morales, Sabri Alamri, Stefan S. Dimov, Tim Kunze, Andrés Fabián Lasagni, Elmar Bonaccurso. (2020) Design Rules for Laser‐Treated Icephobic Metallic Surfaces for Aeronautic Applications. Advanced Functional Materials, 1910268.

 

Abstract

Ice accretion on external aircraft surfaces due to the impact of supercooled water droplets can negatively affect the aerodynamic performance and reduce the operational capability and, therefore, must be prevented. Icephobic coatings capable of reducing the adhesion strength of ice to a surface represent a promising technology to support thermal or mechanical ice protection systems. Icephobicity is similar to hydrophobicity in several aspects and superhydrophobic surfaces embody a straightforward solution to the ice adhesion problem. Short/ultrashort pulsed laser surface treatments are proposed as a viable technology to generate superhydrophobic properties on metallic surfaces. However, it has not yet been verified whether such surfaces are generally icephobic under representative icing conditions. This study investigates the ice adhesion strength on Ti6Al4V, an alloy commonly used for aerospace components, textured by means of direct laser writing, direct laser interference patterning, and laser‐induced periodic surface structures laser sources with pulse durations ranging from nano‐ to femtosecond regimes. A clear relation between the spatial period, the surface microstructure depth, and the ice adhesion strength under different icing conditions is investigated. From these observations, a set of design rules can be defined for superhydrophobic surfaces that are icephobic, too.

Link(s)

https://onlinelibrary.wiley.com/doi/full/10.1002/adfm.201910268

PhD degree awarded to Antonio García Girón

On 28th February 2020, our Early Stage Researcher Antonio García Girón, from the Laser4Fun project, successfully defended his thesis for the degree of Doctor of Philosophy.

The work titled “Laser-based surface functionalisation: advances in durability and 3D processing” was carried out in the University of Birmingham under the supervision of Professor Stefan Dimov, studying some limitations of the laser surface functionalisation. The examination board was composed by Dr. C. Kong, Dr. S. Bigot and Dr. N. Gao, and the viva took place at the University of Birmingham in the morning on 28th February 2020.

Summary of Antonio’s research
Surface functionalization is gaining interests for industry and research due to the new attractive properties that can be “imprinted” on metal components, e.g. bacteria repellence or hydrophobicity among others. Considering the available alternative technologies to achieve such functional responses, direct laser writing is gaining a popularity due to its cost-effectiveness, selectivity and relatively short processing time. It allows surface properties to be modified or tuned by patterning and texturing at micron or submicron scales. However, laser surface functionalization has some limitations, too, such as the durability of the produced topographies and hence of their functionality, and also capabilities to apply it on free-form surfaces. In this context, the focus of the research presented in this thesis is on addressing these open issues. In particular, a combination of plasma surface alloying and laser patterning is proposed in order to increase hardness of produced functional surfaces, and thus to increase their wear resistance and durability. Also, a method to study the effects of the process disturbances in patterning 3D surfaces is proposed, especially on resulting topographies and their functional responses. All together, the research advances the knowledge in laser surface patterning and addresses key constraints for the broader use of this technology by industry.

Development of an Analytical Model for Optimization of Direct Laser Interference Patterning

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

Bogdan Voisiat, Alfredo I. Aguilar-Morales, Tim Kunze and Andrés Fabián Lasagni. Development of an Analytical Model for Optimization of Direct Laser Interference Patterning. Materials 13 (200), 2020.

Abstract

Direct laser interference patterning (DLIP) has proven to be a fast and, at the same time, high-resolution process for the fabrication of large-area surface structures. In order to provide structures with adequate quality and defined morphology at the fastest possible fabrication speed, the processing parameters have to be carefully selected. In this work, an analytical model was developed and verified by experimental data, which allows calculating the morphological properties of periodic structures as a function of most relevant laser-processing parameters. The developed
model permits to improve the process throughput by optimizing the laser spot diameter, as well as pulse energy, and repetition rate. The model was developed for the structures formed by a single scan of the beam in one direction. To validate the model, microstructures with a 5.5 m spatial period were fabricated on stainless steel by means of picosecond DLIP (10 ps), using a laser source operating at a 1064 nm wavelength. The results showed a di erence of only 10% compared to the experimental results.

Link(s)

https://doi.org/10.3390/ma13010200

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