An in-depth evaluation of sample and measurement induced influences on static contact angle measurements

Static contact angle measurements are one of the most popular methods to analyze the wetting behavior of materials of any kind. Although this method is readily applicable without the need of sophisticated machinery, the results obtained for the very same material may vary strongly. The sensitivity of the measurement against environmental conditions, sample preparation and measurement conduction is a main factor for inconsistent results. Since often no detailed measurement protocols exist alongside published data, contact angle values as well as elaborated wetting studies do not allow for any comparison. This paper therefore aims to discuss possible infuences on static contact angle measurements and to experimentally demonstrate the extent of these efects. Sample storage conditions, cleaning procedures, droplet volume, water grade and droplet application as well as the infuence of evaporation on the static contact angle are investigated in detail. Especially sample storage led to diferences in the contact angle up to 60%. Depending on the wetting state, evaporation can reduce the contact angle by 30–50% within 10 min in dry atmospheres. Therefore, this paper reviews an existing approach for a climate chamber and introduces a new measuring setup based on these results. It allows for the observation of the wetting behavior for several minutes by successfully suppressing evaporation without negatively afecting the surface prior to measurement by exposure to high humidity environments

Applying Ultrashort Pulsed Direct Laser Interference Patterning for Functional Surfaces

Surface structures in the micro- and nanometre length scale exert a major influence on performance and functionality for many specialized applications in surface engineering. However, they are often limited to certain pattern scales and materials, depending on which processing technique is used. Likewise, the morphology of the topography is in complex relation to the utilized processing methodology. In this study, the generation of hierarchical surface structures in the micro- as well as the sub-micrometre scale was achieved on ceramic, polymer and metallic materials by utilizing Ultrashort Pulsed Direct Laser Interference Patterning (USP-DLIP). The morphologies of the generated patterns where examined in relation to the unique physical interaction of each material with ultrashort pulsed laser irradiation. In this context, the pattern formation on copper, CuZn37 brass and AISI 304 stainless steel was investigated in detail by means of a combination of experiment and simulation to understand the individual thermal interactions involved in USP-DLIP processing. Thereby, the pattern’s hierarchical topography could be tailored besides achieving higher process control in the production of patterns in the sub-µm range by USP-DLIP

Effects of Ultrashort Pulsed Direct Laser Writing on Ni/Al Reactive Multilayer Foils

Reactive multilayer foils (RMFs) for joining processes have attracted a great deal of attention over the last few years. They are capable of exothermic self-propagating reactions and can serve as localized heat sources for joining applications when ignited by suitable means. Using short and ultrashort pulsed lasers with carefully selected parameters, cutting and shaping of RMFs makes it possible to tailor heat release characteristics without triggering the reaction. The present study is an investigation of microstructural changes induced by femtosecond laser machining of a commercially available Ni/Al-based RMF. The effects of the specific laser parameters pulse duration and repetition rate on the heat-affected zone (HAZ) are investigated by scanning and transmission electron microscopy. Debris consisting of oxide deposits can be found at a distance of several tens of microns from the cut edge. A negligible HAZ extending to less than 100 nm was observed for all parameters tested and no signs of ignition of a self-propagating reaction were observed. These results underline the suitability of femtosecond lasers for metal machining with minimal heat input

Single‐step Production of Photocatalytic Surfaces via Direct Laser Interference Patterning of Titanium

State of the art approaches to produce photocatalytic surfaces generally require multiple processing steps to achieve highly active surfaces. Following recent trends to facilitate the production of active surfaces, this work presents a single-step method to create porous photocatalytic surfaces via direct laser interference patterning (DLIP) of a titanium substrate with pulses in the picosecond range. The resulting surfaces contain a variety of titanium oxides while both their composition and morphology can be controlled through the laser process parameters. This makes it possible to tailor these surfaces for specific applications such as antimicrobial surfaces, implant materials or water treatment. Surface characterization was executed by applying scanning electron microscopy complemented by focused ion beam cross-sectioning and energy dispersive X-ray spectroscopy as well as gracing incidence X-ray diffractometry. The photocatalytic activity achieved by different laser parameters is assessed by methylene blue degradation under UV-A light. As DLIP is already established in industrial applications, this approach could greatly facilitate the use of photocatalytic surfaces for water treatment or medical applications, as it does not require nanoparticle synthesis or additional coating steps

Denial of long-term issues with agriculture on tropical peatlands will have devastating consequences

Non peer reviewe

Mesostructural Design and Manufacturing of Open-Pore Metal Foams by Investment Casting

The present paper describes the manufacturing process of open-pore metal foams by investment casting and the mesostructural/morphological evolution resulting from a new technique of modifying the precursor. By this technique, the precursor is coated with a polymer layer whereby a thickening of the struts occurs. Relative densities in the range of 1.85≤ρrel≤25% of open-pore metal foams can be achieved with high accuracy. The samples investigated have pore densities of ρP=7 ppi, 10 ppi, and 13 ppi. The relevant processing parameters needed for a homogenous formation of the polymer layer are determined for two different coating materials and the resulting open-pore foam’s mesostructure is characterized qualitatively and quantitatively. The alloy used for investment casting open-pore metal foamsis AlZn11. The microstructural evolution of these foams is evaluated as a function of the mesostructure. Differences in the microstructure are observed for foams with low and high relative densities and discussed in terms of cooling subsequent to investment casting

Multi-pulse agglomeration effects on ultrashort pulsed direct laser interference patterning of Cu

Surface functionalization by biomimetic patterns in the micro- and nanometer scale is well-established in a wide range of applications. The finely tuned surface properties are directly related to both primary and sub-pattern morphology of the applied topographies, which must be well-adjusted for maximum functionalization effi ciency. In this light, the role of proceeding surface modification and its effect on pattern formation alongside multi-pulse ultrashort pulsed direct laser interference patterning (USP-DLIP) of Cu are investigated in detail by applying a multi-method characterization approach. It was shown that aside of topographical remodeling, USP DLIP processing parallelly affects chemistry and the mechanical deformation state of the substrate surface, which in turn considerably influences laser/material interaction via incubation. An in-depth investigation of the in dividual and combined impacts of these substrate alterations on localized optical absorptance reveals how pri mary and sub-pattern formation dynamically respond to process induced surface modification. The DLIP-specific incubation impact on pattern morphology increases with inverted relation to pattern scale. The findings of this study provide a profound insight in the predominant physical interactions involved in pattern formation arising from the mutual influence between laser irradiation and substrate modification during USP-DLIP-processing of Cu allowing for high precision micro- and nanometer scaled pattern design

Effects of Ultrashort Pulsed Direct Laser Writing on Ni/Al Reactive Multilayer Foils

Reactive multilayer foils (RMFs) for joining processes have attracted a great deal of attention over the last few years. They are capable of exothermic self-propagating reactions and can serve as localized heat sources for joining applications when ignited by suitable means. Using short and ultrashort pulsed lasers with carefully selected parameters, cutting and shaping of RMFs makes it possible to tailor heat release characteristics without triggering the reaction. The present study is an investigation of microstructural changes induced by femtosecond laser machining of a commercially available Ni/Al-based RMF. The effects of the specific laser parameters pulse duration and repetition rate on the heat-affected zone (HAZ) are investigated by scanning and transmission electron microscopy. Debris consisting of oxide deposits can be found at a distance of several tens of microns from the cut edge. A negligible HAZ extending to less than 100 nm was observed for all parameters tested and no signs of ignition of a self-propagating reaction were observed. These results underline the suitability of femtosecond lasers for metal machining with minimal heat input

There & Back again: Developing a tool for testing of antimicrobial surfaces for space habitat design

Human space habitat design and hygiene systems are increasingly relevant topics particularly due to the planned human missions to deep space in the future. In crewed space missions, thus in confined indoor living habitats microorganisms are impossible to eliminate since each individual astronaut is carrying diverse microbial communities. Besides beneficial microorganisms, which play an important role in maintaining skin and gut health, there are also opportunistic pathogens which can manifest in an indoor space environment and may cause infections in astronauts. The microbial burden of a closed habitat is a significant factor contributing to the crew's health and wellbeing. Hereby, surfaces can pose as a reservoir for various microorganisms. Additionally, some microorganisms can compromise functionality of onboard systems. Hence, consideration and evaluation of microbial dispersal, growth, and adaptation of microorganisms to monitor and prevent microbial contamination of harmful bacteria is crucial, especially in the context of space travel. One promising approach to reducing microbial contamination is the use of antimicrobial surfaces. In “Touching Surfaces” novel copper-based antimicrobial surfaces were tested under real space conditions on the ISS, in schools, and in clinical settings. Touching Surfaces was part of the Cosmic Kiss mission of ESA astronaut Matthias Maurer and tested onboard the ISS. Upon return to Earth, the Touch Arrays were analyzed regarding their microbial community using next generation sequencing and culture- dependent isolation, as well as material integrity by electron microscopy to determine antimicrobial efficiency, which will then be related to the environmental conditions on the ISS. One key objective of Touching Surfaces is the evaluation of antimicrobial surfaces to reduce microbial contamination on the ISS. The hardware of Touching Surfaces allows easy implementation and testing of different surfaces. Results of Touching Surfaces will aid in developing a conveniently implementable tool for future interdisciplinary health and space habitat design