In the present study, sustainable carbon fibers (CF) have been prepared from cellulose filaments and subsequently used as strain-sensing elements in composites. Using three continuous thermal processing steps (stabilization at 230 °C, low-temperature carbonization at 900 °C, and high-temperature carbonization at 1500 °C) followed by a discontinuous ultra-high temperature treatment at 2250 °C, CF offering a large variety of profiles regarding mechanical and electrical properties were prepared. A notable dependency trend was observed concerning the influence of treatment temperature, with the tensile modulus exhibiting a consistent increase with rising treatment temperature, reaching a maximum of 96 GPa. In contrast, the elongation at break showed an opposite trend. Additionally, improved order of the carbon structure, accompanied by decreasing electrical resistance, was also observed at higher thermal treatment temperatures. Three CF samples taken after low, high, and ultra-high temperature treatment were used as strain sensor elements in glass fiber reinforced polymer composites. All cellulose-based CF were viable for fracture-based strain sensing, but the CF sample taken after the high-temperature carbonization exhibited the most favorable sensor performance. A high gauge factor of 101, combined with low baseline resistance and consistent behavior across repeated loading cycles and relaxation times, was observed for this sample. Higher resistance and a lower gauge factor were observed for the specimens based on the ultra-high-temperature-treated CF despite better conductivity at the fiber level, highlighting that a combination of electrical and mechanical properties influences the strain sensing behavior.

Wheat straw represents a promising resource for structural materials due to its inherent strength and availability as an underutilized agricultural by-product. However, structural features such as small diameters and a hollow, low-density design, as well as a hydrophobic, waxy surface layer, hinder conventional processing. We present an approach to overcome these hindrances by engineering delignified and densified straw strands into a mechanically strong unidirectional composite material. Wheat straw split into strands along the fiber direction was subjected to water-based and mild alkaline pre-treatments and subsequently densified. As a result, the average tensile strength and modulus of elasticity of straw strands improved to impressive 466 MPa and 26 GPa, respectively. Simultaneously, chemical changes to the surface enabled better adhesive bonding. The resulting unidirectional straw composites exhibited a flexural strength of 190 MPa and an elastic modulus of 20 GPa, well within the range of established wood and bamboo-based materials.

ABSTRACTThe combination of different surface‐sensitive techniques is frequently used in material sciences to analyze complex systems. How these methods compare in terms of quantitative and qualitative information is often unclear. In this study, we directly compare low‐energy ion scattering spectroscopy (LEIS), secondary ion mass spectrometry (SIMS), and angle‐resolved X‐ray photoelectron spectroscopy (AR‐XPS) depth profiling analyses. Therefore, we use the Zn–Al–Mg model coatings after alkaline and acidic treatments in model solutions. The combined use of AR‐XPS and LEIS depth profiling proved effective in studying compositional and elemental changes in the surface oxides of Zn–Al–Mg coatings after alkaline and acidic treatments. Additionally, by combining these methods, SIMS depth profiling can be effectively calibrated for matrix effects. Here, we find that, for example, Mg is considerably more sensitive to SIMS detection, based on effective secondary ionisation. Such effects must be considered for data interpretation.

A self-developed liquid in situ cell gives insights into the diffusion of hydrogen in steel and its interaction with iron oxides. The cell initiates a corrosive reaction on one side of a galvanized steel sample within an X-ray photoelectron spectroscopy (XPS) system while changes of iron oxides on the opposite side attributed to diffused hydrogen are recorded. The reduction leads to a continuous alteration in the high-resolution Fe2p peak which is iteratively measured during hydrogen permeation. A detailed analysis of the process, involving layer thickness evaluation with the modified Strohmeier equation leads to a model of the developed oxide structure.

For the first time, an alkyl-chain free variant of polythieno[3,4-b]pyrazine (PTP) was created in a conductive state via oxidative chemical vapour deposition (oCVD). The charge transport properties of this new PTP are superior to those of the state-of-the-art ones by ten-fold with a conductivity of 0.5 S cm(-1) and the material is found in the metallic regime of the metal-insulator-transition as the conductivity is vastly independent on temperature. Herein, we investigate the chemical and physical composition of the material in order to explain this improvement and discuss the results in light of the polythiophenes produced using the same method. Using GIWAXS, we discover large crystalline features combined with smaller, highly organized assemblies and gain insight into the chain length. The chemical composition of the material is determined via XPS and FTIR and further supplemented by computational methods. We employ DFT calculations (omega B97X-V/def2-QZVP) to understand the differences between unsubstituted and alkylated PTP. The former shows stronger proclivity to form planar structures, and the conjugation is broken upon distortion. Alternatively, in the latter case, such disorder does not considerably affect the conjugation. Furthermore, we simulate the effects of doping based on XPS results and reveal the possibility of protonation, despite the low pK(a) of the materials. Furthermore, this protonation allows the materials to achieve a cis conformer despite the typical expectation suggesting the prevalence of the trans form. Molecular dynamics simulations (NPT MD) of 24 dodecamers confirm the prevalence of a trans conformer. However, at multiple occasions, trimers of the cis motif form. The simulations predict stronger charge transport in the trans conformer. However, the cis isomer exhibits relevant levels and an extremely low HOMO-LUMO difference (<0.1 eV). This indicates the possibility of high conductivities and explains the hallmarks of metallic charge transport we observe experimentally.

Epoxy coatings cured with the latent curing agent dicyandiamide (DICY) are well-established. During coating of waterborne epoxy varnishes onto the metal substrate, chemical interactions take place, which were evaluated in this paper for different metal substrates. Moreover, their effect on the fatigue crack growth kinetics of bonded laminates was assessed. First, different pure metal sheets were immersed in a boiling solution of DICY in distilled water. Metals with a lower isoelectric point (IEP) (pH < 5) revealed the formation of a higher amount of protonated amine. In contrast, for metals with a higher IEP (pH > 8) the formation of imine was preferred. Furthermore, epoxy coated metal sheets were prepared by cryo ultra-low-angle microtomy (cryo-ULAM) and the reaction products were elucidated by X-ray photoelectron spectroscopy (XPS). Close to the metal/epoxy interface, reaction products were ascertained, which corroborated the results of the immersion test. Finally, the effect of the IEP of the substrate on the crack growth kinetics of bonded laminates was evaluated by cyclic fatigue experiments on double cantilever beam specimens. The higher the IEP of the metal substrate, the better was the crack growth resistance in the threshold and stable crack growth regime. Overall, this study clearly confirmed that chemical interactions are taking place during manufacturing of metal/waterborne epoxy laminates, which have a significant impact on the adherence and crack growth resistance.

Essential for the durability of photovoltaic (PV) modules is the polymeric encapsulant. In addition to the well-established ethylene vinyl acetate copolymers (EVA), polyolefin elastomers (POE) are gaining market relevance. The main objective of this paper was to elucidate the ageing and degradation mechanisms of PV relevant glass laminates based on UV-transparent EVA and POE encapsulants by X-ray photoelectron spectroscopy (XPS).Special focus was given to the polymer/glass interfaces. Therefore, glass laminates were damp heat aged and debonded by monotonic compressive shear testing. Subsequently, the polymer side of the fractured surfaces was characterized by XPS and Fourier-transform infrared spectroscopy (FTIR). The polar EVA encapsulant revealed more pronounced deterioration than the less polar POE material.Significant differences were already discernible after 1kh of damp heat exposure. The diffusion of Na ions from the glass substrate into the polymer matrix and the formation of Na salts at the interface were ascertained for EVA and to a less extent also for POE. While EVA laminates failed primarily close to the interface, but still within the EVA material, glass residues were detected on the fractured POE surfaces indicating interface-near glass corrosion and a fracture path propagating back and forth within POE and glass.

Zr-based conversion coatings represent an environmentally conscious alternative to traditional phosphating and chromating in the automotive industry. In this study, we employ XPS and LEIS to investigate the formation of Zr-conversion layers on Zn-Mg-Al alloy after alkaline and acidic model pretreatments. On alkaline pretreated surfaces, a Zr-oxide/oxyfluoride layer and an underlying Mg-Al-fluoride layer are formed, whereas acidic pretreatment results in only an oxidic layer. The thickness of the Zr-layer depends on pretreatment pH and immersion time. Acidic treatment achieves an approximately 23 nm-thick Zr-oxide/oxyfluoride layer after 1 min, while prolonged treatment increases the thickness of the oxidic layer for strong alkaline and acidic conditions. Mild alkaline pretreatments, however, do not benefit from extended immersion. F-induced corrosion pits are observed after mild alkaline treatment. The strong alkaline pretreatment proved to be the most efficient in creating a double-layered Zr-conversion coating with increased oxidic layer thickness over time.

Ethylene vinyl acetate (EVA) copolymers are commonly used as encapsulation material and as adhesive layer for backsheet laminates of photovoltaic (PV) modules. While Fourier-Transform Infrared spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC) are well established to analyse EVA encapsulants in PV modules, X-ray Photoelectron Spectroscopy (XPS) is seldomly used. Hence, the objective of this paper was to evaluate the potential and limitations of XPS for advanced analysis and testing of EVA encapsulants. Consequently, EVA grades of different vinyl acetate (VA) comonomer content were characterized and evaluated systematically by XPS, FTIR and DSC. Independent on the analytic technique linear relationships between the obtained values and VA contents were confirmed. Slightly higher VA contents on the surface deduced by XPS were attributed to a surface layer rich of amorphous phase material. In addition, XPS analysis of peroxide modified encapsulants with a VA comonomer content of 30.2 wt% revealed a higher carbon content on the surface after crosslinking. Hence, it is proposed that peroxide crosslinking is associated with deacetylation and the subsequent release of low molar mass decomposition products. Overall, the exceptional surface sensitivity of XPS was clearly confirmed for analysis and testing of EVA grades, highlighting the potential of the method for further degradation and interaction studies of components of PV modules.

Grain boundary wetting as a preliminary stage for zinc-induced grain boundary weakening and embrittlement in a Zn-coated press-hardened 20MnB8 steel was analyzed using electron backscatter diffraction, Auger electron spectroscopy, energy dispersive X-ray analysis, atom probe tomography and transmission electron microscopy. Microcracks at prior austenite grain boundaries were observed. Structures that developed after microcrack formation were identified: for example, Zn/Fe intermetallic phases with grain sizes smaller than 100 nm were present at the crack surfaces and the wedge-shaped crack tips. An electrolytically coated reference sample that underwent the same heat treatment as the press-hardened material but without the application of tensile stress was investigated in order to find the initial cause of the microcracks. On this sample, Zn, in the order of one atomic layer, was found along prior austenite grain boundaries several micrometers away from the actual Zn/Fe phases in the coating. The resulting grain boundary weakening with the Zn wetting of prior austenitic grain boundaries during austenitization and/or hot forming is a necessary precondition for microcrack formation.

In this study the oxide layer of technical 6xxx aluminium surfaces, pickled as well as passivated, were comparatively investigated by means of transmission electron microscopy (TEM), Auger electron and X-ray photoelectron spectroscopy (AES, XPS), the latter in two different operating modes, standard and angle resolved mode. In addition, confocal microscopy and focused ion beam cutting were used for structural studies of the surfaces and for specimen preparation. The results illustrate in detail the strengths and weaknesses of each measurement technique. TEM offers a direct way to reliably quantify the thickness of the oxide layer, which is in the range of 5 nm, however, on a laterally restricted area of the surface. In comparison, for AES, the destructiveness of the electron beam did not allow to achieve comparable results for the thickness determination. XPS was proven to be the most reliable method to reproducibly quantify the average oxide thickness. By evaluating the angle resolved XPS data, additional information on the average depth distribution of the individual elements on the surface could be obtained. The findings obtained in this study were then successfully used for the investigation of the increase in the aluminium oxide thickness on technical samples during an aging test of 12 months under standard storage conditions.

The aim of this contribution is to present a comprehensive approach to study the extent of hydrogen entry into a hot-dip-galvanized DP1000 steel, which is exposed to corrosive conditions. For this purpose, the Z100 coating was immersed in 5% sodium chloride solution at room temperature. The distribution of hydrogen and the spots of increased hydrogen entry were detected with scanning Kelvin probe (SKP) and scanning Kelvin probe force microscopy (SKPFM). Effects of hydrogen inserted during corrosion on the mechanical properties were determined in slow-strain rate tests (SSRT). Hydrogen quantification was achieved via thermal desorption mass spectrometry (TDMS), giving additional insights into the mobility of the inserted hydrogen within the steel by distinguishing diffusible and trapped hydrogen.

Alkaline cleaning of Zn–Al–Mg coated hot-dip galvanized steel is a central process in the industrial galvanized steel production. This process removes carbonaceous contaminants from the surface and modifies the surface chemistry profoundly. We implement a combined analytical and surface science approach to characterize the dissolution mechanism and surface chemistry of Zn-Al-Mg coatings after treatment with industrial cleaners with pH 9.3 and 12.7, respectively. Our data indicate that weak alkaline cleaning can significantly increase the surface concentration of Zn-oxide, while strong alkaline cleaning dissolves the native oxide and generates a transient Zn/Mg-hydroxide on the surface. The observed dissolution mechanisms are largely consistent with the expectations from the Pourbaix diagrams, i.e. at pH 12.7 aluminium dissolution is expected while Mg is stable and forms a transient passive film. In contrast, mild alkaline cleaning at pH 9.3 is dominated by Mg and Zn dissolution, while the native Al passive film remains stable. Hence the cleaning provides an effective direct modification of the surface chemistry for subsequent process steps during the coating. Mild alkaline cleaning offers an increase of Zn at the surface, which has important implications for subsequent conversion and adhesive applications, that have been traditionally optimized for pure Zn coatings.

In the automotive industry, the application of dry lubricants on aluminium is indispensable for achieving a high-quality forming behaviour. To provide a short production time, these forming aids are not removed during the joining step. The aim of this study is the characterisation of the influence of dry lubricants on the bond strength and the corrosion resistance of a 6xxx aluminium alloy for automotive applications. For this purpose, samples with a well-defined surface were coated with 1 g/m2 dry lubricant and joined with a commercial thermosetting 1K epoxy structural adhesive. The bond strength was measured with lap shear tests. To evaluate the corrosion resistance of the adhered aluminium samples, an immersion test in a 5 wt.% NaCl solution was used. Based on the fracture pattern analysis, the corrosion behaviour could be described, and the possible corrosion mechanisms are proposed. The influence of the load quantity of the dry lubricants is observed microscopically and mechanically. The environmentally induced degradation process of the adhesive is examined by an investigation of the volumetric change during the testing and with scanning electron microscopy. Using a simulation, the changes in the adhesive polymer matrix at the metal–adhesive interface caused by the dry lubricants are examined using polymer test procedures like dynamic mechanical analysis, differential scanning calorimetry and tensile tests. The results show a significant effect of the forming aid on the corrosion resistance of the adhered aluminium samples against the corrosive infiltration of the metal–adhesive interface.

Aliovalent-doped metal oxide nanocrystals exhibiting localized surface plasmons (LSPRs) are applied in systems that require reflection/scattering/absorption in infrared and optical transparency in visible. Indium tin oxide (ITO) is currently leading the field, but indium resources are known to be very restricted. Antimony-doped tin oxide (ATO) is a cheap candidate to substitute the ITO, but it exhibits less advantageous electronic properties and limited control of the LSPRs. To date, LSPR tuning in ATO NCs has been achieved electrochemically and by aliovalent doping, with a significant decrease in doping efficiency with an increasing doping level. Here, we synthesize plasmonic ATO nanocrystals (NCs) via a solvothermal route and demonstrate ligand exchange to tune the LSPR energies. Attachment of ligands acting as Lewis acids and bases results in LSPR peak shifts with a doping efficiency overcoming those by aliovalent doping. Thus, this strategy is of potential interest for plasmon implementations, which are of potential interest for infrared upconversion, smart glazing, heat absorbers, or thermal barriers.

Polymeric materials play an emerging role in biosensing interfaces. Within this regard, polymers can serve as a superior surface for binding and printing of biomolecules. In this study, we characterized 11 different polymer foils [cyclic olefin polymer (COP), cyclic olefin copolymer (COC), polymethylmethacrylate (PMMA), DI-Acetate, Lumirror 4001, Melinex 506, Melinex ST 504, polyamide 6, polyethersulfone, polyether ether ketone, and polyimide] to test for the applicability for surface functionalization, biomolecule micropatterning, and fluorescence microscopy approaches. Pristine polymer foils were characterized via UV-vis spectroscopy. Functional groups were introduced by plasma activation and epoxysilane-coating. Polymer modification was evaluated by water contact angle measurement and X-ray photoelectron spectroscopy. Protein micropatterns were fabricated using microcontact printing. Functionalized substrates were characterized via fluorescence contrast measurements using epifluorescence and total internal reflection fluorescence microscopy. Results showed that all polymer substrates could be chemically modified with epoxide functional groups, as indicated by reduced water contact angles compared to untreated surfaces. However, transmission and refractive index measurements revealed differences in important optical parameters, which was further proved by fluorescence contrast measurements of printed biomolecules. COC, COP, and PMMA were identified as the most promising alternatives to commonly used glass coverslips, which also showed superior applicability in subcellular micropatterning experiments.

The detection and quantification of carbon by conventional energy dispersive X-ray spectroscopy (EDXS) performed under standard conditions is not feasible due to occurring contaminations in common electron microscopes. In contrast, novel ultra high vacuum EDXS (UHV-EDXS) was used to acquire elemental mappings of carbon on dual phase (DP) steel, which exhibits a microstructure consisting of ferrite and martensite. These phases differ in hardness, local dislocation density and, most importantly, in their carbon content. Since the UHV conditions in combination with a customized windowless EDXS detector ensured a minimization of hydrocarbon contamination during the measurements and a maximization of the sensitivity for the detection of light elements, UHV-EDXS carbon mappings could successfully be obtained, which clearly reflect the ferrite and martensite microstructure of the investigated DP steels, as confirmed by electron back scatter diffraction (EBSD). Most importantly, it was possible to quantify the carbon content of individual grains with concentrations as low as 0.25 wt%. Furthermore, nano-hardness tests were performed on the very same grains which were characterized by UHV-EDXS and EBSD. It is shown that the hardness of the martensite grains is correlated to their carbon content, as directly determined by UHV-EDXS. With this new method an additional tool for advanced material characterization of multiphase materials on the level of individual grains is now available.

In this paper, biobased carbons were used as fillers in poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). The mechanical and electrical properties of these 100% biocomposites were analyzed. First, biocarbons were prepared from wood dust and cellulose fibers using carbonization temperatures ranging 900–2300 °C. XRD revealed significant improvements of the graphitic structure with increasing temperatures for both precursors, with slightly higher ordering in wood-dust-based carbons. An increase of the carbon content with continuous removal of other elements was observed with increasing temperature. The carbonized cellulose fiber showed an accumulation of Na and O on the fiber surface at a carbonization temperature of 1500 °C. Significant degradation of PHBV was observed when mixed with this specific filler, which can, most probably, be attributed to this exceptional surface chemistry. With any other fillers, the preparation of injection-molded PHBV composites was possible without any difficulties. Small improvements in the mechanical performance were observed, with carbonized fibers being slightly superior to the wood dust analogues. Improvements at higher filler content were observed. These effects were even more pronounced in the electrical conductivity. In the range of 15–20 vol.% carbonized fibers, the percolation threshold could be reached, resulting in an electrical conductivity of 0.7 S/cm. For comparison, polypropylene composites were prepared using cellulose fibers carbonized at 2000 °C. Due to longer fibers retained in the composites, percolation could be reached in the range of 5–10 vol.%. The electrical conductivity was even higher compared to that of composites using commercial carbon fibers, showing a great potential for carbonized cellulose fibers in electrical applications.

Atmospheric corrosion is one of the major sources of hydrogen in a high-strength-steel product in service. Even low concentrations of absorbed hydrogen can cause a hydrogen embrittlement-related material degradation. The extent of atmospheric corrosion and thus the related hydrogen entry is highly dependent on the environmental parameters, such as the relative humidity. The present work focused on the hydrogen entry at low relative humidity, where atmospheric corrosion rates are expected to be low. Hydrogen insertion and distribution in CP1000 steel induced by corrosion under dried and rewetted single droplets of aqueous NaCl and MgCl2 solution were studied using the Scanning Kelvin Probe (SKP) and the resulting amounts of diffusible hydrogen were analyzed using thermal desorption mass spectrometry (TDMS). Corrosion product analyses were carried out with SEM/EDX, XRD, and Mössbauer spectroscopy. The results revealed the strong impact of salt type and concentration on the hydrogen entry into steel. The hygroscopic effect of MgCl2 and the formed corrosion products were responsible for the prolonged insertion of hydrogen into the steel even at very low levels of relative humidity.