Abstract
Polymers are used in a variety of different areas, including applications in food packaging, automotive and the semiconductor industry. Information about degradation of these materials ...during application, but also uptake of pollutants from the surrounding environment is therefore of great interest. Conventional techniques used for polymer characterization such as FT-IR or Raman spectroscopy, but also thermo-analytical techniques offer insights into degradation processes but lack the possibility to detect uptake of inorganic species. Moreover, these techniques do not allow the measurement of depth profiles, thus information about degradation or pollutant uptake with sample depth is not accessible. In this work, we propose LA-ICP-MS and LIBS as powerful analytical tools for polymer characterization, overcoming the limitations of conventional analytical techniques used for polymer analysis. Applicability of the developed procedures is demonstrated by the analysis of artificially weathered polyimides and modern art materials, indicating that the degradation of the polymer but also the uptake of corrosive gases is not limited to the sample surface. Finally, a tandem LA-ICP-MS/LIBS approach is employed, which combines the advantages of both laser-based procedures, enabling the simultaneous analysis of polymer degradation and cadmium uptake of polystyrene after exposure to UV radiation and treatment with artificial sea water.
Polyimides feature a vast number of industrial applications due to their high thermal stability and insulation properties. These polymers exhibit an exceptional combination of thermal stability and ...mechanical toughness, which allows the semiconductor industry to use them as a mechanical stress buffer. Here, we perform all-atom molecular dynamics (MD) simulations for such materials to assess their predictive capability with respect to their mechanical properties. Specifically, we demonstrate that the OPLS-AA force field can be used to successfully describe an often-used polyimide (i.e., Kapton
) with respect to its Young's modulus and Poisson's ratio. Two different modes to extract these mechanical properties from MD simulations are presented. In particular, our continuous deformation mode simulations almost perfectly replicate the results from real-world experimental data and are in line with predictions using other MD force fields. Our thorough investigation of Kapton
also includes an analysis of the anisotropy of normal stresses, as well as the effect of simulation properties on the predicted Young's moduli. Furthermore, the polyimide pyromellitic dianhydride/2-(4-aminophenyl)-1H-benzimidazole-5-amine (PMDA-BIA) was investigated to draw a more thorough picture of the usability of the OPLS-AA force field for polyimides.
This study aims to investigate the photoelectrochemical behavior of the n-type 4H-SiC, focusing on aqueous, hydroxide-based electrolytes. Despite its high stability, this wide-bandgap semiconductor ...material undergoes electrochemical reactions, such as anodic oxidation or etching, under specific conditions. Since electrons are the majority charge carriers in n-type semiconductors, oxidation processes require above-bandgap illumination. Then, the reaction rate is influenced by the number of electron holes available for an oxidation process and the velocity of the transport of hydroxide ions to/from the surface. The goal is to focus on the essential reaction parameters (i.e., potential and electrolyte concentration) to clarify the reaction mechanism in aqueous (alkaline) electrolytes. Methods with controllable hydrodynamic conditions are required to investigate the transport processes in the electrolyte. Even though the rotating disk electrode (RDE) is a commonly used and powerful method, it is not well suited for our purpose. Photoelectrochemical etching of SiC is extraordinary because it involves both mass transfer phenomena and gas evolution but also needs high-intensity illumination from an appropriate light source. Hence, a new concept for an inverted rotating cell was developed and implemented. This setup was used to study the effect of the mass transport of hydroxide ions on the photoelectrochemical behavior of SiC in each potential region at varying rotation speeds. In order to interpret the experimental findings, a distinct electrical network model was formulated for simulating the results, aiding in unraveling the underlying reaction mechanism. Electrochemical measurements were complemented by surface-sensitive analytical techniques. XPS was the method of choice to investigate the composition of the sample surface before and after etching. SEM and AFM allow the characterization of the surface morphology in the initial stages of etching. The totality of this information provides a complete picture of the complex processes in the vicinity of the semiconductor electrode.
Graphical abstract
•High-temperature cyclic voltammetry controls metal oxidation.•Potential controls oxygen partial pressure on metal surfaces.•Interference-free combination of a potentiostat and an impedance ...meter.•Electrical properties of metal oxides measured during growth.•Investigation of defect chemistry at controlled oxygen partial pressures.
In recent years, copper oxide (Cu2O) has gained significant attention for its multifaceted role as a catalyst, photocatalyst and semiconductor. Possessing a p-type conductivity and a bandgap of 2.17 eV, Cu2O emerges as an ideal candidate for applications such as water splitting and photovoltaic cells. However, to utilize its full potential, an in-depth understanding of the electrical properties of Cu2O in terms of defect density and defect mobility is required. This knowledge forms the basis for the targeted production of oxides with precisely tuned electrical properties.
Extensive research on thermal oxidation under varied conditions has been performed to clarify the mechanisms governing oxide formation and growth. However, the in-situ investigation of the electrical properties of the oxide layers during their formation process is challenging.
This work introduces a new method for the controlled oxidation of copper, while concurrently offering an in-depth investigation of the electrical properties of these nanometer-thick oxide layers. The implemented arrangement of potentiostat and frequency response analyzer enables their artifact-free combination. Performing HT-CV measurements in a solid electrolyte cell-setup allows to control the (potential-dependent) oxygen pressure at the copper surface. Using HT-CV, the current represents the kinetics of the redox reactions and the electric charge corresponds to the amount of substance converted. In-situ electrochemical impedance data are used to determine the electrical properties of the controlled grown layers. As a result, the defect density is obtained as a function of the oxygen partial pressure.
The determination of diffusion coefficients in solid materials as a measure of particle mobility is of great scientific interest. This applies both to desired diffusion, such as in fuel cell- and ...dialysis membranes, and to undesired diffusion in insulating materials. In any case, diffusion is a measure of performance. Especially for solvated ions, the permeability of the solvent must also be considered.
In this work, a measurement method for the simultaneous determination of coupled ion diffusion and water permeability in polymer membranes is presented. For this purpose, measurement methods for the determination of concentration-, volume- and membrane-potential changes are integrated into a single, miniaturized concentration cell.
A system of ordinary differential equations is developed for the general description of the coupled transport processes. This makes it possible to model the interdependent solute concentration and solvent volume changes. The coefficients of interest are defined by fitting the model parameters to the measured data.
To evaluate the new combined measurement setup, a freestanding ion exchange membrane with largely known properties is used. The membrane of choice is a Nafion® NR211 membrane, since Nafion® is one of the most investigated PEM in literature and allows a comparison of computational and experimental results with existing data.
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•Simultaneous determination of transport coefficients.•Measurement setup for simultaneous measurement of transport processes.•System of coupled differential equations to model the dependent transport processes.•Nafion™ NR211 ion exchange membrane transport parameter determination.
Synthetic polymers and plastics have become one of the most important materials in our modern world and everyday life with all kinds of applications mainly due to their wide range of excellent and ...tuneable properties. Several novel materials consisting of multiple different synthetic polymers or composite materials like natural-fiber-reinforced polymer composites have already been reported in literature. Additionally, materials consisting of multiple synthetic polymers already found their way in our daily lives (e.g. double-sided adhesive tape). With emerging materials consisting of different structured synthetic polymers, the need for analytical methods characterizing these kinds of sample also arises. Conventionally, analytical techniques such as FT-IR or Raman spectroscopy are used for polymer classification. Although, these techniques offer laterally resolved investigations they lack the possibility of analyzing depth profiles. In this work, we present laser induced breakdown spectroscopy (LIBS) as a novel and powerful analytical method for spatially resolved polymer classification. As a feasibility study, two exemplary structured synthetic polymer samples (2D structured and multilayer system) have been analyzed using LIBS and the spatial distribution of 5 different synthetic polymers, namely acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), polyethylene (PE), polyacrylate (PAK) and polyvinylchloride (PVC) have been successfully classified using multivariate statistical approaches (principal component analysis (PCA) and k-means clustering). Spatially resolved classification results were validated by comparing the obtained distribution of the 2D structured sample to the elemental distribution of a contamination present in one of the synthetic polymers. Classification of the polymeric multilayer system was validated by comparing the obtained results to a microscopic cross-section. It was shown that LIBS cannot only be used to investigate 2D structured polymer samples but also for direct analysis of depth profiles. Besides synthetic polymer classification, LIBS provides simultaneous analysis of the elemental composition of the sample, which increases the total amount of information accessible with only one measurement.
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•LIBS combined with multivariate statistics can be used for polymer classification.•Imaging of the distribution of a sample consisting of 2 polymers using LIBS.•3D depth profiling of a sample consisting of multiple polymer layers.
Understanding mass transfer effects (e.g., condensation and absorption) of hydrogen peroxide is essential for clean room decontamination technology. For example, absorption of hydrogen peroxide in ...polymers often causes unwanted effects in the final aeration phase of a decontamination cycle. This currently leads to significant challenges in the design and operation of clean rooms or isolators. We address here the absorption of H
2
O
2
in polymers, which is a key for an understanding of mass transfer effects. Specifically, we developed a novel experimental setup to measure the desorption rate from a polymer sheet. Together with a model for the diffusion in a polymer, we are able to theoretically predict the absorption and desorption kinetics of hydrogen peroxide. We then performed measurements of still unknown properties of hydrogen peroxide in polymers, i.e., the saturation concentration and the diffusion coefficient using our experimental setup. As expected, the diffusion in the polymer is the rate-limiting step for the absorption and the release of H
2
O
2
. We find that considerable amounts of H
2
O
2
can be absorbed in certain polymers on a time scale of less than an hour and may lead to a temporary violation of the Occupational Safety and Health Administration safety level in a typical clean room.
•Defined formation of metal oxides: High-temperature cyclic voltammetry.•Raman spectroscopy identifies the electrochemically formed metal oxides.•Application for the investigation of intermetallic ...diffusion.
High-temperature cyclic voltammetry (HT-CV) is a versatile technique for accurately characterizing metal oxidation processes. This method uses YSZ (Yttria-stabilized zirconia), a solid-state oxygen ion conductor, as an electrolyte. By applying defined potentials, different oxide species are produced. Hence, thermodynamic processes such as the stability of oxides and kinetic properties, like growth rates, can be investigated. However, in electrochemical reactions the current cannot be assigned to specific reactions unequivocally. To address this issue, in situ analytical methods are necessary. This is crucial when investigating diffusion processes and reaction products, as they require additional analytical information.
This work presents a novel method that combines high-temperature electrochemistry with Raman spectroscopy to investigate metal oxidation processes and diffusion phenomena directly at the solid-electrolyte/metal interface. The HT-CV method is used to achieve controlled oxidation states of metals. To this end, a commercial Raman heating stage was adapted to enable electrochemical measurements in the cell. The use of a transparent YSZ single crystal allows Raman measurements, as the laser penetrates through the material to the metal(oxide)/electrolyte interface. With Raman spectroscopy, oxides produced under controlled conditions can be analyzed. Furthermore, optical microscope images of the oxides can be taken during their formation. Our combined method also enables the investigation of metallic interdiffusion. The electrochemical control of the potential allows for the selective oxidation of diffusing species whilst the layer through which the diffusion takes place remains in the reduced state. The results obtained with Raman spectroscopy confirm the existence of the species predicted from electrochemical experiments.
In the last years, LA-ICP-MS has become an attractive technique for analyzing solid samples from various research fields. However, application in material science is often hampered by the limited ...availability of appropriate certified reference materials, which are a precondition for accurate quantification. Thus, frequently in-house prepared standards are used, which match the sample's composition and include all elements of interest at the required concentration levels. However, preparing and characterizing such standards is often labor-intensive and time-consuming.
This work proposes a new approach for the fabrication of matrix-matched standards based on the concept of standard addition. In the first step, the analytes of interest are homogeneously deposited onto the sample surface using liquid standards and a spraying device. For analysis, the generated thin layer is ablated simultaneously with the underlying sample. Thereby deviations in the ablation process and particle transport can be avoided. It could be shown that the developed method is highly versatile and could be easily adapted to the actual needs. Using silicon, silicon carbide, copper, aluminum, and glass as a matrix, excellent linear correlations between observed signal intensities and deposited amounts were found for the elements Zn, Ag, In, and Pb (R2 - values greater than 0.99).
The method was applied to determine the content of sulfur, zinc, silver, indium, and lead in a commercial Kapton® polyimide film. The obtained results could be verified based on the homogeneously distributed sulfur by conventional liquid ICP-MS analysis after sample digestion, showing similar precision and accuracy. Lead was found to show a very inhomogeneous distribution in the Kapton® film, with concentration below the LOD at most measured locations and irregularly occurring spots with significantly higher concentrations. Finally, a quantitative depth profile of sulfur in a Kapton® film has been measured to assess the uptake of SO2 after a weathering experiment.
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•A new method for matrix-matched standard preparation for quantitative LA-ICP-MS analysis was developed.•Spray deposition of liquid standards result in evenly distributed residues on the sample surface.•The method is applied for quantitative determination of sulfur in a polymer, results are verified with a reference method.•The method is applied for quantitative elemental mapping of Pb in a polymer, showing an inhomogeneous distribution.•Versatile applicability of the approach is demonstrated with multielement standards on various sample materials.
Due to their outstanding chemical and physical properties, polyimides are widely used in industrial applications. The degree of imidization of polyimides significantly influences their properties, ...making it an important factor in tailoring the material for specific applications. Imidization refers to the process of converting a precursor poly(amic acid) by removing water, and it is essential to analyze this process in detail to tune the final structure and properties of the material. Conventional techniques for this task include Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), or differential scanning calorimetry (DSC), but they lack the possibility of spatially and/or depth-resolved analysis or do not enable in-line monitoring capabilities. To overcome these limitations, we propose laser-induced breakdown spectroscopy (LIBS) as a powerful tool for the monitoring of the imidization reaction. To establish a measurement method, a total of 130 in-house prepared, self-synthesized samples were thermally cured to exhibit varying imidization degrees. IR spectroscopy served as a reference technique during method development, and a novel formula for calculating the degree of imidization, based on the C
2
and H signal trends, was introduced. The calculated imidization degrees of model thin films based on LIBS were in good accordance with the IR reference method although minor differences between the two methods were expected due to varying information depth and the size of the sampled area. Additionally, the robustness of the procedure was demonstrated by depth profiling of a stacked model polymer, spiking with commercially available additives and, ultimately, by analyzing industry-relevant polymer samples.
Graphical Abstract
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