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Hexakis(n-alkyloxy)triphenylene) (HATn) consisting of an aromatic triphenylene core and alkyl side chains are model discotic liquid crystal (DLC) systems forming a columnar mesophase. In the mesophase, the molecules of HATn self-assemble in columns, which has one-dimensional high charge carrier mobility along the columns. Here, a homologous series of HATn with different length of the alkyl chain (n=5,6,8,10,12) is investigated using differential scanning calorimetry (DSC), broadband dielectric spectroscopy (BDS) and advanced calorimetric techniques including fast scanning calorimetry (FSC) and specific heat spectroscopy (SHS). The investigation of the phase behavior was done utilizing DSC experiments and the influence of the alkyl chain length on the phase behavior was revealed. By the dielectric investigations probing the molecular mobility, a γ-relaxation due to localized fluctuations as well as two glassy dynamics the αcore and αalkyl relaxation were observed in the temperature range of the plastic crystalline phase. Moreover, the observed glassy dynamics were further studied employing advanced calorimetry. All observed relaxation processes are attributed to the possible specific molecular fluctuations and discussed in detail. From the results a transition at around n=8 from a rigid constrained (n=5,6) to a softer system (n=10,12) on a molecular lenght scale was revealed with increasing alkyl chain length. A counterbalance of two competing effects of a polyethylene like behavior of the alkyl chains in the intercolumnar domains and self-organized confinement is discussed in the context of a hindered glass transition.
Polymers with intrinsic microporosity are promising candidates for the active separation layer in gas separation membranes. These polymers are characterized by a high permeability and reasonable permselectivity. The reasonable permselectivity of these materials is somehow surprising because for microporous systems a more Knudsen-like diffusion is expected rather than a size dependent temperature activated sieving process. It was argued in the framework of a random gate model that molecular fluctuations on a time scale from ps to ns are responsible for the permselectivity.
Here a series of microporous polynorbornenes with bulky SiMe3 side groups and a rigid backbone is considered which have different microporosities characterized by BET surface area values.
First inelastic time-of-flight neutron scattering measurements were carried out to investigate the low frequency density of state (VDOS). The measured data show the characteristic low frequency excess contribution to the VDOS above the Debye sound wave level, generally known as the Boson peak in glass-forming materials. It was found that the maximum position of the Boson peak correlates with the BET surface area.
For two selected comparable polynorbornenes elastic scans as well as QENS measurements by a combination of neutron time-of-flight and backscattering were carried out. A low temperature relaxation process was found for both polymers. This process was assigned to the methyl group rotation. It was analysed in terms of a jump diffusion in a three-fold potential. The analysis of the dependence of the elastic incoherent structure factor on the scattering vector yields the number of methyl groups which might be immobilized.
Polymers with intrinsic microporosity are promising candidates for the active separation layer in gas separation membranes. These polymers are characterized by a high permeability and reasonable permselectivity. The latter point is somehow surprising because for microporous systems a more Knudson-like diffusion is expected then a size dependent temperature activated sieving process. It was argued in the framework of a random gate model that molecular fluctuations on a time scale from ps to ns are responsible for the permselectivity.
Her a series of microporous polynorbornenes with bulky Si side groups and a rigid backbone are considered which have different microporosity characterized by BET surface area values.
First inelastic time-of-flight neutron scattering measurements were carried out to investigate the low frequency density of state (VDOS). The measured data show the characteristic low frequency excess contribution to the VDOS above the Debye sound wave level, generally known as the Boson peak in glass-forming materials. It was found the maximum position of the Boson peak correlates with the BET surface area value.
For two selected comparable polynorbornenes elastic scans as well as QENS measurements by a combination of neutron time-of-flight and backscattering are carried out. A low temperature relaxation process was found for both polymers. This process was assigned to the methyl group rotation. It was analysed in terms of a jump diffusion in a three-fold potential. The analysis of the dependence of the elastic incoherent structure factor on the scattering vector yields the number of methyl groups which might be immobilized.
Polymers with intrinsic microporosity are promising candidates for the active separation layer in gas separation membranes. Here, by means of inelastic neutron scattering, the vibrational density of states (VDOS) and the molecular mobility were investigated for PIM-1, the prototypical polymer with intrinsic microporosity. The results are compared to data measured for a more conventional high-performance polyimide used in gas separation membranes (Matrimid).
The measured data show the characteristic low frequency excess contribution to the VDOS above the Debye sound wave level, generally known as the Boson peak in glass-forming materials. In comparison to the Boson peak of Matrimid, that of PIM-1 is shifted to lower frequencies. This shift is discussed considering the microporous, sponge-like structure of PIM-1 as providing a higher compressibility at the molecular scale than for conventional polymers.
Elastic fixed window scans were measured on a neutron backscattering spectrometer to have an overview about the molecular dynamics at a time scale of ca. 1 ns. The temperature dependence of the estimated mean squared displacement shows a step-like increase in the temperature range from 100 K to 250 K indicating the onset of some molecular mobility. The nature of this motional process was analyzed in detail by quasielastic neutron scattering combining Time-of-Flight and backscattering where the data are discussed with regard to both the q- and the temperature dependence.
Polymers at interfaces play a major role in a broad variety of applications ranging from engineering purposes (for instance polymer based nanocomposites) to high tech implications (for instance light emitting diodes).
Here, thin films with thicknesses down to few nanometers are prepared on different substrates as model systems for polymer composites. The thin films are investigated by a combination of surface analytical and volume sensitive methods. As surface analytical methods atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements (CAM) are employed. As volume sensitive broadband dielectric spectroscopy (BDS), specific heat spectroscopy (SHS), and ellipsometry are used. Especially attention is paid to understand the glass transition behavior of thin films because the glass transition is the key phenomenon determines the application of polymers also in thin films.
To understand the glass transition behavior of thin films, which is controversially discussed in literature, a three layer model is discussed. Firstly, a mobile surface layer is assumed at polymer air interface of the film due to missing of segment/segment interactions. Secondly, in the middle of the film a bulk-like layer should be expected. Thirdly, for polymers having non-repulsive interactions with the substrate an irreversibly adsorbed layer is expected to be formed. Due the adsorption the molecular mobility of the segments in this layer is slowed down. What is measured for the glass transition of thin films is a complicated average of all of these effects. The different layers are hardly to address separately. Therefore, in the presentation especially model systems are selected and investigated to verify the layer model.
Polymers with intrinsic microporosity are promising candidates for the active separation layer in gas separation membranes. Here, by means of inelastic neutron scattering, the vibrational density of states (VDOS) and the molecular mobility were investigated for PIM-1, the prototypical polymer with intrinsic microporosity. The results are compared to data measured for a more conventional high-performance polyimide used in gas separation membranes (Matrimid).
The measured data show the characteristic low frequency excess contribution to the VDOS above the Debye sound wave level, generally known as the Boson peak in glass-forming materials. In comparison to the Boson peak of Matrimid, that of PIM-1 is shifted to lower frequencies. This shift is discussed considering the microporous, sponge-like structure of PIM-1 as providing a higher compressibility at the molecular scale than for conventional polymers.
Elastic fixed window scans were measured on a neutron backscattering spectrometer to have an overview about the molecular dynamics at a time scale of ca. 1 ns. The temperature dependence of the estimated mean squared displacement shows a step-like increase in the temperature range from 100 K to 250 K indicating the onset of some molecular mobility. The nature of this motional process was analyzed in detail by quasielastic neutron scattering combining Time-of-Flight and backscattering where the data are discussed with regard to both the q- and the temperature dependence.
A selected series of dipole functionalized triphenylene-based discotic liquid crystals (DLCs) was synthesized and investigated in a systematic way to reveal the phase behavior and molecular dynamics. The later point is of particular importance to understand the charge transport in such systems which is the key property for their applications such as organic field effect transistors, solar cells or as nanowires in molecular electronics, and also to tune the properties of DLCs. The mesomorphic properties were studied by polarizing optical microscopy, X-ray diffraction, and differential scanning calorimetry, which were compared to the corresponding unfunctionalized DLC. The molecular dynamics were investigated by a combination of state-of-the-art broadband dielectric spectroscopy (BDS) and advanced calorimetry such as fast scanning calorimetry (FSC) and specific heat spectroscopy (SHS). Besides localized fluctuations, surprisingly multiple glassy dynamics were detected for all materials for the first time. Glassy dynamics were proven for both processes unambiguously due to the extraordinary broad frequency range covered. The α1-process is attributed to fluctuations of the alky chains in the intercolumnar space because a polyethylene-like glassy dynamics is observed. This corresponds to a glass transition in a confined three-dimensional space. The α2-process found at temperatures lower than α1-process, is assigned to the fluctuation of translational in plane movements of the triphenylene core inside distorted columns. This can be considered as a glass transition of a one-dimensional fluid. Therefore, obtained results are of general importance to understand the glass transition, which is an unsolved problem of condensed matter science.
The basics of broadband dielectric spectroscopy were introduced in detail. The analysis of the data was discussed. As application of broadband dielectric spectroscopy the alpha-relaxation (dynamic glass transition) and the chain dynamics of polymers were ilustrated. Further the application of dielectric spectroscopy to polymerbased nanocomposites and high preformance polymers was discussed in detail.
Bacterial biofilms pose serious problems in medical and industrial settings. One of the major societal challenges lies in the increasing resistance of bacteria against biocides used in antimicrobial treatments, e.g., via overabundant use in medicine, industry, and agriculture or cleaning and disinfection in private households. Hence, new efficient bacteria-repellent strategies avoiding the use of biocides are strongly desired. One promising route to achieve bacteria-repellent surfaces lies in the contactless and aseptic large-area laser-processing of technical surfaces. Tailored surface textures, enabled by different laser-processing strategies that result in topographic scales ranging from nanometers to micrometers may provide a solution to this challenge. This article presents a current state-of-the-art review of laser-surface subtractive texturing approaches for controlling the biofilm formation for different bacterial strains and in different environments. Based on specific properties of bacteria and laser-processed surfaces, the challenges of anti-microbial surface designs are discussed, and future directions will be outlined.
This 6 minute long MP4-video presents some key results of the European research project "BioCombs4Nanofibers" to the broader public. Inspired by nature, some concepts of certain types of spiders are transferred to technology in order to develop bacteria-repellent surfaces through laser surface nanostructuring.
Funding notice: This study was funded by the European Union's research and innovation program under the FET Open grant agreement No. 862016 (BioCombs4Nanofibers, http://biocombs4nanofibers.eu).
In this study, femtosecond laser-induced sub-micrometer structures are generated to modify polyethylene (PE) surface topographies. These surfaces were subjected to bacterial colonization studies with Escherichia coli and Staphylococcus aureus as test strains. The results reveal that the nanostructures do not influence S. aureus coverage, while the adhesion of E. coli is reduced.
Ultrashort laser pulse micromachining features a high precision. By increasing the repetition rate of the applied laser to several 100 kHz, laser processing becomes quick and cost-effective and make this method attractive for industrial applications. Upon exceeding a critical laser intensity, hard X-ray radiation is generated as a side effect. Even if the emitted X-ray dose per pulse is low, the accumulated X-ray dose becomes significant for high-repetition-rate laser systems so that radiation safety must be considered.
Outer membrane lipopolysaccharides (LPS) play a crucial role in determining attachment behavior and pathogenicity of bacteria. The aim of this study was to develop a simple procedure for anchoring bacterial lipopolysaccharides to polystyrene (PS) microparticles as a model system for in situ attachment studies. By using a swellcapture methodology, commercially available LPS of Pseudomonas aeruginosa (strain ATCC 27316 serotype 10.22) was anchored onto PS microparticles in a proof-of-concept study. A detailed chemical and morphological characterization has proven the success of LPS incorporation. It was shown that the coverage and structure of the LPS film was concentration dependent. The procedure can easily be adapted to LPS of other bacterial strains to generate a synthetic model toolkit for attachment studies.
Since the original report in 2004 by Novoselov and Geim, Graphene gained incredible attention due to its fascinating properties. In the past 20 years, the synthesis and functionalization of graphene has evolved significantly[3]. Different synthesis techniques were developed which led to other graphenerelated materials such as graphene oxide (GO) or elemental-doped graphene. Further chemical functionalization can enhance but also alter or reduce specific properties of the graphene. To reveal the nature of these materials a proper physico‑chemical characterization with different analytical techniques is crucial.
Single-layer GO flakes kindly provided by Graphenea (Spain) were prepared for systematic image analysis. These flakes were disposed on an alignment-marked SiO2 substrate and correlatively imaged by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and Raman spectroscopy. The high lateral resolution and/ or extreme surface sensitivity of the mentioned
techniques is necessary to explore monolayers. The ToF-SIMS images match well with the SEM and AFM images and provide information about the chemistry. With 2D Raman spectroscopy it is possible to differentiate between the number of stacked single-layer flakes. This is visualized in a 3D image (Figure b). Well-defined GO flakes could be used as a reference material for imaging of graphene-like structures but also of other types of 2D materials.
In addition to these monolayer GO flakes, commercial graphene-containing inks (Haydale) with a more complex morphology were also correlatively imaged. ToF-SIMS and SEM images were merged to identify the origin of different chemical fragments. The findings correlate closely with the expectation that the specific functionalizations (with fluorine and nitrogen as marker elements) are present only on the graphene flakes as presumed from the SEM images. Energy-dispersive X-ray spectroscopy (EDX) supports these results, yet with a much lower sensitivity compared to ToF-SIMS.
Since the original report in 2004 by Novoselov and Geim, Graphene gained incredible attention due to its fascinating properties. In the past 20 years, the synthesis and functionalization of graphene has evolved significantly[3]. Different synthesis techniques were developed which led to other graphenerelated materials such as graphene oxide (GO) or elemental-doped graphene. Further chemical functionalization can enhance but also alter or reduce specific properties of the graphene. To reveal the nature of these materials a proper physico‑chemical characterization with different analytical techniques is crucial.
Single-layer GO flakes kindly provided by Graphenea (Spain) were prepared for systematic image analysis. These flakes were disposed on an alignment-marked SiO2 substrate and correlatively imaged by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (ToF-SIMS) and Raman spectroscopy. The high lateral resolution and/ or extreme surface sensitivity of the mentioned
techniques is necessary to explore monolayers. The ToF-SIMS images match well with the SEM and AFM images and provide information about the chemistry. With 2D Raman spectroscopy it is possible to differentiate between the number of stacked single-layer flakes. This is visualized in a 3D image (Figure b). Well-defined GO flakes could be used as a reference material for imaging of graphene-like structures but also of other types of 2D materials.
In addition to these monolayer GO flakes, commercial graphene-containing inks (Haydale) with a more complex morphology were also correlatively imaged. ToF-SIMS and SEM images were merged to identify the origin of different chemical fragments. The findings correlate closely with the expectation that the specific functionalizations (with fluorine and nitrogen as marker elements) are present only on the graphene flakes as presumed from the SEM images. Energy-dispersive X-ray spectroscopy (EDX) supports these results, yet with a much lower sensitivity compared to ToF-SIMS.
Der Mangel an Anwendungsrichtlinien und Validierungsverfahren für struktur-eingebettete faseroptische Dehnungssensoren, insbesondere auf Faser-Bragg-Gitter (FBG)-Basis, führte bislang dazu, dass diese Sensoren trotz ihrer hervorragenden Eigenschaften im Bereich der kommerziellen Material- und Strukturüberwachung nur in geringem Umfange eingesetzt wurden. Fragen zur Degradation der Sensoren unter Beanspruchung, Alterung durch klimatische Einflüsse und Enthaftung infolge Belastung der Struktur konnten bisher nur theoretisch simuliert oder anhand exemplarischer Proben für einzelne einflussnehmende Parameter im Labor untersucht werden. Die Erfassung des Sensorverhaltens im Bauteil unter komplexen Umwelteinflüssen während des Bauteilbetriebes, um damit eine Aussage zur Zuverlässigkeit der Sensormessdaten zu gewinnen, war bisher nicht möglich.
Im Forschungsprojekt FAMOS² wurde deshalb von 2014 bis 2018 die Realisierung eines Autodiagnoseverfahrens für faseroptische Dehnungssensoren erarbeitet, um die Funktionszuverlässigkeit und Langzeitstabilität der Sensoren während des Bauteilbetriebes innerhalb einer Bauteilstruktur bewerten zu können. Im Rahmen des Forschungsprojektes wurde gezeigt, dass ein FBG-Sensor mit einer speziell angepassten magnetostriktiven Schicht magnetisch so angeregt werden kann, dass mit einer zugeschnittenen Messmethodik zu jedem Zeitpunkt eine Bewertung der Sensorzuverlässigkeit unter Betriebsbedingungen möglich ist. Die auf den Sensor aufgebrachte magnetostriktive Schicht erzeugt bei Anregung mit einem passenden Magnetfeld eine gepulste, synthetische Dehnung. Diese Dehnung steht in einem definierten Verhältnis zum anregenden Magnetfeld und wird optisch über die Verschiebung der Bragg-Wellenlänge ausgelesen. Die Konstanz dieses Verhältnisses stellt dann ein Maß für die korrekte Funktionsfähigkeit des Sensors dar. Das Beschichtungs-verfahren, das magnetische Anregungs- und optische Ausleseverfahren, wie auch die Validierung des Sensors unter Berücksichtigung faseroptischer Effekte wurden während des Projekts konzeptionell entwickelt, aufgebaut und charakterisiert. Qualitativ kann mit diesem Verfahren zunächst eine Gut-/Schlecht-Beurteilung des Sensors vorgenommen werden. Perspektivisch bietet das Verfahren jedoch auch die Möglichkeit, verschiedene Versagensmechanismen bestimmen und klassifizieren zu können. Es zeichnete sich schon während des Projektverlaufs ab, dass sich aus den erzielten Ergebnissen über das Autodiagnoseverfahren hinaus weitere Anwendungsmöglichkeiten für den Einsatz des kombinierten magnetostriktiv-faseroptischen Sensorprinzips, beispielsweise als reiner Magnetfeldsensor, ergeben.
Nach Abschluss dieses Forschungsprojekts besteht nun die Möglichkeit, den Funktionszustand faseroptischer Dehnungssensoren jederzeit unabhängig von Alter, Belastung oder Kenntnis eines Referenzzustands zu einem bestimmten Zeitpunkt bestimmen zu können. Aufbauend auf diesen Ergebnissen können weiterführende Forschungen die Messmethodik vertiefend charakterisieren und weitere Anwendungsfälle erschließen.
Size-exclusion chromatography (SEC) was used to monitor changes of the molecular masses of thermoplastic polyether – and polyester urethane (TPU) exposed to thermal, hydrolytic, and photo-oxidative (UV) Degradation conditions for several days. The thermal treatment was performed at elevated temperatures (100–200 °C) under oxidative (air) as well as non-oxidative (nitrogen) conditions to evaluate the specific influence of oxygen on the degradation. At higher temperatures (≥175 °C) a fast decrease of the molecular masses of both PU accompanied by a high degree of crosslinking was found. At lower temperatures (≤150 °C) the polymers remained widely unaffected by thermal degradation within the investigated degradation interval of up to two weeks. Surprisingly, the influence of oxygen (air) was found to be less distinct. In contrast to that, UV treatment at 25 °C at less than 10% rel. humidity (RH) resulted in a fast crosslinking, whereas the molecular masses of both PU decreased slower than for thermal treatments. The depth of penetration of the UV radiation was estimated using 3D printed PU samples with different thicknesses. Hydrolysis based degradation effects were less significant. Only slight molecular mass changes were detected at temperatures ≤80 °C within a time span of 14 days, while no crosslinking could be measured. Considering the degradation results at the investigated exposure parameters, it could be shown that esterbased PU in general exhibits a significant higher stability compared to ether-based materials.
Polyether and -ester urethanes (PU) were exposed to artificial weathering at 40 °C and artificial UV radiation in a weathering chamber. In 3 parallel exposures, humidity was varied between dry, humid, and wet conditions. Material alteration was investigated by various analytical techniques like size exclusion chromatography
(SEC), liquid chromatography-infrared spectroscopy (LC-FTIR), thermal-desorption gas chromatography-mass spectrometry (TD-GC-MS), fluorescence mapping and dynamic mechanical analysis (DMA). Our results show that depending on the weathering conditions, different degradation effects can be observed. By means of SEC an initial strong decrease of the molar masses and a broadening of the mass distributions was found. After a material dependent time span this was followed by a plateau where molar mass changes were less significant. A minor moisture-dependent degradation effect was only found for polyester PU. Fluorescence measurements on two materials revealed an increase in the luminescence intensity upon weathering process reaching a saturation level after about 500 h. The changes in the optical properties observed after different exposure conditions and times were very similar. The TD-GC-MS data showed the fate of the stabilizers and antioxidant in the course of weathering. LC-FTIR measurements revealed a change in peak intensities and the ratio of urethane and carbonyl bands.
Mechanochemically synthesized metal–organic Framework material HKUST-1 in combination with acrylonitrile butadiene styrene polymer was used to form a polymer metal–organic framework composite material by a simple extruder.
This composite filament was used for 3D printing. Xray diffraction measurements were used to prove the homogeneous distribution of the metal–organic framework in the polymer on a centimeter scale, whereas X-ray Absorption Edge Tomography using a synchrotron radiation source was able to evaluate the 3D distribution of the metal–organic framework material both in the filament and the resultant printed sample with a resolution of a few lm. Our very first data indicate that, apart from a few clusters having significantly higher Cu concentration, HKUST-1 is distributed homogeneously down to the 100 lm length scale in both polymer bulk materials in the form of clusters with a size of a few lm. Absorption Edge Tomography in combination with data fusion also allows for the calculation of the metal–organic framework amount located on the external polymer surface.
Degradation of polyurethanes in various environments – Effects on molecular mass and crosslinking
(2019)
The increasing application of polyurethanes (PU) in safety relevant sectors (fire protection, insulation, medicine technique) requires detailed knowledge of the stability and reliability of these materials. Different climate factors are supposed to induce diverse and overlapping degradation reactions. The knowledge of these degradation mechanisms is necessary for an estimation of the period of application depending on usage of the material. An essential property of a polymeric system is represented by the molecular weight. Since a change of the molecular weight is a measure for the chemical stability of a polymer, size-exclusion chromatography (SEC) was used to monitor changes of the molecular weight of thermoplastic polyether- and polyester urethane (TPU) exposed to thermal, hydrolytic and photo-oxidative (UV) degradation conditions for several days. Thermal treatments were performed at elevated temperatures (100 - 200 °C) under oxidative (air) as well as non-oxidative (nitrogen) conditions to evaluate the specific influence of oxygen on the degradation. At higher temperatures (≥ 175 °C) a fast decrease of the molecular masses of both PU accompanied by a high degree of crosslinking was found. At lower temperatures (≤ 150 °C) the polymers remained widely unaffected by thermal degradation within the investigated degradation interval of up to two weeks, which was already known from FTIR spectroscopy[1]. In contrast to that, UV treatment at 25 °C at less than 10 % rel. humidity (RH) resulted in a fast crosslinking, whereas the molecular masses of both PU decreased slower than during the thermal treatments. The depth of penetration of the UV radiation was determined using 3D printed PU samples with different thicknesses. Hydrolysis based degradation effects were less significant. Only slight molecular mass changes were detected at temperatures ≤ 80 °C within a time span of 14 days, while no crosslinking could be measured. Considering the degradation results at the investigated exposure parameters, it could be shown that ester-based PU in general exhibits a significant higher stability compared to ether-based materials.
Surface-functionalized polymer beads encoded with molecular luminophores and nanocrystalline emitters such as semiconductor nanocrystals, often referred to as quantum dots (QDs), or magnetic nanoparticles are broadly used in the life sciences as reporters and carrier beads. Many of these applications require a profound knowledge of the chemical nature and total number of their surface functional groups (FGs), that control bead charge, colloidal stability, hydrophobicity, and the interaction with the environment and biological systems. For bioanalytical applications, also the number of groups accessible for the subsequent functionalization with, e.g., biomolecules or targeting ligands is relevant. In this study, we explore the influence of QD encoding on the amount of carboxylic acid (COOH) surface FGs of 2 μm polystyrene microparticles (PSMPs). This is done for frequently employed oleic acid and oleylamine stabilized, luminescent core/shell CdSe QDs and two commonly used encoding procedures. This included QD addition during bead formation by a thermally induced polymerization reaction and a post synthetic swelling procedure. The accessible number of COOH groups on the surface of QD-encoded and pristine beads was quantified by two colorimetric assays, utilizing differently sized reporters and electrostatic and covalent interactions. The results were compared to the total number of FGs obtained by a conductometric titration and Fourier transform infrared spectroscopy (FTIR). In addition, a comparison of the impact of QD and dye encoding on the bead surface chemistry was performed. Our results demonstrate the influence of QD encoding and the QD-encoding strategy on the number of surface FG that is ascribed to an interaction of the QDs with the carboxylic acid groups on the bead surface. These findings are of considerable relevance for applications of nanoparticle-encoded beads and safe-by-design concepts for nanomaterials.
Polymers at interfaces play a major role in a broad variety of applications ranging from engineering purposes (for instance polymer based nanocomposites) to high tech implications (for instance light emitting diodes).
Here, thin films with thicknesses down to few nanometers are prepared on different substrates as model systems for polymer composites. The thin films are investigated by a combination of surface analytical and volume sensitive methods. As surface analytical methods atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements (CAM) are employed. As volume sensitive broadband dielectric spectroscopy (BDS), specific heat spectroscopy (SHS), and ellipsometry are used. Especially attention is paid to understand the glass transition behavior of thin films because the glass transition is the key phenomenon determines the application of polymers also in thin films.
To understand the glass transition behavior of thin films, which is controversially discussed in literature, a three layer model is discussed. Firstly, a mobile surface layer is assumed at polymer air interface of the film due to missing of segment/segment interactions. Secondly, in the middle of the film a bulk-like layer should be expected. Thirdly, for polymers having non-repulsive interactions with the substrate an irreversibly adsorbed layer is expected to be formed. Due the adsorption the molecular mobility of the segments in this layer is slowed down. What is measured for the glass transition of thin films is a complicated average of all of these effects. The different layers are hardly to address separately. Therefore, in the presentation especially model systems are selected and investigated to verify the layer model.
Microplastic particles with sizes between 1 to 1000 μm are widely distributed worldwide. Origin, transport pathways and fate are poorly known, as sampling, sample preparation and detection methods are major challenges. In addition, reference materials that mimic environmental particles are lacking. Most challenging is the yield of MP particle production and the need for resource-intensive grinding with liquid nitrogen. In this paper, a machine is designed to produce aged microplastic particles as reference material candidates with high yield. The machine is based on ultraviolet aging of a thin foil and mechanical fragmentation using clean air. An example of aging and fragmentation of high density polyethylene with additional physical and chemical characterization of shape, size, aging state by carbonyl index and density is presented.
Ellipsometry is a matured experimental method, whose roots reach back into the early phase of modern optics itself. It is often attributed to be invented by Paul Drude in the last decade of the 19th century, but similar techniques had already been applied for years before Drude started his work. With this Special Issue about ellipsometry and related techniques, we hope to bring more attention to this method and advance and propagate it to be used by a broader community. We have collected a good mixture of articles: some texts are more in the line of users’ tutorial and best practice guides; others are intended to show recent developments of the method. With this collection, we also hope to show the generally rapidly expanding possibilities of ellipsometry and polarimetry to draw attention of new users and previously unrelated communities to this valuable tool.
The paper presents rheometric results and hydration curves for cementitious systems based on cement mixed with different aqueous phases at solid volume fraction of = 0.45. The varied aqueous phases were deionized water, limewater, the filter residue of a cement paste mixed at w/c = 2.0, and the filtrate of cement paste at solid volume fraction of 0.45. Each cementitious system provided different amounts and sizes of particles formed in the aqueous phase. The pastes were observed with and without polycarboxylate ether based superplasticizer. It was observed that the presence of particles causes higher PCE saturation dosages to achieve a minimum value, but the minimum value is only affected in the case of large particles. In all cases with and without PCE, the presence of small particles causes increased plastic viscosity. In addition, with decreased number and size of hydrates in the aqueous phase the hydration was retarded, which was specifically pronounced in the presence of PCE
In the present talk the basics of the Raman spectroscopy and particularly of Raman microscopy are explained. Advantages and disadvantages of the method are highlighted through selected case studies. In the second part of the lecture examples of correlative imaging with electron, X-ray, ion and optical microscopies from micro- to the nanoscale are highlighted.
Light concentration opens up the path to enhanced material efficiency of solar cells via increased conversion efficiency and decreased material requirement. For true material saving, a fabrication method allowing local growth of high quality absorber material is essential. We present two scalable fs-laser based approaches for bottom-up growth of Cu(In,Ga)Se2 micro islands utilizing either site-controlled assembly of In(,Ga) droplets on laser-patterned substrates during physical vapor deposition, or laser-induced forward transfer of (Cu,In,Ga) layers for local precursor arrangement. The Cu(In,Ga)Se2 absorbers formed after selenization can deliver working solar devices showing efficiency enhancement under light concentration.
We present an approach towards the in situ solid state NMR monitoring of mechanochemical reactions in a ball mill. A miniaturized vibration ball mill is integrated into the measuring coil of a home-built solid state NMR probe, allowing for static solid state NMR measurements during the mechanochemical reaction within the vessel. The setup allows to quantitatively follow the product evolution of a prototypical mechanochemical reaction, the formation of zinc phenylphosphonate from zinc acetate and phenylphosphonic acid. MAS NMR investigations on the final reaction mixture confirmed a reaction yield of 89% in a typical example. Thus, NMR spectroscopy may in the future provide complementary information about reaction mechanisms of mechanochemical reactions and team up with other analytical methods which have been employed to follow reactions in situ, such as Raman spectroscopy or X-ray diffraction.
Optical constants of In2O3-SnO2 (Indium tin oxide, ITO)
Minenkov et al. 2024: on glass; n,k 0.191–1.69 µm
Optical constants of In2O3-SnO2 (Indium tin oxide, ITO)
Minenkov et al. 2024: on Si wafer, top; n,k 0.191–1.69 µm
Optical constants of In2O3-SnO2 (Indium tin oxide, ITO)
Minenkov et al. 2024: on Si wafer, bottom; n,k 0.191–1.69 µm
Biofilms cause complications and high costs in both industry and medicine. Of particular interest are bacterial infections of prosthetic materials, which usually cannot be eliminated due to the high antibiotic resistance known for bacteria forming biofilms. The search for new materials and coatings with lower colonization potential and antibacterial activity is of great importance to reduce biofilm formation. However, there is no standardized procedure to examine the colonization characteristics of bacteria in the Biofilm state in situ. Here, we describe an automated epifluorescence microscopy system for the semi-quantitative analysis of three-dimensional (3D) biofilms on various surfaces. To analyze adherent bacteria, three materials (glass, steel and titanium) were incubated with bacteria in a flow chamber system. After fluorescence staining of the bacteria, automated image capturing, quantification of the bacteria, measurement of the colonized area and determination of the 3D biofilm height were carried out by using novel software.
Furthermore, the materials were examined for their surface topography using white light scanning interferometry. Titanium compared to glass showed a significantly higher number of adherent bacteria.
We argue that this was due to the higher microroughness of titanium. The colonized area was in accordance with the number of adherent bacteria and was also significantly larger on titanium coupons compared to glass. Maximum 3D biofilm height on glass coupons was significantly lower compared to the ones on steel and titanium. This novel method enables the standardized, automated investigation of the colonization with bacteria on different materials. This approach can considerably support the characterization of new material surfaces and their innovative coatings by analyzing the amount of attached Bacteria and thickness of biofilms in situ and eliminates the need of conventional cultivation.
Mechanochemistry has proven to be a highly effective method for the synthesis of organic compounds. We studied the kinetics of the catalyst-free Knoevenagel reaction between 4-nitrobenzaldehyde and malononitrile, activated and driven by ball milling. The reaction was investigated in the absence of solvents (neat grinding) and in the presence of solvents with different polarities (liquid-assisted grinding). The reaction was monitored using time-resolved in situ Raman spectroscopy and powder X-ray diffraction (PXRD). Our results indicate a direct relationship between solvent polarity and reaction kinetics, with higher solvent polarity leading to faster product (2-(4-nitrobenzylidone)malononitrile) formation. For the first time, we were able to isolate and determine the structure of an intermediate 2-(hydroxy(4-nitrophenyl)methyl)malononitrile based on PXRD data.
To investigate early stage corrosion processes of stainless steel 1.4301 taking place during the biofilm formation of the organism Shewanella putrefaciens electrochemical impedance spectroscopy (EIS) in a multielectrode approach has been used. The multielectrode array consisted of up to 25 electrically isolated electrodes made of stainless steel wires of diameters ranging from 100 µm to 500 µm. They were connected to a multichannel microelectrode analyzer (MMA) electrically coupled through zero resistance ammeters. Current flow between electrodes in the array as well as changes in impedance of individual electrodes over time were recorded and analyzed with respect to the onset of localized corrosion and biofilm formation. The results were complemented by optical microscopy, SEM and AFM images which were taken immediately after the respective experiment. To verify that the multielectrode arrays correctly indicated the initial stages of the corrosion process and of biofilm formation they were introduced in a flow cell reaction vessel containing test specimens made from stainless steel 1.4301, which were checked regularly for signs of localized corrosion and biofilms. Preceding results with the multielectrode array in solutions containing high amounts of chloride ions and hydrogen peroxide at low pH also showed that it is possible with the MMA to monitor individual electrodes becoming local anodes as local corrosion set in, while the remaining electrodes predominantly acted as cathodes.
A method is described for high-resolution label-free molecular imaging of human bone tissue. To preserve the lipid content and the heterogeneous structure of osseous tissue, 4 μm thick human bone sections were prepared via cryoembedding and tape-assisted cryosectioning, circumventing the application of organic solvents and a decalcification step. A protocol for comparative mass spectrometry imaging (MSI) on the same section was established for initial analysis with time-of-flight secondary ion mass spectrometry (TOF-SIMS) at a lateral resolution of 10 μm to <500 nm, followed by atmospheric pressure scanning microprobe matrix-assisted laser desorption/ionization (AP-SMALDI) Orbitrap MSI at a lateral resolution of 10 μm. This procedure ultimately enabled MSI of lipids, providing the lateral localization of major lipid classes such as glycero-, glycerophospho-, and sphingolipids. Additionally, the applicability of the recently emerged Orbitrap-TOF-SIMS hybrid system was exemplarily examined and compared to the before-mentioned MSI methods.
This chapter provides an introduction in secondary ion mass spectrometry as one of the leading surface chemical analysis and imaging techniques with molecular specificity in the field of material sciences. The physical basics of the technique are explained along with a description of the typical instrumental setups and their modes of operation. The application paragraph specifically focuses on nanoparticle analysis by SIMS in terms of surface spectrometry, imaging, analysis in organic and complex media, and depth profiling.
A review of the existing literature is provided, and selected studies are showcased. Limitations and pitfalls as well as current technical developments of SIMS application in nanoparticle surface chemical analysis are equally discussed.
While noncovalent interactions at two-dimensional nanobiointerfaces are extensively investigated, less knowledge about covalent interactions at this interface is available. In this work, boronic acid-functionalized 2D MoS2 was synthesized and its covalent multivalent interactions with bacteria and nematodes were investigated. Polymerization of glycidol by freshly exfoliated MoS2 and condensation of 2,5-thiophenediylbisboronic acid on the produced platform resulted in boronic acid-functionalized 2D MoS2. The destructive interactions between 2D MoS2 and bacteria as well as nematodes were significantly amplified by boronic acid functional groups. Because of the high antibacterial and antinematodal activities of boronic acid-functionalized 2D MoS2, its therapeutic efficacy for diabetic wound healing was investigated. The infected diabetic wounds were completely healed 10 days after treatment with boronic acid-functionalized 2D MoS2, and a normal structure for recovered tissues including different layers of skin, collagen, and blood vessels was detected.
Amyloid fibrils are polymers formed by proteins under specific conditions and in many cases they are related to pathogenesis, such as Parkinson’s and Alzheimer’s diseases. Their hallmark is the presence of a β-sheet structure. High resolution structural data on these systems as well as information gathered from multiple complementary analytical techniques is needed, from both a fundamental and a pharmaceutical perspective. Here, a previously reported de novo designed, pH-switchable coiled coil-based peptide that undergoes structural transitions resulting in fibril formation under physiological conditions has been exhaustively characterized by transmission electron microscopy (TEM), cryo-TEM, atomic force microscopy (AFM), wide-angle X-ray scattering (WAXS) and solid-state NMR (ssNMR). Overall, a unique 2-dimensional carpet-like assembly composed of large coexisiting ribbon-like, tubular and funnel-like structures with a clearly resolved protofilament substructure is observed. Whereas electron microscopy and scattering data point somewhat more to a hairpin model of β-fibrils, ssNMR data obtained from samples with selectively labelled peptides are in agreement with both, hairpin structures and linear arrangements.
We report on ultrasmall zinc oxide single-crystalline nanoparticles of narrow size distribution and long-term colloidal stability. These oleate-stabilized nanoparticles were synthesized using microwave-assisted synthesis for 5 min, corresponding to a 99% decrease in synthesis time, when compared to the conventional synthesis method. It was observed that the average particle radius increases from 2.6 ± 0.1 to 3.8 ± 0.1 nm upon increasing synthesis temperature from 125 to 200 °C. This change also corresponded to observed changes in the optical band gap and the fluorescence energy of the particles, from 3.44 ± 0.01 to 3.36 ± 0.01 eV and from 2.20 ± 0.01 to 2.04 ± 0.01 eV, respectively. Small-angle X-ray scattering, dynamic light scattering, and UV–vis and fluorescence spectroscopy were employed for particle characterization. Debye–Scherrer analysis of the X-ray diffraction (XRD) pattern reveals a linear increase of the crystallite size with synthesis temperature. The consideration of the convolution of a Lorentz function with a Gaussian function for data correction of the instrumental peak broadening has a considerable influence on the values for the crystallite size. Williamson–Hall XRD analyses in the form of the uniform deformation model, uniform stress deformation model, and uniform deformation energy density model revealed a substantial increase of strain, stress, and deformation energy density of the crystallites with decreasing size. Exponential and power law models were utilized for quantification of strain, stress, and deformation energy density.
This paper reports the formation of zinc phosphate nanoparticles from the artificial digestion of zinc chloride. Initially, the formation of amorphous primary particles with a mean radius of 1.1 nm is observed, alongside the formation of larger, protein stabilized aggregates. These aggregates, with a radius of gyration of 37 nm, are observed after 5 minutes of exposure to artificial saliva and are shown to be colloidally stable for a minimum time of two weeks. The initially formed primary particles are thought to consist of amorphous zinc phosphate, which is then transformed into crystalline Zn3(PO4)2·4H2O over the course of two weeks. Our results demonstrate that the interaction of inorganic salts with bodily fluids can induce the formation of de novo nanoparticles, which in turn, provides insights into how zinc‐enriched foods may also facilitate the formation of nanoparticles upon contact with saliva. As such, this may be considered as an undesirable (bio)mineralization.
Herein, a simple one-pot procedure is reported to obtain aqueous zinc oxide (ZnO) nanoparticle dispersions from ZnO nanoparticles dispersed in cyclohexane. In the process, polyoxyethylene (20) sorbitan monooleate (polysorbate 80, Tween 80) functions as a phase transfer agent and colloidal stabilizer. The particles grow in a defined manner during the transfer, presumably via coalescence. The final particle radii are tuneable in the range from 2.3 ± 0.1 nm to 5.7 ± 0.1 nm depending on the incubation time of the dispersion at 90 °C. Small-angle X-ray scattering is employed to determine the particle radius distributions before and after phase transfer. The larger ZnO particle radii are associated with a redshift of the optical bandgap and luminescence emission, as expected for semiconductor nanoparticles. The particles presented here exhibit a relative size distribution width of 20%, rendering them attractive for applications in, e.g., biology or catalysis. The latter application is demonstrated at the photocatalytic degradation of methylene blue dye.
Reaction procedures have been improved to achieve higher yields and shorter reaction times: one possibility is the usage of microwave reactors. In the literature, this is under discussion, for example, nonthermal effects resulting from the microwave radiation are claimed. Especially for the synthesis of nanomaterials, it is of crucial importance to be aware of influences on the reaction pathway. Therefore, we compare the syntheses of ultra-small silver nanoparticles via conventional and microwave heating. We employed a versatile one-pot polyol synthesis of poly(acrylic acid)-stabilized silver nanoparticles, which display superior catalytic properties. No microwave-specific effects in terms of particle size distribution characteristics, as derived by small-angle X-ray scattering and dynamic light scattering, are revealed. Because of the characteristics of a closed system, microwave reactors give access to elevated temperatures and pressures. Therefore, the speed of particle formation can be increased by a factor of 30 when the reaction temperature is increased from 200 to 250 °C. The particle growth process follows a cluster coalescence mechanism. A postsynthetic incubation step at 250 °C induces a further growth of the particles while the size distribution broadens. Thus, utilization of microwave reactors enables an enormous decrease of the reaction time as well as the opportunity of tuning the particle size. Possibly, decomposition of the stabilizing ligand at elevated temperatures results in reduced yields. A compromise between short reaction times and high yields can be found at a temperature of 250 °C and a corresponding reaction time of 30 s.
Ever since increasing a reaction’s yield while shortening the reaction time is the main objective in synthesis optimization. Microwave reactors meet these demands. In literature however their usage is under discussion due to claims of the existence of non-thermal effects resulting from the microwave radiation. Especially for nano-reference-material syntheses it is of crucial importance to be aware of influences on the reaction pathway. Therefore, we compare ultra-small silver nanoparticles with mean radii of 3 nm, synthesized via conventional and microwave heating.
We employed a versatile one-pot polyol synthesis of poly(acrylic acid) (PAA) stabilized silver nanoparticles, which display superior catalytic properties. No microwave specific effects in terms of particle size distribution characteristics, as derived by small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS), are revealed. Due to the microwave reactor’s characteristics of a closed system, syntheses can be carried out at temperatures beyond the solvent’s boiling point. Particle formation was accelerated by a factor of 30 by increasing the reaction temperature from 200 °C to 250 °C. The particle growth process follows a cluster coalescence mechanism.
A post-synthetic incubation step at 250 °C induces a further growth of the particles while the size distribution broadens. Thus, utilization of microwave reactors enables an enormous decrease of the reaction time as well as the opportunity of tuning the particles’ size. Possibly, decomposition of the stabilizing ligand at elevated temperatures results in reduced yields. A temperature of 250 °C and a corresponding reaction time of 30 s represent a compromise between short reaction times and high yields.
Zinc oxide (ZnO) as a wide-bandgap II-VI semiconductor finds application in areas like optoelectronics, photocatalysis as well as in detection systems. While band-gap engineering in macroscopic ZnO can be performed by alloying, the band-gap of ZnO nanoparticles is also dependent on their size. Since small-angle X-ray scattering (SAXS) provides a much higher resolution in terms of ultra-small nanoparticle size analysis compared to other techniques, it allows for a careful examination of the correlation between particle size and band-gap.
We report on the microwave-assisted synthesis of oleate-capped, photoluminescent zinc oxide nanoparticles with adjustable size as dispersions in organic solvents. The spherical particles were obtained by hydrolysis of the metal precursor in presence of a strong base at temperatures above the solvent’s boiling point. Hence, the reaction is dramatically accelerated and within seconds – instead of hours at lower temperatures –, narrowly dispersed particle systems are yielded. The particles’ sizes as derived from SAXS strongly depend on the reaction temperature and time. Choosing the right reaction conditions, the particle size and thus their band gap can be finely tuned. A size increase can be achieved both by increasing the reaction temperature and the reaction time.
See Figure 1 for an exemplary comparison of five-minute syntheses at different temperatures. Here, the yielded particles display diameters between 5.0 and 7.6 nm and corresponding band-gaps of 3.32 up to 3.41 eV. The size increase is accompanied by a red-shift of the UV/Vis absorption edges and fluorescence emission.
Furthermore, these particles can be transferred into water by coating with polysorbates.
Zinc is an essential trace element and is ingested daily by humans, partly in dissolved form. The first contact is with saliva, in which many ions are dissolved whose solubility product with zinc can be low. This could result in compounds forming, possibly in nanoparticular form, which could have different effects on the organism than pure zinc ions. Available biopolymers, e.g. α-amylase, can in turn stabilise as-formed nanostructures.
In this study, we report on the saliva stage of the artificial digestion of zinc chloride as a model substance for zinc ions. To facilitate in situ measurements, the sample is continuously passed through a small-angle x-ray scattering (SAXS) system. This custom-made machine is capable of measuring over a wide q-range and thereby able to resolve structures from around 250 nm down to the crystal structure. It is thus an excellent tool for investigating both the particle size distribution and the atomic structure of the sample.
By curve fitting (see Figure 1), we found that shortly after addition of zinc chloride to saliva, small particles with a mean radius of 1.9 ± 0.1 nm and a distribution width of 0.6 ± 0.1 nm formed. These particles are aggregated to compact mass fractals with a fractal aggregate size of 14.7 ± 0.1 nm and a fractal dimension of 2.96 ± 0.02. Approximately 7200 single particles stick together by protein and form mass fractals, whose radii of gyration were found to be 36 ± 1 nm. To determine the compound that was formed, infrared spectroscopy was used in addition to the SAXS measurements, and zinc phosphate was identified as the product.
Zinc oxide (ZnO) nanoparticles find manifold applications, most prominently in photovoltaics, where their unique optical properties are exploited. Particularly important are their band gap energy of 3.37 eV, which can be widely tuned through doping, and a large exciton binding energy of 60 mV. As a wide-bandgap II-VI semiconductor, the optical band gap energy and fluorescence energy become size-dependent when moving to particle radii of a few nanometers.
To gain a deeper insight into this issue, we report on a microwave-assisted, size-selective synthesis of pure ZnO nanoparticles. By hydrolysis of the metal precursor in presence of a strong base at temperatures exceeding the solvent’s boiling point, the reaction is dramatically accelerated, and narrowly dispersed, spherical particles are yielded within seconds – instead of hours at lower temperatures. The determination of their size distributions in high resolution using small-angle x-ray scattering (SAXS) allows for a precise mapping of the optical properties (UV/Vis absorption and fluorescence) to particle size.
We observed that the mean particle radii increase from 2.6 ± 0.1 nm with increasing synthesis temperature from 125 °C to 200 °C. This is accompanied by a red shift of the optical band gap and the fluorescence energies, the latter of which can be seen in Figure 1. Thus, undoped ZnO nanoparticles with narrow size distributions and pre-defined size as well as optical properties can be obtained through a microwave-assisted synthesis.
Zinc is an essential trace element and is ingested daily by humans, partly in dissolved form. The first contact is with saliva, in which many ions are dissolved whose solubility product with zinc can be low. This could result in compounds forming, possibly in nanoparticular form, which could have different effects on the organism than pure zinc ions.
In this study, we report on the saliva stage of the artificial digestion of zinc chloride as a model substance for zinc ions. To facilitate in situ measurements, the sample is continuously passed through a small-angle x-ray scattering (SAXS) system. This custom-made machine is capable of measuring over a wide q-range and thereby able to resolve structures from around 250 nm down to the crystal structure. It is thus an excellent tool for investigating both the particle size distribution and the atomic structure of the sample.
By curve fitting, we found that shortly after addition of zinc chloride to saliva, small particles with a mean radius of 1.9 ± 0.1 nm and a distribution width of 0.6 ± 0.1 nm formed. These particles are aggregated to compact mass fractals with a fractal aggregate size of 14.7 ± 0.1 nm and a fractal dimension of 2.96 ± 0.02. Approximately 7200 single particles form each mass fractal, whose radius of gyration was found to be 36 ± 1 nm. The growth of these structures continues over the course of several weeks. To determine the compound that was formed, infrared spectroscopy was used in addition to the SAXS measurements, and zinc phosphate was identified as the product.
Zinc oxide nanostructures possess optical properties that are dependent on particle shape and size. Here, we report on the synthesis of elongated zinc oxide tubes via the in-situ aggregation of spherical particles. Using a custom-built, lab-based instrument, x-ray scattering can be investigated over more than three decades in scattering vector q, allowing for a complete investigation from atomic distances up to larger-than-nano structures.
For this study, the hydrolytic synthesis of stearate stabilized zinc oxide nanostructures in tetrahydrofuran was performed and the reaction mixture was continuously fed through the SAXS/WAXS apparatus by means of a peristaltic pump. For comparison to nanospheres, oleate-functionalized zinc oxide particles were synthesized in a microwave-assisted fashion, and depending on reaction temperature, sphere radii could be adjusted between 2.6 and 3.8 nm, changing the optical and crystal lattice properties.
The evaluation of the in-situ measurements showed that at the beginning of the synthesis of the stearate-stabilized zinc oxide, similar, spherical particles are formed as in the oleate-based synthesis. In contrast, as the reaction progresses, the stearate-capped particles aggregate into elongated rods with radii of a few nanometres, which eventually form the nanotubes. These have radii of 30-50 nm and lengths of several hundred nanometres. Nevertheless, these structures still possess optical properties like the ultra-small zinc oxide spheres, i.e. a bright, yellow fluorescence. Therefore, we assume that the originally formed, ultra-small spheres, are still present within the tube structure, but separated by stearate, and thus determine their fluorescence properties.
The accurate EDS microanalysis of light elements such as boron and carbon by spectrum imaging will be demonstrated using a sintered hard ceramic material composed of the three major phases titanium boride (TiB2), titanium carbide (TiC), silicon carbide (SiC) and minor phases, sub-μm in size.
The combination of these three materials leads to improved mechanical and tribological properties. Silicon carbide is a material used for mechanical seals. It has the disadvantage of reduced failsafe running functions, causing increased wear when running dry. The added titanium components (TiC and TiB2) improve the failsafe running functions. This technology has already been transferred to industrial applications.
We studied the dissolution behavior of β NaYF4:Yb(20%), Er(2%) UCNP of two different sizes in biologically relevant media i.e., water (neutral pH), phosphate buffered saline (PBS), and Dulbecco’s modified Eagle medium (DMEM) at different temperatures and particle concentrations. Special emphasis was dedicated to assess the influence of different surface functionalizations, particularly the potential of mesoporous and microporous silica shells of different thicknesses for UCNP stabilization and protection. Dissolution was quantified electrochemically using a fluoride ion selective electrode (ISE) and by inductively coupled plasma optical emission spectrometry (ICP OES). In addition, dissolution was monitored fluorometrically. These experiments revealed that a thick microporous silica shell drastically decreased dissolution. Our results also underline the critical influence of the chemical composition of the aqueous environment on UCNP dissolution. In DMEM, we observed the formation of a layer of adsorbed molecules on the UCNP surface that protected the UCNP from dissolution and enhanced their fluorescence. Examination of this layer by X ray photoelectron spectroscopy (XPS) and mass spectrometry (MS) suggested that mainly phenylalanine, lysine, and glucose are adsorbed from DMEM. These findings should be considered in the future for cellular toxicity studies with UCNP and other nanoparticles and the design of new biocompatible surface coatings.
Efficient water electrolysis requires highly active electrodes. The activity of corresponding catalytic coatings strongly depends on material properties such as film thickness, crystallinity, electrical conductivity, and chemical surface speciation. Measuring these properties with high accuracy in vacuum-free and nondestructive methods facilitates the elucidation of structure−activity relationships in realistic environments. Here, we report a novel approach to analyze the optical and electrical properties of highly active oxygen evolution reaction (OER) catalysts via spectroscopic ellipsometry (SE). Using a series of differently calcined, mesoporous, templated iridium oxide films as an example, we assess the film thickness, porosity, electrical resistivity, electron concentration, electron mobility, and interband and intraband transition energies by modeling of the optical spectra. Independently performed analyses using scanning electron microscopy, energy-dispersive X-ray spectroscopy, ellipsometric porosimetry, X-ray reflectometry, and absorption spectroscopy indicate a high accuracy of the deduced material properties. A comparison of the derived analytical data from SE, resonant photoemission spectroscopy, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy with activity measurements of the OER suggests that the intrinsic activity of iridium oxides scales with a shift of the Ir 5d t2g sub-level and an increase of p−d interband transition energies caused by a transition of μ1-OH to μ3-O species.
Ellipsometry-based approach for the characterization of mesoporous thin films for H2 technologies
(2021)
Porous thin layer materials are gaining importance in different fields of technology and pose a challenge to the accurate determination of materials properties important for their function. In this work, we demonstrate a hybrid measurement technique using ellipsometry together with other independent methods for validation. Ellipsometry provides information about the porosity of different mesoporous films (PtRuNP/OMC = 45%; IrOx = 46%) as well as about the pore size (pore radius of ca. 5 nm for PtRuNP/OMC). In addition, the electronic structure of a material, such as intraband transitions of a mesoporous IrOx film, can be identified, which can be used to better understand the mechanisms of chemical processes. In addition, we show that ellipsometry can be used as a scalable imaging and visualization method for quality assurance in production. These require accurate and traceable measurements, with reference materials playing an important role that include porosity and other related properties. We show that our novel analytical methods are useful for improving analytical work in this entire field.
Catalysts are important components in chemical processes because they lower the activation energy and thus determine the rate, efficiency and selectivity of a chemical reaction. This property plays an important role in many of today’s processes, including the electrochemical splitting of water. Due to the continuous development of catalyst materials, they are becoming more complex, which makes a reliable evaluation of physicochemical properties challenging even for modern analytical measurement techniques and industrial manufacturing.
We present a fast, vacuum-free and non-destructive analytical approach using multi-sample spectroscopic ellipsometry to determine relevant material parameters such as film thickness, porosity and composition of mesoporous IrOx–TiOy films. Mesoporous IrOx–TiOy films were deposited on Si wafers by sol–gel synthesis, varying the composition of the mixed oxide films between 0 and 100 wt%Ir. The ellipsometric modeling is based on an anisotropic Bruggeman effective medium approximation (a-BEMA) to determine the film thickness and volume fraction of the material and pores. The volume fraction of the material was again modeled using a Bruggeman EMA to determine the chemical composition of the materials. The ellipsometric fitting results were compared with complementary methods, such as scanning electron microscopy (SEM), electron probe microanalysis (EPMA) as well as environmental ellipsometric porosimetry (EEP).
Porous materials play an important role in several fields of technology, especially for energy applications like photovoltaics, electrolysis or batteries. The activity of porous films is affected by properties like porosity, film thickness, chemical composition of the material as well as the crystallinity of the framework. The complex morphology of such porous films constitutes a challenge even for modern analytical techniques and requires new approaches employing the combination/complementation of data of different analytical methods. In this contribution we characterize thin mesoporous iridium-titanium mixed oxide film properties by Electron Probe Microanalysis (EPMA) with energy dispersive X-ray spectroscopy (EDS) at an SEM.
For the determination of porosity of Ir oxide thin films, electron probe microanalysis (EPMA) can be used as part of a combined SEM/EDS/STRATAGem analysis. The mass deposition (in μg cm-2) of films was calculated with the analysis software STRATAGem via k-values measured with EDS. The average density of coated films was obtained from the mass deposition and the film thickness as measured by the cross-section SEM. The porosity was calculated by dividing the average film density by the bulk (theoretical) density of the film material.
Film porosities were counterchecked by spectroscopic ellipsometry (SE) using the Bruggeman effective medium approximation (BEMA).
The results obtained by both analytical approaches/methods used, SEM/EDS/STRATAGem and SE were in good agreement.
Hydrogen features a very high specific energy density and is therefore a promising candidate for clean fuel from renewable resources. Water electrolysis can convert electrical energy into storable and transportable hydrogen gas. Under acidic conditions, platinum is the most active and stable monometallic catalyst for the hydrogen evolution reaction (HER). Yet, platinum is rare and needs to be used efficiently. Here, we report a synthesis concept for colloidal bimetallic platinum–ruthenium and rhodium–ruthenium nanoparticles (PtRuNP, RhRuNP) and their incorporation into ordered mesoporous carbon (OMC) films. The films exhibit high surface area, good electrical conductivity and well-dispersed nanoparticles inside the mesopores. The nanoparticles retain their size, crystallinity and composition during carbonization. In the hydrogen evolution reaction (HER), PtRuNP/OMC catalyst films show up to five times higher activity per Pt than Pt/C/Nafion® and PtRu/C/Nafion® reference catalysts.
Thin mesoporous metal oxide films are versatile and attractive candidates for several energy applications like photovoltaics, electrolysis or batteries. Due to their high surface area and ordered pore structure, mesoporous metal oxides demonstrate higher activities. The performance of the porous films is affected by properties like size and shape of the mesopores as well as the crystallinity of the framework. The exact determination and metrological evaluation of the complex morphology of thin mesoporous films requires a new analytical approach employing to combined data of different analytical methods. In this contribution we present a novel evaluation procedure for spectroscopic ellipsometry (SE) to analyse thin mesoporous iridium oxide films.
Mesoporous iridium oxide films were prepared via dip-coating of a solution containing a triblock-copolymer as structure directing agent and an iridium precursor in ethanol. Deposited films were calcined in air at temperatures between 300 and 600 °C. Their morphology was studied with SEM and an electron probe microanalysis (EPMA)and correlated via SE with a Bruggeman effective medium approximation (BEMA). The developed SE model described the film thickness as well as the porosity.
Figure 1a shows a top-view SEM image of mesoporous IrO2 film calcined at 375 °C. The image reveals that the films exhibit a well-ordered mesopore structure with an average pore diameter of 16 nm and a periodic distance between pore centres of 24 nm (FFT inset). Figure 1b is a parity plot of film thicknesses determined by cross-section SEM versus SE of IrO2 film samples prepared at different calcination temperatures. The porosity from the SE model is in good agreement to the porosity values obtained by EPMA.
The contribution will assess in detail the novel approach to analyse the morphology and porosity of thin metal oxide films with spectroscopic ellipsometry. Moreover, the advantages of the new developed approach will be discussed as well as combination of datasets from multiple measurements to development new methods for innovative energy technologies.
Thin mesoporous metal oxide films are versatile and attractive candidates for several energy applications like photovoltaics, electrolysis or batteries. Due to their high surface area and ordered pore structure, mesoporous metal oxides demonstrate higher activities. The performance of the porous films is affected by properties like size and shape of the mesopores as well as the crystallinity of the framework. The exact determination and metrological evaluation of the complex morphology of thin mesoporous films requires a new analytical approach employing to combined data of different analytical methods. In this contribution we present a novel evaluation procedure for spectroscopic ellipsometry (SE) to analyse thin mesoporous iridium oxide films. Mesoporous iridium oxide films were prepared via dip-coating of a solution containing a triblock-copolymer as structure directing agent and an Iridium precursor in ethanol. Deposited films were calcined in air at temperatures between 300 and 600 °C. Their morphology was studied with SEM and an electron probe microanalysis (EPMA) and correlated via SE with a Bruggeman effective medium approximation (BEMA). The developed SE model described the film thickness as well as the porosity.
... The contribution will assess in detail the novel approach to analyse the morphology and porosity of thin metal oxide films with spectroscopic ellipsometry. Moreover, the advantages of the new developed approach will be discussed as well as combination of datasets from multiple measurements to development new methods for innovative energy technologies.
Thin mesoporous metal oxide films are versatile and attractive candidates for several energy applications like photovoltaics, electrolysis or batteries. Due to their high surface area and ordered pore structure, mesoporous metal oxides demonstrate higher activities. The performance of the porous films is affected by properties like size and shape of the mesopores as well as the crystallinity of the framework. The exact determination and metrological evaluation of the complex morphology of thin mesoporous films requires a new analytical approach employing to combined data of different analytical methods. In this contribution we present a novel evaluation procedure for spectroscopic ellipsometry (SE) to analyse thin mesoporous iridium oxide films.
Mesoporous iridium oxide films were prepared via dip-coating of a solution containing a triblock-copolymer as structure directing agent and an iridium precursor in ethanol. Deposited films were calcined in air at temperatures between 300 and 600 °C. Their morphology was studied with SEM and an electron probe microanalysis (EPMA) and correlated via SE with a Bruggeman effective medium approximation (BEMA). The developed SE model described the film thickness as well as the porosity.
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The contribution will assess in detail the novel approach to analyse the morphology and porosity of thin metal oxide films with spectroscopic ellipsometry. Moreover, the advantages of the new developed approach will be discussed as well as combination of datasets from multiple measurements to development new methods for innovative energy technologies.
Rising energy demand and the impending climate change require the development of a sustainable, fossil-free fuel and chemical production on a global scale. Hydrogen production via water electrolysis will be a fundamental cornerstone in this endeavor. The activity and stability of respective electrode coatings strongly depends on the coating's properties, i.e. phase composition, crystallinity, electrical conductivity, accessible surface, wettability and many other factors. The key to the development of improved catalysts is a better understanding of the relations between their performance, stability and physicochemical properties. However, those relations can be complex, and are strongly influenced also by the reaction environment. Hence, operando analysis of the catalyst material during catalysis at realistic potentials and current densities is highly desirable. Yet, many analytical techniques cannot be applied in liquid environments at realistic potentials and current densities.
We propose environmental ellipsometric analysis in a dedicated electrochemical flow cell as a new method to evaluate gas evolution reactions operando under realistic working conditions. Figure 1 illustrates schematically the developed technique. Key factors to success are highly active model-type catalysts with template-controlled porosity, a suitable sample environment, a deep understanding of the spectroscopic method and respective model development, as well as concise cross validation with numerous other analytical techniques.
The method was developed and validated by analyzing a calcination series (300 - 600°C) of mesoporous templated IrOx films ex-situ and operando under oxygen evolution reaction (OER) conditions. The employed environmental electrochemical spectroscopic ellipsometric analysis (ECSE) revealed during OER the change of optical and electronic properties, i.e. the dielectric functions (real ε1 and imaginary part ε2), electrical and electronic properties such as resistivity (ρ) and band-to-band transitions (p-d band transitions). Film thickness and porosity were validated by means of scanning electron microscopy (SEM), X-ray reflectometry (XRR) or ellipsometric porosimetry (EP), electrical and electronic properties by means of conductivity measurements, X-ray photoelectron spectroscopy (XPS) or UV-Vis-NIR absorption spectroscopy. The electronic structures of the catalysts from valence electron energy loss spectra (VEELS) derived from the real (ε1) and imaginary part (ε2) of the dielectric function from SE measurements reveal a direct correlation with electrochemical activities in OER.
In the presentation reversible and irreversible potential-dependent changes of the catalyst properties during operation will be discussed along with the dynamics of gas formation, transport and dissolution at different potentials.
Rising energy demand and the impending climate change require the development of a sustainable, fossil-free fuel and chemical production on a global scale. Hydrogen production via water electrolysis will be a fundamental cornerstone in this endeavor. The activity and stability of respective electrode coatings strongly depends on the coating's properties, i.e. phase composition, crystallinity, electrical conductivity, accessible surface, wettability and many other factors. The key to the development of improved catalysts is a better understanding of the relations between their performance, stability and physicochemical properties. However, those relations can be complex, and are strongly influenced also by the reaction environment. Hence, operando analysis of the catalyst material during catalysis at realistic potentials and current densities is highly desirable. Yet, many analytical techniques cannot be applied in liquid environments at realistic potentials and current densities.
We propose environmental ellipsometric analysis in a dedicated electrochemical flow cell as a new method to evaluate gas evolution reactions operando under realistic working conditions. Figure 1 illustrates schematically the developed technique. Key factors to success are highly active model-type catalysts with template-controlled porosity, a suitable sample environment, a deep understanding of the spectroscopic method and respective model development, as well as concise cross validation with numerous other analytical techniques.
The method was developed and validated by analyzing a calcination series (300 - 600°C) of mesoporous templated IrOx films ex-situ and operando under oxygen evolution reaction (OER) conditions. The employed environmental electrochemical spectroscopic ellipsometric analysis (ECSE) revealed during OER the change of optical and electronic properties, i.e. the dielectric functions (real ε1 and imaginary part ε2), electrical and electronic properties such as resistivity (ρ) and band-to-band transitions (p-d band transitions). Film thickness and porosity were validated by means of scanning electron microscopy (SEM), X-ray reflectometry (XRR) or ellipsometric porosimetry (EP), electrical and electronic properties by means of conductivity measurements, X-ray photoelectron spectroscopy (XPS) or UV-Vis-NIR absorption spectroscopy. The electronic structures of the catalysts from valence electron energy loss spectra (VEELS) derived from the real (ε1) and imaginary part (ε2) of the dielectric function from SE measurements reveal a direct correlation with electrochemical activities in OER.
In the presentation reversible and irreversible potential-dependent changes of the catalyst properties during operation will be discussed along with the dynamics of gas formation, transport and dissolution
In the face of rising energy demand and the impending climate change the development of a sustainable, fossil-free fuel and chemical production is of global importance. One possible goal is the development of electrochemical conversion processes using catalysts. Porous materials play an important role in such energy applications. The key to the development of improved catalysts is a better understanding of the relations between their performance, stability and physico-chemical properties. However, the complex morphology of such catalysts constitutes a challenge even for modern analytical techniques.
Spectroscopic ellipsometry (SE) is a versatile method for studying material properties by using appropriate models (e.g. film thickness, optical and electronic properties). The fact that the material properties cannot be taken directly from the measured spectra, the developed models have to be validated. In a first step, the model for the ellipsometric fit studies of a calcination series of mesoporous iridium oxide films (300 – 600 °C) was investigated and validated with respect to their material properties. Moreover, the electronic structures of the catalysts reveal a direct correlation with electrochemical activities. The development of an environmental cell offers the possibility of investigations under real conditions. This will allow changes in the optical and electronic properties during the electrocatalytic oxygen evolution reaction.
In the face of rising energy demand and the impending climate change the development of a sustainable, fossil-free fuel and chemical production is of global importance. One possible goal is the development of electrochemical conversion processes using catalysts. Porous materials play an important role in such energy applications. The activity and stability of each catalyst is highly dependent on the properties of the coating, i.e., phase composition, crystallinity, accessible surface area, and many other factors. The key to the development of improved catalysts is a better understanding of the relations between their performance, stability and physico-chemical properties. However, the complex morphology of such catalysts constitutes a challenge even for modern analytical techniques. Spectroscopic ellipsometry (SE) is a versatile method for studying material properties by using appropriate models (e.g., film thickness, optical and electronic properties). Ellipsometric models need to be validated in order to produce accurate results. In a first step, the model for the ellipsometric fit studies of a calcination series of mesoporous iridium oxide films (300 – 600 °C) was investigated and validated with respect to their material properties.[4] The information on electronic structure of the catalysts shows a direct correlation with electrochemical activities. The development of an environmental electrochemical cell offers the possibility of investigations under operando conditions. Thus, changes in optical and electronic properties can be induced and monitored during the electrocatalytic oxygen evolution reaction.
Hydrogen production via water electrolysis will be an essential cornerstone in development of sustainable, fossil-free fuel and chemical production on a global scale. The activity and stability of each catalyst is highly dependent on the properties of the coating, i.e., phase composition, crystallinity, accessible surface area, and many other factors. The key to developing improved catalysts is a better understanding of the relationships between their performance, stability, and physicochemical properties. However, these relationships can be complex and are also strongly influenced by the reaction environment. Therefore, operando analysis of the catalyst material during catalysis at realistic potentials and current densities is highly desirable. However, many analytical techniques cannot be applied in liquid environments at realistic potentials and current densities.
We propose environmental ellipsometric analysis in a dedicated electrochemical flow cell as a method to evaluate gas evolution reactions operando under realistic working conditions. Figure 1 illustrates schematically the developed technique. Key factors to success are highly active model-type catalysts, a suitable sample environment, and a deep understanding of the appropriate model development, as well as concise cross validation with numerous other analytical techniques.
The method was developed and validated by analyzing a calcination series (300 – 600 °C) of mesoporous templated IrOx films ex-situ and operando under oxygen evolution reaction (OER) conditions. The employed environmental electrochemical spectroscopic ellipsometric (ECSE) analysis revealed during OER the change of optical and electronic properties, i.e. the dielectric functions, resistivity and band-to-band transitions (p-d band transitions). Film thickness and porosity were validated by means of scanning electron microscopy (SEM), X-ray reflectometry (XRR) or ellipsometric porosimetry (EP), electrical and electronic properties by means of conductivity measurements, X-ray photoelectron spectroscopy (XPS) or UV-Vis-NIR absorption spectroscopy. The electronic structures of the catalysts from valence electron energy loss spectra (VEELS) derived from ε1 and ε2 from SE measurements reveal a direct correlation with electrochemical activities in OER.
In the presentation reversible and irreversible potential-dependent changes of the catalyst properties during operation will be discussed along with the dynamics of gas formation, transport and dissolution at different potentials.
Porous materials play an important role in several fields of technology, especially for energy applications like photovoltaics, electrolysis or batteries. The activity of porous films is affected by properties like porosity, film thickness, chemical composition of the material as well as the crystallinity of the framework. The complex morphology of such porous films constitutes a challenge for modern analytical techniques and requires approaches employing the combination/complementation of data of different analytical methods. In this contribution we characterize thin mesoporous iridium-titanium mixed oxide film properties by spectroscopic ellipsometry (SE).
Mesoporous iridium oxide - titanium oxide (IrOx-TiOx) films were prepared via dip-coating of a solution containing a triblock-copolymer as structure-directing agent, an iridium precursor as well as a titanium precursor in ethanol. Deposited films with different amounts of iridium (0 wt%Ir to 100 wt%Ir) were synthesized and calcined in air. The thin films were analyzed with SE using the Bruggeman effective medium approximation (BEMA) for modelling. The results were compared with electron probe microanalysis (EPMA) as part of a combined SEM/EDS/STRATAGem Analysis.
Porous materials play an important role in several fields of technology, especially for energy applications like photovoltaics, electrolysis or batteries. The activity of porous films is affected by properties like porosity, film thickness, chemical composition of the material as well as the crystallinity of the framework. The complex morphology of such porous films constitutes a challenge even for modern analytical techniques and requires new approaches employing the combination/complementation of data of different analytical methods. In this contribution we characterize thin mesoporous iridium-titanium mixed oxide film properties by Electron Probe Microanalysis (EPMA) with energy dispersive X-ray spectroscopy (EDS) at an SEM.
Porous materials play an important role in several fields of technology, especially for energy applications like photovoltaics, electrolysis or batteries. The activity of porous films is affected by properties like porosity, film thickness, chemical composition of the material as well as the crystallinity of the framework. The complex morphology of such porous films constitutes a challenge even for modern analytical techniques and requires new approaches employing the combination/complementation of data of different analytical methods. In this contribution we characterize thin mesoporous iridium-titanium mixed oxide film properties by Electron Probe Microanalysis (EPMA) with energy dispersive X-ray spectroscopy (EDS) at an SEM.
In der klinischen Diagnostik werden für zytometrische Messverfahren bereits eine Reihe von Reagenzien eingesetzt zur Markierung von Antikörper eingesetzt, um die Detektion von Biomarkern mittels Fluoreszenz- oder Flugzeitmassenspektrometrie zu ermöglichen.
Seit kurzem ist auch eine Imaging Mass Cytometry Kombination direkt erhältlich, wodurch der Nachweis von Biomarkern in Gewebeschnitten erreicht werden kann. Dazu wird eine Kopplung von Laser Ablation und induktiv gekoppeltem Plasma Massenspektrometrie eingesetzt, wobei ähnlich der Massenzytometrie, zuvor Antikörper mit Metallen markiert, und im Anschluss mit dem Gewebeschnitt inkubiert werden. Durch die hohe Ortsauflösung können die Biomarker lokalisiert, und zukünftig vielleicht auch quantifiziert werden.
Insbesondere Lanthanide eignen sich als Markierungsmetalle, da sie einen niedrigen Untergrund und chemisch ähnliches Verhalten zueinander aufweisen. Allein durch diese Elemente können bereits etwa 15 Parameter unterschieden werden, was durch isotopenreine Standards weiter gesteigert werden kann.
Vom Markierungsgrad abhängig werden unterschiedlich viele Metalle am Antikörper gebunden, und beeinflussen so die Sichtbarkeit im ICP-MS. Nanopartikel könnten daher eine deutliche Steigerung der Sensitivität bewirken. GdVO4 Nanokristalle scheinen bisher sehr vielversprechend und bieten neben multiparametrischen Anwendungen auch Multimodalität.
Die Synthese der Nanokristalle zeigte hohe Homogenität und Reproduzierbarkeit in Partikelgröße in der Zusammensetzung. Ein erstes Experiment mit einer Zellkultur konnte bereits die effiziente Markierung der Zellen unter Beweis stellen, wobei durch hohe Signalstärke auch subzelluläre Auflösung in der LA-ICP-MS erreicht werden konnte.
In-situ SAXS techniques
(2018)
This project studies the orientation of nanoparticles under the influence of external stimuli such as electric fields, magnetic fields and ultra-sonic vibrations. A set of functional sample holders that fit inside the sample chamber of a state-of-the-art Small Angle X-ray Scattering (SAXS) machine, called the “Multi-scale Analyzer for Ultrafine Structures” (MAUS).
The MAUS has been custom engineered to serve as a miniaturized Synchrotron, thus enabling standard material to be characterized to a high standard. Our work is needed to detail the fine characterization of reference nano-particles, not only on the nano-scale, but also coupled with external agents.
A second aim of this project is to verify a few proof-of-concept designs for the alignment of nano-particles. Where the alignment of nano-particles In-Situ is intended to further develop 3D printing technologies, and SAXS is an ideal choice to study the alignment of an oriented ensemble.
For more information about the MAUS;
https://www.bam.de/Content/DE/Pressemitteilungen/2018/AnalyticalSciences/2018-01-31-mit-maus-an-die-spitze-der-nano-forschung.html
In-Situ SAXS Techniques
(2018)
Our project's aim is to enhance the capabilities of additive manufacturing techniques, where enabling a Two-Photon-Polymerization (TPP) 3D printer of producing arrays of precisely aligned nanoparticles is of an enormous value. As heterogeneous functional nanostructures with arrays of oriented nanoparticles are very promising in many fields; electrochemistry, energy storage, nanoelectronics among other vital fields.
The feasibility and the convenience of orienting nanoparticles using magnetic, electric fields and ultrasonic vibrations will be systematically investigated, using Small Angle X-ray Scattering (SAXS), since SAXS can provide detailed information about the orientation characteristics of nano-Ensembles. Corresponding to our prerequisites, a set ad hoc functional sample holders, sample stages and other In-Situ SAXS solutions were developed, and incorporated to be compatible with a state-of-the-arts SAXS machine, called Multi-scale Analyzer for Ultrafine Structures (MAUS).
The MAUS has been customized and engineered to serve as a miniaturized synchrotron, and that is exactly what we need.
Experiments attempting to orient superparamagnetic nanoparticles will be discussed, where the outcomes will not only help in understanding the mechanics of field-particle interactions, it will also help in further developing the adequate needed set of corrections to the SAXS data, that is especially regards oriented samples.
We present a workflow for obtaining fully trained artificial neural networks that can perform automatic particle segmentations of agglomerated, non-spherical nanoparticles from scanning electron microscopy images “from scratch”, without the need for large training data sets of manually annotated images. The whole process only requires about 15 minutes of hands-on time by a user and can typically be finished within less than 12 hours when training on a single graphics card (GPU). After training, SEM image analysis can be carried out by the artificial neural network within seconds. This is achieved by using unsupervised learning for most of the training dataset generation, making heavy use of generative adversarial networks and especially unpaired image-to-image translation via cycle-consistent adversarial networks. We compare the segmentation masks obtained with our suggested workflow qualitatively and quantitatively to state-of-the-art methods using various metrics. Finally, we used the segmentation masks for automatically extracting particle size distributions from the SEM images of TiO2 particles, which were in excellent agreement with particle size distributions obtained manually but could be obtained in a fraction of the time.
This dataset accompanies the following publication, first published in Scientific Reports (www.nature.com/articles/s41598-021-84287-6):
B. Ruehle, J. Krumrey, V.-D. Hodoroaba, Scientific Reports, Workflow towards Automated Segmentation of Agglomerated, Non-Spherical Particles from Electron Microscopy Images using Artificial Neural Networks, DOI: 10.1038/s41598-021-84287-6
It contains electron microscopy micrographs of TiO2 particles, the corresponding segmentation masks, and their classifications into different categories depending on their visibility/occlusion. Please refer to the publication and its supporting information for more details on the acquisition and contents of the dataset, as well as the GitHub repository at https://github.com/BAMresearch/automatic-sem-image-segmentation
In this contribution different ways are explored with the aim to generate suitable training data for ‘non-ideal’ samples using various approaches, e.g., computer-generated images or unsupervised learning algorithms such as generative adversarial networks (GANs). We used these data to train simple CNNs to produce segmentation masks of SEM images and tested the trained networks on real SEM images of complex nanoparticle samples. The novel use of CNN for the automated analysis of the size of nanoparticles of complex shape and with a high degree of agglomeration has proved to be a promising tool for the evaluation of particle size distribution on a large number of constituent particles. Further development and validation of the preliminary model, respectively larger training and validation data sets are necessary.
We present a workflow for obtaining fully trained artificial neural networks that can perform automatic particle segmentations of agglomerated, non-spherical nanoparticles from electron microscopy images “from scratch”, without the need for large training data sets of manually annotated images. This is achieved by using unsupervised learning for most of the training dataset generation, making heavy use of generative adversarial networks and especially unpaired image-to-image translation via cycle-consistent adversarial networks. The whole process only requires about 15 minutes of hands-on time by a user and can typically be finished within less than 12 hours when training on a single graphics card (GPU). After training, SEM image analysis can be carried out by the artificial neural network within seconds, and the segmented images can be used for automatically extracting and calculating various other particle size and shape descriptors.
Neuartige Materialien, die bekannte (Werk-)Stoffe mit neuen Funktionalitäten ausstatten, spielen eine zunehmend wichtige Rolle im Bereich der Materialforschung und -prüfung. Das Spektrum neuartiger Materialien reicht von der gezielten Oberflächenfunktionalisierung und -strukturierung makroskopischer Materialien, dünnen Beschichtungen bis hin zu mikro- und nanoskaligen Kompositmaterialien und funktionalen Materialien an der Schnittstelle zur Biologie, Biotechnologie, nachhaltige Energiespeicherung und Sensorik. Dabei bieten neuartige Materialien die Chance, Werkstoffe und Produkte mit erweiterter oder verbesserter Funktionalität zu erhalten und Sicherheit bereits im Designprozess zu berücksichtigen. Durch dieses breite Anwendungsspektrum und die Herausforderungen, die solche Materialien für die Sicherheit in Chemie und Technik mit sich bringen, sind diese in allen Themenfeldern der BAM repräsentiert (Material, Analytical Sciences, Energie, Infrastruktur und Umwelt).
Die Aufgaben der BAM erstrecken sich dabei von der Herstellung von Referenzmaterialien für Industrie, Forschung und Regulation, über die Erstellung von standardisierten Referenzverfahren für nachhaltige Messungen im Umwelt- und Lebenswissenschaftsbereich bis hin zur Bereitstellung von belastbaren und zitierbaren Referenzdaten. Durch die genaue Charakterisierung neuartiger Materialien können potentiell problematische Substanzen identifiziert und deren Risiken besser abgeschätzt werden. In diesem Beitrag werden einige aktuelle Beispiele aus diesen Bereichen vorgestellt.
The damaging impact of hydrogen on the austenitic stainless steel AISI 304 L was analysed.
To this aim, samples were charged electrochemically with the hydrogen isotope deuterium (2H, D) and examined with time-of-flight secondary ion mass spectrometry (ToF-SIMS) and electron backscatter diffraction (EBSD). The fusion of the obtained chemical and structural information revealed local enrichment of deuterium in austenite, transformation into martensite, crack formation and severe roughening of the specimen surface. The results indicated that martensite was not only formed during charging but also during Desorption and ToF-SIMS examinations. Furthermore, cross-sections of deuterium-charged samples revealed that in preferred deformation bands a g/ε/a 0 evolution is taking place.
By means of microscopic analyses and carrier gas hot extraction (CGHE), it was found that the use of NaAsO2 as recombination poison decreased the uptake of hydrogen significantly and resulted in severe precipitation on the specimen surfaces. This is in contrast to the popular presumption that NaAsO2 enhances the uptake of hydrogen (and
deuterium) during electrochemical charging by hampering its recombination from Atoms to molecules.
During the energy transformation from fossil fuels to renewable energy sources, the use of hydrogen as fuel and energy storage can play a key role. This presents new challenges to industry and the scientific community alike. The storage and transport of hydrogen, which is nowadays mainly realized by austenitic stainless steels, remains problematic, which is due to the degradation of mechanical properties and the possibility of phase transformation by hydrogen diffusion and accumulation. The development of materials and technologies requires a fundamental understanding of these degradation processes. Therefore, studying the behavior of hydrogen in austenitic steel contributes to an understanding of the damage processes, which is crucial for both life assessment and safe use of components in industry and transportation. As one of the few tools that is capable of depicting the distribution of hydrogen in steels, time-of-flight secondary ion mass spectrometry was conducted after electrochemical charging. To obtain further information about the structural composition and cracking behavior, electron-backscattered diffraction and scanning electron microscopy were performed. Gathered data of chemical composition and topography were treated employing data fusion, thus creating a comprehensive portrait of hydrogen-induced effects in the austenite grade AISI 304L. Specimens were electrochemically charged with deuterium instead of hydrogen. This arises from the difficulties to distinguish between artificially charged hydrogen and traces existing in the material or the rest gas in the analysis chamber. Similar diffusion and permeation behavior, as well as solubility, allow nonetheless to draw conclusions from the experiments.
Hydrocarbons fuel our economy. Furthermore, intermediate goods and consumer products are often hydrocarbon-based. Beside all the progress they made possible, hydrogen-containing substances can have severe detrimental effects on materials exposed to them. Hydrogen-assisted failure of iron alloys has been recognised more than a century ago. The present study aims to providing further insight into the degradation of the austenitic stainless steel AISI 304L (EN 1.4307) exposed to hydrogen. To this end, samples were electrochemically charged with the hydrogen isotope deuterium (2H, D) and analysed by scanning electron microscopy (SEM), electron back-scatter diffraction (EBSD) and time-of-flight secondary ion mass spectrometry (ToF-SIMS). It was found that deuterium caused a phase transformation from the original γ austenite into ε- and α’-martensite. Despite their low solubility for hydrogen, viz. deuterium, the newly formed phases showed high deuterium concentration which was attributed to the increased density of traps. Information about the behaviour of deuterium in the material subjected to external mechanical load was gathered. A four-point-bending device was developed for this purpose. This allowed to analyse in-situ pre-charged samples in the ToF-SIMS during the application of external mechanical load. The results indicate a movement of deuterium towards the regions of highest stress.
Due to their excellent combination of ductility, strength and corrosive resistance, austenitic stainless steels (ASS) are widely used in many industrial applications. Thus, these steel grades can be found as structural components in the (petro-)chemical industry, in offshore applications and more recent for storage and transport of hydrogen fuel. Steels employed for these applications are exposed to aggressive environments and hydrogen containing media. The ingress and accumulation of hydrogen into the microstructure is commonly observed during service leading to a phenomenon called “hydrogen embrittlement”. A loss in ductility and strength, the formation of cracks and phase transformations are typical features of this hydrogen-induced degradation of mechanical properties.
Although, great efforts are made to understanding hydrogen embrittlement, there is an ongoing debate of the underlying mechanisms. This knowledge is crucial for the safe use and durability of components on the one side and the development of new materials on the other.
Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was proven to be a powerful tool for depicting the distribution of the hydrogen isotope deuterium in the microstructure of austenitic and duplex steels. The combination with imaging techniques such as electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM), delivering structural and morphological information, creates a comprehensive picture of the hydrogen/deuterium-induced effects in the materials. All the gathered data is treated with principal component analysis (PCA) and data fusion to enhance the depth of information.
The mobility of hydrogen and deuterium in a steel microstructure is affected by external mechanical stress. To investigate the behaviour of deuterium in a strained microstructure, a new in situ experimental approach was developed. This gives the possibility of analysing samples in the SIMS instrument simultaneously to four-point-bending-tests.
Specimens made from ASS AISI 304L were electrochemically charged with deuterium instead of hydrogen. This necessity stems from the difficulty to separate between artificially charged hydrogen and hydrogen existing in the pristine material or adsorbed from the rest gas in the analysis chamber. Nonetheless, similar diffusion, permeation and solubility data allow to draw qualitative conclusions from the experiments, which are relevant for the application addressed.
The reduction of harmful emissions to the environment is one of the most urgent challenges of our time. To achieve this goal, it is inevitable to shift from using fossil fuels to renewable energy sources. Within this transition, hydrogen can play a key role serving as fuel in transportation and as means for energy storage.
The storage and transport of hydrogen using austenitic stainless steels as the infrastructure, as well as the use of these grades in hydrogen containing aggressive environments, remains problematic. The degradation of the mechanical properties and the possibility of phase transformation by ingress and accumulation of hydrogen are the main drawbacks. Advanced studies of the behaviour of hydrogen in austenite is necessary to fully understand the occurring damage processes. This knowledge is crucial for the safe use of components in industry and transportation facilities of hydrogen.
A powerful tool for depicting the distribution of hydrogen in steels, with high accuracy and resolution, is time-of-flight secondary ion mass spectrometry (ToF-SIMS). We here present a comprehensive research on the hydrogen degradation processes in AISI 304L based on electrochemical charging and subsequent ToF-SIMS experiments. To obtain furthermore information about the structural composition and cracking behaviour, electron-backscattered diffraction (EBSD) and scanning electron microscopy (SEM) were performed afterwards. All the gathered data was treated employing data fusion, thus creating a thorough portrait of hydrogen diffusion and its damaging effects in AISI 304L.
Specimens were charged with deuterium instead of hydrogen. This necessity stems from the difficulty to separate between artificially charged hydrogen and traces existing in the material or adsorbed from the rest gas in the analysis chamber. Similar diffusion and permeation behaviour, as well as solubility, allow nonetheless to draw onclusions from the experiments.
Material Acceleration Platforms (MAPs) represent a transformative approach to the development of resilient and sustainable technology value chains. These platforms can identify candidate chemistries and structures via simulations, and database searches and leverage machine learning-based rapid screening to accelerate the discovery and deployment of novel materials, thereby addressing critical challenges in modern technology sectors.
Incorporating high-fidelity advanced characterization in the early phases of material development is crucial for early de-risking. Advanced characterization techniques, such as X-ray diffraction, advanced electrochemical and spectroscopic techniques provide comprehensive insights into the structural, chemical, and physical properties of materials. Long-term testing further contributes to the de-risking process by evaluating the durability and stability of materials under various environmental and operational conditions. Early identification of potential degradation mechanisms enables the refinement of material compositions and processing methods, ultimately leading to the development of more resilient materials.
Early upscaling attempts are integral to assessing the feasibility of material leads generated through machine learning-based rapid screening to evaluate the scalability of synthesis and processing techniques. This step is critical for identifying potential challenges in manufacturing, such as issues related to reproducibility, yield, and cost-effectiveness. Process design has to be a major part of the MAP-based material design to cope with the increasing share of secondary raw materials in supply chains.
This presentation will briefly summarize possible strategies to address these issues and provide deep-dives on best practices. As the demand for advanced materials continues to grow, MAPs will play an increasingly vital role in driving technological advancements and addressing global challenges.
The energy crisis becomes more prominent in higher altitude countries like Germany, with higher annual energy demand. Thus, the generation of higher energy density fuel like hydrogen from renewable resources become the only way to solve the zero-emission energy system while avoiding the expensive batteries as an energy storage option. Therefore, water electrolysis cells to produce hydrogen and oxygen by storing of solar/wind energy in chemical bonds is a fruitful alternative for renewable and long-term energy generation. Thus, designing inexpensive water-splitting electrocatalyst material becomes a field of research of utmost importance. High entropy metal hydroxide organic frameworks (HE-MHOFs) are composed of high entropy hydroxide layer inside MOFs, resulting in a high degree of structural complexity and diversity than conventional MOFs. The concept of ‘high entropy’ refers to multiple types of metal ions (Metal = TM) in a near equimolar ratio in the same framework, creating a high degree of disorder and many possible structural configurations. Here, the HE-MHOF successfully synthesized by a conventional solvothermal process, crystallizes in the single phase with significant lattice distortion. A special-quasi-random (SQS) structure was simulated with equimolar compositions (~20% TM = Mn, Co, Ni, Cu and Zn) and a comparison was made with the ICP-AES (inductively coupled plasma atomic emission spectroscopy), XANES (X-ray absorption near edge structure) and XAFS (X-ray absorption fine structure) observations. Further, the elemental mapping (Energy dispersive Spectroscopy) of HE-MHOF shows the presence of all five different metals in the same crystallite to substantiate the ‘high entropy’ state of the MOF. The HE-MHOF offers improved thermal stability than mono-metallic MHOF and exhibit unique properties compared to traditional monometallic (Ni2+) MOF variants. Firstly, to elucidate the effect of the multimetallic system on the catalytic performance, we have performed density functional theory (DFT) calculations to investigate pre-redox cycles involved in the catalytic activation of HE (and Ni)-MOFs. HE-MHOF is further investigated as an electrocatalyst for oxygen evolution reaction (OER) due to its special high entropy hydroxide layered structure and electronic properties. Our DFT results have examined the traditional proton-coupled electron transfer (PCET) steps involving the single transition-metal site. The scrutiny of d-band centers and their behaviour in catalytic upgradation is investigated with density of states (DOS) analysis. It exhibits outstanding performance towards oxygen evolution reaction (OER) comparable to the experimental findings, which is also comparable to state-of-the-art OER catalysts based on precious metals such as iridium oxide and platinum carbon. We have considered different electrolyte solutions to elucidate the fast kinetics oxygen evolution reaction in the presence of various external nucleophilic anions. In hydroxyl-based MOFs, electrolytes' influence can substantially enhance catalytic activities. Here, with the help of DFT simulations, we have investigated the effect of the nucleophilicity of anion on each elementary reaction involved in the PCET mechanism of OER.
Sequence-defined poly(amino phosphodiester)s containing main-chain tertiary amines were synthesized by automated solid-phase phosphoramidite chemistry. These polymers were prepared using four monomers with different substituents. The formed polymers were characterized by HPLC and mass spectrometry. These methods evidenced preparation of molecularly-defined polymers. Furthermore, the presence of tertiary amines in the polymer backbones facilitates sequencing by tandem mass spectrometry.
We present Jobflow, a domain-agnostic Python package for writing computational workflows tailored for high-throughput computing applications. With its simple decorator-based approach, functions and class methods can be transformed into compute jobs that can be stitched together into complex workflows. Jobflow fully supports dynamic workflows where the full acyclic graph of compute jobs is not known until runtime, such as compute jobs that launch
other jobs based on the results of previous steps in the workflow. The results of all Jobflow compute jobs can be easily stored in a variety of filesystem- and cloud-based databases without the data storage process being part of the underlying workflow logic itself. Jobflow has been intentionally designed to be fully independent of the choice of workflow manager used to dispatch the calculations on remote computing resources. At the time of writing, Jobflow
workflows can be executed either locally or across distributed compute environments via an adapter to the FireWorks package, and Jobflow fully supports the integration of additional workflow execution adapters in the future.
Jobflow is a free, open-source library for writing and executing workflows. Complex workflows can be defined using simple python functions and executed locally or on arbitrary computing resources using the FireWorks workflow manager.
Some features that distinguish jobflow are dynamic workflows, easy compositing and connecting of workflows, and the ability to store workflow outputs across multiple databases.
The degradation of the chemotherapy drug 5-fluorouracil by a non-pristine metal surfaces is studied.Using density functional theory, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy we show that the drug is entirely degraded by medical-grade silver surfaces, already at body temperature,and that all of the fluorine has left the molecule, presumably as HF. Remarkably, this degradation is even more severe than that reported previously for 5-fluorouracil on a pristine monocrystalline silver surface(in which case 80% of the drug reacted at body temperature) [1]. We conclude that the observed reaction is due to a reaction pathway, driven by H to F attraction between molecules on the surface, which results in the direct formation of HF; a pathway which is favoured when competing pathways involving reactive Ag surface sites are made unavailable by environmental contamination. Our measurements indicate that realistically cleaned, non-pristine silver alloys, which are typically used in medical applications, can result in severe degradation of 5-fluorouracil, with the release of HF – a finding which may have important implications for the handling of chemotherapy drugs.
Micro-concentrator solar cells offer an attractive way to further enhance the efficiency of planar-cell technologies while saving absorber material. Here, two laser-based bottom-up processes for the fabrication of regular arrays of CuInSe2 and Cu(In,Ga)Se2 microabsorber islands are presented, namely one approach based on nucleation and one based on laser-induced forward transfer.
Additionally, a procedure for processing these microabsorbers to functioning micro solar cells connected in parallel is demonstrated. The resulting cells show up to 2.9% efficiency and a significant efficiency enhancement under concentrated Illumination.
Das Fügeverfahren Kleben bietet viele Vorteile wie z.B. das Verbinden schwieriger Materialklassen, geringe thermische Belastung (Strukturveränderung/-schwächung) der Fügepartner und eine Lastverteilung über den gesamten Fügebereich. Die Auswahl an verfügbaren Klebstoffen und Vorbehandlungsoptionen ist dabei ebenfalls vielfältig. Einige Polymere weisen darüber hinaus Eigenschaften auf, die eine Herstellung von festen und dauerhaft beanspruchbaren Klebverbindungen erschweren. Mittels Oberflächenbehandlung, z.B. durch Plasmafeinreinigung bzw. –aktivierung, können die Grenzflächern solcher Polymere - bezogen auf die Eignung als Fügeteilpartner – optimiert werden. Schnelle Prüfverfahren zur Ermittlung von Verbundeigenschaften sind somit erforderlich.
Das Messprinzip Centrifugal Adhesion Testing Technologie verwendet die radial gerichtete Zentrifugalkraft als Belastungsgröße des zu testenden Verbunds, die durch Variation der Drehzahl gesteuert wird. Bei Erreichen der kritischen Beanspruchung trennt sich ein aufgeklebter Prüfstempel vom Substrat. Zeitgleich wird ein positionsbezogenes IR-Signal aus dem drehenden Rotor an das Basisgerät gesendet und zusammen mit der Drehzahl an die PC-Software übertragen. Für jede Probe wird die Bruchkraft berechnet und in Echtzeit angezeigt. Der Adhesion Analyser LUMiFrac® untersucht bis zu acht Prüfkörper unter identischen Bedingungen. Das neue Messprinzip erfüllt die Anforderungen von DIN EN 15870, DIN EN 14869-2, ISO 4624 sowie DIN EN 13144.
Die Multiprobentestung ermöglicht schnelle Charakterisierungen von Klebverbindungen. So kann der Effekt einer Plasmabehandlung von Bauteilen auf die Verbundfestigkeit zeitsparend bestimmt werden. Die gezielte Veränderung unterschiedlicher Plasma-Parameter, wie beispielsweise, die Plasmazusammensetzung, der Abstand vom Plasmabrenner zur Oberfläche oder die Verweildauer unter dem Brenner, beeinflußt die Festigkeit des Klebsystems und ist dem LUMiFrac direkt quantifizierbar.
Neben der Festigkeitsbestimmung von Klebverbindungen ist die Haftung von Schichtsystemen ein wichtiger Anwendungsbereich. Ergebnisse für Zug- und Scherbeanspruchung, realisiert mit unterschiedlichen Prüfkörper-Geometrien, werden vorgestellt. Ferner werden verschiedene festigkeitsbeeinflussende Faktoren, wie Prüfgeschwindigkeit oder Substratverformung bei Beanspruchung untersucht
The majority of all products have coated surfaces designed to fulfil different requirements. Building constructions are exposed to external influences like a wide temperature and humidity range, rain and UV radiation to name a few. The extension of machine life for metal cutting tools, like drills or milling cutters is another field of application for coated surfaces. The surfaces have to be modified in a way to maintain their specific functionality. Although adhesion testing of coatings is of great interest, it is still a challenge to obtain reliable quantitative results and to meet economic requirements.
In this talk we deal with the curing behaviour of different 2-component epoxy paint systems for corrosion protection of metal constructions. After preparation of specimens the strength was determined in specified time intervals during curing. It could be shown that epoxy paints differ significantly on curing time as well as final strength. The second experimental study deals with coating systems on glass fibre reinforced plastics which are used for wind power turbines to reduce abrasive wear and ice adhesion for aerodynamic and safety reasons.
All measurements have been carried out by CAT-TechnologyTM (Centrifugal Adhesion Testing), which uses the radially directed centrifugal force as test-load. The multi-sample test instrument analyses up to eight test specimen under identical testing conditions. By varying the rotational speed (100 rpm up to 13,000 rpm), forces from 0.1 N to 6.5 kN are applied. Upon reaching the critical rupture force, the stamp separates from the substrate and a sample related IR-signal is sent from the spinning rotor. For each test specimen breaking force is calculated and displayed in real-time. The innovative measurement principle meets the requirements of DIN EN 15870 and ISO 4624.
Electrochemical methods offer great promise in meeting the demand for user-friendly on-site devices for Monitoring important parameters. The food industry often runs own lab procedures, for example, for mycotoxin analysis, but it is a major goal to simplify analysis, linking analytical methods with smart technologies. Enzyme-linked immunosorbent assays, with photometric detection of 3,3’,5,5’-tetramethylbenzidine (TMB),form a good basis for sensitive detection. To provide a straightforward approach for the miniaturization of the detectionstep, we have studied the pitfalls of the electrochemical TMB detection. By cyclic voltammetry it was found that the TMB electrochemistry is strongly dependent on the pH and the electrode material. A stable electrode response to TMB could be achieved at pH 1 on gold electrodes. We created a smartphonebased, electrochemical, immunomagnetic assay for the detection of ochratoxin A in real samples, providing a solid basis forsensing of further analytes.
Steps Forward in the Application of 3,3’,5,5’- Tetramethylbenzidine (TMB) in Amperometric Assays
(2022)
Electrochemical methods make great promise to meet the demand for user-friendly on-site devices for monitoring important parameters. Food industry often runs own lab procedures, e.g. for mycotoxin analysis, but it is a major goal to simplify analysis, linking analytical methods with miniaturized technologies. Enzyme-linked immunosorbent assays, with photometric detection of the horseradish peroxidase (HRP) substrate, 3,3’,5,5’-tetramethylbenzidine (TMB), form a good basis for sensitive detection. To provide a straight-forward approach for the miniaturization of the detection step, we have studied the pitfalls of the electrochemical TMB detection. By cyclic voltammetry it was found that the TMB electrochemistry is strongly dependent on the pH and the electrode material.
It was found that screen-printed gold electrodes and a highly acidic pH value (pH 1) are well-suited to perform the electrochemical detection of TMB, due to the reversible character of the redox reaction under these conditions. This set-up provides a good signal stability over several measuring cycles, providing the basis for analysing multiple samples. In contrast to this, for carbon screen-printed electrodes, it was found that the signal response has changed after the electrochemical reaction with TMB at pH 1. At a weakly acidic pH value (pH 4), neither with carbon nor with gold electrodes a reproducible electrochemical detection of TMB could be achieved [1].
Based on these findings we created a smartphone-based, electrochemical, immunomagnetic assay for the detection of ochratoxin A and ergometrine in real samples. Therefore, a competitive assay was performed on magnetic beads using HRP and TMB/H2O2 to generate the signal. Enzymatically oxidized TMB was quantified after addition of H2SO4 by amperometry with screen-printed gold electrodes in a custom-made wall-jet flow cell. The results are in good correlation with the established photometric detection method, providing a solid basis for sensing of further analytes in HRP-based assays using the newly developed miniaturized smartphone-based, electrochemical, immunomagnetic assay.
Electrochemical methods make great promise to meet the demand for user-friendly on-site devices for monitoring important parameters. Food industry often runs own lab procedures, e.g., for mycotoxin analysis, but it is a major goal to simplify analysis, linking analytical methods with miniaturized technologies. Enzyme-linked immunosorbent assays, with photometric detection of the horseradish peroxidase (HRP) substrate 3,3’,5,5’-tetramethylbenzidine (TMB), form a good basis for sensitive detection. To provide a straight-forward approach for the miniaturization of the detection step, we have studied the pitfalls of the electrochemical TMB detection. By cyclic voltammetry, it could be shown that TMB electrochemistry is strongly dependent on the pH and the electrode material.
It was found that screen-printed gold electrodes and a very low pH value (pH 1) are well-suited to perform the electrochemical detection of TMB, due to the reversible character of the redox reaction under these conditions. Under these conditions, a good signal stability over several measuring cycles is achieved, providing the basis for analyzing multiple samples. In contrast to this, for carbon screen-printed electrodes, it was found that the signal response has changed after the electrochemical reaction with TMB at pH 1. At moderately acidic conditions (pH 4), neither with carbon nor with gold electrodes a reproducible electrochemical detection of TMB could be achieved.
Based on these findings, we created a smartphone-based, electrochemical, immunomagnetic assay for the detection of ochratoxin A (OTA) and ergometrine in food samples. A competitive assay is performed on magnetic beads using HRP and TMB/H2O2 to generate the signal. Enzymatically oxidized TMB is quantified after addition of H2SO4 by amperometry with screen-printed gold electrodes in a custom-made wall-jet flow cell. The results are in good correlation with the established photometric detection method, providing a solid basis for sensing of further analytes in HRP-based assays using the newly developed miniaturized smartphone-based, electrochemical, immunomagnetic assay.
Laser-induced plasma (LIP) has drawn significant amount of attentions in the past decades, particular in elemental analyses for solid or liquid samples. Through proper focusing of the highly energetic laser beam, the plasma can also be ignited in the ambient air, where airborne analytes can be ionized. Such an effect enabled the use of airborne LIP as an ambient ionization source for mass spectrometric analyses. In contrast to other ambient desorption/ionization sources, airborne LIP does not require a specific discharge medium or expensive gas stream. Meanwhile, the airborne LIP produces reagent ion species for both proton-transfer and charge-transfer reactions in addition to the vacuum ultraviolent photons that are capable of promoting single photon ionization, which can be utilized to ionize polar and non-polar analytes. In order to gauge the analytical performance of airborne LIP, it is critical to understand the undergoing chemistry and physics during and after the plasma formation.
Due to the ambient nature of airborne LIP, the variations of air composition and flow strongly affect the plasma behaviors. Preliminary result suggested the addition of a laminar flow of nitrogen gas favored the formation of protonated species (MH+) against the molecular ones (M+). Although the gas addition approach cannot fully tune the ionization process towards the specific production of pseudo-molecular species versus molecular ones, the alternation of molecular ion formation can be used for analyte recognitions through post processing of the ion patterns. The pulsed character of the used lasers makes the reagent ion equilibrium both transient- and highly fluid-dynamically controlled. The acoustic shock-waves induced by the airborne LIP get affected by an applied gas streams towards the plasma center, influencing the molecular-ion and ion-ion interactions in the near proximity of the plasma.
To understand the airborne LIP formation, the temporally and spatially resolved optical emission spectra were recorded. The results will be correlated to time-resolved mass-spectrometric investigations of the ion profile during different stages of the plasma formation. As one example, the formation of pyrylium ion originating from aromatic compounds will be highlighted.
Microplastic (MP) contamination in natural water circulation is a concern for environmental issues and human health. Various types of polymer materials have been identified and were detected in MP analytic test procedures. Beyond MP polymer type, particle size and form play a major role in water analysis due to possible negative toxicologic effects on flora and fauna. However, the correct quantitative measurement of MP size distribution over several orders of magnitude is strongly influenced by sample preparation, filtration materials and processes, and microanalytical techniques, as well as data acquisition and analysis. In this paper, a reference methodology is presented aiming at an improved quantitative analysis of MP particles. An MP analysis workflow is demonstrated including all steps from reference materials to sample preparation, filtration handling, and MP particle size distribution analysis. Background-corrected particle size distributions (1–1000 µm) have been determined for defined polyethylene (PE) and polyethylene terephthalate (PET) reference samples. Microscopically measured particle numbers and errors have been cross-checked with the total initial mass. In particular, defined reference MP samples (PE, PET) are initially characterized and applied to filtration experiments. Optical microscopy imaging on full-area Si filters with subsequent image analysis algorithms is used for statistical particle size distribution analysis. To quantify the effects of handling and filtration, several blind tests with distilled water are carried out to determine the particle background for data evaluation. Particle size distributions of PE and PET reference samples are qualitatively and quantitatively reproduced with respect to symmetry, and maximum and cut-off diameter of the distribution. It is shown that especially MP particles with a radius of >50 µm can be detected and retrieved with high reliability. For particle sizes <50 µm, a significant interference with background contamination is observed. Data from blank samples allows a correction of background contaminations. Furthermore, for enhanced sampling statistics, the recovery of the initial amount of MP will be qualitatively shown. The results are intended as an initial benchmark for MP analytics quality. This quality is based on statistical MP particle distributions and covers the complete analytic workflow starting from sample preparation to filtration and detection. Microscopic particle analysis provides an important supplement for the evaluation of established spectroscopic methods such as Fourier-transform infrared spectroscopy or Raman spectroscopy.