INMdok (Leibniz Institute for New Materials)
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Granular metal–carbon nanocomposites as piezoresistive sensor films – Part 2: Modeling longitudinal and transverse strain sensitivity
Get PDFEngineering Micropatterned Dry Adhesives: From Contact Theory to Handling Applications
Get PDFAbstract Reversible adhesion is the key functionality to grip, place, and release objects nondestructively. Inspired by nature, micropatterned dry adhesives are promising candidates for this purpose and have attracted the attention of research groups worldwide. Their enhanced adhesion compared to nonpatterned surfaces is frequently demonstrated. An important conclusion is that the contact mechanics involved is at least as important as the surface energy and chemistry. In this paper, the roles of the contact geometry and mechanical properties are reviewed. With a focus on applications, the effects of substrate roughness and of temperature variations, and the long‐term performance of micropatterned adhesives are discussed. The paper provides a link between the current, detailed understanding of micropatterned adhesives and emerging applications
Photoactivatable Hsp47: A Tool to Control and Regulate Collagen Secretion & Assembly
Get PDFHsp47 is a chaperone protein with a fundamental role in the folding, stability and intracellular transport of procollagen triple helices. A light-responsive Hsp47 recombinant protein, engineered to control in situ the production and assembly of cellular collagen is here demonstrated. This novel light-driven tool enables unprecedented fundamental studies of collagen biosynthesis and associated diseases
Redox electrolytes for non-flow electrochemical energy storage
Get PDFIn recent decades, a new type of electric energy storage system has emerged with the principle that the electric charge can be stored not only at the interface between the electrode and the electrolyte, but also in the electrolyte by the redox activities of the bulk electrolyte itself. Such redox electrolytes are promising for non-flow energy storage (redox electrolyte aided hybrid energy storage systems, REHES) particularly when they are combined with electrodes made of nanoporous carbon. In this PhD work, I have established a fundamental understanding regarding ion diffusion, process kinetics, and adsorption of redox ions. For that, different REHES systems have been investigated including tetrapropylammonium iodide, zinc iodide, potassium iodide, potassium ferricyanide, vanadyl sulfate, tin sulfate, and tin fluoride. The basic understanding of REHES systems enabled the targeted improvement of the device performance throughout this PhD work. Compared to the energy storage capacity of a conventional (non-redox) electrical double layer capacitor of 4 Wh/kg (ca. 80 F/g), the use of the ZnI2 redox electrolyte yielded significantly higher performance of up to 226 Wh/kg. Furthermore, the specific power was also enhanced from 1.3 kW/kg to 20 kW/kg. As a key conclusion, this PhD work demonstrates the high attractiveness of REHES systems not only from a performance point of view, but also regarding low cost and simplicity of the system.Die Forschung der letzten Jahrzehnte hat eine neue Art der elektrochemischen Energiespeicherung hervorgebracht, bei der elektrische Ladung nicht nur an der Grenzfläche zwischen der Elektrode und dem Elektrolyten gespeichert wird, sondern auch im Elektrolyten selbst durch dessen Redoxaktivität. Diese Redox-Elektrolyte sind für hybride Energiespeichersysteme ohne extern-mechanische Bewegung des Elektrolyten (REHES) vielversprechend, insbesondere, wenn hochporöse Kohlenstoffmaterialien als Elektroden verwendet werden. In dieser Doktorarbeit wurden verschiedene REHES-Systeme hinsichtlich der Diffusion, der elektrochemischen Kinetik und der Adsorption von Redox-Ionen untersucht, um grundlegende Effekte und Prozesse aufzuklären. Die Kombination grundlegender Elektrochemie und Materialcharakterisierung ermöglichte es, die Leistungsparameter von REHES im Vergleich zum Stand der Technik deutlich zu verbessern. Die Energiespeicherkapazität des herkömmlichen wässrigen elektrischen Doppelschichtkondensators ohne Redoxelektrolyt von 4 Wh/kg (entspricht 80 F/g) wurde zum Beispiel im ZnI2 System auf bis zu 226 Wh/kg gesteigert, während die spezifische Leistung von 1.3 kW/kg auf 20 kW/kg verbessert werden konnte. Als Ergebnis zeigt sich, dass REHES ein besonders vielversprechender Ansatz zur Darstellung hochleistungsfähiger elektrochemischer Energiespeicher ist. Weitere Vorteile von REHES sind ein vereinfachtes Zellkonzept und die Verwendung von potentiell kostengünstige Einzelkomponenten
Polymer-derived carbides and carbons with and without nitrogen-doping for electrochemical energy applications
Get PDFPorous carbon materials are widely used in electrochemical applications for intermediate energy storage or water desalination. This work aimed to synthesize nanoporous carbons with well-controlled properties (e.g., specific surface area, average pore size, chemical composition) to correlate them to the performance in electrochemical applications (e.g., supercapacitors, LiS batteries). Especially the surface chemistry of highly porous carbons with different oxygen and nitrogen groups influences the electrochemical behavior. The carbon materials were obtained from polymeric precursors, including phenolic resins and polysilsesquioxanes. A physical activation with CO 2 or NH 3 that additionally introduced nitrogen groups was applied to adjust the porosity of the phenolic resin-derived carbons. Thereby, it was possible to obtain materials with different properties from the same precursor. The polysilsesquioxanes were first pyrolyzed and then thermally treated with chlorine gas to produce carbide-derived carbons. The porosity was tuned by the composition of the precursor and the synthesis temperature. The intermediate product (silicon oxycarbide) is also an attractive electrode material for Li-ion batteries. It was shown that optimization of the carbon content resulted in extended cycling stability
The 2018 correlative microscopy techniques roadmap
Get PDFDevelopments in microscopy have been instrumental to progress in the life sciences, and many new techniques have been introduced and led to new discoveries throughout the last century. A wide and diverse range of methodologies is now available, including electron microscopy, atomic force microscopy, magnetic resonance imaging, small-angle x-ray scattering and multiple super-resolution fluorescence techniques, and each of these methods provides valuable read-outs to meet the demands set by the samples under study. Yet, the investigation of cell development requires a multi-parametric approach to address both the structure and spatio-temporal organization of organelles, and also the transduction of chemical signals and forces involved in cell–cell interactions. Although the microscopy technologies for observing each of these characteristics are well developed, none of them can offer read-out of all characteristics simultaneously, which limits the information content of a measurement. For example, while electron microscopy is able to disclose the structural layout of cells and the macromolecular arrangement of proteins, it cannot directly follow dynamics in living cells. The latter can be achieved with fluorescence microscopy which, however, requires labelling and lacks spatial resolution. A remedy is to combine and correlate different readouts from the same specimen, which opens new avenues to understand structure–function relations in biomedical research. At the same time, such correlative approaches pose new challenges concerning sample preparation, instrument stability, region of interest retrieval, and data analysis. Because the field of correlative microscopy is relatively young, the capabilities of the various approaches have yet to be fully explored, and uncertainties remain when considering the best choice of strategy and workflow for the correlative experiment. With this in mind, the Journal of Physics D: Applied Physics presents a special roadmap on the correlative microscopy techniques, giving a comprehensive overview from various leading scientists in this field, via a collection of multiple short viewpoints
Salt concentration and charging velocity determine ion charge storage mechanism in nanoporous supercapacitors
Get PDFA fundamental understanding of ion charge storage in nanoporous electrodes is essential to improve the performance of supercapacitors or devices for capacitive desalination. Here, we employ in situ X-ray transmission measurements on activated carbon supercapacitors to study ion concentration changes during electrochemical operation. Whereas counter-ion adsorption was found to dominate at small electrolyte salt concentrations and slow cycling speed, ion replacement prevails for high molar concentrations and/or fast cycling. Chronoamperometry measurements reveal two distinct time regimes of ion concentration changes. In the first regime the supercapacitor is charged, and counter- and co-ion concentration changes align with ion replacement and partially co-ion expulsion. In the second regime, the electrode charge remains constant, but the total ion concentration increases. We conclude that the initial fast charge neutralization in nanoporous supercapacitor electrodes leads to a non-equilibrium ion configuration. The subsequent, charge-neutral equilibration slowly increases the total ion concentration towards counter-ion adsorption
Granular metal–carbon nanocomposites as piezoresistive sensor films – Part 1: Experimental results and morphology
Get PDFTailored ligands for hybrid materials from colloidal inks
Get PDFInorganic nano-objects with organic shells form an interesting class of nanostructured materials when they are assembled into larger units - hybrid materials. The industrial use of materials produced via this bottom-up route is impeded by the lack of simple production processes. A promising process is their production from colloidal inks; however, the targeted control of the nano-objects’ superstructure formation must be improved. Here interfaces and the organic shells are crucial, as they strongly affect the assembly characteristics of the hybrid nano-objects. Here, the colloidal and supramolecular chemistry of the ligand shell is studied. Ligandstabilized wire-like and rod-like nano-objects were synthesized, modified, and their assembly behavior in conjunction with the dispersant medium was elucidated. After that, two different hybrid materials were produced using an ink-based approach. First, gold nanorods were coated with a conjugated polymer ligand shell that enabled both good colloidal stability and electrical conductivity of the hybrid structures directly after drying of the ink without sintering. Second, ultrathin gold nanowires were spun into hierarchical fibers, exploiting the interaction of their ligand shells with the surrounding dispersant medium.Anorganische Nanoobjekte mit organischen Ligandenhüllen bilden eine interessante Klasse nanoskalig strukturierter Materialien, wenn sie zu größeren Einheiten zusammengesetzt werden - die Hybridmaterialien. Das Fehlen einfacher Produktionsprozesse verhindert bislang deren industrielle Nutzung. Ein vielversprechender Ansatz für einen einfachen Produktionsprozess von Hybridmaterialien ist deren Herstellung aus kolloidalen Tinten. Hierzu muss allerdings die Kontrolle über die gezielte Nanoobjektanordnung während des Verarbeitungsprozesses verbessert werden. Die Ligandenhüllen spielen dabei eine entscheidende Rolle, da sie die Anordnungseigenschaften der Nanoobjekte stark beeinflussen. Um die kolloidale und supramolekulare Chemie der Ligandenhülle besser zu verstehen wurden ligandenstabilisierte, stäbchenförmige Nanoobjekte synthetisiert, modifiziert und deren Anordnungsverhalten in Verbindung mit dem Dispergiermittel aufgeklärt. Auf der Basis dieser Erkenntnisse wurden erfolgreich zwei unterschiedliche Hybridmaterialien aus Tinten hergestellt. Zum einen wurden Gold-Nanostäbe mit einer leitfähigen Polymer-Ligandhülle beschichtet, die gleichzeitig gute kolloidale Stabilität der Nanostäbe in Tinten und elektrische Leitfähigkeit der Hybridstrukturen direkt nach dem Trocknen der Tinte ermöglicht. Zum anderen wurde das Zusammenspiel der Ligandenhüllen ultradünner Goldnanodrähte mit dem Dispergiermedium ausgenutzt, um die Drähte zu hierarchischen Hybridfasern zu spinnen
Surface oxidation of metallic glasses and its effects on nanotribology
Get PDFFundamental mechanisms of friction and wear on the atomic scale were studied for different oxidation states of metallic glass surfaces. Bulk metallic glass was prepared by suction casting and characterised by X-Ray Diffraction and Dynamic Scanning Calorimetry. Surfaces were oxidised in controlled atmosphere and characterised by Electron Microscopy and X-ray Photoelectron Spectroscopy. Tribological experiments on the nano-scale were performed by Atomic Force Microscopy in ultra-high vacuum on a continuous load scale extending over three decades with different cantilevers. The oxide layer on Zr60Cu30Al10 consists mainly of an amorphous matrix of ZrO2 and Al2O3 with embedded crystalline Cu2O nanoparticles. Stick-slip friction was found on both, the metallic glass and on the oxidised surface. Comparative experiments revealed higher friction and wear after oxidation. Due to the surface roughness, friction is scale dependent on the oxidised surface. Sharp indenters were found to penetrate the oxide surface resulting in cutting wear. Indenters with larger contact areas initiate plowing and eventually delamination from the surface of metallic glass. On the clean metallic glass, plastic deformation was attributed to plowing mechanisms, independent on the contact area.Es werden grundlegende Mechanismen von Reibung und Verschleiß auf atomarer Skala auf metallischen Gläsern verschiedener Oxidationsstufen untersucht. Metallisches Glas wurde durch Saugguss hergestellt und mittels Röntgenbeugung und Dynamische Differenzkalorimetrie charakterisiert. Die Oberflächen wurden in kontrollierter Atmosphäre oxidiert und durch Elektronenmikroskopie und Röntgenphotoelektronenspektroskopie charakterisiert. Nanotribologische Experimente wurden mittels Rasterkraftmikroskopie im Ultrahochvakuum mit Normalkräften durchgeführt, deren Größenordnungen sich über drei Dekaden erstrecken. Die Oxidschicht auf Zr60Cu30Al10 besteht hauptsächlich aus einer amorphen Matrix aus ZrO2 und Al2O3 in welche kristalline Cu2O-Nanopartikel eingebettet sind. Stick-Slip Reibung wurde sowohl auf dem metallischen Glas als auch auf der oxidierten Oberfläche gemessen. Vergleichende Messungen zeigten eine höhere Reibung und einen höoheren Verschleiß nach der Oxidation. Aufgrund der Oberfläachenrauhigkeit ist die Reibung auf der oxidierten Oberfläche abhängig von der Größenskala der Messung. Spitze Indenter ermöglichen das Eindringen in die Oxidschicht, was zu einem Aufschneiden der Oberfläche führt. Indenter mit größeren Kontaktflächen führen zunächst zu Plowing und schließlich zur Delamination der Oxidschicht vom metallischen Glas. Auf dem nicht oxidierten metallischen Glas wurde die plastische Verformung, unabhängig von der Kontaktfläche, Plowingmechanismen zugeordnet