INMdok (Leibniz Institute for New Materials)
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Roll-to-Roll Manufacturing of Micropatterned Adhesives by Template Compression
Get PDFFor the next generation of handling systems, reversible adhesion enabled by micropatterned dry adhesives exhibits high potential. The versatility of polymeric micropatterns in handling objects made from various materials has been demonstrated by several groups. However, specimens reported in most studies have been restricted to the laboratory scale. Upscaling the size and quantity of micropatterned adhesives is the next step to enable successful technology transfer. Towards this aim, we introduce a continuous roll-to-roll replication process for fabrication of high-performance, mushroom-shaped micropatterned dry adhesives. The micropatterns were made from UV-curable polyurethane acrylates. To ensure the integrity of the complex structure during the fabrication process, flexible templates were used. The compression between the template and the wet prepolymer coating was investigated to optimize replication results without structural failures, and hence, to improve adhesion. As a result, we obtained micropatterned adhesive tapes, 10 cm in width and several meters in length, with adhesion strength about 250 kPa to glass, suitable for a wide range of application
On the Nature of the Transparent Teeth of the Deep-Sea Dragonfish, Aristostomias scintillans
No full textThe dragonfish is a voracious predator of the deep sea with an arsenal of tools to hunt prey and remain concealed. In contrast to its dark pigmented skin, the dragonfish is equipped with transparent teeth. Here, we establish the structure, composition, and mechanical properties of the transparent teeth for the first time. We find the enamel-like layer to consist of nanocrystalline hydroxyapatite domains (∼20 nm grain size) embedded in an amorphous matrix, whereas in the dentin layer the nanocrystalline hydroxyapatite coats nanoscale collagen fibrils forming nanorods. This nanoscale structure is responsible for the much-reduced Rayleigh light scattering, which is further ensured by the sufficiently thin walls. Here, we suggest that the nanostructured design of the transparent dragonfish teeth enables predatory success as it makes its wide-open mouth armed with saber-like teeth effectively disappear, showing no contrast to the surrounding blackness of the fish nor the background darkness of the deep sea
Modeling the Contact Mechanics of Hydrogels
Get PDFA computationally lean model for the coarse-grained description of contact mechanics of hydrogels is proposed and characterized. It consists of a simple bead-spring model for the interaction within a chain, potentials describing the interaction between monomers and mold or confining walls, and a coarse-grained potential reflecting the solvent-mediated effective repulsion between non-bonded monomers. Moreover, crosslinking only takes place after the polymers have equilibrated in their mold. As such, the model is able to reflect the density, solvent quality, and the mold hydrophobicity that existed during the crosslinking of the polymers. Finally, such produced hydrogels are exposed to sinusoidal indenters. The simulations reveal a wavevector-dependent effective modulus E∗(q) with the following properties: (i) stiffening under mechanical pressure, and a sensitivity of E∗(q) on (ii) the degree of crosslinking at large wavelengths, (iii) the solvent quality, and (iv) the hydrophobicity of the mold in which the polymers were crosslinked. Finally, the simulations provide evidence that the elastic heterogeneity inherent to hydrogels can suffice to pin a compressed hydrogel to a microscopically frictionless wall that is undulated at a mesoscopic length scale. Although the model and simulations of this feasibility study are only two-dimensional, its generalization to three dimensions can be achieved in a straightforward fashion
Faradaic electrode materials for next-generation electrochemical water desalination
Get PDFAn ever-growing global population leads to higher water consumption and demand for advanced remediation technologies. Thus, water stress intensifies in many countries around the world. Most global water remediation is accomplished by established techniques, such as reverse osmosis and thermal desalination. To lower the energy consumption per processed water volume, engineers and scientists investigate novel techniques like capacitive deionization technology (CDI). CDI based on carbon electrodes promises energy-efficient desalination by ion electrosorption but is limited to the remediation of brackish water, that is, very low salt concentration media. My doctoral thesis explores next-generation electrodes for electrochemical water desalination based on Faradaic materials. Unlike carbon, these materials accomplish ion removal by reversible electrochemical processes, such as ion insertion of crystalline structures or redox-reactions of dissolved ions. Faradaic materials not only provide a large potential for enhanced desalination capacity but also enable the remediation of seawater, that is, aqueous media with high molar strength. These features can be accomplished while maintaining a low level of energy consumption to enable energy- efficient water desalination for a more sustainable future.Das weltweite Bevölkerungswachstum führt zu einem höheren Wasserverbrauch und erhöhtem Bedarf an effektiven Aufbereitungstechnologien. Entsprechend verschärfen sich die Probleme in Bezug auf Zugang und Verfügbarkeit von Trinkwasser in vielen Ländern der Welt. Wissenschaflter*Innen erforschen daher Wasserentsalzungstechnologien, die bessere Energieeffizienz bieten können als die derzeit gängigen Methoden wie Umkehrosmose oder thermische Verfahren. Eine besonders vielversprechende, energie-effiziente Technologie zur Entsalzung ist die kapazitive Deionisierung (CDI). CDI basiert auf Ionenelektrosorption, kann aber nur für Brackwasser eine hohe Energieeffizienz und Entsalzungsleistung darstellen. Die vorliegende Dissertationsschrift erforscht daher neue Faraday’sche Elektrodenmaterialien um Wasser effizient und effektiv zu entsalzen. Hierzu eigenen sich insbesondere Kristallstrukturen, die Ionen durch Insertation aufnehmen können, oder redox-aktive Ionen, welche im wässrigen Medium in Lösung sich befinden. Solche Materialien bieten nicht nur eine hohe Entsalzungskapazität sondern sind auch nicht mehr auf Brackwasser limitiert: sie erlauben sogar die energie-effiziente Entsalzung von Meerwasser und haben damit das Potential, eine vielversprechende Technologie für eine nachhaltigere Zukunft zu sein
Development and pilot testing of a model for establishing innovative cooperation with SMEs
Get PDFIm Rahmen des Projektes sollen geeignete Vorgehensweisen, sowie praxistaugliche Methoden zur erfolgreichen Gewinnung von KMUs für gemeinsame Innovationsprojekte konzipiert und erprobt werden. Bei den Methoden wurde Augenmerk auf die Identifizierung von innovationsfähigen und –willigen Firmen gelegt; sowie deren gezielte Ansprache. Ferner sollte ein Kooperationsmodell zwischen INM und spezifischen Unternehmen erstellt werden, das den jeweiligen Zielen, Anforderungen und Rahmenbedingungen beider Partner gerecht wird.[...
Reduced Faradaic Contributions and Fast Charging of Nanoporous Carbon Electrodes in a Concentrated Sodium Nitrate Aqueous Electrolyte for Supercapacitors
Get PDFThe Faradaic processes related to electrochemical water reduction at the nanoporous carbon electrode under negative polarization are reduced when the concentration of aqueous sodium nitrate (NaNO3) is increased or the temperature is decreased. This effect enhances the relative contribution of ion electrosorption to the total charge storage process. Hydrogen chemisorption is reduced in aqueous 8.0 m NaNO3 due to the low degree of hydration of the Na+ cation; consequently, less free water is available for redox contributions, driving the system to exhibit electrical double-layer capacitive characteristics. Hydrogen adsorption/desorption is facilitated in 1.0 m NaNO3 due to the high molar ratio. The excess of water shifts the local pH in carbon nanopores to neutral values, giving rise to a high overpotential for dihydrogen evolution in the latter. The dilution effect on local pH shift in 1.0 m NaNO3 can be reduced by decreasing the temperature. A symmetric activated carbon cell assembled with 8.0 m NaNO3 exhibits a high capacitance and coulombic efficiency, a larger contribution of ion electrosorption to the overall charge storage process, and a stable capacitance performance at 1.6 V
High strength nanocrystalline Cu–Co alloys with high tensile ductility
Get PDFA supersaturated single-phase Cu–26 at.% Co alloy was produced by high-pressure torsion deformation, leading to a nanocrystalline microstructure with a grain size smaller than 100 nm. The nonequilibrium solid solution decomposed during subsequent isothermal annealing. In situ high-energy X-ray diffraction was used to map changes linked to the separating phases, and the development of a nanoscale Cu–Co composite structure was observed. To gain further information about the relationship of the microstructure and the mechanical properties after phase separation, uniaxial tensile tests were conducted on as-deformed and isothermally annealed samples. Based on the in situ diffraction data, different isothermal annealing temperatures were chosen. Miniaturized tensile specimens with a round cross section were tested, and an image-based data evaluation method enabled the evaluation of true stress–strain curves and strain hardening behavior. The main results are as follows: all microstructural states showed high strength and ductility, which was achieved by a combination of strain-hardening and strain-rate hardening
Implementation and Long-Term Evaluation of a Hearing Aid Supported Tinnitus Treatment Using Notched Environmental Sounds
Get PDFRecent work has shown that sharp spectral edges in acoustic stimuli might have advantageous effects in the treatment of tonal tinnitus. In the course of this paper, we evaluate the long-term effects of spectrally notched hearing aids on the subjective tinnitus distress. By merging recent experimental work with a computational tinnitus model, we modified the commercially available behind-the-ear hearing aids so that a frequency band of 0.5 octaves, centered on the patient's individual tinnitus frequency, was blocked out. Those hearing aids employ a steep notch filter that filters environmental sounds to suppress the tinnitus-related changes in neural firing by lateral inhibition. The computational model reveals a renormalization of pathologically increased neural response reliability and synchrony in response to spectrally modified input. The target group, fitted with spectrally notched hearing aids, was matched with a comparable control group, fitted with standard hearing aids of the same type but without a notch filter. We analyze the subjective self-assessment by tinnitus questionnaires, and we monitor the objective distress correlates in auditory evoked response phase data. Both, subjective and objective results show a noticeable trend of a larger therapeutic benefit for notched hearing correction
Redox-electrolytes for non-flow electrochemical energy storage: A critical review and best practice
Get PDFOver 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 bulk electrolyte by redox activities of the electrolyte itself. Those redox electrolytes are promising for non-flow hybrid energy storage systems, or redox electrolyte-aided hybrid energy storage (REHES) systems; particularly, when they are combined with highly porous carbon electrodes. In this review paper, critical design considerations for the REHES systems are discussed as well as the effective electrochemical characterization techniques. Appropriate evaluation of the electrochemical performance is discussed thoroughly, including advanced analytical techniques for the determination of the electrochemical stability of the redox electrolytes and self-discharge rate. Additionally, critical summary tables for the recent progress on REHES systems are provided. Furthermore, the unique synergistic combination of porous carbon materials and redox electrolytes is introduced in terms of the diffusion, adsorption, and electrochemical kinetics modulating energy storage in REHES systems
In Situ Observation Reveals Local Detachment Mechanisms and Suction Effects in Micropatterned Adhesives
Get PDFFibrillar adhesion pads of insects and geckoes have inspired the design of high-performance adhesives enabling a new generation of handling devices. Despite much progress over the last decade, the current understanding of these adhesives is limited to single contact pillars and the behavior of whole arrays is largely unexplored. In the study reported here, a novel approach is taken to gain insight into the detachment mechanisms of whole micropatterned arrays. Individual contacts are imaged by frustrated total internal reflection, allowing in situ observation of contact formation and separation during adhesion tests. The detachment of arrays is found to be governed by the distributed adhesion strength of individual pillars, but no collaborative effect mediated by elastic interactions can be detected. At the maximal force, about 30% of the mushroom structures are already detached. The adhesive forces decrease with reduced air pressure by 20% for the smooth and by 6% for the rough specimen. These contributions are attributed to a suction effect, whose strength depends critically on interfacial defects controlling the sealing quality of the contact. This dominates the detachment process and the resulting adhesion strength