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Start date: 1984 × Type: Text × WGL Institute: INM ×

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Now showing 1 - 10 of 569
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    Mechanisms of bonding effected by nanoparticles in zirconia coatings applied by spraying of suspensions
    (Saarbrücke : Leibniz-Institut für Neue Materialien, 2008) Adam, Jens; Aslan, Mesut; Drumm, Robert; Veith, Michael
    Zirconia coatings consisting of a mixture of coarse and fine grained zirconia powders prepared by spraying of suspensions and subsequent thermal treatment at limited temperatures (up to 500°C) are poor in adherence and in intrinsic mechanical strength. We have shown elsewhere that mechanical properties of these coatings can be improved clearly by adding a small amount of nanoscaled zirconia. Here, the structural and the chemical development of this coating material and of the nanoparticles is examined to gain information about the underlying bonding mechanisms. The applied temperature is relatively low in comparison to the usual onset temperature of accelerated sintering. Nevertheless, the results show that diffusion controlled material transport mechanisms play their role in bonding. The condensation of surface OH groups may participate in bonding, too. These first results confirm the potential of nanoparticles to act as inorganic binder. Additional research effort to clarify the underlying mechanisms in detail is of interest. For the practical side, it can be concluded that the resulting effect of mechanical consolidation of ceramic structures at relatively low temperatures enables new ceramic applications, for example a new type of ceramic coatings on metallic substrates.
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    A block copolymer templated approach for the preparation of nanoporous polymer structures and cellulose fiber hybrids by ozone treatment
    (Cambridge : RSC Publ., 2022) Gemmer, Lea; Hu, Qiwei; Niebuur, Bart-Jan; Kraus, Tobias; Balzer, Bizan N.; Gallei, Markus
    Functional amphiphilic block copolymers (BCPs) are versatile, smart, and promising materials that are often used as soft templates in nanoscience. BCPs generally feature the capability of microphase-separation leading to various interesting morphologies at the nanometer length scale. Materials derived from BCPs can be converted into porous structures while retaining the underlying morphology of the matrix material. Here, a convenient and scalable approach for the fabrication of porous functional polyvinylpyridines (P2VP) is introduced. The BCP polyisoprene-block-P2VP (PI-b-P2VP) is obtained via sequential anionic polymerization of the respective monomers and used to form either BCP films in the bulk state or a soft template in a composite with cellulose fibers. Cross-linking of the BCPs with 1,4-diiodobutane is conducted and subsequently PI domains are selectively degraded inside the materials using ozone, while preserving the porous and tailor-made P2VP nanostructure. Insights into the feasibility of the herein presented strategy is supported by various polymer characterization methods comprising nuclear magnetic resonance (NMR), size exclusion chromatography (SEC), and differential scanning calorimetry (DSC). The resulting bulk- and composite materials are investigated regarding their morphology and pore formation by scanning electron microscopy (SEM), atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS). Furthermore, chemical conversions were examined by energy dispersive X-ray spectroscopy (EDS), attenuated total reflection Fourier-transformation infrared spectroscopy (ATR-FTIR) and water contact angle (WCA) measurements. By this convenient strategy the fabrication of functional porous P2VP in the bulk state and also within sustainable cellulose composite materials is shown, paving the synthetic strategy for the generation of a new family of stimuli-responsive sustainable materials.
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    Fabrication of metal nanoparticle arrays by controlled decomposition of polymer particles
    (Bristol : IOP Publishing, 2013) Brodoceanu, Daniel; Fang, Cheng; Voelcker, Nicolas Hans; Bauer, Christina T.; Wonn, Anne; Kroner, Elmar; Arzt, Eduard; Kraus, Tobias
    We report a novel fabrication method for ordered arrays of metal nanoparticles that exploits the uniform arrangement of polymer beads deposited as close-packed monolayers. In contrast to colloidal lithography that applies particles as masks, we used thermal decomposition of the metal-covered particles to precisely define metal structures. Large arrays of noble metal (Au, Ag, Pt) nanoparticles were produced in a three-step process on silicon, fused silica and sapphire substrates, demonstrating the generality of this approach. Polystyrene spheres with diameters ranging between 110 nm and 1 µm were convectively assembled into crystalline monolayers, coated with metal and annealed in a resistive furnace or using an ethanol flame. The thermal decomposition of the polymer microspheres converted the metal layer into particles arranged in hexagonal arrays that preserved the order of the original monolayer. Both the particle size and the interparticle distance were adjusted via the thickness of the metal coating and the sphere diameter, respectively.
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    Bioinspired pressure actuated adhesive system
    (Saarbrücken : Leibniz-Institut für Neue Materialien, 2011) Paretkar, Dadhichi R.; Kamperman, Marleen; Schneider, Andreas S.; Arzt, Eduard
    We developed a dry snythetic adhesive system inspired by gecko feet that can switch reversibly from adhesion to non-adhesion with applied pressure as external stimulus. Micropatterned polydimethylsiloxane (PDMS) surfaces with pillars of 30 µm length and 10 µm diameter were fabricated using photolithography and moulding. Adhesion properties were determined with a flat probe as a function of preload. For low and moderate applied compressive preloads, measured adhesion was 7.5 times higher on the patterned surfaces than on flat controls whereas for high preloads adhesion dropped to very low values. In situ imaging showed that the increased preload caused the pillars to deform by bending and/or buckling and to lose their adhesive contact. The elasticity of PDMS aids the pillar recovery to the upright position upon removal of preload enabling repeatability of the switch. Such systems have promising properties e.g. for industrial pick-and-carry operations.
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    Flexible and transparent electrodes imprinted from Au nanowires: stability and ageing
    (Cambridge : Royal Society of Chemistry, 2022) Engel, Lukas F.; González-García, Lola; Kraus, Tobias
    We study the stability of flexible transparent electrodes (FTEs) that were self-assembled from ultra-thin gold nanowires (AuNW) by direct nanoimprinting of inks with different particle concentrations (1 to 10 mg mL−1). The resulting lines were less than 3 μm wide and contained bundles of AuNW with oleylamine (OAm) ligand shells. Small-angle X-ray scattering confirmed a concentration-independent bundle structure. Plasma sintering converted the wire assemblies into lines with a thin metal shell that contributes most to electrical conductivity and covers a hybrid core. We studied the relative change in sheet resistance and the morphology of the FTEs with time. The sheet resistance increased at all concentrations, but at different rates. The metal shell aged by de-wetting and pore formation. The hybrid core de-mixed and densified, which led to a partial collapse of the shell. Residual organics migrated through the shell via its pores. Lines formed at low concentration (cAu = 2 to 3 mg mL−1) contained less residual organics and aged slower than those formed at high cAu ≥ 5 mg mL−1. We passivated the conductive shell with thin, adsorbed layers of PEDOT:PSS and found that it decelerated degradation by slowing surface diffusion and hindering further rupture of the shell. Thick capping layers prevented degradation entirely and stopped pore formation.
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    Visualisation of HER2 homodimers in single cells from HER2 overexpressing primary formalin fixed paraffin embedded tumour tissue
    (London : BioMed Central, 2019) Peckys, D.B.; Hirsch, D.; Gaiser, T.; De, Jonge, N.
    Background: HER2 is considered as one of the most important, predictive biomarkers in oncology. The diagnosis of HER2 positive cancer types such as breast- and gastric cancer is usually based on immunohistochemical HER2 staining of tumour tissue. However, the current immunohistochemical methods do not provide localized information about HER2's functional state. In order to generate signals leading to cell growth and proliferation, the receptor spontaneously forms homodimers, a process that can differ between individual cancer cells. Materials and methods: HER2 overexpressing tumour cells were dissociated from formalin-fixed paraffin-embedded (FFPE) patient's biopsy sections, subjected to a heat-induced antigen retrieval procedure, and immobilized on microchips. HER2 was specifically labelled via a two-step protocol involving the incubation with an Affibody-biotin compound followed by the binding of a streptavidin coated quantum dot (QD) nanoparticle. Cells with membrane bound HER2 were identified using fluorescence microscopy, coated with graphene to preserve their hydrated state, and subsequently examined by scanning transmission electron microscopy (STEM) to obtain the locations at the single molecule level. Label position data was statistically analysed via the pair correlation function, yielding information about the presence of HER2 homodimers. Results: Tumour cells from two biopsies, scored HER2 3+, and a HER2 negative control sample were examined. The specific labelling protocol was first tested for a sectioned tissue sample of HER2-overexpressing tumour. Subsequently, a protocol was optimized to study HER2 homodimerization in single cells dissociated from the tissue section. Electron microscopy data showed membrane bound HER2 in average densities of 201-689 proteins/μm2. An automated, statistical analysis of well over 200,000 of measured protein positions revealed the presence of HER2 homodimers in 33 and 55% of the analysed images for patient 1 and 2, respectively. Conclusions: We introduced an electron microscopy method capable of measuring the positions of individually labelled HER2 proteins in patient tumour cells from which information about the functional status of the receptor was derived. This method could take HER2 testing a step further by examining HER2 homodimerization directly out of tumour tissue and may become important for adjusting a personalized antibody-based drug therapy. © 2019 The Author(s).
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    The 2018 correlative microscopy techniques roadmap
    (Bristol : IOP Publishing, 2018) Ando, Toshio; Bhamidimarri, Satya Prathyusha; Brending, Niklas; Colin-York, H; Collinson, Lucy; De Jonge, Niels; de Pablo, P J; Debroye, Elke; Eggeling, Christian; Franck, Christian; Fritzsche, Marco; Gerritsen, Hans; Giepmans, Ben N G; Grunewald, Kay; Hofkens, Johan; Hoogenboom, Jacob P; Janssen, Kris P F; Kaufmann, Rainer; Klumpermann, Judith; Kurniawan, Nyoman; Kusch, Jana; Liv, Nalan; Parekh, Viha; Peckys, Diana B; Rehfeldt, Florian; Reutens, David C; Roeffaers, Maarten B J; Salditt, Tim; Schaap, Iwan A T; Schwarz, Ulrich S; Verkade, Paul; Vogel, Michael W; Wagner, Richard; Winterhalter, Mathias; Yuan, Haifeng; Zifarelli, Giovanni
    Developments 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.
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    Light-Emitting Devices – Luminescence from Low-Dimensional Nanostructures
    (London : IntechOpen, 2014) Mousavi, S.H.; Jafari Mohammdi, S.A.; Haratizadeh, H.; Oliveira, Peter W. de
    [no abstract available]
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    Gradients of Al/Al2O3 nanostructures for screening mesenchymal stem cell proliferation and differentiation
    (Wuhan : Scientific Research Publishing, 2013) Veith, Michael; Dufloux, Cécile; Ghaemi, Soraya Rasi; Cenk, Aktas; Voelcker, Nicolas H.
    By decomposing a molecular precursor we fabricated a novel surface based on an aluminium/aluminiumoxide composite incorporating nanotopography gradient to address high-throughput and fast analysis method for studying stem cell differentiation by nanostructures. Depending on the topography of the nanostructures, mesenchymal stem cells exhibit a diverse proliferation and differentiation behavior.