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search.filters.applied.f.access: openAccess × End date: 2022 × Start date: 2020 × DDC: 670 × Type: Article ×

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Now showing 1 - 10 of 21
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    Thermoelectric Performance of Polypropylene/Carbon Nanotube/Ionic Liquid Composites and Its Dependence on Electron Beam Irradiation
    (Basel : MDPI, 2022-1-11) Voigt, Oliver; Krause, Beate; Pötschke, Petra; Müller, Michael T.; Wießner, Sven
    The thermoelectric behavior of polypropylene (PP) based nanocomposites containing single walled carbon nanotubes (SWCNTs) and five kinds of ionic liquids (Ils) dependent on composite composition and electron beam irradiation (EB) was studied. Therefore, several samples were melt-mixed in a micro compounder, while five Ils with sufficiently different anions and/or cations were incorporated into the PP/SWCNT composites followed by an EB treatment for selected composites. Extensive investigations were carried out considering the electrical, thermal, mechanical, rheological, morphological and, most significantly, thermoelectric properties. It was found that it is possible to prepare n-type melt-mixed polymer composites from p-type commercial SWCNTs with relatively high Seebeck coefficients when adding four of the selected Ils. The highest Seebeck coefficients achieved in this study were +49.3 µV/K (PP/2 wt.% SWCNT) for p-type composites and −27.6 µV/K (PP/2 wt.% SWCNT/4 wt.% IL type AMIM Cl) for n-type composites. Generally, the type of IL is decisive whether p-or n-type thermoelectric behavior is achieved. After IL addition higher volume conductivity could be reached. Electron beam treatment of PP/SWCNT leads to increased values of the Seebeck coefficient, whereas the EB treated sample with IL (AMIM Cl) shows a less negative Seebeck coefficient value.
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    Does the Type of Polymer and Carbon Nanotube Structure Control the Electromagnetic Shielding in Melt-Mixed Polymer Nanocomposites?
    (Basel : MDPI, 2020-1-15) Biswas, Sourav; Muzata, Tanyaradzwa S.; Krause, Beate; Rzeczkowski, Piotr; Pötschke, Petra; Bose, Suryasarathi
    A suitable polymer matrix and well dispersed conducting fillers forming an electrically conducting network are the prime requisites for modern age electromagnetic shield designing. An effective polymer-based shield material is designed that can attenuate 99.9% of incident electromagnetic (EM) radiation at a minimum thickness of <0.5 mm. This is accomplished by the choice of a suitable partially crystalline polymer matrix while comparing non-polar polypropylene (PP) with polar polyvinylidene fluoride (PVDF) and a best suited filler nanomaterial by comparing different types of carbon nanotubes such as; branched, single-walled and multi-walled carbon nanotubes, which were added in only 2 wt %. Different types of interactions (polar-polar and CH-π and donor-acceptor) make b-MWCNT more dispersible in the PVDF matrix, which together with high crystallinity resulted in the best electrical conductivity and electromagnetic shielding ability of this composite. This investigation additionally conceals the issues related to the thickness of the shield material just by stacking individual thin nanocomposite layers containing different carbon nanotube (CNT) types with 0.3 mm thickness in a simple manner and finally achieves 99.999% shielding efficiency at just 0.9 mm thickness when using a suitable order of the different PVDF based nanocomposites.
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    Remarkable Mechanochromism in Blends of a π-Conjugated Polymer P3TEOT: The Role of Conformational Transitions and Aggregation
    (Weinheim : Wiley-VCH, 2020) Zessin, Johanna; Schnepf, Max; Oertel, Ulrich; Beryozkina, Tetyana; König, Tobias A.F.; Fery, Andreas; Mertig, Michael; Kiriy, Anton
    A novel mechanism for well-pronounced mechanochromism in blends of a π-conjugated polymer based on reversible conformational transitions of a chromophore rather than caused by its aggregation state, is exemplified. Particularly, a strong stretching-induced bathochromic shift of the light absorption, or hypsochromic shift of the emission, is found in blends of the water-soluble poly(3-tri(ethylene glycol)) (P3TEOT) embedded into the matrix of thermoplastic polyvinyl alcohol. This counterintuitive phenomenon is explained in terms of the concentration dependency of the P3TEOT's aggregation state, which in turn results in different molecular conformations and optical properties. A molecular flexibility, provided by low glass transition temperature of P3TEOT, and the fact that P3TEOT adopts an intermediate, moderately planar conformation in the solid state, are responsible for the unusual complex mechanochromic behavior. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Waveguide-Integrated Broadband Spectrometer Based on Tailored Disorder
    (Weinheim : Wiley-VCH Verlag, 2020) Hartmann, Wladick; Varytis, Paris; Gehring, Helge; Walter, Nicolai; Beutel, Fabian; Busch, Kurt; Pernice, Wolfram
    Compact, on-chip spectrometers exploiting tailored disorder for broadband light scattering enable high-resolution signal analysis while maintaining a small device footprint. Due to multiple scattering events of light in the disordered medium, the effective path length of the device is significantly enhanced. Here, on-chip spectrometers are realized for visible and near-infrared wavelengths by combining an efficient broadband fiber-to-chip coupling approach with a scattering area in a broadband transparent silicon nitride waveguiding structure. Air holes etched into a structured silicon nitride slab terminated with multiple waveguides enable multipath light scattering in a diffusive regime. Spectral-to-spatial mapping is performed by determining the transmission matrix at the waveguide outputs, which is then used to reconstruct the probe signals. Direct comparison with theoretical analyses shows that such devices can be used for high-resolution spectroscopy from the visible up to the telecom wavelength regime. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Narrow Stimulated Resonance Raman Scattering and WGM Lasing in Small Conjugated Polymer Particles for Live Cell Tagging and Tracking
    (Weinheim : Wiley-VCH, 2020) Haehnle, Bastian; Lamla, Markus; Sparrer, Konstantin M.J.; Gather, Malte C.; Kuehne, Alexander J.C.
    Conjugated polymer particles are brightly fluorescing and stable materials for live cell imaging. Combination of conjugated polymers with a whispering gallery mode (WGM) resonator allows laser emission from microscale particles. Once internalized by cells, the mode pattern of the laser emission can be used for tagging and tracking, as each laser spectrum represents a bar code to identify individual cells. However, currently these particle systems are limited by their large size, which might interfere with cellular functions. Here, stimulated resonance Raman scattering (SRRS) in small conjugated polymer microparticles is presented as a new method for generating narrow emission as an alternative to WGM-based laser emission. This opens up spectral range for multiplexing optical readout and multicolor imaging of live cells. The synthesis of monodisperse micrometer-sized poly(fluorene-co-divinylbenzene) particles is discussed and their WGM and SRRS emission are characterized. Finally, how these particles and their emission can be employed in live cell imaging and tagging is showcased. © 2020 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH
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    The Potential of Combining Thermal Scanning Probes and Phase-Change Materials for Tunable Metasurfaces
    (Weinheim : Wiley-VCH, 2020) Michel, Ann-Katrin U.; Meyer, Sebastian; Essing, Nicolas; Lassaline, Nolan; Lightner, Carin R.; Bisig, Samuel; Norris, David J.; Chigrin, Dmitry N.
    Metasurfaces allow for the spatiotemporal variation of amplitude, phase, and polarization of optical wavefronts. Implementation of active tunability of metasurfaces promises compact flat optics capable of reconfigurable wavefront shaping. Phase-change materials (PCMs) are a prominent material class enabling reconfigurable metasurfaces due to their large refractive index change upon structural transition. However, commonly employed laser-induced switching of PCMs limits the achievable feature sizes and restricts device miniaturization. Thermal scanning-probe-induced local switching of the PCM germanium telluride is proposed to realize near-infrared metasurfaces with feature sizes far below what is achievable with diffraction-limited optical switching. The design is based on a planar multilayer and does not require fabrication of protruding resonators as commonly applied in the literature. Instead, it is numerically demonstrated that a broad-band tuning of perfect absorption can be realized by the localized tip-induced crystallization of the PCM. The spectral response of the metasurface is explained using resonance mode analysis and numerical simulations. To facilitate experimental realization, a theoretical description of the tip-induced crystallization employing multiphysics simulations is provided to demonstrate the great potential for fabricating compact reconfigurable metasurfaces. The concept can be applied not only for plasmonic sensing and spatial frequency filtering, but also be transferred to all-dielectric metasurfaces. © 2020 Wiley-VCH GmbH
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    Plasmonic Properties of Colloidal Assemblies
    (Weinheim : Wiley-VCH, 2021) Rossner, Christian; König, Tobias A.F.; Fery, Andreas
    The assembly of metal nanoparticles into supracolloidal structures unlocks optical features, which can go beyond synergistic combinations of the properties of their primary building units. This is due to inter-particle plasmonic coupling effects, which give rise to emergent properties. The motivation for this progress report is twofold: First, it is described how simulation approaches can be used to predict and understand the optical properties of supracolloidal metal clusters. These simulations may form the basis for the rational design of plasmonic assembly architectures, based on the desired functional cluster properties, and they may also spark novel material designs. Second, selected scalable state-of-the-art preparative strategies based on synthetic polymers to guide the supracolloidal assembly are discussed. These routes also allow for equipping the assembly structures with adaptive properties, which in turn enables (inter-)active control over the cluster optical properties. © 2021 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH
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    Spectrometer‐free Optical Hydrogen Sensing Based on Fano‐like Spatial Distribution of Transmission in a Metal−Insulator−Metal Plasmonic Doppler Grating
    (Weinheim : Wiley-VCH, 2021) Chen, Yi‐Ju; Lin, Fan‐Cheng; Singh, Ankit Kumar; Ouyang, Lei; Huang, Jer‐Shing
    Optical nanosensors are promising for hydrogen sensing because they are small, free from spark generation, and feasible for remote optical readout. Conventional optical nanosensors require broadband excitation and spectrometers, rendering the devices bulky and complex. An alternative is spatial intensity-based optical sensing, which only requires an imaging system and a smartly designed platform to report the spatial distribution of analytical optical signals. Here, a spatial intensity-based hydrogen sensing platform is presented based on Fano-like spatial distribution of the transmission in a Pd-Al2O3-Au metal-insulator-metal plasmonic Doppler grating (MIM-PDG). The MIM-PDG manifests the Fano resonance as an asymmetric spatial transmission intensity profile. The absorption of hydrogen changes the spatial Fano-like transmission profiles, which can be analyzed with a “spatial” Fano resonance model and the extracted Fano resonance parameters can be used to establish analytical calibration lines. While gratings sensitive to hydrogen absorption are suitable for hydrogen sensing, hydrogen insensitive gratings are also found, which provide an unperturbed reference signal and may find applications in nanophotonic devices that require a stable optical response under fluctuating hydrogen atmosphere. The MIM-PDG platform is a spectrometer-free and intensity-based optical sensor that requires only an imaging system, making it promising for cellphone-based optical sensing applications. © 2021 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH.
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    Tunable Circular Dichroism by Photoluminescent Moiré Gratings
    (Weinheim : Wiley-VCH, 2020) Aftenieva, Olha; Schnepf, Max; Mehlhorn, Börge; König, Tobias A.F.
    In nanophotonics, there is a current demand for ultrathin, flexible nanostructures that are simultaneously easily tunable, demonstrate a high contrast, and have a strong response in photoluminescent polarization. In this work, the template-assisted self-assembly of water-dispersed colloidal core–shell quantum dots into 1D light-emitting sub-micrometer gratings on a flexible substrate is demonstrated. Combining such structures with a light-absorbing metallic counterpart by simple stacking at various angles results in a tunable Moiré pattern with strong lateral contrast. Furthermore, a combination with an identical emitter-based grating leads to a chiroptical effect with a remarkably high degree of polarization of 0.72. Such a structure demonstrates direct circular polarized photoluminescence, for the first time, without a need for an additional chiral template as an intermediary. The suggested approach allows for reproducible, large-area manufacturing at reasonable costs and is of potential use for chiroptical sensors, photonic circuit applications, or preventing counterfeit. © 2020 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH
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    Tailored Disorder in Photonics: Learning from Nature
    (Weinheim : Wiley-VCH, 2021) Rothammer, Maximilian; Zollfrank, Cordt; Busch, Kurt; Freymann, Georg von
    Disorder and photonics have long been seen as natural adversaries and designers of optical systems have often driven systems to perfection by minimizing deviations from the ideal design. Especially in the field of photonic crystals and metamaterials but also for optical circuits, disorder has been avoided as a nuisance for many years. However, starting from the very robust structural colors found in nature, scientists learn to analyze and tailor disorder to achieve functionalities beyond what is possible with perfectly ordered or ideal systems alone. This review article covers theoretical and materials aspects of tailored disorder as well as experimental results. Furthermore selected examples are highlighted in greater detail, for which the intentional use of disorder adds additional functionality or provides novel functionality impossible without disorder. © 2021 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH