51 results
Search Results
Now showing 1 - 10 of 51
- ItemRemarkable 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, AntonA 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
- ItemNarrow 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
- ItemThe 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
- ItemColloidal Self-Assembly Concepts for Plasmonic Metasurfaces(Weinheim : Wiley-VCH, 2019) Mayer, Martin; Schnepf, Max J.; König, Tobias A.F.; Fery, AndreasMetallic nanostructures exhibit strong interactions with electromagnetic radiation, known as the localized surface plasmon resonance. In recent years, there is significant interest and growth in the area of coupled metallic nanostructures. In such assemblies, short- and long-range coupling effects can be tailored and emergent properties, e.g., metamaterial effects, can be realized. The term “plasmonic metasurfaces” is used for this novel class of assemblies deposited on planar surfaces. Herein, the focus is on plasmonic metasurfaces formed from colloidal particles. These are formed by self-assembly and can meet the demands of low-cost manufacturing of large-area, flexible, and ultrathin devices. The advances in high optical quality of the colloidal building blocks and methods for controlling their self-assembly on surfaces will lead to novel functional devices for dynamic light modulators, pulse sharpening, subwavelength imaging, sensing, and quantum devices. This progress report focuses on predicting optical properties of single colloidal building blocks and their assemblies, wet-chemical synthesis, and directed self-assembly of colloidal particles. The report concludes with a discussion of the perspectives toward expanding the colloidal plasmonic metasurfaces concept by integrating them with quantum emitters (gain materials) or mechanically responsive structures. © 2018 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemMagnetic Hysteresis at 10 K in Single Molecule Magnet Self‐Assembled on Gold(Weinheim : Wiley-VCH, 2021) Chen, Chia-Hsiang; Spree, Lukas; Koutsouflakis, Emmanouil; Krylov, Denis S.; Liu, Fupin; Brandenburg, Ariane; Velkos, Georgios; Schimmel, Sebastian; Avdoshenko, Stanislav M.; Federov, Alexander; Weschke, Eugen; Choueikani, Fadi; Ohresser, Philippe; Dreiser, Jan; Büchner, Bernd; Popov, Alexey A.Tremendous progress in the development of single molecule magnets (SMMs) raises the question of their device integration. On this route, understanding the properties of low‐dimensional assemblies of SMMs, in particular in contact with electrodes, is a necessary but difficult step. Here, it is shown that fullerene SMM self‐assembled on metal substrate from solution retains magnetic hysteresis up to 10 K. Fullerene‐SMM DySc2N@C80 and Dy2ScN@C80 are derivatized to introduce a thioacetate group, which is used to graft SMMs on gold. Magnetic properties of grafted SMMs are studied by X‐ray magnetic circular dichroism and compared to the films of nonderivatized fullerenes prepared by sublimation. In self‐assembled films, the magnetic moments of the Dy ions are preferentially aligned parallel to the surface, which is different from the disordered orientation of endohedral clusters in nonfunctionalized fullerenes. Whereas chemical derivatization reduces the blocking temperature of magnetization and narrows the hysteresis of Dy2ScN@C80, for DySc2N@C80 equally broad hysteresis is observed as in the fullerene multilayer. Magnetic bistability in the DySc2N@C80 grafted on gold is sustained up to 10 K. This study demonstrates that self‐assembly of fullerene‐SMM derivatives offers a facile solution‐based procedure for the preparation of functional magnetic sub‐monolayers with excellent SMM performance.
- ItemTunable 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
- ItemWhen Ultimate Adhesive Mechanism Meets Ultimate Anti‐Fouling Surfaces - Polydopamine Versus SLIPS: Which One Prevails?(Weinheim : Wiley-VCH, 2020) Prieto-López, Lizbeth Ofelia; Herbeck-Engel, Petra; Yang, Li; Wu, Qian; Li, Juntang; Cui, JiaxiWhat happens when the extremely adhesive and versatile chemistry of polydopamine (PDA) is in contact with the extremely slippery surfaces known as slippery liquid‐infused porous substrates (SLIPS)? Inspired by the pitcher plant, SLIPS possess excellent repellence against a variety of complex liquids and have been proposed as promising antifouling surfaces because of their successful performance even in marine environments. In the counterpart, inspired by the adhesive proteins enabling the strong adhesion of mussels to multiple substrates, PDA has been extensively studied for its ability to adhere on nearly every type of substrate. The interaction between various SLIPS systems and the highly fouling medium from the oxidative polymerization of dopamine is explored here. A PDA coating is observed on all the SLIPS evaluated, modifying their hydrophobicity in most cases. In‐depth study of silicone‐based SLIPS shows that hydrophobicity of PDA coated SLIPS partially recovers with time due to percolation of the lubricant through the coating. “Strongly” bound PDA species are attributed to the formation of dopamine‐polydimethylsiloxane species on the crosslinked matrix, rendering a coating that withstands repeated washing steps in various solvents including water, hexane, and toluene. The results not only satisfy scientific curiosity but also imply a strategy to modify/bond SLIPS.
- ItemBuilding Hierarchical Martensite(Weinheim : Wiley-VCH, 2020) Schwabe, Stefan; Niemann, Robert; Backen, Anja; Wolf, Daniel; Damm, Christine; Walter, Tina; Seiner, Hanuš; Heczko, Oleg; Nielsch, Kornelius; Fähler, SebastianMartensitic materials show a complex, hierarchical microstructure containing structural domains separated by various types of twin boundaries. Several concepts exist to describe this microstructure on each length scale, however, there is no comprehensive approach bridging the whole range from the nano- up to the macroscopic scale. Here, it is described for a Ni-Mn-based Heusler alloy how this hierarchical microstructure is built from scratch with just one key parameter: the tetragonal distortion of the basic building block at the atomic level. Based on this initial block, five successive levels of nested building blocks are introduced. At each level, a larger building block is formed by twinning the preceding one to minimize the relevant energy contributions locally. This naturally explains the coexistence of different types of twin boundaries. The scale-bridging approach of nested building blocks is compared with experiments in real and reciprocal space. The approach of nested building blocks is versatile as it can be applied to the broad class of functional materials exhibiting diffusionless transformations. © 2020 The Authors. Advanced Functional Materials published by Wiley-VCH GmbH
- ItemMagnetic Nanoparticle Chains in Gelatin Ferrogels: Bioinspiration from Magnetotactic Bacteria(Weinheim : Wiley-VCH, 2019) Sturm, Sebastian; Siglreitmeier, Maria; Wolf, Daniel; Vogel, Karin; Gratz, Micha; Faivre, Damien; Lubk, Axel; Büchner, Bernd; Sturm, Elena V.; Cölfen, HelmutInspired by chains of ferrimagnetic nanocrystals (NCs) in magnetotactic bacteria (MTB), the synthesis and detailed characterization of ferrimagnetic magnetite NC chain-like assemblies is reported. An easy green synthesis route in a thermoreversible gelatin hydrogel matrix is used. The structure of these magnetite chains prepared with and without gelatin is characterized by means of transmission electron microscopy, including electron tomography (ET). These structures indeed bear resemblance to the magnetite assemblies found in MTB, known for their mechanical flexibility and outstanding magnetic properties and known to crystallographically align their magnetite NCs along the strongest <111> magnetization easy axis. Using electron holography (EH) and angular dependent magnetic measurements, the magnetic interaction between the NCs and the generation of a magnetically anisotropic material can be shown. The electro- and magnetostatic modeling demonstrates that in order to precisely determine the magnetization (by means of EH) inside chain-like NCs assemblies, their exact shape, arrangement and stray-fields have to be considered (ideally obtained using ET). © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemCell-Instructive Multiphasic Gel-in-Gel Materials(Weinheim : Wiley-VCH, 2020) Kühn, Sebastian; Sievers, Jana; Stoppa, Aukha; Träber, Nicole; Zimmermann, Ralf; Welzel, Petra B.; Werner, CarstenDeveloping tissue is typically soft, highly hydrated, dynamic, and increasingly heterogeneous matter. Recapitulating such characteristics in engineered cell-instructive materials holds the promise of maximizing the options to direct tissue formation. Accordingly, progress in the design of multiphasic hydrogel materials is expected to expand the therapeutic capabilities of tissue engineering approaches and the relevance of human 3D in vitro tissue and disease models. Recently pioneered methodologies allow for the creation of multiphasic hydrogel systems suitable to template and guide the dynamic formation of tissue- and organ-specific structures across scales, in vitro and in vivo. The related approaches include the assembly of distinct gel phases, the embedding of gels in other gel materials and the patterning of preformed gel materials. Herein, the capabilities and limitations of the respective methods are summarized and discussed and their potential is highlighted with some selected examples of the recent literature. As the modularity of the related methodologies facilitates combinatorial and individualized solutions, it is envisioned that multiphasic gel-in-gel materials will become a versatile morphogenetic toolbox expanding the scope and the power of bioengineering technologies. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim