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End date: 2024 × Start date: 2020 × Subject: self-assembly ×

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Now showing 1 - 10 of 16
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    Self-Assembly of Polymer-Modified FePt Magnetic Nanoparticles and Block Copolymers
    (Basel : MDPI, 2023) Hartmann, Frank; Bitsch, Martin; Niebuur, Bart-Jan; Koch, Marcus; Kraus, Tobias; Dietz, Christian; Stark, Robert W.; Everett, Christopher R.; Müller-Buschbaum, Peter; Janka, Oliver; Gallei, Markus
    The fabrication of nanocomposites containing magnetic nanoparticles is gaining interest as a model for application in small electronic devices. The self-assembly of block copolymers (BCPs) makes these materials ideal for use as a soft matrix to support the structural ordering of the nanoparticles. In this work, a high-molecular-weight polystyrene-b-poly(methyl methacrylate) block copolymer (PS-b-PMMA) was synthesized through anionic polymerization. The influence of the addition of different ratios of PMMA-coated FePt nanoparticles (NPs) on the self-assembled morphology was investigated using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). The self-assembly of the NPs inside the PMMA phase at low particle concentrations was analyzed statistically, and the negative effect of higher particle ratios on the lamellar BCP morphology became visible. The placement of the NPs inside the PMMA phase was also compared to theoretical descriptions. The magnetic addressability of the FePt nanoparticles inside the nanocomposite films was finally analyzed using bimodal magnetic force microscopy and proved the magnetic nature of the nanoparticles inside the microphase-separated BCP films.
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    Nanoporous Block Copolymer Membranes with Enhanced Solvent Resistance Via UV-Mediated Cross-Linking Strategies
    (Weinheim : Wiley-VCH, 2021) Frieß, Florian V.; Hu, Qiwei; Mayer, Jannik; Gemmer, Lea; Presser, Volker; Balzer, Bizan N.; Gallei, Markus
    In this work, a block copolymer (BCP) consisting of poly((butyl methacrylate-co-benzophenone methacrylate-co-methyl methacrylate)-block-(2-hydroxyethyl methacrylate)) (P(BMA-co-BPMA-co-MMA)-b-P(HEMA)) is prepared by a two-step atom-transfer radical polymerization (ATRP) procedure. BCP membranes are fabricated applying the self-assembly and nonsolvent induced phase separation (SNIPS) process from a ternary solvent mixture of tetrahydrofuran (THF), 1,4-dioxane, and dimethylformamide (DMF). The presence of a porous top layer of the integral asymmetric membrane featuring pores of about 30 nm is confirmed via scanning electron microscopy (SEM). UV-mediated cross-linking protocols for the nanoporous membrane are adjusted to maintain the open and isoporous top layer. The swelling capability of the noncross-linked and cross-linked BCP membranes is investigated in water, water/ethanol mixture (1:1), and pure ethanol using atomic force microscopy, proving a stabilizing effect of the UV cross-linking on the porous structures. Finally, the influence of the herein described cross-linking protocols on water-flux measurements for the obtained membranes is explored. As a result, an increased swelling resistance for all tested solvents is found, leading to an increased water flux compared to the pristine membrane. The herein established UV-mediated cross-linking protocol is expected to pave the way to a new generation of porous and stabilized membranes within the fields of separation technologies.
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    Can One Series of Self-Organized Nanoripples Guide Another Series of Self-Organized Nanoripples during Ion Bombardment: From the Perspective of Power Spectral Density Entropy?
    (Basel : MDPI, 2023) Li, Hengbo; Li, Jinyu; Yang, Gaoyuan; Liu, Ying; Frost, Frank; Hong, Yilin
    Ion bombardment (IB) is a promising nanofabrication tool for self-organized nanostructures. When ions bombard a nominally flat solid surface, self-organized nanoripples can be induced on the irradiated target surface, which are called intrinsic nanoripples of the target material. The degree of ordering of nanoripples is an outstanding issue to be overcome, similar to other self-organization methods. In this study, the IB-induced nanoripples on bilayer systems with enhanced quality are revisited from the perspective of guided self-organization. First, power spectral density (PSD) entropy is introduced to evaluate the degree of ordering of the irradiated nanoripples, which is calculated based on the PSD curve of an atomic force microscopy image (i.e., the Fourier transform of the surface height. The PSD entropy can characterize the degree of ordering of nanoripples). The lower the PSD entropy of the nanoripples is, the higher the degree of ordering of the nanoripples. Second, to deepen the understanding of the enhanced quality of nanoripples on bilayer systems, the temporal evolution of the nanoripples on the photoresist (PR)/antireflection coating (ARC) and Au/ARC bilayer systems are compared with those of single PR and ARC layers. Finally, we demonstrate that a series of intrinsic IB-induced nanoripples on the top layer may act as a kind of self-organized template to guide the development of another series of latent IB-induced nanoripples on the underlying layer, aiming at improving the ripple ordering. The template with a self-organized nanostructure may alleviate the critical requirement for periodic templates with a small period of ~100 nm. The work may also provide inspiration for guided self-organization in other fields.
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    Block Copolymers Featuring Highly Photostable Photoacids Based on Vinylnaphthol: Synthesis and Self-Assembly
    (Weinheim : Wiley-VCH, 2020) Wendler, Felix; Tom, Jessica C.; Sittig, Maria; Biehl, Philip; Dietzek, Benjamin; Schacher, Felix H.
    The synthesis of a photoresponsive amphiphilic diblock quarterpolymer containing 5-vinyl-1-naphthol (VN) as a photostable photoacidic comonomer is presented. The preparation is realized via a sequential reversible addition fragmentation chain transfer (RAFT) polymerization starting from a nona(ethylene glycol) methyl ether methacrylate (MEO9MA/“O”) hydrophilic block, which is then used as a macro-RAFT agent in the terpolymerization of styrene (S), 2-vinylpyridine (2VP), and TBS-protected VN (tVN). The terpolymerization proceeds in a controlled fashion and two diblock quarterpolymers, P(Om)-b-P(Sx-co-2VPy-co-VNz), with varying functional comonomer compositions are prepared. These diblock quarterpolymers form spherical core-corona micelles in aqueous media according to dynamic light scattering (DLS) and cryogenic transmission electron microscopy (cryo-TEM). Upon irradiation, the photoacids within the micellar core experience a drastic increase in acidity causing a proton transfer from the photoacid to neighboring 2VP units. As a result, the hydrophilic/hydrophobic balance of the entire assembly is shifted, and the encapsulated cargo is released. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Prospects of Coupled Organic-Inorganic Nanostructures for Charge and Energy Transfer Applications
    (Weinheim : Wiley-VCH, 2021) Steiner, Anja Maria; Lissel, Franziska; Fery, Andreas; Lauth, Jannika; Scheele, Marcus
    We review the field of organic–inorganic nanocomposites with a focus on materials that exhibit a significant degree of electronic coupling across the hybrid interface. These nanocomposites undergo a variety of charge and energy transfer processes, enabling optoelectronic applications in devices which exploit singlet fission, triplet energy harvesting, photon upconversion or hot charge carrier transfer. We discuss the physical chemistry of the most common organic and inorganic components. Based on those we derive synthesis and assembly strategies and design criteria on material and device level with a focus on photovoltaics, spin memories or optical upconverters. We conclude that future research in the field should be directed towards an improved understanding of the binding motif and molecular orientation at the hybrid interface. © 2020 The Authors. Published by Wiley-VCH GmbH
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    Synthesis of Polyampholyte Janus-like Microgels by Coacervation of Reactive Precursors in Precipitation Polymerization
    (Weinheim : Wiley-VCH, 2020) Xu, Wenjing; Rudov, Andrey; Oppermann, Alex; Wypysek, Sarah; Kather, Michael; Schroeder, Ricarda; Richtering, Walter; Potemkin, Igor I.; Wöll, Dominik; Pich, Andrij
    Controlling the distribution of ionizable groups of opposite charge in microgels is an extremely challenging task, which could open new pathways to design a new generation of stimuli-responsive colloids. Herein, we report a straightforward approach for the synthesis of polyampholyte Janus-like microgels, where ionizable groups of opposite charge are located on different sides of the colloidal network. This synthesis approach is based on the controlled self-assembly of growing polyelectrolyte microgel precursors during the precipitation polymerization process. We confirmed the morphology of polyampholyte Janus-like microgels and demonstrate that they are capable of responding quickly to changes in both pH and temperature in aqueous solutions. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.
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    Wafer-Scale High-Quality Microtubular Devices Fabricated via Dry-Etching for Optical and Microelectronic Applications
    (Weinheim : Wiley-VCH, 2020) Saggau, Christian N.; Gabler, Felix; Karnaushenko, Dmitriy D.; Karnaushenko, Daniil; Ma, Libo; Schmidt, Oliver G.
    Mechanical strain formed at the interfaces of thin films has been widely applied to self-assemble 3D microarchitectures. Among them, rolled-up microtubes possess a unique 3D geometry beneficial for working as photonic, electromagnetic, energy storage, and sensing devices. However, the yield and quality of microtubular architectures are often limited by the wet-release of lithographically patterned stacks of thin-film structures. To address the drawbacks of conventionally used wet-etching methods in self-assembly techniques, here a dry-release approach is developed to roll-up both metallic and dielectric, as well as metallic/dielectric hybrid thin films for the fabrication of electronic and optical devices. A silicon thin film sacrificial layer on insulator is etched by dry fluorine chemistry, triggering self-assembly of prestrained nanomembranes in a well-controlled wafer scale fashion. More than 6000 integrated microcapacitors as well as hundreds of active microtubular optical cavities are obtained in a simultaneous self-assembly process. The fabrication of wafer-scale self-assembled microdevices results in high yield, reproducibility, uniformity, and performance, which promise broad applications in microelectronics, photonics, and opto-electronics. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Nanoscale Faceting and Ligand Shell Structure Dominate the Self-Assembly of Nonpolar Nanoparticles into Superlattices
    (Weinheim : Wiley-VCH, 2022) Bo, Arixin; Liu, Yawei; Kuttich, Björn; Kraus, Tobias; Widmer-Cooper, Asaph; de Jonge, Niels
    Self-assembly of nanoscale structures at liquid–solid interfaces occurs in a broad range of industrial processes and is found in various phenomena in nature. Conventional theory assumes spherical particles and homogeneous surfaces, but that model is oversimplified, and nanoscale in situ observations are needed for a more complete understanding. Liquid-phase scanning transmission electron microscopy (LP-STEM) is used to examine the interactions that direct the self-assembly of superlattices formed by gold nanoparticles (AuNPs) in nonpolar liquids. Varying the molecular coating of the substrate modulates short-range attraction and leads to switching between a range of different geometric structures, including hexagonal close-packed (hcp), simple hexagonal (sh), dodecahedral quasi-crystal (dqc), and body-centered cubic (bcc) lattices, as well as random distributions. Langevin dynamics simulations explain the experimental results in terms of the interplay between nanoparticle faceting, ligand shell structure, and substrate–NP interactions.
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    Kinetic Control over Self-Assembly of Semiconductor Nanoplatelets
    (Washington, DC : American Chemical Society, 2020) Momper, R.; Zhang, H.; Chen, S.; Halim, H.; Johannes, E.; Yordanov, S.; Braga, D.; Blülle, B.; Doblas, D.; Kraus, T.; Kraus, T.; Bonn, M.; Wang, H.I.; Riedinger, A.
    Semiconductor nanoplatelets exhibit spectrally pure, directional fluorescence. To make polarized light emission accessible and the charge transport effective, nanoplatelets have to be collectively oriented in the solid state. We discovered that the collective nanoplatelets orientation in monolayers can be controlled kinetically by exploiting the solvent evaporation rate in self-assembly at liquid interfaces. Our method avoids insulating additives such as surfactants, making it ideally suited for optoelectronics. The monolayer films with controlled nanoplatelets orientation (edge-up or face-down) exhibit long-range ordering of transition dipole moments and macroscopically polarized light emission. Furthermore, we unveil that the substantial in-plane electronic coupling between nanoplatelets enables charge transport through a single nanoplatelets monolayer, with an efficiency that strongly depends on the orientation of the nanoplatelets. The ability to kinetically control the assembly of nanoplatelets into ordered monolayers with tunable optical and electronic properties paves the way for new applications in optoelectronic devices.
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    Covalent Linkage of BODIPY-Photosensitizers to Anderson-Type Polyoxometalates Using CLICK Chemistry
    (Weinheim : Wiley-VCH, 2021) Cetindere, Seda; Clausing, Simon T.; Anjass, Montaha; Luo, Yusen; Kupfer, Stephan; Dietzek, Benjamin; Streb, Carsten
    The covalent attachment of molecular photosensitizers (PS) to polyoxometalates (POMs) opens new pathways to PS-POM dyads for light-driven charge-transfer and charge-storage. Here, we report a synthetic route for the covalent linkage of BODIPY-dyes to Anderson-type polyoxomolybdates by using CLICK chemistry (i. e. copper-catalyzed azide-alkyne cycloaddition, CuAAC). Photophysical properties of the dyad were investigated by combined experimental and theoretical methods and highlight the role of both sub-components for the charge-separation properties. The study demonstrates how CLICK chemistry can be used for the versatile linkage of organic functional units to molecular metal oxide clusters. © 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH