Filters

2018 - 201912020 - 20223

More filters

2021 - 20234
Reset filters

Settings

Start date: 2020 Ă— Publisher: Weinheim : Wiley-VCH Ă— Subject: self-assembly Ă— WGL Institute: INM Ă—

Search Results

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Dye-Loaded Mechanochromic and pH-Responsive Elastomeric Opal Films
    (Weinheim : Wiley-VCH, 2021) Winter, Tamara; Boehm, Anna; Presser, Volker; Gallei, Markus
    In this work, the preparation and fabrication of elastomeric opal films revealing reversible mechanochromic and pH-responsive features are reported. The core–interlayer–shell (CIS) particles are synthesized via stepwise emulsion polymerization leading to hard core (polystyrene), crosslinked interlayer (poly(methyl methacrylate-co-allyl methacrylate), and soft poly(ethyl acrylate-co-butyl acrylate-co-(2-hydroxyethyl) methacrylate) shell particles featuring a size of 294.9 Â± 14.8 nm. This particle architecture enables the application of the melt-shear organization technique leading to elastomeric opal films with orange, respectively, green brilliant reflection colors dependent on the angle of view. Moreover, the hydroxyl moieties as part of the particle shell are advantageously used for subsequent thermally induced crosslinking reactions enabling the preparation of reversibly tunable mechanochromic structural colors based on Bragg's law of diffraction. Additionally, the CIS particles can be loaded upon extrusion or chemically by a postfunctionalization strategy with organic dyes implying pH-responsive features. This convenient protocol for preparing multi-responsive, reversibly stretch-tunable opal films is expected to enable a new material family for anti-counterfeiting applications based on external triggers.
  • Thumbnail Image
    Item
    Nanoporous Block Copolymer Membranes with Enhanced Solvent Resistance Via UV-Mediated Cross-Linking Strategies
    (Weinheim : Wiley-VCH, 2021) FrieĂŸ, 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.
  • Thumbnail Image
    Item
    Ordered Mesoporous TiO2 Gyroids: Effects of Pore Architecture and Nb-Doping on Photocatalytic Hydrogen Evolution under UV and Visible Irradiation
    (Weinheim : Wiley-VCH, 2018) Dörr, Tobias Sebastian; Deilmann, Leonie; Haselmann, Greta; Cherevan, Alexey; Zhang, Peng; Blaha, Peter; de Oliveira, Peter William; Kraus, Tobias; Eder, Dominik
    Pure and Nb-doped TiO2 photocatalysts with highly ordered alternating gyroid architecture and well-controllable mesopore size of 15 nm via co-assembly of a poly(isoprene)-block-poly(styrene)-block-poly(ethylene oxide) block copolymer are synthesized. A combined effort by electron microscopy, X-ray scattering, photoluminescence, X-ray photoelectron spectroscopy, Raman spectroscopy, and density functional theory simulations reveals that the addition of small amounts of Nb results in the substitution of Ti4+ with isolated Nb5+ species that introduces inter-bandgap states, while at high concentrations, Nb prefers to cluster forming shallow trap states within the conduction band minimum of TiO2. The gyroidal photocatalysts are remarkably active toward hydrogen evolution under UV and visible light due to the open 3D network, where large mesopores ensure efficient pore diffusion and high photon harvesting. The gyroids yield unprecedented high evolution rates beyond 1000 µmol h−1 (per 10 mg catalyst), outperforming even the benchmark P25-TiO2 more than fivefold. Under UV light, the Nb-doping reduces the activity due to the introduction of charge recombination centers, while the activity in the visible triple upon incorporation is owed to a more efficient absorption due to inter-bandgap states. This unique pore architecture may further offer hitherto undiscovered optical benefits to photocatalysis, related to chiral and metamaterial-like behavior, which will stimulate further studies focusing on novel light–matter interactions.
  • Thumbnail Image
    Item
    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.