3 research outputs found

    Guiding Block Copolymers into Sequenced Patterns via Inverted Terrace Formation

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    Corrugated SiCN ceramic substrates fabricated by a facile replication process using nonlithographic PDMS masters were employed for the directed assembly of block copolymer microdomains. During thermal annealing of polystyrene-<i>b</i>-polybutadiene diblock copolymer, the material transport was guided by a wrinkled substrate to form regular modulations in the film thickness. As a consequence of the thickness-dependent morphological behavior of cylinder forming block copolymer, the film surface appears as sequenced patterns of alternative microphase-separated structures. The ordering process is attributed to the formation of inverted terraces which match the substrate topography, so that the resulting surface patterns are free from the surface relief structures within macroscopically large areas. The issues of the film thickness, the substrate surface energy, and the pattern geometry are addressed. Our approach demonstrates an effective synergism of external confinement and internal polymorphism of block copolymers toward complex hierarchically structured patterned surfaces

    Synthesis and Internal Structure of Finite-Size DNA–Gold Nanoparticle Assemblies

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    Spatially defined networks of 15 nm-sized DNA-functionalized gold nanoparticles (DNA–AuNPs) were studied using dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), as well as optical extinction spectroscopy (OES). We use a combination of these techniques with Monte Carlo simulations of pair-distance distribution function (PDDF) curves and generalized Mie theory simulations as well as in situ-transmission electron microscopy (in situ-TEM) to analyze the internal structure of the finite-size assemblies. The DLS data show that monodisperse, spherical networks with hydrodynamic radii of ca. 30 nm are found for reaction mixtures of complementarily functionalized DNA–AuNPs between 1:15 and 1:20. Different interparticle distances within these assemblies are identified and quantified. By controlling the network morphology through selection of the reaction mixture, center-shell geometries are obtained. The number of shell-AuNPs surrounding each center-AuNP is determined from the SAXS data and Monte Carlo simulations. This number is quantified to be ca. 10, with the exact number depending on the linking DNA double strand. The optical spectra of the networks are found to be consistent with the structural properties. The structural information gained here enables a quantitative description of optical and other physical properties, which is expected to prove useful for the construction and application of such systems, for example, in drug release, gene regulation, or external-stimuli-responsive materials

    Experimental and Theoretical Understanding of Nitrogen-Doping-Induced Strong Metal–Support Interactions in Pd/TiO<sub>2</sub> Catalysts for Nitrobenzene Hydrogenation

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    By doping the TiO<sub>2</sub> support with nitrogen, strong metal–support interactions (SMSI) in Pd/TiO<sub>2</sub> catalysts can be tailored to obtain high-performance supported Pd nanoparticles (NPs) in nitrobenzene (NB) hydrogenation catalysis. According to the comparative studies by X-ray diffraction, X-ray photoelectron spectroscopy (XPS), and diffuse reflectance CO FTIR (CO–DRIFTS), N-doping induced a structural promoting effect, which is beneficial for the dispersion of Pd species on TiO<sub>2</sub>. High-angle annular dark-field scanning transmission electron microscopy study of Pd on N-doped TiO<sub>2</sub> confirmed a predominant presence of sub-2 nm Pd NPs, which are stable under the applied hydrogenation conditions. XPS and CO–DRIFTS revealed the formation of strongly coupled Pd–N species in Pd/TiO<sub>2</sub> with N-doped TiO<sub>2</sub> as support. Density functional theory (DFT) calculations over model systems with Pd<sub><i>n</i></sub> (<i>n</i> = 1, 5, or 10) clusters deposited on TiO<sub>2</sub>(101) surface were performed to verify and supplement the experimental observations. In hydrogenation catalysis using NB as a model molecule, Pd NPs on N-doped TiO<sub>2</sub> outperformed those on N-free TiO<sub>2</sub> in terms of both catalytic activity and stability, which can be attributed to the presence of highly dispersed Pd NPs providing more active sites, and to the formation of Pd–N species favoring the dissociative adsorption of the reactant NB and the easier desorption of the product aniline