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- ItemStructure-property relationships in nanoporous metallic glasses(Amsterdam [u.a.] : Elsevier Science, 2016) Şopu, D.; Soyarslan, C.; Sarac, B.; Bargmann, S.; Stoica, M.; Eckert, J.We investigate the influence of various critical structural aspects such as pore density, distribution, size and number on the deformation behavior of nanoporous Cu64 Zr36 glass. By using molecular dynamics and finite element simulations an effective strategy to control the strain localization in nanoporous heterostructures is provided. Depending on the pore distribution in the heterostructure, upon tensile loading the nanoporous glass showed a clear transition from a catastrophic fracture to localized deformation in one dominant shear band, and ultimately to homogeneous plastic flow mediated by a pattern of multiple shear bands. The change in the fracture mechanism from a shear band slip to necking-like homogeneous flow is quantitative interpreted by calculating the critical shear band length. Finally, we identify the most effective heterostructure with enhanced ductility as compared to the monolithic bulk metallic glass. The heterostructure with a fraction of pores of about 3% distributed in such a way that the pores do not align along the maximum shear stress direction shows higher plasticity while retaining almost the same strength as the monolithic glass. Our results provide clear evidence that the mechanical properties of nanoporous glassy materials can be tailored by carefully controlling the design parameters.
- ItemProtein-Assisted Assembly of Modular 3D Plasmonic Raspberry-like Core/Satellite Nanoclusters: Correlation of Structure and Optical Properties(Washington, DC : Soc., 2016) Höller, Roland P. M.; Dulle, Martin; Thomä, Sabrina; Mayer, Martin; Steiner, Anja Maria; Förster, Stephan; Fery, Andreas; Kuttner, Christian; Chanana, MunishWe present a bottom-up assembly route for a large-scale organization of plasmonic nanoparticles (NPs) into three-dimensional (3D) modular assemblies with core/satellite structure. The protein-assisted assembly of small spherical gold or silver NPs with a hydrophilic protein shell (as satellites) onto larger metal NPs (as cores) offers high modularity in sizes and composition at high satellite coverage (close to the jamming limit). The resulting dispersions of metal/metal nanoclusters exhibit high colloidal stability and therefore allow for high concentrations and a precise characterization of the nanocluster architecture in dispersion by small-angle X-ray scattering (SAXS). Strong near-field coupling between the building blocks results in distinct regimes of dominant satellite-to-satellite and core-to-satellite coupling. High robustness against satellite disorder was proved by UV/vis diffuse reflectance (integrating sphere) measurements. Generalized multiparticle Mie theory (GMMT) simulations were employed to describe the electromagnetic coupling within the nanoclusters. The close correlation of structure and optical property allows for the rational design of core/satellite nanoclusters with tailored plasmonics and well-defined near-field enhancement, with perspectives for applications such as surface-enhanced spectroscopies.
- ItemMechanical Robustness of Graphene on Flexible Transparent Substrates(Washington, DC : Soc., 2016) Kang, Moon H.; Prieto López, Lizbeth O.; Chen, Bingan; Teo, Ken; Williams, John A.; Milne, William I.; Cole, Matthew T.This study reports on a facile and widely applicable method of transferring chemical vapor deposited (CVD) graphene uniformly onto optically transparent and mechanically flexible substrates using commercially available, low-cost ultraviolet adhesive (UVA) and hot-press lamination (HPL). We report on the adhesion potential between the graphene and the substrate, and we compare these findings with those of the more commonly used cast polymer handler transfer processes. Graphene transferred with the two proposed methods showed lower surface energy and displayed a higher degree of adhesion (UVA: 4.40 ± 1.09 N/m, HPL: 0.60 ± 0.26 N/m) compared to equivalent CVD-graphene transferred using conventional poly(methyl methacrylate) (PMMA: 0.44 ± 0.06 N/m). The mechanical robustness of the transferred graphene was investigated by measuring the differential resistance as a function of bend angle and repeated bend–relax cycles across a range of bend radii. At a bend angle of 100° and a 2.5 mm bend radius, for both transfer techniques, the normalized resistance of graphene transferred on polyethylene terephthalate (PET) was around 80 times less than that of indium–tin oxide on PET. After 104 bend cycles, the resistance of the transferred graphene on PET using UVA and HPL was found to be, on average, around 25.5 and 8.1% higher than that of PMMA-transferred graphene, indicating that UVA- and HPL-transferred graphene are more strongly adhered compared to PMMA-transferred graphene. The robustness, in terms of maintained electrical performance upon mechanical fatigue, of the transferred graphene was around 60 times improved over ITO/PET upon many thousands of repeated bending stress cycles. On the basis of present production methods, the development of the next-generation of highly conformal, diverse form factor electronics, exploiting the emerging family of two-dimensional materials, necessitates the development of simple, low-cost, and mechanically robust transfer processes; the developed UVA and HPL approaches show significant potential and allow for large-area-compatible, near-room temperature transfer of graphene onto a diverse range of polymeric supports.
- ItemHydrolysis Stability of Bidentate Phosphites Utilized as Modifying Ligands in the Rh-Catalyzed n-Regioselective Hydroformylation of Olefins(Washington, DC : ACS, 2016) Zhang, Baoxin; Jiao, Haijun; Michalik, Dirk; Kloß, Svenja; Deter, Lisa Marie; Selent, Detlef; Spannenberg, Anke; Franke, Robert; Börner, ArminThe stability of ligands and catalysts is an almost neglected issue in homogeneous catalysis, but it is crucial for successful application of this methodology in technical scale. We have studied the effect of water on phosphites, which are the most applied cocatalysts in the n-regioselective homogeneous Rh-catalyzed hydroformylation of olefins. The stability of the bidentate nonsymmetrical diphosphite L1, as well as its two monophosphite constituents L2 and L3, toward hydrolysis was investigated by means of in situ NMR spectroscopy under similar conditions as applied in industry. Hydrolysis pathways, intermediates, and kinetics were clarified. DFT calculations were used to support the experimentally found data. The acylphosphite unit L2, which reacts with water in an unselective manner, was proven to be much less stable than the phenolphosphite L3. The stability of the bidentate ligand L1 can be therefore mainly attributed to its phenolphosphite moiety. With an excess of water, the hydrolysis of L1 and L2 as well as their Rh-complexes is first-order with respect to the phosphite. Surprisingly, coordination to Rh significantly stabilizes the monodentate ligand L2, while in strong contrast, the bidentate ligand L1 decomposes faster in the Rh complex. NMR spectroscopy provided evidence for the existence of species from decomposition of phosphites, which can likewise coordinate as ligands to the metal. Electron-withdrawing groups in the periphery of the acylphosphite moiety decrease the stability of L1, whereas 3,5-disubstituted salicylic acid derivatives with bulky groups showed superior stability. These modifications of L1 also give rise to different catalytic performances in the n-regioselective hydroformylation of n-octenes and 2-pentene, from which the 3,5-di-t-butyl-substituted ligand offered a higher n-regioselectivity accompanied by a lowering of the reaction rate in comparison to the parent ligand L1.
- ItemRenegotiating Open-Access-Licences for Scientific Films(Amsterdam : IOS Press, 2016) Brehm, ElkeScientific publishing is not limited to text any more, but more and more extends also to digital audio-visual media. Thus services for publishing these media in portals designed for scientific content, oriented towards the demands of scientists and which comply with the requirements of Open Access Licenses must be provided. Among others, it is the goal of the Competence Centre for Non-textual-materials of TIB to collect, archive and provide access to scientific audio-visual media in the TIB AV-Portal under the best possible (open) conditions. This applies to older films, as for example the film collection of the former IWF Knowledge and Media gGmbH i. L. (IWF) and to new films. However, even if the acquisition of the necessary rights for audio-visual media is complex, the renegotiation of Open-Access- Licenses for older films is very successful. This paper focuses on the role of Open Access in the licensing strategy of TIB regarding scientific films, the respective experience of TIB and the presentation in the AV-Portal, but also touches upon prerequisites and procedures for the use of Orphan Works.
- ItemThe ties that bind - On the impact of losing a consortium member in a cooperatively operated digital preservation system(2016) Lindlar, MichelleCooperatively operated digital preservation systems offer institutions of varying size the chance to actively participate in digital preservation. In current times of budget cuts they are also a valuable asset to larger memory institutions. While the benefits of cooperatively operated systems have been discussed before, the risks associated with a consortial solution have not been analyzed in detail. TIB hosts the Goportis Digital Archive which is used by two large national subject libraries as well as by TIB itself. As the host of this comparatively small preservation network, TIB has started to analyze the particular risk which losing a consortium member poses to the overall system operation. This paper presents the current status of this work-in-progress and highlights two areas: risk factors associated with cost and risk factors associated with the content. While the paper is strictly written from the viewpoint of the consortial leader/ host of this specific network, the underlying processes shall be beneficial to other cooperatively operated digital preservation systems.
- ItemSCOAP3/SCOAP3-DH – Gold Open Access in High Energy Physics(Amsterdam : IOS Press, 2016) Kutz, AngelikaSCOAP3 is a global partnership which converts high-quality subscription journals in the field of High-Energy Physics to Open Access through redirection of existing subscription funds. Since January 1, 2014 the SCOAP3 Gold Open Access Repository is providing free access to scientific articles in high quality journals in the field of High Energy Physics. This article describes this international pilot which flips the current subscription-based financing of scientific publication to an output-based financing model (fair share). This includes a description of the unique mechanisms of SCOAP3 as well as its governance structure and short view on the national German contributing partners, especially the German universities (SCOAP3-DH).
- ItemIron-Based Binary Catalytic System for the Valorization of CO2 into Biobased Cyclic Carbonates(Washington, DC : ACS Publ., 2016) Büttner, Hendrik; Grimmer, Christoph; Steinbauer, Johannes; Werner, ThomasThe atom economic conversion of epoxidized vegetable oils and fatty acid derivatives with CO2 into cyclic carbonates permits the synthesis of novel oleo compounds from renewable resources as well as the valorization of CO2 as a C1-building block. Organic phosphorus salts proved to be selective catalysts for this reaction. In a widespread screening 11 inexpensive and nontoxic iron salts were evaluated as cocatalysts to enhance the reaction rate. In the presence of 0.25 mol % iron chloride the selectivity and conversion were significantly improved. The reaction parameters were optimized under solvent-free conditions, and the scope and limitation were evaluated for 9 epoxidized fatty acid esters and 4 epoxidized vegetable oils. The biobased carbonates were isolated in excellent yields up to 95% and can be considered to be based on 100% CO2 in respect to carbon. This binary catalyst system features high efficiency and plain simplicity while valorizing CO2 into cyclic carbonates based on renewable feedstocks.
- ItemCrystal structures of two ansa-titanocene tri-fluoro-methane-sulfonate complexes bearing the Me2Si(C5Me4)2 ligand(Chester : International Union of Crystallography, 2016) Kessler, Monty; Godemann, Christian; Spannenberg, Anke; Beweries, TorstenThe crystal structures of two ansa-titanocene tri-fluoro-methane-sulfonate complexes bearing the Me2Si(C5Me4)2 ligand are reported, namely [di-methylbis-(η5-tetra-methyl-cyclo-penta-dien-yl)silane](tri-fluoro-methane-sulfonato-κ2O,O')titanium(III) toluene monosolvate, [Ti(CF3O3S)(C20H30Si)]·C7H8, 1, and chlorido-[di-methyl-bis-(η5-tetra-methyl-cyclo-penta-dien-yl)silane](tri-fluoro-methane-sulfonato-κO)titanium(IV), [Ti(CF3O3S)(C20H30Si)Cl], 2. Both complexes display a bent metallocene unit, the metal atom being coordinated in a distorted tetra-hedral geometry, with the tri-fluoro-methane-sulfonate anion acting as a bidentate or monodentate ligand in 1 and 2, respectively. In 1, weak π-π stacking inter-actions involving the toluene solvent mol-ecules [centroid-to-centroid distance = 3.9491 (11) Å] are observed.
- ItemInfluence of microwave plasma treatment on the surface properties of carbon fibers and their adhesion in a polypropylene matrix(London [u.a.] : Institute of Physics, 2016) Scheffler, C.; Wölfel, E.; Förster, T.; Poitzsch, C.; Kotte, L.; Mäder, G.; Madsen, Bo; Biel, A.; Kusano, Y.; Lilholt, H.; Mikkelsen, L.P.; Mishnaevsky Jr., L.; Sørensen, B.F.A commercially available carbon fiber (CF) with an epoxy-based sizing (EP-sized CF) and an unsized CF have been plasma treated to study the effect on the fiber-matrix adhesion towards a polypropylene matrix. The EP-sized fiber was chosen because of its predictable low adhesion in a polypropylene (PP) matrix. The fibers have been modified using a microwave low-pressure O2/CO2/N2-gas plasma source (Cyrannus®) developed at IWS in a batch process. One aim of this study was the evaluation of parameters using high energies and short time periods in the plasma chamber to see the effect on mechanical performance of CF. These results will be the fundamental work for a planned continuous plasma modification line. The CF surface was characterized by determining the surface energies, single fiber tensile strength and XPS analysis. The adhesion behavior before and after plasma treatment was studied by single fiber pull-out test (SFPO) and scanning electron microscopy (SEM). It was shown that the CO2- and O2-plasma increases the number of functional groups on the fiber surface during short time plasma treatment of 30 s. Carboxylic groups on the unsized CF surface resulting from O2-plasma treatment lead to an enhanced fiber-matrix adhesion, whereas the fiber strength was merely reduced.