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6 Materialschutz und Oberflächentechnik

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Autor

  • Unger, Wolfgang (86)
  • Hodoroaba, Vasile-Dan (83)
  • Bonse, Jörn (59)
  • Schönhals, Andreas (57)
  • Thünemann, Andreas F. (50)
  • Krüger, Jörg (48)
  • Woydt, Mathias (36)
  • Sturm, Heinz (30)
  • Lippitz, Andreas (29)
  • Friedrich, Jörg Florian (22)
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  • XPS (43)
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Organisationseinheit der BAM

  • 6 Materialschutz und Oberflächentechnik (591)
  • 6.1 Oberflächenanalytik und Grenzflächenchemie (193)
  • 6.6 Nano-Tribologie und Nanostrukturierung von Oberflächen (124)
  • 6.5 Polymere in Life Science und Nanotechnologie (99)
  • 6.3 Makro-Tribologie und Verschleißschutz (83)
  • 6.4 Technologien mit Nanowerkstoffen (77)
  • 1 Analytische Chemie; Referenzmaterialien (58)
  • 6.7 Oberflächenmodifizierung und -messtechnik (46)
  • 5 Werkstofftechnik (42)
  • 1.3 Strukturanalytik (35)
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2,6-Diaminopyridine and Acrylamide-Based Copolymers with Upper Critical Solution Temperature-type Behavior in Aqueous Solution (2019)
Asadujjaman, Asad ; Ahmadi, Vahid ; Franc, Antoine Michel Claude ; Bertin, Annabelle
A novel cop olyme r based on supramolecular motif2,6-diaminopyridin e and water-soluble acrylamide, poly[N-(6-ace tamidopyridin-2-yl) acrylamide-co-acrylamide], was synthe-size d via rev ersible addi tion–fragmentation chain transfer (RAFT)polymerization with various monomer compositions. The thermo-respon sive behavior of the copolymers was studied by turbidime-try and dynamic light scattering (DLS). The obtained copolymersshowed an upper critical solution temperature (UCST)-typ e phasetransition behavior in water and electrolyte solution. The phasetransition temperature was found to increase with decreasingam ount of acrylamide in the copolymer and increasing concentra-tion of the solution. Furth ermore, the phase transition temperatureva ried in aqueous solutions of electrolytes according to the naturean d concentration of the electrolyte in accordance with theHoffmeister series. A dramatic solvent isotope effect on thetransition temperature was o bserved in this study, as the transitiontemperature was almost 10–12C higher in D2OthaninH2Oatthesame concentration and acrylamide co mposition. The size of theaggregates below the transition temperature was larger in D2Ocompared to that in H2O that can be explained by deuterium iso-tope effect. The thermoresponsive behavior of the copolymers wasalso investigated in different cell medium and found to be exhibitedUCST-type phase transition behavior in different cell medium.Such behavior of the copo lyme rs can be useful in many a pplica-tions including biomedical, microfluidics, optical materials, and indrug delivery.
A combined quantum chemical/molecular dynamics study of X-rayphotoelectron spectra of polyvinyl alcohol using oligomer models (2015)
Ehlert, Christopher ; Kröner, D. ; Saalfrank, P.
X-ray photoelectron spectroscopy (XPS) is a powerful tool for probing the local chemical environment ofatoms near surfaces. When applied to soft matter, such as polymers, XPS spectra are frequently shifted andbroadened due to thermal atom motion and by interchain interactions. We present a combined quantummechanical QM/molecular dynamics (MD) simulation of X-ray photoelectron spectra of polyvinyl alcohol(PVA) using oligomer models in order to account for and quantify these effects on the XPS (C1s) signal. Inour study, molecular dynamics at finite temperature were performed with a classical forcefield and by abinitio MD (AIMD) using the Car–Parrinello method. Snapshots along the trajectories represent possibleconformers and/or neighbouring environments, with different C1s ionization potentials for individualC atoms leading to broadened XPS peaks. The latter are determined by -Kohn Sham calculations. Wealso examine the experimental practice of gauging XPS (C1s) signals of alkylic C-atoms in C-containingpolymers to the C1s signal of polyethylene.We find that (i) the experimental XPS (C1s) spectra of PVA (position and width) can be roughly repre-sented by single-strand models, (ii) interchain interactions lead to red-shifts of the XPS peaks by about0.6 eV, and (iii) AIMD simulations match the findings from classical MD semi-quantitatively. Further, (iv)the gauging procedure of XPS (C1s) signals to the values of PE, introduces errors of about 0.5 eV.
A contribution to intelligent automatic validation of structure-integrated fibre optic strain sensors (2017)
Schukar, Vivien ; Köppe, Enrico ; Hofmann, Detlef ; Mitzkus, Anja ; Gong, Xin ; Sahre, Mario ; Bartholmai, Matthias ; Beck, Uwe
An auto-validation tool for the reliability quantification of materials integrated fiber Bragg grating (FBG) strain sensors have been developed and tested. The FBG strain sensor was jacketed with a magnetostrictive layer based on iron-nickel which, when excited by a specific magnetic field, adds an artificial strain to the sensor. The fixed relationship between magnetic induction and wavelength shift of the FBG strain sensor characterizes the bond strength and adhesion between the sensor and the surrounding structure. Due to an easily applicable magnetic field, it is possible to validate the sensor performance in a non-contact, fast way without disturbing the data-acquisition process.
A dendritic amphiphile for efficient control of biomimetic calcium phosphate mineralization (2017)
Hentrich, D. ; Taabache, Soraya ; Brezesinski, G. ; Lange, Nele ; Unger, Wolfgang ; Kübel, C. ; Bertin, Annabelle ; Taubert, A.
The phase behavior of a dendritic amphiphile containing a Newkome-type dendron as the hydrophilic moiety and a cholesterol unit as the hydrophobic segment is investigated at the air–liquid interface. The amphiphile forms stable monomolecular films at the air–liquid interface on different subphases. Furthermore, the mineralization of calcium Phosphate beneath the monolayer at different calcium and phosphate concentrations versus mineralization time shows that at low calcium and Phosphate concentrations needles form, whereas flakes and spheres dominate at higher concentrations. Energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and electron diffraction confirm the formation of calcium phosphate. High-resolution transmission electron microscopy and electron diffraction confirm the predominant formation of octacalcium phosphate and hydroxyapatite. The data also indicate that the final products form via a complex multistep reaction, including an association step, where nano-needles aggregate into larger flake-like objects.
A detailed assignment of NEXAFS resonances of imidazolium based ionic liquids (2016)
Ehlert, Christopher ; Holzweber, Markus ; Lippitz, Andreas ; Unger, Wolfgang ; Saalfrank, Peter
In Near Edge X-Ray Absorption Fine Structure (NEXAFS) spectroscopy X-Ray photons are used to excite tightly bound core electrons to low-lying unoccupied orbitals of the system. This technique offers insight into the electronic structure of the system as well as useful structural information. In this work, we apply NEXAFS to two kinds of imidazolium based ionic liquids ([CnC₁im]⁺[NTf₂]⁻ and [C₄C₁im]⁺[I]⁻). A combination of measurements and quantum chemical calculations of C K and N K NEXAFS resonances is presented. The simulations, based on the transition potential density functional theory method (TP-DFT), reproduce all characteristic features observed by the experiment. Furthermore, a detailed assignment of resonance features to excitation centers (carbon or nitrogen atoms) leads to a consistent interpretation of the spectra.
A method to test the performance of an energy-dispersive X-ray spectrometer (EDS) (2014)
Hodoroaba, Vasile-Dan ; Procop, M.
A test material for routine performance evaluation of energy-dispersive X-ray spectrometers (EDS) is presented. It consists of a synthetic, thick coating of C, Al, Mn, Cu, and Zr, in an elemental composition that provides interference-free characteristic X-ray lines of similar intensities at 10 kV scanning electron microscope voltage. The EDS energy resolution at the C-K, Mn-Lα, Cu-Lα, Al-K, Zr-Lα, and Mn-Kα lines, the calibration state of the energy scale, and the Mn-Lα/Mn-Kα intensity ratio as a measure for the low-energy detection efficiency are calculated by a dedicated software package from the 10 kV spectrum. Measurements at various input count rates and processor shaping times enable an estimation of the operation conditions for which the X-ray spectrum is not yet corrupted by pile-up events. Representative examples of EDS systems characterized with the test material and the related software are presented and discussed.
A new model for nano-TiO2 crystal birth and growth in hydrothermal treatment using an oriented attachment approach (2017)
Lavric, V. ; Isopescu, R. ; Maurino, V. ; Pellegrino, F. ; Pellutiè, L. ; Ortel, Erik ; Hodoroaba, Vasile-Dan
The synthesis of TiO2 was studied in an original hydrothermal process that uses triethanolamine titanium complex Ti(TeoaH)2 as a Ti precursor and triethanolamine (TeoaH3) as a shape controller to obtain bipyramidal anatase nanoparticles. Backed-up by experimental evidence, i.e., time profiles for Ti(IV) species concentrations together with crystal shape and particle size distributions measured by dynamic light scattering and electron microscopy, a mathematical model was built. The model includes chemical reactions responsible for TiO2 generation in solution and the subsequent anatase nucleation and crystal growth. The oriented attachment mechanism was adopted to explain the build-up of crystals with equilibrium anatase structure (Wulff structure) and time-varying shape factor. This complex mathematical model was solved writing and validating an in-house software using the Matlab (Natick, MA, USA) environment. The process was simulated for a batch time of 50 h, and the results, in terms of main species concentration and crystal size distributions, are in rather good agreement with the experimental measurements.
A new molecular understanding of the thermal degradation of PA 66 doped with metal oxides: Experiment and computation (2015)
Dümichen, Erik ; Braun, Ulrike ; Sturm, Heinz ; Kraemer, R. ; Deglmann, P. ; Gaan, S. ; Senz, R.
The thermal molecular degradation of polyamide 66 (PA 66) doped with (partially supported) metal oxide particles (Fe2O3, ZnO, Al2O3) was investigated qualitatively and quantitatively using common analysis techniques like thermogravimetry coupled with IR-spectroscopic evolved gas analysis (TGA-FTIR). Using pyrolysis coupled with gas chromatography mass spectrometry (Py-GC-MS), qualitative conclusions were drawn about the complex hydrocarbon products. However, the combination of TGA with solid-phase extraction, followed by thermal desorption gas chromatography mass spectrometry (TED-GC-MS), allows qualitative and even semi-quantitative conclusions about the decomposition pathway of PA 66 in the presence of various metal oxide particles. The investigations under inert conditions showed that the presence of metal particles increases the rate of decarboxylation and deamination reactions, as well as the formation rate of cyclopentanone and pyridine derivatives. These species are a consequence of various condensation reactions. The condensation reactions release a large amount of water, thus triggering the hydrolysis of PA 66. Molecular thermal degradation mechanisms were developed for the main decomposition as well as for the condensation reactions and supported by quantum chemical calculations. The catalytic effect of the metal oxides in PA 66 increases in the following order: PA 66 = PA 66 – Al2O3 < PA 66 – Fe2O3 < PA 66 – ZnO.
A photoswitchable rotaxane operating in monolayers on solid support (2016)
Schwarz, F. ; Heinrich, Thomas ; Lippitz, Andreas ; Unger, Wolfgang ; Schalley, C.
A novel photoswitchable rotaxane was synthesised and its switching behaviour in solution was analysed with NMR and UV-Vis. A monolayer of rotaxanes was deposited on glass surfaces and the on-surface photoswitching was investigated. Angle-resolved NEXAFS spectra revealed a preferential orientation that reversibly changes upon switching.
A sealable ultrathin window sample cell for the study of liquids by means of soft X-ray spectroscopy (2017)
Grötzsch, D. ; Streeck, C. ; Nietzold, Carolin ; Malzer, W. ; Mantouvalou, I. ; Nutsch, A. ; Dietrich, Paul ; Unger, Wolfgang ; Beckhoff, B. ; Kanngießer, B.
A new sample cell concept for the analysis of liquids or solid-liquid interfaces using soft X-ray spectroscopy is presented, which enables the complete sealing of the cell as well as the Transport into vacuum via, for example, a load-lock system. The cell uses pressure monitoring and active as well as passive pressure regulation systems, thereby facilitating the full control over the pressure during filling, sealing, evacuation, and measurement. The cell design and sample preparation as well as the crucial sealing procedure are explained in detail. As a first proof-of-principle experiment, successful nitrogen K-edge fluorescence yield near-edge X-ray absorption fine structure experiments of a biomolecular solution are presented. For this purpose, it is shown that the careful evaluation of all involved parameters, such as window type or photon flux, is desirable for optimizing the experimental result.
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