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Organisationseinheit der BAM
- 6 Materialchemie (142) (entfernen)
Eingeladener Vortrag
- nein (88)
One of the holy grails in chemistry is to reconstruct some of life’s functions with synthetic materials. In this contribution, we demonstrate that “simple” macromolecular architectures such as dendritic amphiphiles, Janus dendrimers, thermoresponsive and hybrid organic-inorganic (co)polymers enable to mimic some of the functions of proteins for biomineralization, natural bactericides, biological membranes or the stimuli-responsive cytoskeleton.
We present an in situ PXRD investigation of the mechanochemical cocrystal formation of pyrazinamide with pimelic acid in two milling jar materials. DFT calculations of the two synthesized polymorphs suggest that the relative stability is based on a conformation change of pyrazinamide in the cocrystal.
UCST-type thermoresponsive polymers (i.e. that phase separate from solution upon cooling) present a tremendous potential not only in aqueous media where they can be used in drug delivery, diagnostic and microfluidic applications, but also in water/alcohol mixtures, where they can be used for instance in sensing systems for alcohol-soluble drugs. However, only a few thermoresponsive polymers have been reported that present an UCST in a relevant temperature range and “green” solvents such as water or ethanol.
In this context, acrylamide-based monomers can be very useful building blocks for designing novel non-ionic UCST-type polymers because of their hydrophilic nature (with the appropriate side chain) and propensity to form hydrogen bonds. We will present our latest results on the UCST-type thermoresponsive behaviour of acrylamide- and 2,6-diaminopyridine-based homopolymers and copolymers in water or water/alcohol mixtures, and give some insights about the rational design of UCST polymers relying on H-bonding.
The wear rates of self-amted alumina couples show that friction as well as wear is largely determined by the above mentioned hydro-thermal conditions. The presence of water and ist amount available in the surrounding system either in liquid or in gaseous from plays a key role for friction and wear behavior and cabe benefical for the tribological profile of steam degradation resistant materials. Hot steam enhances the tribo-chemical formations of oxides and hydroxides on MgO-ZrO2, alumina and antimony impregnated carbon.
For almost 150 years it is known that hydrogen has a deleterious effect on the mechanical properties of metallic components. Nowadays, the problem of hydrogen assisted degradation is highly relevant in energy related fields due to the massive use of steel as a structural component in these applications and its sensitivity to hydrogen. Since the discovery of hydrogen assisted cracking (HAC), researchers studied intensively and suggested possible explanations and mechanisms in order to define how hydrogen is affecting the material. In general, it is considered that hydrogen changes the mechanical properties more in terms of ductility (deformation capacities) than in strength (load capacities). Hydrogen concentration is one of three crucial factors in the degradation process, together with the microstructure of the material and the internal/external mechanical load. The relatively high concentration of hydrogen resulting in this loss of ductility can originate during production or before service (e.g. welding processes) and during service (i.e. catholically protected systems to eliminate corrosion processes in sour environments).
In parallel to the theoretical work, tremendous efforts were, and are still, invested in searching for a proper method to elucidate, map and quantify the hydrogen in the microstructure, which is the basis for this work. For steels, the focus is mainly on the observations of diffusion processes and the interaction of hydrogen with the microstructure
in regions with high local stresses/strains (for example around evolving cracks). The challenge for reaching this goal arises from the fact that accurate indication of hydrogen by means of position, unlike heavier atoms, can be made only by mass spectrometry or by interaction with another element (e.g. silver decoration, special coating and resonant nuclear reaction by nitrogen). In addition to this, the difficulty recording the hydrogen behavior while it rapidly diffuses through the material, leaving only the unpredicted failure, should be taken into account.
Although using powerful characterization methods, models and computational simulations, the key to defining the mechanisms behind HAC is still under debate and not fully understood. The relationship between material and hydrogen is determined by three factors, i.e., the material structure and microstructure – determining the physical properties, the mechanical load applied on the material and the hydrogen concentration. It is well known that in order to have a complete definition of HAC these three factors must be examined locally with the minimal scale and the maximal resolution reachable. The major gap is the lack in such a characterization method or a technique by which one has the ability to detect and observe the hydrogen in the metallic microstructure. The commonly used techniques nowadays are capable of characterization of the microstructure without the ability to observe the hydrogen distribution. Global hydrogen concentration and localized hydrogen observation are possible by some techniques which are incapable of indicating a change in the structure or microstructure therefore a comprehensive overview can be gained only by combining several methods.
In the presented research, secondary ion mass spectrometry (SIMS) was adopted as the main tool to detect and locally map the hydrogen distribution in two types of duplex stainless steel grades: EN 1.4462 (standard 2205 duplex stainless steel) and EN 1.4162 (2101 lean duplex stainless steel). The term duplex stainless steel (DSS) refers to the austenitic-ferritic microstructure of the steel where the combination of physical and mechanical properties of the two phases is achieved. The DSS was selected as a case study for this work due to the wide use of this grade in many energy and the lack of knowledge on hydrogen behavior in two-phase containing microstructures. ToFSIMS was exploited in-situ and ex-situ in three experimental approaches during or following
an electrochemical charging procedure. This type of hydrogen charging was selected as it simulated a procedure of cathodic protection of most sub-water oil and gas extraction and delivery systems. The experimental procedures were:
1. Ex-situ charging followed by ToF-SIMS imaging for basic understanding of hydrogen distribution.
2. Ex-situ charging followed by in-situ mechanical loading to obtain information on hydrogen behavior around a propagating crack.
3. In-situ permeation of hydrogen through a steel membrane inside the ToF-SIMS to obtain information on diffusion behavior of hydrogen in a two-phase microstructure.
The comprehensive view of the effect of hydrogen on steel was gained by using supplementary methods, such as high resolution scanning electron microscopy (HR-SEM), focused ion beam (FIB) and electron back-scattered diffraction (EBSD). The state of the art in this work lies in applying both: in-situ experimental approaches and data treatment of the ToF-SIMS raw data. The data treatment includes the combination of data from several sources (data fusion).
The results for the ex-situ charging followed by static sample imaging and data fusion showed that when the analyzed surface is directly exposed to the electrolyte the degradation is pronounced differently in the ferrite, austenite and interface. The degradation mechanisms in the ferrite and austenite were reflected by the formation of cracks on the surface of both, where a high concentration of hydrogen was obtained. This result supports the assumption that hydrogen is attracted to highly deformed regions. The advantage of using in-situ charging/permeation in comparison to ex-situ charging is that the effect of hydrogen on the ferrite and austenite phases when the hydrogen is evolving from within the microstructure is realized, in comparison to when the analyzed surface is initially exposed directly to the electrolyte. In both experiments the ferrite was observed as a fast diffusion path for the hydrogen. The faster diffusion of hydrogen through the ferrite is expected due to the higher diffusion coefficient, however, a direct proof for the diffusion sequence in this scale was never shown. Most significant results were achieved by the ‘core’ experiments of this research. These experiments included the design of a novel dynamic mechanical loading device to apply an external load during SIMS imaging of a hydrogen precharged-notched sample. For the first time it was shown that plastic deformation induced by applying a mechanical load is resulting in a redistribution of hydrogen locally around the notch.
Eine neue Art einer Ring-Expansion Polymerization (REP) von zyklischen Polylaktiden mittels neuer Katalysatoren wird präsentiert.
MALDI-TOF Massenspektrometrie und andere analytische Techniken wurden zur Aufklärung des Mechanismus eingesetzt. Dabei zeigte sich, dass im Gegensatz zu anderen REP, ausschließlich zyklische Polymere gebildet wurden. Diese stellen neue Kandidatenmaterialien für zukünftige neue CRM dar.
In Glasfasern eingeschriebene Bragg-Gitter (FBG: fibre-based Bragg gratings) sind über die Verschiebung der Bragg-Wellenlänge in der Lage, Stauchungen und Dehnungen von Glasfasern hochgenau zu erfassen. In Kompositwerkstoffe eingebettete faseroptische Sensoren können Bauteile bezüglich ihrer mechanischen Integrität überwachen und früh-zeitig Informationen über Materialveränderungen gewinnen.
Um die Zuverlässigkeit eines solchen Sensors zu gewährleisten, ist es wichtig, die korrekte Funktion des Sensors im Verbund mit der Werkstoff-Matrix on-line und in-situ sicherzu-stellen. Im Rahmen des DFG-Projekts FAMOS² (FAser-basierter Magneto-Optischer SchichtSensor) wurde ein selbstdiagnosefähiger Schichtsensor entwickelt, der mit Hilfe von magnetostriktiven Aktorschichten aus Nickel bzw. Eisen-Nickel validiert werden kann.
Der FAMOS²-Schichtsensor wird durch ein PVD (physical vapour deposition)/ECD (electro-chemical deposition) Hybridschichtsystem realisiert, das auf dem Fasermantel im Bereich des FBG haftfest, homogen und langzeitfunktional abzuscheiden ist. Dabei wird in einem ersten Schritt ein etwa 100 Nanometer dünnes PVD-Schichtsystem aus Chrom und Kupfer als Haftvermittler auf der Glasfaser bzw. als leitfähige Startschicht für den nachfolgenden ECD-Prozess abgeschieden. Um eine rotationssymmetrische Schich-tabscheidung zu gewährleisten, erfolgt während der PVD-Beschichtung eine Rotation der Glasfasern. In einem zweiten Schritt wird dann unter Verwendung eines klassischen Watts-Elektrolyten in einer speziell entwickelten ebenfalls rotationssymmetrisch aufgebau-ten ECD-Durchströmungszelle dann die etwa 30 Mikrometer dicke, magnetostriktive Ak-torschicht auf dem PVD-Schichtsystem abgeschieden, im Vergleich sowohl reine Nickel-Schichten als auch Nickel-Eisen-Schichten.
Ein äußeres Magnetfeld dehnt die magnetostriktive Aktorschicht und damit auch die Faser reversibel. Diese Dehnung führt zu einer Verschiebung der Bragg-Wellenlänge, welche direkt mit der Stärke eines zu messenden oder zu Validierungszwecken vorgegebenen Magnetfeldes korreliert. Die Anpassung der Beschichtungsverfahren an die Fasergeome-trie und die mechanischen Eigenschaften der Hybridschichten werden hinsichtlich der me-chanischen Integrität des faseroptischen Sensors diskutiert und der Nachweis der Selbst-diagnosefähigkeit erbracht.
In Glasfasern eingeschriebene Bragg-Gitter (FBG: fibre-based Bragg gratings) sind über die Verschiebung der Bragg-Wellenlänge in der Lage, Stauchungen und Dehnungen von Glasfasern hochgenau zu erfassen. In Kompositwerkstoffe eingebettete faseroptische Sensoren können Bauteile bezüglich ihrer mechanischen Integrität überwachen und früh-zeitig Informationen über Materialveränderungen gewinnen.
Um die Zuverlässigkeit eines solchen Sensors zu gewährleisten, ist es wichtig, die korrekte Funktion des Sensors im Verbund mit der Werkstoff-Matrix on-line und in-situ sicherzu-stellen. Im Rahmen des DFG-Projekts FAMOS² (FAser-basierter Magneto-Optischer SchichtSensor) wurde ein selbstdiagnosefähiger Schichtsensor entwickelt, der mit Hilfe von magnetostriktiven Aktorschichten aus Nickel bzw. Eisen-Nickel validiert werden kann.
Der FAMOS²-Schichtsensor wird durch ein PVD (physical vapour deposition)/ECD (electro-chemical deposition) Hybridschichtsystem realisiert, das auf dem Fasermantel im Bereich des FBG haftfest, homogen und langzeitfunktional abzuscheiden ist. Dabei wird in einem ersten Schritt ein etwa 100 Nanometer dünnes PVD-Schichtsystem aus Chrom und Kupfer als Haftvermittler auf der Glasfaser bzw. als leitfähige Startschicht für den nachfolgenden ECD-Prozess abgeschieden. Um eine rotationssymmetrische Schich-tabscheidung zu gewährleisten, erfolgt während der PVD-Beschichtung eine Rotation der Glasfasern. In einem zweiten Schritt wird dann unter Verwendung eines klassischen Watts-Elektrolyten in einer speziell entwickelten ebenfalls rotationssymmetrisch aufgebau-ten ECD-Durchströmungszelle dann die etwa 30 Mikrometer dicke, magnetostriktive Ak-torschicht auf dem PVD-Schichtsystem abgeschieden, im Vergleich sowohl reine Nickel-Schichten als auch Nickel-Eisen-Schichten.
Ein äußeres Magnetfeld dehnt die magnetostriktive Aktorschicht und damit auch die Faser reversibel. Diese Dehnung führt zu einer Verschiebung der Bragg-Wellenlänge, welche direkt mit der Stärke eines zu messenden oder zu Validierungszwecken vorgegebenen Magnetfeldes korreliert. Die Anpassung der Beschichtungsverfahren an die Fasergeome-trie und die mechanischen Eigenschaften der Hybridschichten werden hinsichtlich der me-chanischen Integrität des faseroptischen Sensors diskutiert und der Nachweis der Selbst-diagnosefähigkeit erbracht.
Collective Orientational Order and Phase Behavior of a Discotic Liquid Crystal under Confinement
(2018)
Discotic liquid crystals (DLCs) are a promising class of soft matter for electronic applications. This is due to their ability to self-organize into columns in a hexagonal columnar mesophase, driven by the overlapping of the π orbitals of their aromatic cores. This leads to a high charge-carrier mobility along the column axis. Previous studies on DLCs showed that their properties, such as phase transition temperatures and enthalpies, are susceptible to nanoconfinement. In this study, 2,3,6,7,10,11 hexakis[hexyloxy] triphenylene (HAT6) was confined into parallel aligned cylindrical nanopores of anodic aluminum oxide (AAO) membranes by melt infiltration. Furthermore, the pore surfaces of a series of membranes were chemically modified, resulting in a more hydrophobic pore surface than the unmodified ones. Collective orientational order and phase behavior of HAT6 confined into modified and unmodified nanopores of AAO were investigated by broadband dielectric spectroscopy and differential scanning calorimetry respectively.
Hyperbranched PAMAM/ Kaolinite Nanocomposites: Decoupling phenomenon and conductivity mechanism
(2018)
Increasing demands of the daily life requires a continuous discovering of new and tailored properties of materials that can be utilized in covering the requirements in several fields. Hyperbranched polymers (HBPs) are macromolecules that are characterized by a highly branched structure and multiplicity of reactive end groups, which could be promising for numerous applications. Here, hyperbranched poly(amidoamine) (HPAMAM)/ Ka nanocomposites was prepared via an in-situ polymerization and an ex-situ method. The latter approach leads to a partly intercalated structure of the nanocomposites, while the former method results in an exfoliated morphology. Α combination of different techniques such as broadband dielectric spectroscopy (DBS), SXAS, FTIR, TEM, and DSC are employed to study the prepared samples. For the HPAMAM/ Ka-DCA nanocomposites (an ex-situ samples), the results indicated that the dc conductivity is increased by 4 orders of magnitude, with increasing concentration of the Ka-DCA. As an interesting result is that a significant decoupling between the characteristic time for conductivity relaxation and the segmental dynamics was observed, which depends on the concentration of the nanofiller. For the HPAMAM/ EDA nanocomposites (an in-situ polymerization), the dc conductivity is also increased with increasing the concentration of the Ka-EDA. The decoupling phenomenon and conductivity mechanism are discussed in detail.