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In-situ Struktur Entwicklung der Polyurethan-Elastomeren unter Verfolgen
No full textIn dieser Arbeit wird in situ Röntgenkleinwinkelstreuung (RKWS) eingesetzt, um die Nanostrukturentwicklung in Polyurethan-Elastomeren während der uniaxialen Dehnung zu verfolgen. Weil Polyurethane aus sehr verschiedenen chemischen Komponenten synthetisiert werden können, wäre es ein großer Fortschritt die Materialeigenschaften vorhersagen zu können. Eine solche Vorhersage müsste die Zusammensetzung und das Herstellungsverfahren berücksichtigen. Deshalb werden hier mechanische und morphologische Daten zusammen getragen, um die Mechanismen der Morphologieentwicklung zu identifizieren und in Beziehung zu den mechanischen Eigenschaften zu stellen. Die Durchschusslängenfunktion (engl.: chord distribution function, (CDF)) wird aus den Streubildern berechnet. Sie ermöglicht es, fundamentale morphologische Parameter zu identifizieren, ohne ein Strukturmodell zu benutzen. Die CDF visualisiert die lokale Struktur in der Umgebung einer DomäneDie Morphologie von Polyurethan wird durch Hartdomänen erzeugt, die in einer Weichphase eingebettet sind: Jeder Peak zeigt, in welcher Richtung und Entfernung sich Nachbardomänen befinden, die den Langperiodenpeak der RKWS erzeugen. Das Integral des CDF-Peaks ist ein Maß für die Besetzungsdichte. Darüber hinaus werden Morphologie-Parameter quantitativ bestimmt. Dazu wird die Grenzflächenverteilung (engl.: interface distribution function (IDF)) ausgewertet. Die IDF ist der meridionale Schnitt durch die CDF. Für Polymermaterialien ist die in situ RKWS ist eine mächtige Methode zur Verfolgung der Strukturevolution während der Dehnung.
Handgegossene thermoplastische Polyurethane (TPU) zeigen breite Verteilungen von Hartdomänengrößen und Weichphasenlücken. Beim Dehnen werden die Hartdomänen zunehmend zerstört, der Volumenanteil v_{h}
kann als Funktion der Dehnung bestimmt werden. Hierfür wird eine einfache empirische Gleichung gefunden. Diese lineare Gleichung ist gültig für alle 6 untersuchten Materialien, bei denen die Zusammensetzung stark variiert. Die Aussage der Gleichung ist, dass die Materialien zerreissen, sobald alle Hartdomänen zerstört sind, d.,h. v_{h}left(varepsilon_{b}right)=0
, wobei varepsilon_{b}
die makroskopische Bruchdehnung ist.
Der Hartdomänenanteil von maschinengegossenem Polyurethan, welches bei 150 °C gealtert ist, nimmt mit der Alterungszeit ab. Beim Dehnen werden Hartdomänen aus gut geordneten Ensembles (engl.: well-arranged ensembles (WAEs)) in Mitleidenschaft gezogen. Dabei geht die Regelmäßigkeit der Anordnung zu ihren Nachbarn verloren und sie gehören danach zu den schlecht geordneten Ensembles, die nur Partikelstreuung zeigen. Die makroskopische Dehnung erfolgt unter Zerstörung der Hartdomänen. Periodische Stapel von Hart-- und Weichdomänen sind bis zu einem gewissen Grad dehnbar. Danach werden die ausgestreckten Entitäten zerstört.
Polyurethane, die Polyole mit Mehrfachfunktionalität (> 3) enthalten zeigen eine schlechte Phasenseparation. Die Materialien sind Thermosets. Nur das 2-funktionale Material ist thermoplastisch. Die ausgebildeten Morphologien und das Deformationsverhalten der Hartdomänen hängen sehr stark von der Polyolarchitektur ab.In this thesis, in-situ small-angle X-ray scattering (SAXS) is employed to track the nanostructure evolution of polyurethane elastomers during uni-axial stretching. Because various chemical components can be used to synthesize a polyurethane, it would be helpful to predict materials properties based on its composition and processing. Therefore mechanical and morphological data are collected in order to identify mechanisms of morphology evolution and their relation to mechanical properties. Chord distribution function (CDF) computed from the recorded SAXS pattern facilitates us to identify fundamental morphological features without having to apply a structural model. CDF visualizes the local structure in the neighborhood of a domain: Each peak shows, in which direction and distance neighbor domains are found that generate a long period. The integral of a peak is a measure of the population density. Furthermore, fitting interface distribution function (a meridian slice from the CDF) estimates the quantitative analysis of polyurethane morphology. The in-situ small-angle X-ray scattering is a versatile technique to track the structure evolution of polymer material under deformation.
Hand-cast thermoplastic polyurethanes exhibit broad distribution of hard domains and soft gaps. The hard domains are sacrificed with increasing the strain, the volume fraction vh
of hard domains can be determined as a function of strain and a simple empirical equation is found. This linear equation is valid for the 6 materials of different composition. It says that the materials break when all hard domains have been destroyed, i.e. vh(eb)=0 with eb being
the strain at break.
The hard domain content of machine-cast polyurethane which is aged at 150 oC
decreases with increasing the ageing time. During stretching, the correlated hard domains in well-arranged ensembles (WAEs) are destructed into uncorrelated hard domains nested in poorly-arranged regions (PARs). All the hard domains are sacrificed to achieve the macroscopic elongation of material. The periodic stacks of hard domain and soft domain are extended up to a constant size, and then these outstretched entities are destructed without any further extension in order to achieve the macroscopic elongation.
The polyurethanes with multi-functionality (>3) polyols are thermosets that to be poorly phase separated whereas a 2-functional polyol is thermoplastic. The developed morphology and the deformation of the hard domains under stress are strongly depending on the architecture of polyol employed
Bewertung der Mikrostruktur von PVDF über Röntgenkleinwinkelstreuung nach der Exposition unter Superkritischen CO2
No full textThermoplastische Polyurethane : Domänenmorphologieentwicklung unter mechanischer und thermischer Belastung als eine Funktion der Zusammensetzung
No full textIn this work three groups of thermoplastic polyurethane (TPU) materials have
been studied. In the first group, Machine-cast TPUs are strained and monitored by small-angle X-ray scattering (SAXS). In the second study TPUs with varying diisocyanates and chain extenders are strained and monitored by (SAXS). In the third study TPUs in presence of nucleating agents are monitored by SAXS under thermal load. Upon stretching hard domains are destroyed. Most stable are the domains of materials with Hard Segment Content (HSC)=30. Domain stability decreases with increasing HSC. Chord distribution functions (CDF) exhibit the same sequence of static long-period bands. The band positions form a Fibonacci series, related to the underlying polyaddition process. This indicates a nearly quasicrystalline arrangement of stringed hard domains, identified as the strain probes of the discrete SAXS. In the second study, the model-free data inspection shows the difference in nanoscopic straining mechanisms. From these results a onedimensional morphological model for the analysis of the longitudinal SAXS is built. Its components are particle scattering and the two strongest scattering entities made of 2 hard domains with some soft phase in between (soft domain). Thus the model comprises 1 (solo) and 2 (duos). For all materials the average hard domains are about 6 nm high, and the domain heights vary by 38 to 48 percent
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Nanostructure evolution studies of bulk polymer materials with synchrotron radiation: progress in method development
No full textUtilising spatial frequency filtering to extract nanoscale layer structure information from isotropic small-angle X-ray scattering data
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Extraction of domain structure information from small-angle scattering patterns of bulk materials
No full textAppropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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