10 research outputs found
Thermoplastische 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
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 textExtraction of domain structure information from small-angle scattering patterns of bulk materials
No full textThe equatorial small-angle scattering during the straining of poly(ether ester) and its analysis
No full textA method for the quantitative analysis of two-dimensional (2D) small-angle X-ray scattering (SAXS) patterns with fiber symmetry by successive information filtering is proposed and applied to a series of images recorded during a straining experiment of a two-phase polymer sample at a synchrotron beamline. The studied equatorial scattering is similar to the frequently discussed void scattering, but originates from an ensemble of rodlike soft domains (needles) in the sample, orientated in the direction of strain. The intensity is extracted and projected onto the equatorial plane, the ideal two-phase structure is extracted, and the 2D chord distribution is computed. This curve describes a 2D two-phase morphology made from needle cross-sections embedded in matrix material. Because interparticular correlation is found to be weak in the chord distribution, pure particle scattering is assumed. Modeling the needle cross-sections by circular disks leads to a simple theory, which allows the deconvolution of a disk diameter distribution from the chord distribution. It is shown how parameters of the disk diameter distribution can be computed without deconvolution. For the selected poly(ether ester) thermoplastic elastomer the study of the soft domain needles indicates strain-induced hardening. While for low elongation ϵ the soft needles are more compressible than the microfibrillar matrix, saturation is observed for ϵ > 2.5
Three-Dimensional Chord Distribution Function SAXS Analysis of the Strained Domain Structure of a Poly(ether ester) Thermoplastic Elastomer
No full textNanostructure development in multicomponent polymer systems characterized by synchrotron X-ray scattering
No full textModern synchrotron beamlines equipped with two-dimensional detectors and high-flux microfocus devices offer interesting possibilities for polymer characterization. This work presents three synchrotron X-ray studies performed in specific multicomponent polymer systems. In the first study, quantification of transcrystallinity in microfibrillar composites (MFC) by wide-angle X-ray scattering (WAXS) and a direct relation between the mechanical properties of the composites and the thickness of the transcrystalline layers is presented. The second study demonstrates monitoring of nanostructure development under controlled strain in MFC and their precursors by small-angle X-ray scattering (SAXS). A speciallydeveloped procedure for data treatment that uses the Chord Distribution Function formalism permitted to prove reversible strain-induced crystallization of matrix material in the MFC materials. In the third study, a 5 5 lm high flux X-ray beam was used to scan in WAXS mode polymer microcapsules (average diameters of 20–50 lm) with polyamide shells in which various solid payloads were incorporated by in-situ polymerization. Exfoliation/intercalation phenomena and local inhomogeneity at micron scale are studied in clay and metal containing polyamide microcapsules that constitute a new platform for the development of polymer hybrids or smart micro devices. It was concluded that relatingmicroscopy and/or mechanical data of various polymer samples to their synchrotron WAXS/SAXS patterns helps to understand the structure–properties relationship in complex polymer systems with controlled composition, morphology and nanostructure
Nanostructure Evolution of Isotropic High-Pressure Injection-Molded UHMWPE during Heating
No full text
The Media Activism of Latin America’s Leftist Governments: Does Ideology Matter?
No full textHas Latin America’s left turn mattered in media politics? Does ideology impact governments’ practices and policies regarding media and journalistic institutions? Through an empirical assessment of discourses on the media, of direct-communication practices, and of media regulation policies on the part of the recent leftist governments of Argentina, Bolivia, Brazil, Chile, Ecuador, Uruguay, and Venezuela, this paper stresses the existence of a specific media activism on the part of leftist governments in Latin America. While showing that the current binary distinctions that stress the existence of two lefts—“populist” and “nonpopulist”—obscure important commonalities and continuities, the author also demonstrates that it is the existence of certain institutional and structural constraints that best accounts for the differ-ences among the various leftist governments in Latin America. In sum, the paper challenges the prevailing neglect of ideology as a relevant factor in explaining developments in gov-ernment–media relationships in the region.media, journalism, Latin America, government, ideology, leftism
