1,721,070 research outputs found
SAXS investigation on the influence of oil dilution on morphological changes in a SBS block copolymer during the first draw cycle
No full textSpin-cast films of one pure SBS and two oil-extended SBS samples were observed during first cycle drawing in the synchrotron radiation beam at Hasylab. For evaluation, from a two-dimensional Vidicon scattering picture the scattering curve was extracted by intersecting perpendicular to the observed layer lines. Using a method described in a preceding paper [1], the scattering curve is analyzed by fitting to one-dimensional two-phase models. Essential for a fit with parameters of physical sense is the assumption of at least two components. One of these two main components is identified with fibrils containing PS cylinders, the axes of which are orientated parallel; the other is identified with fibrils containing cylinders transverse to the drawing direction. For the mechanical properties of the thermoplastic rubber this splitting of cylinder orientation in the drawn state seems to be of some importance. Only the cylinders of the longitudinal component turn out to be rigid, while the cylinders of the transversal component appear to yield and even break. The amount of cylinders allotted to each of the two components in the drawn state varies as a function of the diluent. An extrapolation of topological parameters back to the undrawn state indicates a possible reason, a fair variation of the cylindrical particle dimensions within a "lattice cell" of only slighly varying dimensions. While paraffinic mineral oil dilution causes the cylinders lengths to decrease, thus improving cylinder orientability within the pseudo lattice cell, aromatic oil dilution increases the particles diameters. A remaining faint contribution to the scattering pattern that produces the layer lines is suggested not to be caused by a periodic structure, but by a single and precisely defined polybutadiene matrix length ("string") between two PS cylinders with a considerable height variance. © 1989 Steinkopff
Morphological changes in SBS block copolymers caused by oil extension as determined by absolute small angle X-ray scattering
No full textA series of SBS block copolymers diluted with different amounts (0-60 wt%) of three different kinds of oil were investigated: 1) lithene PM (a low molecular weight polybutadiene); 2) a paraffinic mineral oil with its electron density close to that of the polybutadiene (PB) phase; 3) a highly aromatic mineral oil with an electron density close to the polystyrene (PS) phase. All the oils seem to go into the polybutadiene matrix. Paraffinic oil and lithene form a homogeneous phase with PB; the aromatic oil at low concentrations mixes with the PB phase with a high level of inhomogeneity, while at higher concentration partial phase separation occurs. In the undiluted polymer, styrene forms cylinders in hexagonal packing. The distance between cylinders (about 43 nm) is not significantly changed upon dilution up to 33 wt%. Previously proposed changes in the morphology of PS domains at larger oil contents can be related to observed changes in the long period, in the segment length distributions, and in the homogeneities of the phase (density fluctuations). The electron density difference obtained for pure SBS is lower than the theoretical one calculated from the densities of pure PS and pure PB. Dilution by paraffinic oil improves the phase separation. © 1989 Steinkopff
Structure and Properties of Oil Extended Styrene Butadiene Block Copolymers
No full textThe relationships between mechanical properties and structure of rapidly spin cast styrene-butadiene-styrene (SBS) block copolymers diluted with two different types of mineral oil are discussed. Small angle X-ray scattering (SAXS) measurements indicate that both oils go mainly into the rubbery polybutadiene phase. While during rapid spin casting the paraffinic oil improves the phase separation of polystyrene (PS) and polybutadiene (PB), the opposite is true for the aromatic oil. The measurements also suggest that the oils cause a preferential swelling of the superstructure along the longitudinal direction of the cylindrical PS domains. From this, it can be concluded that a larger number of interconnecting PB chains is present in the cross direction than in the longitudinal one. With increasing oil content, a further decrease of interconnecting chains in the latter direction may be the reason for the decrease of the tensile modulus. Furthermore, above a critical value of dilution (33 wt percent for paraffinic oil, 50 wt percent for the aromatic one), more and more spherical domains are formed instead of the cylindrical ones. This morphological transition explains the step present in the double logarithmic plot of the large strain tensile modulus as a function of oil dilution
A comparative DSC, X-ray and NMR study on the crystallinity of isomeric aliphatic polyamides
No full textIn the polyamides 4.12, 10.6, 8.8 and 6.10 three fractions are present. The WAXD crystallinity is comparable to that of DSC and amounts to 40% in all samples. The rigid fraction obtained by solid state NMR is, however, close to 60%, pointing at 20% rigid amorphous material. A combination of the NMR, WAXD and SAXS results reveals that the latter fraction is situated inside the crystalline phase and not at the crystalline – ‘mobile amorphous’ interface. Accordingly, one third of the crystalline layers with a thickness between 50 and 56 Å is not truly crystalline. From the width of the WAXD 100 reflections it can be deduced that crystalline grains exist with lateral dimensions of approximately 100 Å. Hence a picture emerges of alternating solid and liquid-like layers with the former consisting of crystalline grains separated by rigid amorphous matter
Small-angle X-ray Scattering investigations of styrene-butadiene-styrene block copolymers during stretching
No full textA small-angle X-ray scattering study on styrene-butadiene-styrene block copolymers during stretching is reported. Measurements have been performed at the Hamburg Synchrotron Radiation Laboratory at DESY using a two-dimensional position-sensitive detector. A pattern of layer lines perpendicular to the stretching direction with ellipsoidal envelope is obtained. This indicates a good orientation of cylindrical polystyrene domains along the stretching direction. The diameter-to-length ratio of the cylinders was found to be 0.6, the length being approximately 39 nm. The long period of the undrawn sample is about 47 nm. Upon stretching, initially this value increases almost affinely, while for γ>3 it tends to reach a constant value. The extension at which the curve bends coincides with the inflection point in the stress-strain curve; at higher values of extension, most of the polybutadiene chains are probably completely stretched and further extension is achieved partly by disruption of the polybutadiene matrix. © 1990
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe 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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